Dolby Technical Guidelines 1994

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Dolby Stereo Technical Guidelines

for Dolby Stereo Theatres

PLEASE NOTE THIS PUBLICATION IS FROM 1994 AND MAY NOT

REFLECT THE LATEST TECHNOLOGY IN THE INDUSTRY.

Dolby and the double-D symbol are registered trademarks of Dolby Laboratories.

All other trademarks remain the property of their respective owners.

1994 Dolby Laboratories, Inc. All rights reserved. S05/16463


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DN @DOLBYSTEREOTechnicalGuidelines orDolby Stereo Theatres

0

November1994


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R.ev .33 November,1994

Technical Guidelines for Dolby stereo Theatres--DRAFT

Many peoplecontribute o theseguidelines. particular thanksaredue to David schwind of Charles alterAssociatesor muchof the acousticadvice. ElizabethCohen of cohen Acoustics,John Eargle of JBL and Tomlinson Holman of USC andLucasfilm, provide significant contributions to this ongoingproject' From within Dolby Laboratories here are numerouswitting and un-witting contributors: n particular Tom Bruchs,Sam Chavez,Louis Fielder, John Iles, Lonny Jennings,ScottRobinson,CharlesSeagraveand David Watts.some manufacturers'equipment is specifically cited in thismaterial ' such citat ions are definit ively non-exclusivemanufacturers re welcome o contactDolby Laboratorieswithinformation about any equivalent or superior performanceequipment that they believe shourd be included in futureeditions of theseguidelines. omission of specificequipmentdoesnot imply lack of fitness.

Ioan AllenSeptember 20th 1993

ODolby Laborato ies nc. 1992/1994 s95 9557 10147


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Contents* Architectsand building designers hould note allconstructionand renovationprojects.1.0 ntroduction2.0B-Chain

2.1 DynamicRangeRequirements2.1.1PowerAmplifier Size2.1.2 nformationon New Jiffy

2.2 Screen oudspeakers2.2.1 ocation2.2.2Loudspeaker ype2.2.3LoudspeakerWalls *2.2.4Cross-overs2.2.5CharacteristicCurve2.2.6Measurement

2.3SurroundLoudspeakers2.3.1 ocation2.3.2 oudspeaker ype2.3.3Mounting Angles2.3.4CharacteristicCurve2.3.5Measurement

2.4Sub-woofers2.4.1 ocation2.4.2Notional Cross-over2.4.3Need for BassExtension2.4.4Tuning2.4.5PowerRequirements

items rnarked rt'ith an asterisk for new

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3.0A-Chaina 1J . l

3.2

Analog3 .1 .1J . r . / -a 1 aJ , I . J

3.1 .43.1 .5

Digital3.2.13.2.2a - tJ . L . Ja i t1 / 4

Frequency tesponseSlitExciterLamp/SupplyIllumination UniformityWow and Flutter

AlignmentWow and FlutterIllumination Uniformity

Exciter Lamp/Supply

4.0Acoustics

4.1Criteria *4.tJ Noise Floor4.1.2 Reverberation Time4.1.3Reflections4.1.4 Early Lateral Reflections4.1.5 Rear ScreenDamping

New TheatreDesign*4.2.1New TheatreLocation4.2.2Ceilings4.2.3Floors4.2.4Walls4.2.5Seats

BackgroundNoise *4.3.1HVAC Design4.3.2Maintenance

4.2

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4.4Sound Isolation*4.4.1Ceilingsand Floors4.4.2Doors

5.0CinemaProcessor pdates5.1CP505.2CP555.3CP200

6.0Picture ssues6.1ScreenSize*6.2ScreenType6.3 Light on Screen6.4 Color Temperature6.5Reflectedand Ambient Light6.6 PortholeDesign*6.7Shutters

7.0TestFilms7.1Sound

7.1.1 nalog7.1.2Digital

7.2Picture7.2.1. P40

7.3GeneralPurpose7.4Trailers

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8.0Other Information8.1Dolby Laboratories quipmentManuals

8.1.1CP558.1.2 P658.1.3CP2008.1.4SRAs8.1.5 A108.1.6 A20

8.2 Soundand PictureProjectionStandards8.2.1ANSI202M 1502969)8.2.2Lighton Screen8.2.3Reflected/Ambient ight8.2.4ProjectedmageQualitY

8.3 Other Information SourcesB.3.L echnical ournalsand Magazines8.3.2 nter-SocietyCommittee8.3.3 EA8.3.4 HX

8.4Dolby TechnicalHelp8.4.1Training Courses8.4.2TechnicalHelp Hot-Line

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Fieures2.7: Peakpower levels - A-type,SR,SR.D2.2: Polver neededv. Room Size2.3: StageLoudspeakerCharacteristic urve2.4: SingleMicrophone Equalisation ocation2.5: Multiplexed MicrophonesEqualisationLocation2.6: Good surround location2.7: Surrounds oo far forward2.8: Typical Surround Characteristic urve2.9: Sub-woofer evel setting2.10: Sub-wooferPower Requirements2.I1: Surround Power Requirements3.1:3.3:

Cat. No . 69 Pink Noise Frequency ResponseAnalog v. Digital Problem audibilityDigital Surround Delay Setting

Noise Floor in whole octavesNoise Floor in third octavesAcceptable Reverberation v. Room Volume at 500H2Reverberation Scaling curve for audio bandwidthJunction Box TreatmentRecommended demising wall designScreening Room/Projecti on Room minimum wall design

Optimum subtended screenangleAdjustable masking, 2.35:I and 1.8 5:1,Adjustabie masking, 2.35:1,1.85:1, nd 1.66:1Superior Partition -- Minimum internally reflective,sound isolation port designOptimum Port Glass Projection Angles

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1.0 ntroduction

Modern film sound-tracks ar e proving increasingly demanding toexhibitors; not only is the theatre owner being asked to buy new front-end decoding equipment for a variety of sound-track formats, but thesene w formats ar e placing increasing demands on many aspects oftheatre sound.

Dolby I-aboratorieshas published a seriesof documents over the years,discussing the requirements of each progressively improved sound-track format the company has introduced. This booklet providesguidelines for theatres trying to take full advantage of the mostcommon existing sound-track formats at the time of writing, andanticipateswhat increasing demands the digital sound-track on DolbySR.D pr ints may present.

Ne w Sound-track Formats

we should begin by re-iterating what seems fairly obvious to theengineers involved in film sound-track technology, what is frequentlymissed by some people involved in exhibit ion, and is certainlymisunderstood bv much of the movie-going public -- th e sound-trackformat, mono, Dolby Stereo, Dolby Stereo SR, and now th e digitalsound-track of Dolby sR.D, does not itself define how loud or quiet asound-track will be, or how extended th e frequency response. Thefilm-maker determines the artistic extents of the sound-track, no t theformat designer. Th e film-maker decides during the post-productionprocess how loud the loudest bits of his films should be, how quiet thequietest -- how extended the frequency range should be, how wide thestereo, and how loud the surround effects. The role of the inventor,scientist and engineer involved in the technology of fi lm sound is tomake it possible for the full artistic range of the director to be carriedon the film sound-track. An d the role of the fi lm exhibitor is toensure that this full sound-track capability can be reproduced in thetheatre.

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The two Dolby Stereo ormats most challenging or theatre playbackare Dolby SR and the digital sound-track f Dolby SR.D release rints.The analog SR format is in some respects ess demanding of theatrecriteria,but in someareas,especially he A-chain, requires as carefulattention as the new digital sound-tracks. These guidelines discussthese ssues, nd explain he minimum acceptable laybackparametersfor both of thesenew high-fidelity sound-track ormats.

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2.0B-Chain

2. 1 Dynamic Range Requirements

The most obvious feature of the new high-f idel i ty sound-tracks,analog sR and digital sR.D, is a significant increase n dynamic range.The potential for louder sounds requires attention to loudspeakers,power amplifiers an d sound isolation between screens. Iteproductionof quieter sounds requires attention to sound isolat ion (again), andbackground noise.

2.L.1Power Ampli f ier Size

1. Each channel of the sound system should have a power handlingcapabil i ty easi lycapableof playing back an sR f i lm recorded at 100%modulation level at al l frequencies throughout the audio bandwidth.Th is shou ld be the very min imum capab i l i t y fo r Do lby d ig i ta lpiayback, an d a crest factor (safety margin) ma y require a significantincrease n power ampli f ier size.

Th e dialog level on both th e analog an d digital sRoD sound-tracks willbe at the same acoustic level as that of the dialog of a conventionalDolby stereo film. occasional sound effect "stings" and music, though,can have a levei far greater than found on conventional fi lms, andthis increased peak level capability is one of the great advantages ofboth anaiog sR , and th e digital sound-track on a Dolby stereo sRoDprint. Depending on the signal content, the peak levels on an analogsR sound-track can be 3dB higher, rising to 9 dB higher at frequencyextremes,as shown in Figure 2.1. The digital sound-track can providea peak level 12dB above conventional A-type Dolby stereo films; it isalso important to note that this peak level capability (around 103 dB Cfor each stage/screen cirannel) s constant with frequency.

As a very rough guide, analog sR sound-tracks in small and mediumsized theatres,peak lc'velswill require power amplifiers for th e screen

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channelswith total power output ratings of at least 250 watts. Themono surroundchannel or SRplaybackwill probablyneedat least400watts.

Large theatres wil l requireincremental cost increase ofcompared with a 250 watt unitalways install amplifiers with a

even more power however, thea 500 watt pow-er ampli f ier when

is trivial. If in doubt, a theatre shouldpower safety margin.

