Room Acoustics Qualities - Theater Planning - PDF

Room Acoustics Room Acoustics Qualities Intimacy Big rooms generally sound big, and small rooms generally sound small. Surely some of that distinction comes about in the respective reverberance levels inherent to rooms of different geometric volumes. But it is also believed that the early‐arriving...

Room Acoustics Room Acoustics Qualities Intimacy Big rooms generally sound big, and small rooms generally sound small. Surely some of that distinction comes about in the respective reverberance levels inherent to rooms of different geometric volumes. But it is also believed that the early‐arriving sound contributes to a sense of acoustic intimacy. By bringing earlier early reflections, designers can make a big room sound like a smaller, more intimate one. Intimacy is measured by the initial time delay gap (ITDG), the length of time in milliseconds between the arrival of the direct sound and the arrival of the first sound reflection. Shorter ITDG durations are associated with more intimate rooms. To provide smaller ITDG values, position sound‐reflecting surfaces in close proximity to listeners so that the reflected sound might arrive earlier. ITDG values in large concert halls range from about 20 milliseconds (meaning that the first reflected sound arrives 20 milliseconds after the direct sound) to about 60 milliseconds. Room Acoustics Qualities Intimacy Small rooms are intimate by their very nature, so ITDG values are much lower in chamber music halls, which range from 8‐millisecond ITDGs to 27‐millisecond ITDGs. Fan‐shaped rooms generally have higher initial time delay gap values, and therefore are believed to sound less intimate than rectangular rooms of a similar size. Because their side‐wall geometry fails to direct first‐order sound reflections back to the middle of the hall. Room Acoustics Qualities Diffusion Room Acoustics Qualities Diffusion In a “specular sound reflection,” the angle of incident sound equals the angle of reflected sound. Think of a billiard ball ricocheting off the rail of a billiard table, or light reflecting from a clean mirror. In diffuse sound reflections, or scattering, the sound behaves more like light reflecting from a fogged mirror, dispersing the reflected sound over a wider area. Most materials provide both specular and diffuse reflections; the proportion of specular and diffuse reflections differentiates surfaces. To effectively scatter reflected sound, the degree of texturing must be high; slight variations and modest curves produce slight and modest scattering effects. Room Acoustics Qualities Diffusion By breaking up and scattering sound reflections, diffusing surfaces can mitigate a wall or ceiling that might otherwise generate echo, acoustic glare, or sound focusing. This is especially useful when treating an acoustic defect (and the surface that causes it) with absorption might deprive the space of needed reverberance. Even in the absence of a major acoustic defect, diffusion may be beneficial to rooms for music listening. Every great concert hall maintains a high degree of diffusing surfaces to homogenize the sound across the listening locations, staving off harsh reflections that can make the sound “brittle.” Room Acoustics Qualities Diffusion The type of reflection from a surface depends on the length of the surface relative to the length of the incident sound wavelength. So diffusing surfaces of repeated regular elements, equal in length, may favour reflections in one frequency over those of another. This can cause a shift in the perceived frequency of the reflected sound called “tone coloration,” which sounds like a frequency shift in the direction of a more shrill. While this is often subtle, it is audible to the discerning music listener, and it can be avoided by varying the size of diffusing surfaces throughout the room. Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics For an orchestra to play together tightly so that the sections perform as a singular entity, the members of the orchestra must hear one another play. This quality is called ensemble. It can be promoted with a proper stage acoustic environment designed to provide a short, clear sound path between musicians and a geometry designed to create early loudness‐supporting intra‐orchestra sound reflections. As a topic of widespread systematic research, ensemble is relatively new and about 75 years behind reverberance, so we learn more about stage acoustics with each passing decade. Room Acoustics Qualities Theater Planning Stage Acoustics Just as audiences have grown accustomed to larger seats, orchestras have grown accustomed to ever more expansive stages, and they’ve spread out to meet the space allotted to them—so much so that a modern orchestra playing in a century‐old hall may squeeze together to fully half the area of the same modern orchestra playing in a contemporary hall. Direct sound decays six decibels per doubling of distance, so the spread‐out version of the orchestra in the newer room suffers a substantial loss of direct sound relative to the close‐ together version in the older room. Room Acoustics Qualities Theater Planning Stage Acoustics To prevent this, first the stage size should be limited. As a rule of thumb, use 20 square feet per musician, which for a full 100‐piece orchestra means a performance platform no larger than 2,000 square feet. Of course, 20 square feet per musician is merely an average, and in practice, a wind