ELECTRONIC REINFORCEMENT OF SOUND

REFERENCE:

SCIENCE OF SOUND, 3rd ed., CHAPTER 24

LONG, ARCHITECTURAL ACOUSTICS, CHAPTER 18

SOUND SOURCES IN A ROOM

SOUND FIELDS

POWER CONSIDERATIONS

MAXIMUM SOUND LEVELS FOR VARIOUS USES

TYPE OF USE MAXIMUM LEVEL (dBA)

CLASSROOM 80LECTURE HALL 83SYNAGOGUE 85HOME THEATER 90LEGITIMATE THEATER 90TRADITIONAL CHURCH 90MOVIE THEATER 100FUNDAMENTALIST CHURCH 100SPORTS ARENA 105ROCK CONCERT 110

Source: Long, Chapter 18

LOUDSPEAKERS

DYNAMIC LOUDSPEAKER

MULTIPLE SPEAKERS IN A CABINET

HORN LOUDSPEAKER

HORN CLUSTERS

BANDWIDTHS OF VARIOUS SPEAKERS

TYPE OF LOUDSPEAKER BANDWIDTH (Hz)

1” COMPRESSION DRIVER 1200-16k2” COMPRESSION DRIVER 850-10k1” DOME TWEETER 2000-20k3” CONE DRIVER 700-10k5” CONE DRIVER 350-6k8” CONE DRIVER 250-5k10” CONE DRIVER 200-4k12” CONE DRIVER 150-2k15” CONE DRIVER 80-125018” CONE DRIVER 70-1000

Source: Long, Chapter 18

LOUDSPEAKER SYSTEMS

SINGLE CLUSTER—MAINTAINS PROPER RELATIONSHIP BETWEEN THE SOUND SYSTEM AND THE APPARENT SOURCE

MULTIPLE CLUSTERS—PROVIDES GOOD COVERAGE BUT SPREADS THE APPARENT SOURCE

COLUMN MOUNTED---SUSCEPTIBLE TO INTERFERENCE EFFECTS

DISTRIBUTED—SHOULD INCLUDE TIME DELAY TO MAINATAIN PROPER RELATIONSHIP WITH DIRECT SOUND

PEWBACK SYSTEMS—PROVIDES GOOD COVERAGE IN CHURCHES

TIME DELAY

SOUND THAT ARRIVES UP TO 50 ms AFTER THE DIRECT SOUND WILL REINFOCE THE DIRECT SOUND AND YET PRESERVE THE APPARENT DIRECTION OF THE SOUND SOURCE. TIME DELAY IS ESPECIALLY IMPORTANT IN THE CASE OF SUPPLEMENTARY SPEAKERS POSITIONED IN PROBLEM AREAS, SUCH AS UNDERNEATH A BALCONY OR FOR SPEAKERS MOUNTED ON SIDE WALLS.

HORN LOUDSPEAKERS

LOUDSPEAKER PLACEMENT

LOUDSPEAKER DIRECTIVITY

UNSATISFACTORY ARRANGEMENT OF LOUDSPEAKERS

RADIATION PATTERN AND DIRECTIVITY FACTOR Q FOR A TYPICAL 8-INCH CONE LOUDSPEAKER

ACOUSTIC FEEDBACK

EQUALIZATION

ENHANCEMENT OF REVERBERATION

ADJUSTMENT OF REVERBERATION TIME IS DESIRABLE IN MULTI-PURPOSE HALLS. MAXIMUM CLARITY OF SPEECH DEMANDS A SHORT REVERBERATION TIME, BUT A PIPE ORGAN SOUNDS BEST IN A REVERBERANT ROOM. ONE SOLUTION IS THE USE OF ELECTRONICALLY ENHANCED REVERBERATION OR “ASSISTED RESONANCE”

ONE METHOD OF ENHANCEMENT PLACES A LOUDSPEAKER AND MICROPHONE IN A REVERBERATION CHAMBER

ANOTHER USES A NUMBER OF TRANSDUCERS MOUNTED ON A THIN PLATE OR FOIL (KUHL PLATE)

DIGITAL REVERBERATORS USE DIGITAL SIGNAL PROCESSING (DSP) TO SIMULATE REVERBERATION

ASSISTED RESONANCE SYSTEM

REVERBERATION TIME IN THE ROYAL FESTIVAL HALL (LONDON) WITH AND WITHOUT ASSISTED RESONANCE (Parkin and Mogan, 2970).