It is unlikely that any fi lm mix will take full use of the sRoD digitalcapability for more than an occasional "sting". Bu t examination ofanalog sR tracks shows regular clipping at 100%. so, for a veryminimum, power amplifiers should be able to reproduce th e typicallevels of analog sR. More power is required if a safe margin is to beprovided for sR analog, an d for playback of the digital Dolby stereosound-track.

Total insurance of enough power for a Dolby sR.D digital sound-trackcan be derived from Fig. 2.2. unlike some optimistic nomograms forpower requirements, this model takes no account of room volumeand reverberation time. Transient sounds (o f short duration) ar e no taugmented by reverberation, an d the required power for a givensound-pressure-levelat a specific seat s directly controlled by the directsound field - an inverse-square aw characteristicbased on how far thelistener is from the loudspeaker.l

1 On e of the diff icult ies in calculating sound pressure levels comes from theincreased reverberation times in large rooms. This increased reverberation willonly be applied to steady-state, or quasi-steady-state, signals. Dialog ismainly made up of short staccatosounds (l ike t's, k's, p's). Consequently a mixbalance created in a small room, with a short reverberation time, wili sounddifferent in a big room, with those music components with sustained sound.sbeing augmented by reverberation. Th e dialog may sound relatively qtrieterwith respect to the music. sound pressure levels for the playback of DolbysJereo ar e set up using pink noise, a quasi-steady state signal ,o,r. .u.Theoretically, this means that in a big auditorium (say 1000seatsor more), themusic will play at the same level as in a small room, but the staccatoelementsof dialog will play lower. I t can be argued on a theoretical basis that in areally big theatre, for dialog to have the same level as in a small theatre, thereferenceSPL should be increased from 85dBC to (say) 86 or g7dBC. The result

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The power requirement derived from Fig. 2. 2 is the total power neededfo r a screenchannel. If the system is bi-amped (virtually essential) hepower for each HF and LF section should be approximately two-thirdsof that shown.

For an analog SR sound-track, power amplifier headroom capabilitycan be tested by installing a Cat. No. 85C Dolby pink noise generatorinto the Dolby processor, and assuming Fader 7 is the normaloperating level, turning the fader up by 3 points, i.e. up to Fader 10 .Examine the power amplifier output signal on the oscilloscope, andconfirm that the signal is not cl ipped, which wil l be evidenced bysquaring of the signal peaks. Do not run this test for extended periodsof time, as loudspeakerscould be damaged. Th e test should be repeatedfo r each stage oudspeaker channel.

To verify power amplifier capability for a fully modulated sR.D digitalsound-track, the following test can be used...

A tone burst generator is used to insert a signal into the theatre soundsystem. The output level of the generator is se t such that it wouldgeneratea playback level in the theatre of 103 dB. Ideally, there shouldbe some means of br inging the level up from no sound to themaximum 103 dB level at a referenceseat two-thirds of the way back inthe house with a fader. Th e easiestway is to run the signal into thecinema processor and then use the house fader to control the level.The tone generator should be able to output tones at the followingfrequencies: (for Left, Center, Right, and each Surround Channel)63H2, 200H2, IkHz, 4kHz, and (for subwoofer) 50 Hz. The differentfrequencieswill give a better idea of the capabilities of the system if itlLas speakers that have a defic ient response and therefore needexcessiveeq (which limits headroom). The tone should be gated witha synchronous (zero crossing) switch that has an "on" time of 250 msec(3/4 sec) and an "off" time of 2 sec. In regards to damaging speakersfrom this high-level signal, the short "on" time with a relatively longwould be a consistent dialogstatesignals,sustainedmusic playback level, but an increase in level of steady-or effects.

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"off" t ime should al low for a real ist ic test of the sound systemheadroom without damaging the speakers (or, less ikely, the amps) inthe process. A storage scope is connected to the output of the poweramp for the channel to be tested. The tone-bursts are switched on forthat channel and the fader turned up while observing the scope trace.As the fader is raised to the 103 dB level look on the oscilloscope forsigns of the amplifier clipping. If the maximum level can be reachedwith no sign of clipping and with no audible sign of stress from theloudspeaker, the channel will probably be satisfactory for the demandsof a digital soundtrack.

2.1".2 ew |iffy test film

An updated version of the well-known Jiffy test fi lm is now availablefrom Dolby Laboratories. The new Jiffy test fi lm contains both an SRsoundtrack and a digital soundt rack. There are six minutes ofsubjective audio tests, n some casesdifferent for the analog and digitalsoundtracks, which include high-level tone bursts for checking poweramplifier and loudspeaker capability. The test film also contains somequick visual tests, to verify framing and checking for ghosting an dshutter problems.

2.2Screen oudspeakers2.2.1Location

The Left and Right screen oudspeakers should be mounted at the leftand r ight extremes of the screen width when the masking is ful lyopened fo r p ro jec t ion o f a 2 .35 :L (C inemascope) aspec t ra t ioanamorphic picture. I f screen masking covers these loudspeakerswhen a L.85:Lpicture is being projected, high-frequency attenuationdue to the screenmasking should not exceed2 dB at 8 kHz.

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Th e obvious intention of many elements in a stereo sound-track isthat a sound should seem to emanate from the same location as therelated picture irnage. when an actor closes a door at the left of thepicture, the sound of the closing door should come from the samelocation; when \,vesee a trumpet player close to the right edge of thescreen, he sound shoutrdcome from the same side of the screen. Theobjective of stereo sound is to place the apparent sound sourcesufficiently close to the image of the trumpet, in a way such that soundand picture together seem "real".

Listening to music in the home places no specific demands that stereowidth be accurately defined -- there is no picture to which the soundshould match. Typically, though, the two loudspeakers will subtend atotal included angle of around 60 degrees to the listener. In the homethe distances from the loudspeakers ar e short, and the room surfaces(furnishings) are absorbent -- as a result the l istener wil l heardominantly the direct signal frorn the loudspeakers.

In a commercial theatre, however -- no matter how small, and nomatter how absorbent the materials on the walls and ceiling - the pathlengths are so much greater that what most of the audience hears withnon-transient material is dominantly reverberant information comingfrom many directions, reflected from many room surfaces. This iswhy with a typical theatre layout, measurements show that at best onlyin the first row or two of seats does the near-field direct signaldominate.

As a result, from a prime seat where ,n" ,.*"., subtends an idealprojection angle of 45 degrees, he listener may hear an acoustic widthof only 25 or 30 degrees from loudspeakers typically 40 degrees apart,mounted at the screen ends. Further back, dominance of thereverberant field increases, an d acoustic width therefore narrows stil lrnore. Indeed, in the back rows of most theatres, so much directionalinformation is lost and the sound becomes so diffuse that few, if any,spot effects can be directly associated with the action on the screen.

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This progressive attenuation of stereo width towards the rear of thehouse explains the requirement for maximum possible width inloudspeaker placement. As fi lms ar e mixed to match picture in th edubbing theatre, it is difficult to conceive of situations where th escreen s so large, and the reverberation so short, that the sound imageis too wide for any of the audience no t sitting in the front one-or-tworows.

This requirement for maximum stereo width holds equally true withthe narrower screen mage of a 1.85:1movie, and to the maximumwidth of a 2.351 anamorphic pr int. Even though the masking hasmoved in to sharp-matte the 20"/"narrower picture image, the widestpossible audio image should be retained in this way, thesound/picture match will "work" for the largest possible percentageofthe audience.

Some years ago, narrowing the masking and covering the left andright loudspeakers when projecting a 1.85:1picture caused major audioproblems. (Not surprisingly, when considering the high-frequencyattenuation resulting from black felt!) Happily, new techniques an dmaterials have been developed to answer the problem. Black muslin,or acoustically-transparent, oudspeaker grille cloth (as used fo r high-fidelity loudspeakers) stretched over an "open" frame can be used foran insert covering the small area of the masking obscuring the high-frequency horns. For new theatres, masking cloth (Harkness 2000M)has been developed which appears matte blact, is acoustically virtuallytransparent and is only slightly more expensive than the black felt itmakes obsolete.l

Bu t even if acoustically transparent masking cloth is used, care shouldbe taken that the hard mounting edge (typically plywood) whichsupports the cloth does no t cover any part of the horn mouth. Careshould also be taken that cloih folded back on itself at the mountingedge does not attenuate the high-frequencies, and that "bunching"r Harkness Screens,The Gate Studios, Station Road, Boreham Wood, Herts WD6 1DQ, England,Tel: 081 953 3671,,Fax: 081 207 3657.

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masking cloth in front of a loudspeaker can cause severe high-frequency attenuation.

2.2.2Loudspeaker Type

Figure 2.2 can alsobe used for guidanceas to suitable oudspeakertypes. Manufacturers' i terature should be consulted as to themaximum power handling capabilityof a given loudspeaker. Whilethere are severalmanufacturers ffering a wide variety of loudspeakertypes, most quality theatres oday are nstallingbi-amplified systems,with a constantdirectivity high-frequencyhorn and a direct radiatorcone diaphragm-vented ox low-frequency nit.

2.2.3LoudspeakerWalls

Since the earliest days of loudspeaker design, it has been recognisedthat low-frequency response can be assisted by mounting thetransducer in a plane baff le. An infini te sized baff le puts thetransducer in what is termed a 2 pi space. This better bass efficiency iswhy the classic cinema loudspeaker for many years, the Altec 44, wasprovided with "wings", plane wooden sheets mounted on either sideof the LF unit. This concept wa s extended in the late seventies,whenthree or five ,A,4units would be connected with a wooden frame with asolid plane baffle connecting each unit. A similar idea was used byTomlinson Holman with the THX loudspeaker systeml, where theloudspeaker system is mounted in a wall , covered with soundabsorbent material. This baffle gets close to the theoretically perfect 2pi baffle, but if the wall extends from floor to ceiling it ca n alsoeffectively cancel transmission of rear screen echoes, as discussed later.

