Cleveland, OhioNOISE-CON 2003

2003 June 23-25

Case Studies of Acoustical Design of Rooms for MusicInstruction in SchoolsHyun Paek, Siebein Associates, Inc., 625 NW 60th Street, Suite C, Gainesville, Florida32607, hpaek@siebeinacoustic.com

Gary W. Siebein and Bumjun Kim, School of Architecture, P. O. Box 115702, Universityof Florida, Gainesville, Florida 32611-5702

1. ABSTRACT

This paper will present guidelines for the acoustical design of rooms for music instruction based on theexperience of the authors which includes designing of new music rooms and professional consulting workon existing, problematic rooms of K-12 schools. A series of case studies of rooms for music instruction ofband, chorus and orchestra for K-12 schools will be presented including field measured reverberationtimes, impulse responses, loudness levels and background noise levels. The rooms used for the case studiesvary in shape, volume, and acoustical treatment: 1. rooms with high ceilings and floating planes of sounddiffusing panels; 2. rooms with inclined or flat, hard ceilings at low to moderate heights with someacoustical wall panels; 3. rooms with flat acoustical tile ceilings, manufactured sound diffusing panels andacoustical wall panels. Computer models of rooms for music instruction varying in ceiling height andacoustical treatment were constructed; and comparisons among rooms with low ceilings, shortreverberation times, and high loudness levels are made with rooms with higher ceilings and more sounddiffusing materials. The results of the case studies; acoustical measurements of rooms used for musicinstruction, and interviews with instructors and students indicate that it is important in music rooms toreduce excessive loudness, especially in band rooms; and to control reverberation times based on the typesof music. Combinations of adequate room volume, strategically placed sound absorbent materials toreduce reverberation and acoustic defects as well as sound diffusing materials to allow students andinstructors to hear each other are also required for satisfactory music instruction and practice.

2. INTRODUCTION

Band Rooms are usually too loud when they are fully occupied. They also generally suffer from lowceiling heights; and a lack of sound diffusing and sound absorbing materials on the walls and ceiling of theroom to allow good hearing among the performers while they practice.3 Enough volume and area must beprovided to dissipate the sound energy propagated in the room. There must also be enough soundabsorbing materials in the room to limit the build-up of reverberant energy. When the entire band uses theroom, it is usually necessary to reduce the loudness of the sound from all the instruments playing together.Nationwide, there are increasing numbers of Workers Compensation Claims and law suits filed by musicinstructors, who work all day in rooms with inadequate ceiling heights and acoustical treatment, againstschool boards for alleged hearing loss due to excessive noise levels encountered on the job.

The problems stemming from poorly designed music rooms are the results of several causes. There are noexisting standards for designing rooms for music instruction and many Educational Specifications lackprovisions for the acoustical design of such rooms. Reverberation time guidelines for general teachingclassrooms do not hold true for music classrooms. The locations and areas of sound reflective anddiffusive material and volume desired for proper music instruction, especially for orchestral music andvocal music instruction, usually yields slightly higher reverberation times than those for classrooms. Manydesigners, school boards, and contractors are not fully aware of the basic acoustical elements such as roomvolume, shaping, acoustical finishes and noise control required for spaces for music instruction. Manyarchitects and contractors view them as just another classroom. Sufficient time for acoustical planning

during the early phases of design is usually not provided. The lack of planning results in budgets withinadequate funds for acoustic designing, finishes, and sound isolation systems required for proper musiceducation. Instruction takes place in rooms not designed for a specific type of music education. Somemusic instruction takes place in regular classrooms because the school does not have rooms specificallydesigned for music instruction. Schools experience shifts in the curriculum such as marching bands usingrooms designed for orchestral music with smaller numbers of students such as in the case of Room LCLDAin Figure 6. A drama instructor had stated in an interview that the room being used for drama instructionwas a once a choral rehearsal room. The instructor expressed concerns that spoken words were difficult tohear clearly due to excessive reverberation.