REINFORCEMENT FOR THE HEARING IMPAIRED

SPEECH INTELLIGIBILITY CAN BE INCREASED BY PROVIDING A WAY TO ENHANCE THE SOUND AT THE LISTENER’S EAR. THIS CAN BE DONE BY ONE OF FOUR TYPES OF WIRELESS TRANSMISSION-RECEIVER SYSTEMS:

MAGNETIC INDUCTION—EMPLOYS A LARGE LOOP OF WIRE TO SET UP A MAGNETIC FIELD THAT CAN BE PICKED UP BY HEARING AIDS

FM BROADCASTING—(FCC HAS RESERVED A BAND OF HIGH FREQUENCY

AM BROADCASTING—OPERATES IN THE BROADCAST BAND OR BELOW

INFRARED LIGHT—DON’T OPERATE WELL IN BRIGHTLY-LIGHTED ROOMS

MICROPHONE PLACEMENT

MICROPHONES ARE GENERALLY PLACED IN THE DIRECT FIELD OF THE SPEAKER OR PERFORMER SO THE MICROPHONE OUTPUT IS REDUCED BY 6dB FOR EACH DOUBLING OF THE DISTANCE. THIS REDUCES THE GAIN BEFORE FEEDBACK BY 6dB BUT IT ALSO MEANS THE PERFORMER CAN MOVE A LITTLE WITHOUT PRODUCING A LARGE CHANGE IN LEVEL

WHEN A MICROPHONE IS A SMALL DISTANCE ABOVE THE FLOOR, CANCELLATION OF CERTAIN FREQUENCIES (‘COMB FILTERING’) CAN OCCUR. FOR EXAMPLE, IF THE MICROPHONE WERE 3 m FROM THE SOURCE AND BOTH WERE 1.5 m ABOVE THE FLOOR, THE PATH DIFFERENCE OF THE DIRECT AND ONCE-REFLECTED SOUND WOULD BE 1.23 m AND THE CANCELED FREQUENCY WOULD BE ABOUT 140 Hz.

MULTIPLE OPEN MICROPHONES

WHEN THERE ARE SEVERAL MICROPHONES IN USE AT THE SAME TIME, THE SIGNAL FROM THE LOUDSPEAKER CAN BE PICKED UP BY EACH OF THEM AND COMBINED AT THE MIXER.

IT IS GOOD PRACTICE IN SPEECH SYSTEMS TO USE AN AUTOMATIC MICROPHONE MIXER SO THAT THE SYSTEM GAIN IS THEORETICALLY THE SAME AS IT WOULD BE IF ONLY ONE MICROPHONE WERE ON A A GIVEN TIME.

GRANOFF MUSIC CENTERTUFTS UNIVERSITY

OUTDOOR SOUND SYSTEMS

SOUND POWER TAKES ON CONSIDERABLE IMPORTANCE SINCE THERE IS NO REVERBERANT FIELD FOR REINFORCEMENT.

MULTIPLE LOUDSPEAKERS AND LARGE AMPLIFIERS ARE GENERALLY USED.

LOUDSPEAKERS SHOULD HAVE AS HIGH EFFICIENCY AS POSSIBLE.

SPEAKER CLUSTER AT PRITZKER PAVILLION

PRITZKER PAVILLION IN MILLENIUM PARK, CHICAGO

JAY PRITZKER MUSIC PAVILIONCHICAGO

PRITZKER PAVILION

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