2.2.4Cross-overs

A bi-ampli f ied system, with active cross-overs, is an essentialrequirement of any high-quality contemporary theatre sound system.

ltHX is a registered trademark of Lucasfilm Ltd.

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The most important reason or bi-amping is the capability of powerhandling of bass and treble simultaneously. In addition, an activecross-over nablesa smooth characteristic ve r the cross-over egion,with minimum phase discontinuity. Active cross-oversalso makepossible a signal delay to the low-frequencyunit, improving coherencyof arrivals of HF and LF signals in the seating area, and furtherimproving signalphasecontinuity around the cross-over egion.

2.2.5StageLoudspeaker CharacteristicCurve

The B-chain frequency response of the Left, Center and Right screenchannels should conform to the wide-range characteristic defined in1502969. The response should ext end smoothly from 40 or 50Hz at lowfrequencies to significant ly beyond L0kHz, and ideally as far as 16kHz.The level difference between any two locations in the normal seatingarea, measured in 1/3 octaves rom L50H2 to 10kHz, should not exceed3dBl. SeeFigure 2.3.

The quality of a t heatre's B-chain can be assessed n two areas: first,how closely the curve matches the required frequency response; an dsecond, how uniformly the s ame response is maintained throughoutthe seating area. Matching the required response almost certainlyrequires use of bi-amplification and an active cross-over. The requireduniformity of response will normally make use of constant directivityhigh-frequency horns mandatory.

A complete discussion of B-chain equalization techniques can befound in each Dolby cinema processormanual.

rIn most theatres, the reverberant field dominates in most of the normal seatingarea. In small rooms, however, with a seating capacity of less than, say, 150seats, that sector of the audience seated closer to the screen receive a signaldominated by the direct field. ln such cases,nverse square law lossescan causea noticeable fall-off in energy over the first few rows of the theatre, and maymake it impossible to sustain the quoted 3dB figure. In these small theatres,the installer should verify a smooth fall-off with distance from the screen, andan even distribution laterally across the seating area.

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Note: ihe US A national equivalent standard to 1502969 is ANSIPH22.202M,and the British Standard is BS5550:7.4.1.

2.2.6Measurement

There is a discussion of B-chain measurement techniques in eachDolby cinema processor manual. Until the last few years, it wasnormal practice to use a single calibrated microphone, placed in a"normal" seat location, asymmetrically located with respect to thetheatre's centrelines, and set approximately two-thirds of the way backin the theatre. See Figure 2.4. A conscientious installer would thenmove the microphone to an alternative location, and "average" theequalisation for the best overall results.

In recent years, microphone mutltiplexers have come into increasingprominence, typ ica l ly w i th f our ca l ib ra ted mic rophones .Measurement of four locations in the theatre results in a much moreeven equalisation throughout the seating area. Practical experiencesuggests that best results are achieved with the microphones placedsubstantially in the reverberant field, in a layout such as that shown inFigure 2.5. Again, care should be taken not to place microphones oneach central axis of the theatre, where standing waves ca n causeaberrant conditions.

In mixdown, dubbing theatres, and small review rooms used for printquality control, where the listening/viewing area is small with respectto the size of the room, the microphone locations should be locatedwithin the area of interest.

The microphones should normally be mounted at listener's headheight. However, if the seats have high backs, the microphonesshould be raised up so that they are at least 9 inches above the top ofthe seat, thus avoiding any grazing effects.

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2.3SurroundLoudspeakers2.3.LNumber and Location

The first step in determining th e number, type and location ofsurround loudspeakers, is to consider the l ikely power handlingrequirements. Dolby SR , for example, can require a peak level in themiddle of the auditorium of a minimum of 92 dBC with normalprogram, and as much as 6dB more if the sound-track were used to itsful l low-frequency l imits. For an SR.D digital sound-track, theequivalent level is 103 dBC for a mono surround playback, or 100dBCfor individual left and right surround strings of a stereo surroundinstal lat ion. Assuming no assistance from reverberation ( ie themaximum peak level is that required to deliver a transient sound, seesection 2.1 .1 above), the dimensions of the theatre can be used tocalculate the total loudspeaker power required.

The first thing to do is to calculate the total electrical power required.In some cases he proximity of the surround speakers to a wall maycontribute to their efficiency. However, this factor has been omittedfrom the present calculation since it is only valid for low and middlefrequencies and only if the speakers are against a wall and not spacedaway f rom the actual hard surface.

The desired maximum rms sound pressure level at the listeners' earsis 100 dB per surround channel for a stereo surround configuration.The total electrical power required from each side's power amplifier isgiven by

/ Lp-S+20loe r \l - - lwart.s Io\ lo )whereLp = desiredSPL(100dB in this case)S = spe;rker ensitivity dB SPLat 1 meter distance or i watt inputr = distance rom wall to centerlineof theater n metresSeeFigure2.11

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Having determined the total electrical power required pe r side, wemust now find out how many speakers are required to handle thisamount of power. The number of speakersN is calculated from

N= electricalpower (calculated above) diuided by the power rating perspeaker

This is the minimum number of speakers per surround side requiredto handle the necessarypower. A greater number of speakers may berequired to secure good uniformity of coverage of the audience area.In practice, the numbe r of speakers required is the larger of the tw onumbers derived from coverage requirements and power handlingability.

The speakers should be connected in series/parallel so that they allreceive equal power and the impedance presented to the poweramplifier is around 4 ohms. Most well-designed modern amplifierswill drive 4 ohm loads with a somewhat higher power output thanthey will a B oh m load, bu t as this ability is a function of the details ofeach amplifier, the manufacturer's data should always be consulted.Some amplifiers will drive impedances lower than 4 ohms; again,consult the manual or manufacturer.It may be desirable in some installations to arrange th e series/parallelconnecticln so that the rear-most speakers receive slightly less powerthan the front ones. This is done to match the lower sound levelheard from th e screen speakers in the rear of the auditorium. Ingeneral, this practice is most appropriate in long rooms with shortreverberation times.

Next, consider that this power has to be shared by a given number ofloudspeakers, which should be spread about the back wall, and the tworear side walls of the theatre. Optimum sound balance betweenchannels dictates that surround loudspeakers should be evenly spreadfrom half-way back from the left side-wall, through the auditoriumback wall, to a point half-way up the right wall. This configuration

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takes account of the ratio of screen to surround sound pressure levels,u.,d uiro seems subjectively optimum when the visual dominance ofscreen activity is taken into account. (SeeFigure 2.6). Avoid placingany surround speakers further forward than 50% or 60"/, of the wayfrom the rear to the front of the house. Placing speakers too close toth e screen results in surround sound blending into screen sound foraudience in the middle part of the house (especially when the "draw"of visual screenaction is taken into account -- see Figure 2.7).

2.3.2Loudspeaker Type

Manufacturers' literature should be consulted for the power handlingof a given surround loudspeaker, and this determines the number ofspeakers equired.

Selection of a suitable type of loudspeaker, though, demandsassessmentof more than just power handling capability. Diffusion isalso a major requirement of surround channels, meaning thatsurround signals should never appear to come from a point source.This mea ns that a large number of loudspeakers are always preferableto a few, regardlessof power handling.

Avoiding local ization to a local speaker wi l l a lso be assisted byselecting a speaker without too wide a dispersion, as an excessivelywide dispersion will cause a domination of high-frequencies at the seatclosest,or directly under, a given loudspeaker. For this reason, three-way bookshelf-type units should be avoided, as wide dispersion is oneof the intended design parameters of these units, primarily designedfo r the home for music listening.

2.3.3Mounting Angles

Some types of loudspeakers intended for surround use are mounted ina box with a built-in down angle. Care should be taken not to acceptthis fixed angle as correct for any given auditorium. Depending on themounting height, the angle should be set to achieve the most uniform

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response across a lateral row of seats. In caseswhere a low ceilingresults in the surround speakers being mounted lower than would bedesirable, any downward cant would make a bad situation worse,enhancing local isation to the nearest loudspeaker for those seatsclosest o the walls. In such a situation the loudspeaker drivers shouldbe aimed horizontally, getting a percentage of the dominant directsignal above the heads of listeners n the closestseats.

2.3.4Characteristic Curve

The surround B-chain frequency response should conform to ISo2959from 125 Hz to 8 kHz, after correction for near-field response. Thelevel difference between any two locations in the normal seating area,measured in 1/3 octaves rom 150 Hz to 8 kHz, should no t exceed 3dB.Below 1.50H2 t may not be possible to achieve this 3dB tolerance,depending on the equalizer in use. Care should be taken, though, toachieve the smoothest possible response at these ower frequencies.

Matching the surround character ist ic to the target curve wil linvar iably require equalization, either with an optional moduleavailable from Dolby Laboratories, or in the case of the cP50, use of anoutboard free-standing equaliser. Achieving satisfactory uniformityrequires a moderately large number of surround loudspeakers.ceiling-mounted loudspeakers ar e unacceptable,as all fil ms ar e mixedassuming a hor izontal surround f ield; in addit ion, a very largenumber of ceil ing speakers would be needed to achieve uniform seat-to-seat response.