This paper will present guidelines for the acoustical design of rooms for music instruction based on theexperience of the authors which includes designing of new music rooms and professional consulting workon existing, problematic rooms of K-12 schools. Many projects have required the use of acousticalmeasurements conducted in existing music instruction rooms with inadequate acoustical environments aswell as those constructed with adequate ceiling heights and acoustic treatment. The following guidelineswill be presented along with case studies to illustrate various components essential for the design of adesirable environment for music instruction.

3. Method

A series of case studies of rooms for music instruction of band, chorus and orchestra for K-12 schools havebeen investigated with field measured reverberation times, impulse responses, loudness levels andbackground noise levels. Reverberation time and impulse response measurements were taken in numerousmusic rooms. The reverberation time and impulse response measurements were obtained with a computerbased acoustical measurement system. A laptop computer with WinMLS software was used to generate thesource sound. The noise source was amplified via a Crown Com-Tech 200 amplifier and a JBL MR SeriesLoudspeaker. Impulse responses were taken at varying locations depending on the size and shape of themusic instruction rooms. The microphone was mounted on a stand at seated ear height. The computersound source that excites the space is a maximum length sequence signal that is analyzed to produce animpulse response, which shows the acoustical response of the room at each location. It graphically showsthe loudness or amplitude and time delay of sound reflections arriving at each location. ReverberationTime measurements were measured using a steady state noise with an Ivie PC-40 real time analyzer with anIvie IE-20B pink noise generator, a Crown Com-Tech 200 amplifier and a JBL MR Series Loudspeakerwhen the WinMLS software was not readily available. The measurements were taken at several sourcelocations and several receiver locations depending on the size and shape of a room to get a room averagereverberation time. Background noise levels and sound pressure levels of various instruments and weremeasured whenever possible in the rooms for music instruction.

Diagnostic investigations of poor rooms for music instruction were conducted; interviews with the musicinstructors and students; analysis of acoustic data on projects involving rooms for music instruction servedas the knowledge base for deriving a guideline for the design of rooms for music instruction.

The design guidelines for design of rooms for music instruction presented in this paper are based on fivecomponents listed below.

1. Interviews with music instructors and students.2. Review of the literature.3. Acoustical measurements and diagnostics of rooms for music instruction with varying acoustical

qualities.4. Computer models of rooms under design.5. Case study analysis of recently designed rooms.

4. Design Guidelines for Rooms for Music Instruction

There are six basic factors, which direct the design of rooms for music instruction.

Basic factors for Design of Rooms for Music Instruction

1. Control Loudness. Provide a sense of presence for students playing or singing while controllingthe build up of excessive direct and reverberant energy.

2. Reverberance. Band Rooms: Limit the Reverberation in band rooms to prevent excessiveloudness. Vocal and Orchestra Rooms: Provide enough reverberance for fullness or liveness ofthe music so students will have a sense of how they will sound in a performance hall.

3. Ensemble and Support. Provide diffuse cross-room reflections to allow the instructor to hear eachof the students playing and for the students to hear each other.

4. Clarity. Early reflections from ceiling and wall surfaces in the presence of controlledreverberation to allow each note to be heard.

5. Balanced frequency response. The sound field of the room should maintain timbre of eachinstrument.

6. Limited background noise. Reduce noise generated by mechanical systems and provide soundisolating ceiling, wall, and floor assemblies to give full dynamic range and appreciation of restsand quiet musical passages.

A. Room volume.

Enough volume and floor area must be provided to dissipate the sound energy propagated in the room. Thefloor area of a music room should allow flexibility accounting for conditions such as beginners’ musicclasses having larger number of students. An instructor who taught in a room similar to room C1 in Figure6 complained of loudness of a beginner’s class of 80 students in a floor area designed for 40 to 50 students.The layout of instrument or vocal arrangement used during rehearsal should be incorporated whendetermining the floor area needed. Allow room for storage and movement of larger instruments. Studentsshould not be placed up against walls especially for those with louder instruments to reduce harshreflections.2 Since the floor area is usually defined by program or educational specifications, ceiling heightbecomes critical in providing adequate volume in the room.