The bandwidth of the surround channel on a stereo optical fi lm isintentionally band-limited to around 7 kHz, to avoid the risk ofoperational problems such as bad sound-head azimuth, and excessiveimpulse noise with worn prints. SR.D digital sound-tracks, though,and occasional 70mm magnetic prints have full bandwidth discreteeffects on the surround track, and this will require analysis ofsurround loudspeaker responsebeyond 8 kHz. Surround equalizationis more or less essential or quality theatre sound, as otherwise panned

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sounds cannot move smoothly arou nd the theatre, or from front-to-back. For information on updating older Dolby cinema processors,seeSection 5.0 below.

Severalpsycho-acousticmechanisms ombine to cause he perceivedresponse rom surround speakers o differ from that of the screenloudspeakers.First, the surround information comes from a multiple array ofloudspeakers, as opposed to a single source. Second, part of the signalcomes from behind the listener, and the ear/brain combination reactsdifferently to sources behind the head. Finally, and probably of greatestsignificance, the average movie-goer selects a seat two-thirds of theway back in the theatre, and in a conventionally shaped theatre is thusnormally much closer to the surround loudspeakers than to thespeakers behind the screen. As a result, near-field response will be a fargreater percentage of the surround signal than the screen signal, wherefar-field components normally dominate.

This large number of var iables means that the ideal correctioncharacteristic will be unique for each theatre. Figure 2.8 shows howthe X-curve of 1502969 should be modified for surrouncl use in atypical theatre, where most of the audience is closer to surroundloudspeakers than to the screen.

2.3.5Measurement

Measurement microphones should be left in the same location aswhen used to measure the screen channels. In addi tion, they shouldnormally be left at the same orientation. A stereo surround set-upshould be measured and equalized independently for the left and rightchannels.

Reference evel (generatedwith a Cat. No. 85 Pink Noise Generator) is85 dBC for each stage loudspeaker. A monaural surround channelshould also be se t to 85 dBC, a procedure described in each Dolby

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cinema processor manual. with a stereo surround installation, forDolby SR.D or Dolby Stereo 70mm, the left and right surround chainsshould each be set to 82 dBC at the referencepink noise level.

2.4 Sub-woofersThe instal lat ion must include sub-woofer(s) , dr iven by dedicatedpower amplifiers--analog SR signals have to be derived from a bassextension module in the cinema processor.

Both Dolby Stereo 70mm magnetic and Dolby SR.D digital havededicated low-frequency channels, requiring sub-woofers -- and one ofthe main benefits of Dolby sR with optical sound-tracks is theimprovement in signal handling at frequency extremes. Figure 2.1shows the relat ive peak level capabil i t ies of an SR sound-trackcompared with those of mono and conventional Dolby Stereo. Thesignificant increase in potential low-frequency signal energy requiresthe use of dedicated sub-woofers. Existing theatre bass bins (such as .{4units) are nOt acceptable.

With a Dolby d igital sub-woofer track, the potential levels are evenhigher. Monitor levels ar e set for 10 dB of

"in-bandgain", as shown inFigure 2.9. This level setting procedure requires use of a real-time

analyzer. Attempting to use a sound-level meter for sub-woofer levelsetting is extremely unreliable, for several reasons:

a) Different sub-woofers have different effective low-pass filters,either caused by cabinet/speaker design, or by an actual low-pass filter.Even though the frequency range of interest is only up to 120 Hz withan SR.D track, the varying out-of-band components above I20 Hz canlead to variations of 3 or 4 dB when read on a sound level meter.

b) There can be a substantial variation between meters at lowfrequencies, where C-weighting is not necessarily accurately followed.

c) Room nodes can affect the loudness perceived by a soundlevel meter, whereas the eye can easily see the effect of nodes whenviewing the analyzer.

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As real-time analyzers are always needed to adjust notch-filtering ofroom nodes, as described in Section 2.4.4,use of an analyzer instead ofa sound-level meter does not affect installation time.

Many theatres which have been equipped with sub-woofers over thelast fev,' years have adequate relative low-frequency loudness whencompared with stage channels at mid and low-levels. Some containlimiters such that if overloaded go smoothly into saturation withoutany clipping distortion-in such a case th e signal may not sounddistorted, but the peak levels are not correctly replayed. Badly designedsub-woofers, though, show significant distortion components at alllevelsl , and non-linear frequency response. The bandwidth of thedigital sub-woofer channel on a Dolby digital sound-track extends from5 Hz to 720 Hz. A linear sub-woofer acoustic response is desirablefrom, say,25 Hz to 720Hz The 120 Hz sound-track cut-off is extremelysteep, so a suitable sub-woofer need have little response above thisfrequency.

2.4.1Location

While sub-woofer location is not critical, a single unit should not bemounted on the centre-line of the theatre. If two sub-woofer cabinetsare used, they should be mounted asymmetrically; ie thev should no fbe mounted equally spaced either s ide of the centre- l ine as forchannels 2(Le) and 4(Re) of a 70mm system. This asymmetr icmounting reduces stimulation of standing waves derived from roomdimensions.

To achieve maximum power, two sub-woofers should be mounted asclose together as possible, hus achievi ng cross-coupling. Standing twosub-woofers to one side of the centre channel loudspeaker is probably areasonabie solution. On th e other hand, if the target is to reduce thelevel of spot resonances, he two units should be separately mountedlFor background information see Engebretson, Low-Frequency SoundReproduction, }AES Ma y 7984, and Fielder and Benjamin, SubwooferPerfortnance for Accurate Reproduction of Music, |AES, |une 1988.

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at, say, one-third of the way frorn the left wall, and one-fifth of the wayfrom the right wall, though this, of course, will require more power.

2.4.2Need fo r Bass Extension with Dolbv SR

Modern main-channel loudspeaker systems have better low-frequencyperformance than systems designed a few years ago. However, extremelow frequency signal information requires special processing whenderived from an optical sound-track, in order to suppress "streaking"noise and other processing artifacts. This circuitry, and a parametricequalizer to smooth out the primary room node, is contained on th eoptical bass extension module -- Cat. No. 160 or Cat. No. 56 0 in CP50and CP200 units, Cat. No. 247 in CP55 units, and Cat. No. 441 in CP65units. Also, see Section 5.0 below for information on retrofit modulesfor Dolby SR.D digital playback.

2.4.3Tuning

Al l cinema processor sub-woofer driver modules contain a simpleparametric equalizer. This should always be used, as every room willhave at least one dominant resonant frequency, which if not dampedwill lead to a characteristic low-frequency "ringing" every time thesound-track contains extreme low frequency information. Instructionsfor adjusting the parametric equalizer can be found in each Dolbycinema processor manual.

2.4.4Pow er Requirements

For the playback of an analog optical soundtrack the subwooferchannel power requirements are not substantially different than astage channel, i.e. an amplifier of the same power rating as one usedfor the front stage channel should be adequate.

Fo r playback of an SR.D soundtrack however, th e power requirementsfor the subwoofer become more demanding. Tw o factors worktogether to raise the required amplifier size. One factor is the

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headroom avai lable in the subwoofer channel. Like the boomchannels on a Dolby Stereo 70mm mag print, the subwoofer channel isrecorded 10 dB lower than the other channels on a digital soundtrack.The cinema processor is then adjusted to playback 10 dB higher, thisproviding 10 dB more headroorn to produce effects ike explosions an dstings at more realistic levels. This level requirement irnplies anamplifier power requirement 10 dB or 10 times more than an y otherchannel.

In addition, though, the subwoofers normally used for cinemas ar eless efficient than the stage speakers. Most of the models used are atleast 3-5 dB less efficient than contem porary direct radiator stagespeakers. This means at least an additional 3 dB or two times morepower becauseof the lower efficiency of these speakers. Combined, therequirements become difficult - 13 dB or 20 times the power rating ofone of the screenchannel amps. Figure 2.10 s an outline of the powerrequirments of the subwoofer channel depending on the size of theauditorium and can be used to determine the amps needed. As can beseen from the chart, it makes sense to use a mod el of subwoofer thathas good efficiency since this will keep the power requirementssmaller. However, be aware of claims of unusually high efficiency forsubwoofers.In loudspeaker design the laws of physics limit the maximum amountof efficiency improvement that can be achieved without a tradeoff ineither low frequency response or enclosure size. In other words, for agiven size of speaker enclosure the efficiency of a system can beincreased bu t only at a loss to the low frequency performance of thatsystem. This is why bass bins for stage speakers that are about the samesize as subwoofers are more efficient but they cannot reproduce thedeep bass that can be produced by a true subwoofer design.

Fortunately, there are ways to make the amplifier demands morereasonable. Sometimes it can be relatively easy to get increasedheadroom from the existing system. Fo r example; if the systempresently has two subwoofers each rated at 8 ohms and one stereo amp

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with each half driving one sub, it may be possible to wire the two subsin parallel an d connect them across the amp running in a bridgedmono mode. If the amplifier is of good professional quality with thecapability of driving the equivalent of a 2 ohm load on each channel, itis possible to get as much as 4-5 dB more headroom by simply rewiringthe subwoofers in this fashion.

As mentioned earlier, multiple subwoofer units can be grouped to takeadvantage of mutual coupling. If the units are placed together ideally,doubling the number of subwoofers gives an extra 3 dB of outputIevel due to efficiency gained by mutual coupling. Figure 2.10 showsthe reduction in the ampli f ier power needed if more than onesubwoofer is used, assuming that they are mutually coupled. As anexample, if the system is as above with each half of a stereo ampdriving a single 8 ohm subwoofer, two more subwoofers can beinstalled (mounted close to the other two for coupling) each wired inparallel with each of th e other two, it can provide as much as 6 dBmore headroom than before. Half of the gain is due to the efficiencyincrease of doubling the number of units and the other 3 dB comesfrom the greater power output of the amplifier when driving a 4 ohmload on each channel instead of 8 ohms. Of course, one can always justbuy more and/or bigger amps. This however, quickly becomesunwieldy if the system is something like 10 dB deficient, and it isusually more practical to increase the efficiency of the system as well.