If the ceiling is low, the reflected sound does not have adequate distance to decay before it reaches the earsof the students or the instructor. If the ceiling height is higher, and comprised of diffusing surfaces,reflected sound will be of lower intensity and spread evenly throughout the room. A larger volume forsufficient sound dissipation results in a longer reverberation time if the room is left with small amounts ofsound absorbing material. The control of reverberation time through strategically located sound absorbentand sound diffusing material are essential in providing a desirable sound field in rooms with higherceilings. The ceiling height should vary according to the type of music instruction in the room.

Table 1 illustrates recommended reverberation times and ceiling heights according to the use of the musicrooms. Band rooms require higher ceilings and relatively short reverberation times to reduce the loudnessof high energy brass and percussion instruments. Choral rooms tend to have reduced amounts of soundabsorbing materials compared to band rooms since human voice are less loud than instruments andreverberation is desired at 0.6 to 1.2 seconds in the mid-frequencies for increased “presence” of vocalsounds while maintaining clarity of words. Orchestral Rooms are desired to have longer reverberationtimes than other rooms for music instruction to enhance the sound of instruments through a room responsesimilar to a performance space. Ensemble Rooms and Practice Rooms are usually smaller in volume andfloor area to accommodate small numbers of students. These rooms have shorter reverberation timesbecause of their small volume and sound absorbing materials needed for the control of loudness andreverberation.

B. Interior acoustical systems.

The interior acoustical system consists of a balanced use of sound absorbing and sound diffusing surfacesstrategically laid out on the walls and ceilings of rooms used for music instruction. Sound absorbent panelsare used to reduce reverberant sound energy and loudness. Sound diffusing panels are is used to providelower level scattered reflections that are spread throughout the room for the students and instructors to heareach other. Together as a system, the sound absorbing and diffusing surfaces reduce acoustic defects such

as flutter echoes, sound focusing, and standing waves or resonant modes inherent in rectangular spaces thatdo not have acoustical treatment.

Band instructors and students are exposed to high sound levels due to large numbers of students playingmusical instruments at loud levels. When this activity occurs outside, such as on a football field, there areno surfaces to reflect sound back to the students. The sound levels of 80-90 dBA are a result of the directsound only. The direct sound is the sound that travels from the musical instrument to the student’s earwithout striking any surfaces. This sound is reduced by approximately 5 dB as one doubles the distancefrom the sound source. When the band plays indoors, the sound moves away from each musical instrumentand strikes the room surfaces. It is then reflected back to the students, increasing the sound level above thatwhich occurs outside. Computer models of six rooms and an outdoor condition were constructed toexamine the effect of adding additional absorbent materials to reduce reflected sound energy in the BandRoom. This results in an approximate relative sound levels for varying acoustical conditions in BandRooms as shown in Table 2.

The relative sound levels in Band Rooms with low to moderate ceiling heights with some sound absorbentmaterial are 1-7 dB less than in the Band Rooms with all reflective surfaces. This is heard as noticeablyquieter to people of normal sensibilities. A further reduction of 1-5 dB is possible with additional soundabsorbing and diffusing materials. This would be heard as noticeably quieter to people of normalsensibilities compared to the existing room.

An additional reduction of 1-2 dB is possible with the treatments with Band Rooms of preferred ceilingheights and amounts of absorbing and diffusing materials which would be heard as noticeably quieteragain. This scheme would be heard as 2-11 dB quieter than the Band Room with all reflective surfaceswhich would be heard as half as loud. The sound levels in this room are equal to those that would occur ina totally absorbent room but with a reflected sound field that will result in higher quality instruction.

In addition, the raised ceiling height will help to dissipate the strength of the reflected sound beyond thatshown in the equations due to the greater distance the sound has to travel to the surface before it isreflected. Instruction can occur more easily in the room due to the presence of the diffusing panels on theceiling and walls that provide scattered, low intensity reflected sound from each student to the Instructor’slocation. This allows the instructor to hear each section of the band when they are playing as a group, sofeedback and instruction can be provided as needed. The Band Room with all absorbent surfaces is notpreferred from an acoustical point-of-view because it does not allow the instructor to hear the students asdescribed above. While the sound levels in the absorbent room are the lowest of all enclosed rooms, thequality of instruction will not be optimum.