The placement of the subwoofer can also be critical if increasing theefficiency of the system is needed to keep the amplifier requirementspractical. Generally speaking the units should be mounted as close aspossible to as many boundary surfaces (read walls and floor) aspossible. This means that the subwoofers should be installed (coupledtogether) at least on the floor and if possible next to the back walland/or the side wall behind the screen. Unless the back wall behindthe screen is appreciably greater than 10 feet behind the screen it ismore desirable to have the subs back up against the wall on the floorinstead of up next to the masking. The increase in efficiency ispreferable to the small delay in the bass signal because of the

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subwoofer being slightly behind the stage speakers. Corner mountingof sub-woofers in this way, however, may lead to a more pronouncedprimary room resonance. A further increase in efficiency would resultfrom havi ng the unit on the floor, and mounted in a baffle wall thatextends to the dirnensions of the screen, this of course would help thebass response of the stage channels in their proper locations as w-ell.

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tl Di l0

- l - r - t - I - I - I - r - - t - l - t - r - I - t - r _t - r_- l_I_r__l_ l_ I_I* l_I _r_r_

I?-\ l I t -r--F-l-l--Fl- | t-t- 1--H- | j-H-Hi-F--- \--o-c --o-r+ rr.'Hr--.{FO-..+ O-tt-cHH.--o_

31.5 63 12s 250 500 t K 2K 4K 8K 16K HZ

Dotby tereoA-type l- polbystereosR -r-DolbystereoDigitalFigure2.1 Peakpower evels A-type,SR,SR.D

1 00

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1 1 0ALTEC A4 +108

106104

ALTECAS +102

JBL 46758,4670C _>100EV T59040D, TS940D

98JBL4673A +

96SPEAKER 94SENSITIVITYSPL@1w/ l M g2

90

200w315W500w800w1250W2000w

Power equired or eachscreenloudspeakerhannel.lf bi-amped, se at least2/3ofquotedpower or eachsection.

25 30 40 sO 60 80 100 1207.s 10 't2 1s 18 25 30 35Length t House romScreeno BackWall

15 0rts (FEEr)(METERS)

SINGLESCREENCHANNEL POWERREQUIREMENTS OR 103 dB SPL @ 2/3 BACK FROM SCREEN

Ftgure2.2 PowerNeeded ersusRoomSizeoto

20

- 2- 4- 6- 8

- 1 0-12- 1 4- 1 6- 1 8-20 -3 1 . 5 6 3 125 2 5 0 8 KKKK00 1 6 KH z

/ ! \ t lt l/ r t t t r t t t t t lNotes:a)adjustment o curve for smaller heatres - seel so2969b)adjustment o curve for very large heatres

l l l l l t t t t t r r r r r r r l

\ S\!'t]N\ \ \\\

\\\\

Figure2.3 StageLoudspeaker haracteristic urve


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Figure .4 SingleMicrophone qualizationocation

S C R E E N

Figure2.5 MultiplexedMicrophones qualizationocation


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IlIII

S C R E E N

I I I IGoodSurroundLocation

I

I IFigure .6IIIII

IItII; t i l t ; ;

Figure 2.7 Surrounds Too Far Forward


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dB420-246

- 1 0-12-14-16- 1 8-2031.5 125 4K

Figure .8 TypicalSurroundCharacteristic urve

1 K 1 6 KHz

.a / \ \/

7 \\ f.ai.

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Figure2.9 Sub-Woofer evelSetting

6 -'-> 20HO.OTUHTTS + 25MUTUALLYCOUPLED2 + 50

. 1 - > 1 0 510 6

304085

16 5

4565

1 3025 0

7010 0200400

11 0 17 0 26 5160 26 0 400323 500 8006s0 1000 1600 ..-.._->

SPEAKERSENSITIVITYs P L @ 1 w / l M(srNGLENrT)MEYER 650-R2JBL4642 +

EV TL88OD&BAG END ELFQ18E+,JBL 4645& E-V 3512+BAG ENDELF D18E +

BOSECANNON+

10 4

10 2

92

90

/vt/t/ / / / //777ry77 //7 /77 /77/ / //VA/V/ //i/l/v //ll//v

2500w 1250W

4000w 2000w

6KW 30(X)W

9.6KW 4.8KW

625W 415Wr000w 660w1500w 1000w2400w 1500w

Power requirements may vary dependingon room gain. ConsultDolbyLaboratoriesor information egardingimpedance atingsof variousmodels.

25 30 40 50 50 80 100 ',t20 1s0 (FEET)7.s 10 12 15 18 2s 30 3s 4s (METERS)

Length of House rom Screen o Back Wall

POWERREOUIREMENTSORSUBWOOFERS OR 113dB SPL @ 2/3BACKFROMSCREEN

Figure .10 Subwoofer owerRequirement


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SpeakerSensitivitydB/l watt at1 meterEV FR200BHPSSR70 {>

u$$9oo""dB)10 098

6s {watts)$""^"". Example:- Step 1: Surroundloudspeakersensitivity90 dB.Movehorizontally ohouse width (i n thisexample,32 feet),an dthen move updiagonally o findminimumpowerneeded,250watts.

Step2 See text onhow to find number ofloudspeakersneeded.

EVFRl2.2BJBL8340Kintek340

JBL8333d>JBL8330BostonA70 +EVTS8_2 >

949290888684

-l20 1003024 32 'rc 50 638 1 0 1 2 1 4 1 6 8018 24 (Feel)(Meters)Width ot House

Figure2.11 Powerneededor a singlesurround hannel leftor right) or100dB SPLat centerof house. (See ext,Section2.3.1)

=- s6,/1,/1,/ /

// 7 7 7 7 / 7 ,//VV,n#,/1,/1,/1,/,/1,/1,/1,/,/1,/1,/,/ l,/


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3.0A-Chain3.1. nalog

3.1.1 requencyResponseThe equalizedA-chain frequency esponse,measuredat the Lt and Rtpre-amplifier outputs, should be flat to within +1 dB from 30 Hz to'l.4kHz. When a pink noise test film is used, and the pre-amplifierresponsemeasured n third-octaves,he output should be flat up toand including the 12.5 Hz band, and no more han 3dB down in the'l.6kHzband.Later versions of optical pre-amplifier boards installed in Dolby theatreequipment exhibit improved stability, and better linearity and phaseresponse at high-frequencies. CP50 and CP20 0 units should ideally beupdated with CN108 pre-amplifier cards of Revision C. All CP55 andCP65unit pre-amplifiers have adequate performance. See Section 138below.

A complete discussion of A-chain alignment can be found in eachDolby cinema processor manual.

3.1".2 lit

This bandwidth specification ideally requires a projector sound-headslit height of around 0.00075".A slit height of 0.00100" s unacceptableas impossibly large amounts of hf boost are needed to achieve a flatresponse above 10 kHz. A slit height of less than 0.00050" performsbetter at high frequencies, but the need for increased pre-amplifier gainmay make the system more prone to spurious interference resultingfrom stray light landing on the solar cell.l

r Most prrojectormanufacturers offer retro-fit slit lens assembleieswith a slit height of 0.00050or0.00075'. In addition, slit-lens assemblies or a variety of projectors are manufactured by Sankor Ltd.,distributed by Marble Company Incorporated, P.O. Box 150080,427Hart Lane, Nashville, TN 37276,T el: 675 227 7772, 800-7 9 5905,Fax 615-228-1 01.

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The pink noiseon current Cat. No. 69 optical test film has a frequencyresponse early lat up to 16kHz, as shown in the calibrationchart nFigure 3.1. The old black and white Cat. No.69 test f i lm has beenreplacedby two new test films. Cat. No.69T (Dolby Tone) and Cat.No.69P (pink noise) are both now printed on color stock, whichrepresents eleaseprint behavior more accurately. The color stockfades, however, so the test films should be replacedafter about sixmonths of use.

3.1.3ExciterLamp/SupplyThe exciter amp supply should havea regulatedoutput.An unregulatedexciter lamp supply results in gain variations,baddecode racking,and can causeaudiblehum.A well-designed egulatedsupply will have a ripple level of less han3%.

3.1.4 l lumination Uniformitv

The projector sound-head optical assembly should provide uniformil lumination across he sl i t . when measured with a snake-track testf i lm, output var iat ions should not exceed + 2dB from the averagelevel.

lJneven illumination along the slit is frequently the cause of bad -quality optical sound playback. Level-dependent distortion and badstereo imaging are the two most obvious results.

The most likely causes f uneven llumination are:Dirty opticsor slitMisalignedopticsDirty or carbonizedexciter ampInsufficient voltage for exciter amp

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and less ikely:Uneven slit width resulting rom bad machining

One method of checking llumination uniformity is to run a scanningbeam uniformity test film (snake-track)oop (SMPTETest Film No.P35-SBor equivalent),and to evaluate the summed Lt and Rt pre-amplifier outputs (or the center channel processoroutput with theunit set to mono, Format01)with an AC milli-voltmeter,or preferablyan oscilloscope.A new t est film is also available from Dolby Laboratories to checki l lumination uniformity quickly and simply. The Cat. No.566 testfilm provides an instant visual display of any il lumination problemsand only requires th e us e of a real-time analyzer.

3.1..5Wow and Flutter

The projector should exhibit no audible wow or flutter.

Most contemporary first-class projectors have sound-heads designedand manufactured to a quality such that wow and flutter will notprove a problem. Badly maintained older projectors and some inferiorcontemporary designs, though, can have severe sound-head transportspeed problems -- detectable speed variation is one of the few failingsthat can render a well-aligned A-chain playing an SR optical fi lmaudibly inferior to a 16-bit digital system.