A comparison of impulse response of a room (Figure 2, Room LCLDA) with high ceiling height andvolume with a sound diffusing ceiling and a room with low to moderate ceiling height and large areas offlat surfaces (Figure 6, Room HCHDA1) can be seen in Figure 1. The two sound reflections arriving atapproximately 15 milliseconds after the direct sound in Room HCHDA1 are indicative of multiple lowerlevel sound reflections arriving from a diffusive surface. Large specular sound reflections arriving at 10 to12 milliseconds after the direct sound in Room LCLDA) are indicative of a harsh sound reflection from alow flat ceiling. The reverberant energy shows higher continued amplitude indicative of excessiveloudness in Room LCLDA. Interestingly, the two rooms have the same mid-frequency reverberation times,while having quite different impulse responses and acoustic qualities. Impulse response of RoomHCHDA1 in the top graph in Figure 1 is viewed as very successful with a rich and full but clear soundfield. Room LCLDA in the lower graph was renovated because of complaints of excessive loudness, harshreflections, and the inability to hear students playing.

Rooms for music instruction can be grouped into several categories: 1. rooms with high ceilings andfloating planes of sound diffusing panels as shown in Figures 2 through 4; 2. rooms with inclined acoustictile ceilings and sound diffusing panels as shown in Figure 5; 3. rooms with inclined or flat, hard ceilings atlow to moderate heights with some acoustical wall panels as shown in Figure 6; and 4. rooms with flatacoustical tile ceilings, with little or no acoustical wall panels as shown in Figures 7 and 8.

1. Provide sound absorption on the ceiling. The perimeter of the ceiling should be covered with soundabsorbent material to reduce reverberant sound energy as shown in Figures 2 through 4. Since the centerarea of the ceiling provides the first order reflections to the instructor and the students, sound traveling tothe perimeter corners of the ceiling should be absorbed to reduce reverberant energy as well as to reducestanding waves.

2. Provide sound diffusion in the center portion of the ceiling over the orchestra, choir, or band andinstructor as shown in Figures 2 though 5. The sound diffusing panels will provide cross-room reflectionsto allow musicians to hear each other and allow the teacher or conductor to hear each of the students asthey practice and play. The ceiling should be diffuse and high enough to reduce the possibility of specularreflections arriving at the students or the instructor’s ears as a harsh or focused sound and to allow theinstructor to easily distinguish the sounds generated by a student at a particular location.

3. Provide sound absorbent panels on the upper areas of walls above the sound diffusing surfaces. Soundabsorbent panels should be mounted on the upper walls as shown in Figures 2 through 3. The soundabsorbent panels used may vary from 2 to 4 inches thick depending on the program planned for the room.Sound energy traveling diagonally to the upper corners of the room should be absorbed.

4. Provide sound diffusion on the lower wall surfaces. Sound diffusing surfaces at the walls of the roomwill allow communication among musicians and to insure a smooth decay of sound in the room. Eithersurface mounted diffusing panels or zig-zagging the wall surfaces such as HCHDA3 in Figure 4 will assistin providing sound diffusion in the room as space between storage cabinets and other casework permits.Sound diffusing surfaces on the lower walls will break up standing waves in the plane of musicians’ ears.

5. Splay walls of rooms or work with alternate geometries in plan and section to break up standing waves.

6. Low frequency absorbers or bass traps should be provided for Band Rooms or rooms where percussioninstruments or amplified low frequency instruments will be used. Percussion instruments, which generateloud, low frequency sound, which are not readily absorbed by conventional sound absorbent materials, areespecially a concern. These low frequency sound absorbers can be bass traps in which the interiors of thedevice are lined with thick absorbent material. The bass traps should be placed on at least two corners ofthe upper walls or incorporated into a soffit above to effectively absorb and reduce low frequency standingwaves. Figure 4 showing Band Room HCHDA3 with a base trap has significantly lower reverberationtimes in the low frequencies compared to rooms of similar size and adequate amounts of sound absorbingmaterial such as Band Rooms HCHDA1 (Figure 2) or HCHDA2 (Figure 3).