It is generally accepted that flutt er should be less than 0.15% DINweighted to be inaudible. Measurement methods I are described n IEC386,and a suitable est film is available from the SMPTE (No. P35-FL).A subjective test for wow and flutter is contained in the Jiffy test filmfrom Dolby Laboratories,Cat. No. 251.

1A suitable meter for measuring wow and flutter isInstruments, ]apan-Model Number LFM-39A

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If cleaning and lubrication of the sound-head is carried out accordingto the manufacturer's recommendations, and the measured flutter isstil l unacceptable, a skilled mechanic should be consulted. In somecases,machining and balancing the flywheel and sound-drum, or therebuilding of bearings, can reduce the problems to an acceptable evel.3.2Digital

It is impclrtant to note that factors such as mechanical alignment,i l lumination uniformity, and pr int cleanl iness which affect soundquality of analog playback in a more-or-less inear way, may have noimmediate audible effect in digital playback, bu t serve to reduce themargin for error when defects such as scratches or dir t areencountered.

Figure 3.2 shows, in symbolic form, the effects of misal ignment,uniformity of il lumination, wear, and cleanliness on the reproductionof a nalog and digital prints.

3.2.1Alignment

Digital soundheads manufactured by Dolby Laboratories ar e factoryaligned, and no on-site adjustments to the soundhead should berequired. Verification of correct alignment is described in the DA10d ig i ta l f i lm sound processor ins ta l le r ' s manua l . Mechan ica lalignment of the Soundhead with respect to the projector fi lm pathmay be verified by threading a length of fi lm through the Soundheadand observing equal tension on each edge.

3.2.2t/Vow and Fl utter

The elimination of flutter components at frequencies greater than 96Hz which are not present in the master recording is inherent in thereproduction of sound by the digital processor. This is because theoutput sample rate is held constant for the duration of a perforation.

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Lower frequ ency flutter and wow from mechanical inperfections areattenuated by digital filtering of the sample rate generator controlfunction. Steps in sample rate ar e limited to approximately 0.005%,afactor of around 30 below the audible minimum. A much higher"slew rate" of about 6.4% / second (about L semitone / second) ispermitted during projector ramp-up to speed in order to avoid gettingou t of synchronization with the picture.

Although digital processors from Dolby Laboratories are designed totrack projector speed variations w ith a range from -7"/"at 24 fps to +7ohat 25 fps, best performance will be obtained by maintaining projectorspeed as closely as possible o the intended speed as recorded.

3.2.3 l lumination Uniformitv

The illumination source for Dolby Digital Soundheads is a tungsten-halogen projector bulb. Uniformity of il lumination may be verified byobserving the video signal at the DA10 on a 25MHz osci l l iscope,triggered by any Dolby digital signal; the process is fully described inthe DA10 and DA20 Instal l ion manuals. I l lumination should beuniform over the width of the perforation area to within +0.5 Volt.

3.2.4Exciter Lamp / Supply

Th e digital soundhead exciter lamp supply should be a DC regulatedpower supply set for 11 Vdc, supplying approx. 6 Amps for each lampand fan. Polarity must be observed, not for the lamp, but to ensure thatfan rotation is correct. In an emergency, any DC supply with adequatecapacity and regulat ion of 3"/"or better will serve.

3.2.5Soundheadand Surround Delav

Proper adjustment of Soundhead Delay and Surround Delay arecritical to setup of the Digitai I'rocess or. Complete procedures for delayadjustments are contained in the DA10 and DA20 Installer's Manuals.It should be noted that the optimum surround delay setting for a

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digital processor is different from that for surround playback of ananalog surround track. The requirement fo r playback of a digitalsurround channel is to achieve coherent arr ivals of screen andsurround sounds over the optimum seating area. For an analogsound-track, sl ightly greater delay is required, so as to achievemaskingl of any crosstalk from front channels to the surrounds.

Figure 3.3 provides a table of approximate delays for digital surrounddelays. Aproximately 15mSecshould be added to these numbers fo ranaiog surround delay settings. In a small theatre, the height of thesurround speakersshould be taken into account, bearing in mind thatthe table is based on the difference in path lengths at the optimumseating area to the screen channels and the closest surroundloudspeakers.

rFor a discussion of how acoustic masking is used to suppress crosstalk in 4:2:4matrix systems, see "MultiChannel Audio and Surround Sound in the MovieTheatre and in the Home," Dolby Pub. No. 588/8292

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I ' l[t:: lt=l[:! j.1 Flr=I.a...!11 r "ili j rjr, l: : i l: l! rSri f.:tt ' l[,.][::.::;]"f;:E:,'':,..':i f, l L :!:L1l' t:tt:.1-f.,a 5:,1i - t-.i:i*-;

Figure .1 Gat.No69PinkNoiseFrequency esponse

tud ib leQual i t y tudib leQual i tyProblem*DIGITALIncreas ing Increas ing

Figure .2 Analog ersusDigitalProblem udibility


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Width (i n20 30 40 50 60 7A 80 90 100 1 1 0 120 130 14020 1 0 1 0 1 0 1 0 1 0 l n 1 0 1 0 1 0 1 0 1 0 1 0 1 030 1 0 1 0 I \ J 1 o 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 040 20 20 20 20 20 20 20 20 20 20 2A 20 z v50 30 20 20 20 20 20 20 20 20 20 20 zv z v60 30 30 30 30 30 30 30 30 30 30 30 30 ?n70 40 30 30 30 30 30 30 30 30 30 30 30 3080 50 40 40 40 40 40 40 40 40 40 40 4A 4090 50 50 40 40 40 40 40 40 40 40 40 40 40100 60 50 50 50 50 50 50 50 50 50 50 50 t rn1 1 0 70 60 60 50 50 50 50 50 50 50 50 50120 70 70 60 60 50 50 50 50 50 50 50 50 50130 80 80 70 70 60 60 60 60 60 60 60 60 60140 90 80 80 70 70 60 60 60 60 60 60 60 60

150 90 90 80 80 80 70 70 70 70 70 70 70 70160 100 100 90 90 80 80 70 70 70 70 70 70 70170 1 1 0 1 0 0 100 90 90 80 80 80 80 80 80 80 BO180 1 1 0 1 1 0 100 100 100 90 90 80 80 80 80 80 BO190 120 120 1 1 0 1 1 0 100 100 90 90 90 90 90 90 90200 1 3 0 120 120 1 1 0 1 1 0 100 100 100 90 90 90 90 90

Length(infeet)

Length(inmetres)

width1 0 1 5 20 25 30 35 40 45 501 0 20 20 20 20 20 20 20 20 201 5 20 20 20 20 20 20 20 20 202A 30 30 30 30 30 30 30 30 3025 40 40 40 40 40 40 40 40 4030 50 50 50 50 50 50 50 50 5035 60 60 50 50 50 50 50 50 5040 BO 70 60 60 60 60 60 60 6045 90 BO 70 70 70 70 70 70 7050 100 90 80 80 80 BO 80 80 8055 1 1 0 100 90 90 80 80 80 80 8060 120 1 1 0 1 1 0 1 00 90 90 90 90 9065 130 124 120 1 1 0 100 1 00 100 100 10070 140 140 130 120 1 1 0 1 1 0 1 1 0 1 1 0 1 1 075 150 150 140 130 120 120 1 1 0 1 1 0 1 1 0

Figure .3 DigitalSurroundDelaySetting


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4.0Acoustics4.l Criteria

4.1.1Noise FloorThe steady-state heatre noise floor should preferably be below NC25,with NC30 the worst case acceptable. ntermittent increased noisefloors should not exceedNC35.

Dolby SR and SR.D sound-tracks canwell as louder peaks than conventionalthese subtle components requires extralevels in the theatre.

contain very quiet sounds, asfilm sound-tracks.Playbackofattention o backgroundnoise

Background noises can be broken into two types: steady-state noise,causedby HVAC equipment, refrigerators, projector noise an d distanttraffic rumble; and intermittent noise, caused by adjacent traffic noise,aircraft noise, footfall and adjacent screen breakthrough.

Figure 4.1 details the frequency characteristics of a family of NC curvesin the range of interest. It should be noted that these curves show theNC figures for noise measurements made in whole octave bands, asconventionally used for background noise measurements. Figure 4. 2shows a family of curves for use in third-octave bands.

Normal techniques for background noise measurements are intendedto quantify steady-state noises, and may not adequately define th eannovance of "chatter" noise, such as running projectors. Such noisesshould be subjectively inaudible in the seating area.

Reference:SMPTE RP141-- Background Acoustic Noise Levels

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4.L.2Reverberation Time

The reverberation character ist ic or a theatre should be within theranges shown in Figures 4. 3 and 4.4.

Certain acoustic parameters differ depending whether a space isintended for music performance (a concert hall), or fi lm sound-trackreproduction (a cinema). The most obvious of these is reverberation,which in the cinema should be effectively as lo w as possible, and inthe concert hall may consciously be extended in the design, to improvethe subjective oudness of the music, and to make a more pleasnntsound. In the cinema, the pr ime requirement is a more accuratesound; reverberation needed to make the sound more pleasant isadded dur ing the mix dur ing sound-track production. As mostdubbing theatres are now moderately small, with short reverberationtimes, the mix will add adequate reverberation for all replay theatres.

Within reason, the reverberation characteristic of a theatre should beas short as possible. Excessive everberation results in coloring of thesound an d reduced intell igibil ity of the dialog. Assuming a theatre isbuilt with sound absorbent material on all surfaces, the resultantreverberation character ist ic wi l l increase with room size, inconsequence of greater reflection time delays caused by increased pathlengths. Figure 4.3 shows the recommended reverberation time at500 Hz for varying room volumes.

In normal rooms, absorbency is lowest at low frequencies and greatestat high frequencies, especially as attenuation in air increases withfrequency. As a result, reverberation time will normally increase atlow frequencies,and become increasingly shorter at high frequencies.This changing characteristic should be smooth, and above 150Hz, ifmeasured in third-octaves, there should be no reversals; i.e. no higherband should show a higher reverb-time.

Figure 4.4 shows the acceptable range of reverberation time changewith frequency. This is a scaling curve, and the value at a given

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frequency should be multiplied by the optimum reverberation time at500 Hz found from Figure 4.3.1

4.1..3 eflections

Optimization of reverberation time, though, is not enough to ensuregood acoustics. A good theatre design will also avoid resonancesandreflections. Good practice dictates that the front of the loudspeakerwall should be heavily damped with sound absorbing material, andeven more important, that the rear wall of the auditorium should beheavily damped. Any theatres stil l using ,A.4 ype loudspeakers withwings should apply sound absorbing material to the front surface.Acoustically absorbent material can be added to an existing theatre, butnew theatre designs should also consider issues such as minimumport glass size (see below), as too large a glass area in the projectionroom wall can cause both picture and sound-reflection problems.Other sound reflection problems can come from converted oldtheatres with proscenium arches which face the screen, and ceilingbeams and vertical column faces reflecting sound from the screen.

4.1.4Early Lateral Reflections

Another difference in acoustic requirements between cinema andconcert hal ls relates to the desirabi l i ty of ear ly lateral ref lect ions(sounds that reflect of f th e side walls at the front of the auditorium).In a concert hall, with a music performance, these reflections can beattractive, adding to stereo width, and giving the music more "body".But the same effect with dialog in a cinema can be disastrous to speechintell igibil ity, as the central speech mage becomes diffuse, and thereare multiple delayed reflections. For this reason, the side walls at thefront of a cinema should be as absorbent as possible, and theloudspeakers should have a spatial response tailored to mini mise theamount of signal which can hit the side walls (especially at frequenciesabove, say, 500H2). The controlled directivity from use of horns is the

I Reverberation time measurement techniques are discussed in ISO3382.

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only practical way this can be achieved. Direct radiator coneloudspeakersare no t suitable or stage oudspeakeruse, as not onlywill energy be reflected off the side-walls,bu t signals will also bereflectedoff the ceiling, further muddying dialog clarity.

4.L.5RearScreenDamping

No behind-screen acoustic reflections should be audible in the seatingarea.

Behind screen echoes have historically been responsible fo r many ofthe intell igibil ity problems with cinema sound. The most effectivemethod of achieving screen front/back isolat ion is to mount theloudspeakers as integral elements within a well-damped wall; this willblock all but the lowest frequency back-screenaudio. The front surfaceshould be covered with acoustic absorbent material, damping anyfront/back reflections in the auditorium.

A wall also creates a perfect plane baff le, as descr ibed in classicloudspeaker design literature, thus significantly improving extremelow-frequency response and linearity. This is one of the reasons that aloudspeaker wall is one of the major elements of the THX loudspeakersystem.

Without an isolation wall, attenuation of behind-screen reflectionsbecomes much more difficult. The first and most obvious requirementis that the high-frequency horns should be mounted as close aspossible to the rear of the projection screen, minimizing acousticreflections off the screen surface itself. (The front of the horn shouldnever be more than an inch or two from the screen.) Next, eachloudspeaker assembly should be draped with substantial acousticallyabsorbent material, wrapping the entire assembly up against thescreen. Finaliy, as much of the cavity surface area behind the screen aspossible -- rear wall, side-walls and ceiling -- should be covered inabsorbent material.

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On e further consideration relating to systems without a loudspeakerwall is that the front surface of any large area bass bins, (and evenmore important, if fitted, the speaker wings), should have absorbentmaterial mounted on front surfaces with cut-outs for the woofers.Without such material, significant reflective "ping-pong" echoes canbuild up between the scre en and the parallel rear wall of the theatre.

4.2 New Theatre Design

Interior acoustics are of most importance for dialog intell igibil ity.Excess eflected sound can result in flutter echoes or reverberationwhich diminishes dialogue intelligibility.

It is not necessary to provide specific sound-reflecting surfaces inmotion picture theatres. Most of the surfacescan be sound-absorbing.Some might argue that it would become difficult to sustain adequateloudness; suitable modern power ampli f iers and loudspeakers,however, can easi ly be selected which provide enough power.Experience indicates that sound-absorbing rooms promote excellentspeech ntelligibility provided they are reasonably quiet.

Sound-absorbing material can be used to reduce reverberation andcontrol echoes. Standing waves can result in low-frequency roomresonanceswhich accentuatea "boomy" quality. Standing waves canbe controlled using sound-absorbing material with an air spacebehind,such as a lay- in cei l ing.

4.2.1New Theatre Location

Selecta quiet iocation to reduce the costs of construct ion to preventnoise intrusions. Areas and adiacencies o avoid:

a) Next to window glazing.

b) Building service areas such as toilets, mechanicalelectrical rooms and elevator equipment rooms.

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c) Other noise generating adjacencies.

Remember to review the use of spaces above and below the theatre forpotential noise generation. Avoid locations beneath equipmentrooms, and dance and exercise studios, or above parking garages orsubway train lines. Airport fl ight paths, truck loading areas, and busytraffic intersections should also be considered during site selection, asthe increasedcost of adequate sound isolation may be significant.

Never locate a theatre below a curb-mounted ai r handler with directbottom inlet and discharge, unless the ductwork is fully enclosed inspecial sound attenuation construction.

4.2.2Ceilings

In order to avoid excessivebass, specify a lay-in ceiling with sound-absorbing tiles having an NRC rating of 0.90 or greater. The tiles ar etypically comprised of 1.5" thick fiberglass with a painted glass clothfacing.

4.2.3 loorsUnless absolutely mpossible,aisles and f loors should always becarpeted.

4.2.4WallsSound TransmissionDesignCriteriaWalls, doors and floor/ceiling constructions re rated for their soundtransmission ropertiesaccording o ASTM Standards890, E336,andC413which result in a single igure of merit rating system known asSound TransmissionClass,or STC.The selection of appropriate STC ratings needs to be made on the basisof the background noise criteria selected in the theatre and the level of

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noise anticipated in the adjoining spaces. Continuous backgroundnoise can play an important role in perceived sound isolat ion bymasking transmitted sound. The su m of the STC rating plus NCrating should always equal or exceed 95 at common walls betweentheatres. Other sources of intrusive noise should be evaluated.Al l sound-rated part i t ions must incorporate ful l height slab-to-structure framing containing fibrous insulation and gypsum boardsealedairtight at the head and sill with a bead of acoustic sealant. Allpenetrations must be sealed airtight and recessedboxes fully enclosed.Four-gang and smaller junction boxes can be sealed using sheetcaulking on the back and sides, as shown in Figure 4.5. Larger boxesca n be effectively sealed using one-hour fire-rated gypsum boardconstruction. Comply with the standards outlined in ASTM Standard8497, "Installation of Fixed Partitions of Light Frame Type for thePurpose of Conserving Their Sound Insulation Efficiency."

Figure 4.6 shows minimal and typical multiplex demising wall designsnecessary o a chieve acceptableauditorium isolation.

Table 2 below presents suitable STC ratings. Note that highernumerical STC ratings transmit less sound, and higher NC ratingspermit louder background sound due to the ventilation system.

Table 2: STC Ratings for Common Walls Between Theatres

Minimum in-situSTC Rating Noise Criteria Description

STC60 NC 35 Minimum StandardSTC65 NC 30 TypicalSTC70 NC 25 Desirable

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In order to avoid sound "flanking" the walls, continuous metal roofdecks are d iscouraged wi thou t gypsum board ce i l ings , andindependent floor slabs with an elastic joint are required at srC 65 andgreater walls.

Figure 4.7 shows a more sophisticated wall design, used to ensureisolation between projection rooms and auditorium -- a constructionof this type can be a major element in isolat ing projector andmachinery room noise.

Sound-Absorbing Wall Treatments

The wall behind the audience should be covered in sound-absorbingmaterial entirely.

Typical sound-absorbing panels are comprised of 1.5" thick glass-fiber-core wrapped in porous fabr ic having inherent f lame-resistantproperties. Panels are available with fabric edge wrapped conditionsand with resin hardened edges, metal, or wood frames. Complete pre-fabricated sound-absorbing panels are available.

If the side walls are not angled, avoid hard flat parallel gypsum boardsurfaces facing one another across the room, particularly in theaudience area at ear height, in order to avoid flutter echoes.

4.2.5Seats

Choice of seat design can have a significant effect on acoustic quality,especially in the small theatre. This becomes obvious when standingat the screen and looki ng at what the loudspeaker "sees" -- a majorpart of the sound field will be seats,or optimistically, audience.

First, a seat should be chosen which will be sufficiently damped as tooffer no reflections to the screen. If the seats have fold-up bases(squabs), he undersurface should be damped. Never use seatswith aplastic or metal reflective undersurface.