7. Provide acoustic draperies or other variable acoustic devices when the room must accommodatemultiple functions with variable acoustic needs. Music students belonging to different classes such asorchestra, choir, or band may use the same room to rehearse or practice if the school does not have aseparate space for each class. Instructors may also vary in teaching methods and may require differentacoustic environments for the room at times.

8. Flooring materials vary according to the type of music rehearsed in the rooms. Providing carpet as thefloor finish for band rooms and rehearsal spaces involving loud instruments will help absorb residualreverberant energy as well as to reduce noise from shifting furniture and foot steps. Wood is preferred bymany instructors for orchestra rooms for its claimed tendency to provide “warm” quality in sounds.

C. Background noise levels.

The ANSI Standard S12.60-2002 recommends a maximum one-hour average A-Weighted steadybackground noise level of 35 dBA (approximately NC 25 to 30) for Core-learning spaces with enclosedvolumes > 20,000 cubic feet.1 Ten music rooms were measured for background noise levels with theHVAC system on at normal operating loads. Eight rooms showed higher NC levels than 30 ranging fromNC-32 to NC 40. Two rooms had NC-30 or lower background noise levels. Mechanical system noisecontrol is a critical issue particularly for music rooms, because the music instructor needs to hear the

slightest sounds to effectively teach students. Instructors who teach in rooms with high background noiselevels have complained about not being able to hear their students play, especially in the frequenciescoinciding with the frequencies of the mechanical system noise. Please refer to “Case Studies IllustratingAcoustic Design Guidelines for HVAC Systems in Schools”, a companion paper presented at Noise-Con2003 for more detailed discussion of the control of HVAC noise.

D. Sound Isolation Systems

The walls, ceiling, roof and floor assemblies should be carefully chosen to provide adequate sound isolationof the room. High STC wall assemblies and special details at structural connections and at variouspenetrations will be needed to reduce exterior noise intrusion as well as sounds produced within the roomfrom being transmitted into adjacent rooms. The American National Standards Institute (ANSI) StandardS12.60-2002 recommends Minimum Sound Transmission Class (STC) rating of 60 for Music Rooms. 1The standard does not currently address the sound transmission loss spectra throughout the frequencies ofthe construction assemblies; therefore the type of music involved should be considered.

Some assemblies with STC rating of 60 may not adequately reduce sounds produced by loud, lowfrequency instruments such as drums. Table 3 shows the measured average sound pressure levels of a 40student middle school band playing at full strength. The percussion instruments produce average soundpressure level in excess of 100 -110 dB in the low frequencies and decreases as the frequency increases anddecreases to 75-100 dB in the middle and high frequencies. Most building materials have lowertransmission loss in the lower frequencies. Multi-layer gypsum board walls on double studs, concretemasonry walls with drywall on metal framing with glass fiber in thee cavity, or double wythe concretemasonry walls are often required to reduce sound transmitted to adjacent spaces. However, compositeconstructions and double wythe wall construction assemblies are not within the practical constructionbudget of a K-12 school. Designers who have carefully planned adjacencies by providing buffer spacessuch as storage rooms or corridors between rooms for music instruction and other instructional spaces havesuccessfully dealt with this issue.

Providing buffer spaces between practice rooms, ensemble rooms, and main rehearsal rooms; and providingentry doors to the rooms through a sound lock vestibule or a corridor reduces flanking sound transmissionbetween rooms. Structural isolation of the slabs through expansion joints reduces structurally transmittedsounds from band rooms to adjoining spaces. Acoustically rated door, window, and frame assemblies arefrequently used to reduce noise between acoustically sensitive adjacencies.