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Next, an ideal seat ha s acoustic properties that do not change when aperson sits in it; ie the absorption with respect to frequency does notchange. In this way, regardless of what percentage of the house is filledwith audience, the frequency response wili be the same. Better qualityseat manufacturers will provide inf ormation on this subject; contactDolby Laboratories for information on testing procedures if yo u w ishto carry out your own evalrrati


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consideration could also be given to the use of stanchion supports onthe roof. Noise from the air-handler is transmitted in two ways: directtransmission of rumble through the building structure, an d airbornenoise through the ducted air. If air-handlers have to be mounted onthe roof at auditorium corners as described,extend the ducting as far aspossible before a downturn to reduce airborne noise.

All air handlers and projector exhaust fans must be vibration isolated.

Agnin, never locate air-handling devices on the roof directly over thetheatre.

Air Handling and Distr ibution

Review supply air diffuser selections and specify an NC rating fivepoints less than required.

Lav out supply air ductwork and registers to have equivalent ductlengths between diffusers and the fan.

Only those ducts, pipes and conduits essential to serve a specificauditorium space should be allowed to penetrate ts walls.Supply Air Ductwork

Provide an exclusive duct branch and zone system to serve eachauditorium/screen so as to avoid crosstalk.

Size ductwork mains over the theatre to have one-inch thick internalduct liner.

The discharge sound level of the supply fan being used should bereviewed in order to specify the appropriate duct length and/or soundattenuator.

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Excess urbulencegenerated oisemay be avoided byturns; provide long radius elbows. If unavoidable,turning vanes.

Dampers

using 90o ductspecify air-foil

Dampers should never be located directly behind the face of the airdistr ibution device.

Plumbing and Piping Systems

Avoid locating plumbing and rainwater leaders in the walls or ceilingspaces of the theatre.

Any piping located in the walls or ceiling of the theatre space shouldbe attached with resilient mountings.

Provide a clearancebetween pipes and gypsum board or other finishsurfaces. Do not allow pipes to make rigid metal-to-metal contactbetween ceiling hanger wires, supports, framing, or other structure towhich finishes are attached.

Penetrations

Ducts penetrating the sound-rated wall or floor/ceiling constructionshould be in an insulated sleeve packed with one-inch thick mineralwool fire safing and sealed on both sides using backer rod andacoustical sealant.

Piping penetrations less than three inches in diameter should besealedusing acoustic sealant fi l l ing a 1/4-inch clearance. Larger pipesshould be treated similar to ducts.

Avoid any back-t o-back penetrations, such as electrical panel boards,junction boxes or fire extinguisher cabinets. Offset penetrations twostud cavities.

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4.3.2HVAC Maintenance

Regular HVAC maintenance is essential to ensure t he minimumnoise level the system is capable of. Bearings should be lubricated, andbelt tension and condition verified, at manufacturers' recommendedintervals; most important, fi lters should be cleaned on a scheduledbasis. Dirty filters have been found responsible for a theatre noisef loor 10dB above the measured f igure at the t ime of systeminstal lat ion.

4.4 Sound Isolat ion

4.4.LCeilings and Floors

A suspended gypsum board ceiling must be specified f:

a) Air-handl ing equipment is located above the room (aconcrete floating floor may be necessary n the equipment room).

b) The floor above the theatre is uncarpeted.

c) The floor slab above is not at least six inches of regular weightconcrete.

d) The Sound Transmission Class of the f loor/ceil ir,gconstructionwill be inadequateusing a lay-in tile (i.e., ightweightwood frame construction).Provide mineral wool or fiberglass nsulation above all gypsum boardceilings.The above analysis should also be conducted on the floor/ceilingassemblybelow the theatre. Gypsum board ceilings are generallynecessaryn lightweight wood frame constructionwhere concrete snot used.

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4.4.3Doors

Doors are among the most likely paths of noise intrusions. Vestibulesare the most rel iable means to obtain adequate noise reductionwithout extensive care in specif ication and qual i ty assuranceprocedures during construction, including performance verification ofthe actual instal lat ion. The vestibule should be carpeted, have asound-absorbing lay-in ceiling, and have full-height walls which ar einsulated and faced with wall carpet.

A very simple test for obvious sound leakage is to switch offauditorium lights and look for any visible light leakagearound thedoors.Table 3: Typical STC Ratings for Sound-Rated Doors

STC 35 1-3 4 inch thic k solid-corer,r.'ood oor with doublegasketing at the head andfambs and fixed thresholdwith door bottom.

Useonly at vestibuleorguardedentry conditions.

STC 412 2 -1 / 4 i nch thick sound-ratedwood door and adjustableneoprene head and jambgasketing with flat thresholdand automatic door bottom.

Use only at carpetedcorridorswhich aredesignated squietzones.

STC49 2-L 4 inch thick insulatedsteel door having tandemoffset magnetic gasketsat thehead and iambs with cam-lifthinges and flat threshold.

Require manufacturer'sauthorized representative tosupervise installation andprepare punch list.

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?E 1.03 o.s3 o.Bo o.7: 0.6tr o.str o.4zoF- 0.3IE]U(Dtr o.2Ll.J(r

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Figure .4 ReverberationcalingCurve or AudioBandwidth


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Figure .5 JunctionBoxTreatment

GYPSUM OARD

1/4"GAP.CAULKAIRTTGHTALL AROUNDPERIMETER

OUTLETBOX PADSWRAPPEDAROUND UNCTION OX TOSEALAIBTIGHTNOTE:SEPARATE UNCTIONBOXESONOPPOSITE IDESOF THEWALLBY 16"MINIMUM.

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GYPSUM OARD

a) BETTER HANMASONRY LONE

b) PREFERREDORSR.D

Figure .6 RecommendedemisingWallDesign


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_ 1 r 0 r lwPtcAL I

2 LAYERS5/8"GYP.BD .

BATil NSULATION

TYPICALC4x16MT LSTUDSC 16" o/c

Figure .7 Screening oom/ProjectionoomMinimumWallDesign

Height ot RoomDivided by Widlh

1.0 1_1 1.2 1 .3 r .4 t .5 1 .6 1 .7 1 .8 1 .9 2 .0Length of Room Divided by Wirfth

Note: Enter drawing with ratio of length to width of room. Proceedup to black line,andthen movehorizontallyo f ind ratioof height o width. Example ength o width s 1.5:1.Move rom 1.5up to black ine, hen horizontallyo 0.65. Height hould be 0.65of width.Blackdot representsgood cinema practice. Bad acoustics maywell result rom anydesign outside he hatchedarea.

0.950.900.850.800.750.700.650.60

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\ Op IW\4 ?h 7ffi'.WFigure4.8 OptimumTheatreShape


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5.0CinemaProcessor pdates5.1CPs0

While theoretically he CP50could be updated for the playbackof theDolby SR.D sound-track, he cost of labour and material necessaryapproach the cost of a new Dolby CP65, and so such an updateapproach s stronglydiscouraged.

5.2 CP55 and CP200

Many boards in cinema processors manufactured by Dolby Laboratorieshave been replaced from time-to- t ime with new versions withsuperior performance. Taking full advantage of the specifications of aDolby SR and SR.D film will require updating selectedboards.

Matrix decoders. Significant improvements have been made by Dolbyengineers over the years in the technology used to decode the fourchannels (L,C,R and S) from the two tracks on the fi lm. Currentrnodules provide stable inter-channel separation adequate to beindistinguishable from discrete sound-tracks with much programmaterial. As "discreteness" is frequently quoted to be superior with70mm magnetic when compared with simple matrix decoders usedwith 35mm stereo optical, updating to the latest technology is wellworthwhile for SR plavback.

Current (since 7992) production versions of the Cat. No. 150 decodermodule are Revision E. Currently acceptable modules date back toRevision D, which was introduced at Seri al Number 12000. n additionto super ior decoding performance, the current modules haveincreased headroom for all channels, and a low-noise surround delaycircuit -- both of benefit with the wider dynamic range of Dolby SRfi lms. Cat. No. 150 modules of revisions A, B, and C should bereplaced;old Cat. No. 116 decoders ar e certainly unacceptable for SRplayback.

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Optical pre-amplifiers. Later versions of optical pre-amplifier boardsinstalled in Dolby theatre equipment exhibit significantly improvedhigh-frequency response, improved stability and better linearity an dphase response at high frequencies. CP50 and CP200 units should beupdated with CN108 pre-ampli f ier cards of Revision C, which wasintroduced with Ser ial Number 11570.Al l CP55 and CP65 unit pre-amplifiers have adequate performance.

Dynamic range. Dolby SR and Dolby SR.D playback may also justifyupdating other modules in older CP50 and CP200 cinema processors.Some ear ly boards have performance specif ications more thanadequate o play back conventional mono and Dolby Stereo films, bu texhibit headroom and noise floor character ist ics which could beimproved for the new sound-tracks. Cat. No. 64 equalizer modules ofRevision B, for example, have a significantly lower noise level thanearlier variants.

Cat. No. 441.This surround/sub-woofer card provides two channels ofsurround equalization and the required capabil i t ies for stereosurrounds an d a sub-woofer channel for the playback of an SR.Dsound-track. This module is for use in a CP55, r,vhere t replaces theCat. No.241 module.Cat. No. 560. Provides the same functions as the Cat. No. 44L above, foruse in a CP200, where it replaces the Cat. No. L60.

Cat. No.517. Replaces he Cat. No. 1,L7 n a CP200. Essential o handlethe greater dvnamic range of modern sound-tracks. Provides greaterdynamic range, lower distortion and additional features for playback ofDolby SR an d SR.D.

Cat. No. "t37L. Link card required for use with Cat. No. 517 outputcard - replaces at .No. 1.37n a CP200.

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6.0 Picture Issues

Picture projection qual i ty should conform to exist ing publ ishedstandards.

Needless to say, instal lat ion of a Dolby SR decoder to achieveimproved sound quality in a t

Documents

Dolby Technical Guidelines 1994