5. Conclusions

The successful design of rooms for music instruction involves a rationale that can be as simple asunderstanding the necessary sound field for a given type of music education. Music rooms have beeninadequately designed or acoustically treated in the past resulting in numerous renovations. The re-creationof problems inherent in poorly designed music rooms can be avoided by increasing awareness of therequirements of acoustic treatment to design and engineering professionals. The lack of room volume toeffectively dissipate loud sounds together with insufficient sound diffusing and sound absorbing materialsare common contributors to poor acoustical qualities. Case studies show that providing enough ceilingheight and a properly designed system of acoustical treatment and space shaping can provide a desirableenvironment for music instruction. This involves the planning for music instructional spaces early in thedesign phase and cooperative efforts of the design team. These guidelines for the design of rooms formusic instruction can aid not only design professionals but also the school districts in creating a standardfor future facilities where the architectural component of education can be eliminated as a potential causefor the decrease in the quality of education.

This paper presents design guidelines to provide high quality rooms for music instruction in K-12 schools.The primary design features of these rooms are listed below.

1. Provide adequate room volume to dissipate build-up of excessive sound energy.

2. Diffusing surfaces on ceiling and walls are required to allow students and teachers to hear eachother well.

3. Provide sound absorbent materials on upper walls and ceiling to limit reverberant energy. Lesseramounts of sound absorbent materials are required in orchestral and vocal rooms to provide alonger reverberation time so the sounds are rich and full yet clear.

4. Limit background noise from HVAC systems and adjacent activities so the full dynamic range ofthe music played can be appreciated.

5. Shape rooms or provide bass traps to dissipate standing waves and excessive low frequency noisewhere necessary.

6. Provide variable acoustic devices such as acoustic drapes when the room must accommodatemultiple functions with varying acoustic needs.

It is necessary for school user groups, architects, interior designers, construction managers and contractorsto work with acoustic consultants from the earliest stages of building design through constructionadministration to implement these guidelines and produce high quality rooms for music instruction. Initialplanning of room adjacencies, location of buffer spaces, and the schematic design of the mechanicalsystems all have major impacts on the resulting acoustical quality of the rooms. Funds in excess of thoserequired to build typical classroom and office spaces must be allocated in the project budget for therequired acoustical systems. Construction details for sound isolation systems, sound diffusing panels,sound absorbent panels, and HVAC noise control items should be prepared in an integrated team effort bythe architects, engineers, and acoustic consultants. This should be followed by review of submittals andvalue engineering proposals for acoustic items by the acoustical consultant during constructionadministration. Post occupancy interviews with teachers and students and acoustic measurements ofbackground noise, reverberation times, impulse responses, and noise isolation class (NIC) should be madeto verify conformance with the design criteria and to provide a quantitative basis for making acousticimprovements in subsequent projects.

Tables and Figures

Table 1. Recommended reverberation times and ceiling heights for varying types of musicinstruction.

Table 2. Summary of relative loudness for various room treatments.

Table 3. Measured average sound pressure levels of a 40 student band playing in Room LCLDA andsound transmission loss data of a concrete masonry wall.

Figure 1. Impulse response graphs of Band Room HCHDA1 (above) and Band Room LCLDA (below).

Figure 2. Band Room HCHDA1 and measured reverberations times in seconds at octave bandcenter frequencies.

Figure 3. Band Room HCHDA2 and measured reverberations times in seconds at octave bandcenter frequencies.

Figure 4. Band Room HCHDA3 and measured reverberations times in seconds at octave bandcenter frequencies.

Figure 5. Band Room LCHDA and measured reverberations times in seconds at octave band centerfrequencies.

Figure 6. Band Room LCLDA and measured reverberations times in seconds at octave band centerfrequencies.

Figure 7. Band Rooms ACLDA1 and measured reverberations times in seconds at octave bandcenter frequencies.

Figure 8. Band Room ACLDA2 and measured reverberations times in seconds at octave band centerfrequencies.

REFERENCES

1Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools, American NationalStandards Institute ANSI S12.60-2002 (Acoustical Society of America, New York, 2002)

2Harold P. Geerdes, Planning and Equipping Educational Music Facilities, Music Educators NationalConference (Center for Educational Associations, Reston, Virginia, 1975)

3Edward McCue and Richard H. Talaske, Acoustic design of Music Education Facilities, (AcousticalSociety of America, New York, 1990)

4Robert M. Hoover and Reginald H. Keith, Noise Control for Buildings, Manufacturing Plants, Equipmentand Products, (Hoover and Keith, Inc., 1994)