instrument may need 13 square feet while a tympani needs more than 100 square feet. There is an operational component to all of this as well, beyond the room’s design. Concert hall and orchestra technical staff must work to keep the musicians physically nearer to one another than might feel natural on a large stage. Ideally, no musician will sit more than 25 feet from another musician. Room Acoustics Qualities Theater Planning Stage Acoustics Risers, elevated platforms, each progressively taller than the one in front of it like steps, can lift each row of the orchestra so that the direct paths from the instruments are less obstructed by the other musicians. This is also good for the audience, who benefit from the direct sound just as the musicians do. Yet, not all design moves that benefit the musicians also benefit the audience. With reflected sound, any acoustic energy directed at the (absorbent) orchestra is sound energy not brought to the house that might otherwise be heard as loudness, reverberance, and clarity in the seats. The room should achieve a proper balance between sound directed back to the stage, and sound directed out to those in the house—and that precise equilibrium is difficult to define. Certainly some, if not all, of the surfaces adjacent to the stage, both in plan and section, should Room Acoustics Qualities Theater Planning Stage Acoustics In plan, the walls should be oriented to direct sound to the orchestra, but for this to work properly, the orchestra must not only sit in a tighter formation than might be comfortable, but must also move far upstage, away from the audience, and closer to the upstage wall. An orchestra situated too far downstage risks two acoustic penalties. First, an empty stage surface in front of the orchestra provides an important sound reflection, especially to the rear balconies, but only if the downstage portion is clear of sound‐absorbent musicians. Second, if the orchestra is too far from the upstage wall, reflections off that surface may arrive at both the orchestra and audience too late to be useful for clarity, and perhaps so late that the reflection is heard as an echo. Room Acoustics Qualities Theater Planning Stage Acoustics In section, the ceiling height required to give the room a proper reverberation time might be too high to deliver early reflections to the orchestra. Again, a late reflection could be useless at best, and heard as an echo at worst. To battle this, an overhead canopy may be suspended below the ceiling and above the stage. The suspended plane may be a singular surface, or it may be composed of multiple smaller canopy segments, separated by open areas between them. The canopy or canopies may be dedicated to an area over the orchestra, or they may extend beyond the stage into the over‐audience volume, in an effort to allow for early reflections to the listeners. Room Acoustics Qualities Theater Planning Stage Acoustics Again, a balance must be achieved. If the canopy area is too large, it might choke off the volume above the canopy so that much of the sound entering that over-canopy region never gets out, crippling the room’s reverberance. Multiple canopy segments of similar sizes may color reflection frequency content, because a sound may reflect off, diffuse off, or diffract around a surface, depending on the size of the surface relative to the sound wavelength. If too many surfaces are of one single size, the reflections become narrow‐band or absent in some bands altogether. To reflect low frequencies, the canopies must be sufficiently massive; to allow for early‐enough overhead reflections, the canopy should be set between 22 feet and 40 feet above the stage (it may be adjustable in height to be orchestra‐specific and performance‐ piece‐specific). Room Acoustics Qualities Theater Planning Stage Acoustics In spaces where the orchestra is housed in a dedicated sending‐end volume, segmented and separate from the main volume of the audience in an orchestra shell, the symphony performers may hear themselves as very loud. They are, after all, in a small volume. They may then reduce their sound power and play too softly for the audience, which does not have the same kind of access to the sound levels found within the stage shell. When stage monitors (loudspeakers set on stage and directed back at the performers) amplify the ensemble, the same phenomenon often occurs: musicians, misjudging their own playing levels, instinctively reduce their sound power to a level unacceptably anemic for the listeners in the house. Room Acoustics Qualities Theater Planning Stage Acoustics We measure the stage characteristics that promote ensemble objectively with the metric support (ST1), which gauges the capacity of the performance platform, the stage walls, and the over‐ stage reflective plane to deliver early sound reflections. It is measured in decibels so that ST = L 1 p direct sound - L p early reflections Where ST1 is the stage support in decibels, averaged over the 250‐Hz, 500‐Hz, 1,000‐ Hz, and 2,000‐Hz L octave bands p direct sound is the direct sound level in decibels arriving in the first 10 milliseconds as measured from a microphone one meter from an omnidirectional sound source (and one meter above the floor) Lp early reflections is the total sound level measured at the same location arriving between 20 and 100 milliseconds. The higher the support measures, the more performers are able to clearly hear one another. Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics listening tests suggest that human beings mostly perceive the same subjective acoustic effects, but they weight them differently when establishing preference. For instance, musicians seem to have more of a preference for clarity than nonmusicians. Listening tests on human subjects, and rank ordering of the acoustics of concert halls, suggest that the most important acoustic factors in performance spaces are loudness (more is generally better), reverberance (more is generally better for music, to a limit), spatial impression (more is generally better), warmth (more is generally better, to a limit), and intimacy (more is generally better). Room Acoustics Qualities Theater Planning Stage Acoustics Relationships, interactions, cross‐cutting influences, and overlaps between these important factors and the variables that measure them are found in the human auditory system or materialize in room design. The good symphony halls hit their target reverberation times, are free from excessive noise and acoustic defects such as echoes, are not oversized, and avoid deep balconies. The best rooms have strong, early‐arriving, broadband, lateral sound reflections. Room Acoustics Qualities Theater Planning Stage Acoustics Clarity is surely important, but by its nature, measures of clarity are non‐orthogonal to measures of reverberance. Listeners in a laboratory setting believe that more loudness brings more reverberance. The sense of spatial impression increases with rises in loudness, reverberance, and warmth. Lateral‐arriving reflections, so important in spatial impression, also disproportionately increase perceived loudness (and decrease the perceived distance to the source). Room Acoustics Qualities Theater Planning Stage Acoustics In tests where subjects speak and their speech is played back to them in real time under varying acoustical conditions, loudness is the most important acoustical factor when estimating the size of the simulated room. Spaces with more loudness are judged to be more intimate. Lateral reflections also increase perceived loudness more than sound reflections coming from other directions. Room Acoustics Qualities Theater Planning Stage Acoustics In the design of rooms for unamplified music, minimizing the distance between performer and audience bolsters both clarity and loudness. A steeply raked seating plane provides unobstructed sightlines for clarity, but absorbs more sound (robbing loudness and reverberance). The use of massive materials simultaneously increases the sense of loudness, reverberance, and warmth. Smaller audience sizes, and therefore lower seat counts and more compact seating arrangements, are associated with increased reverberance, increased listener envelopment, and increased loudness (each of which is typically desired). Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Stage Acoustics Room Acoustics Qualities Theater Planning Performance Venue Seats Unamplified music venues generally thirst for ever more reverberance, loudness, and warmth, so designers strive to limit the absorptance of room surfaces. This leaves the absorbent audience seating area with an outsized role as the only surface with a meaningful capacity to dampen sound energy. Limiting the seat count—or, more accurately, the seating area—is key. The best concert halls have smaller seat counts and/or more dense seating configurations. Room Acoustics Qualities Theater Planning Performance Venue Seats So that warmth doesn’t suffer, select seats that are not too absorbent in the low frequencies. So that the room environment during rehearsals most resembles the room environment during performances, specify chairs that have an unoccupied absorption profile similar to their occupied absorption profile. To achieve these objectives, chairs should be made of molded plywood with seat‐bottom upholstery no thicker than two inches (this typically means no springs) and seatback upholstery no thicker than one inch. The seat‐ back upholstery should cover as little of the surface as possible while still maintaining comfort. Don’t cover the armrest or backside with soft surfaces, as that can make the audience plane too absorptive. Indeed, there is anecdotal evidence that just spraying the upholstery with a stain guard can measurably alter the seating plane’s absorption profile. Absorption coefficient laboratory testing of the actual seats that will be Room Acoustics Qualities Theater Planning Performance Venue Seats Room Acoustics Qualities Theater Planning Performance Venue Seats Room Acoustics Qualities Theater Planning Acoustic Defects Room Acoustics Qualities Any room for listening should be free of audible echo, flutter echo, sound focusing, sound creep, and excessive reverberance. These acoustic defects are heavily rooted in source‐path‐receiver geometry and usually easily prevented or cured through proper surface shaping, surface positioning, addition of absorbing materials to a surface, and/or While often texturing conflated, an of a surface echo differs for diffusion. from reverberance. An echo, always unwanted, is the noticeably audible repetition of the original sound, typically arriving after ricocheting off a first or second or third surface. Reverberance is the prolonging of sound through a multitude of room surface sound reflections arriving over a time window from many directions. Think of an echo as a reappearance, recurrence, or replication of the original sound, while reverberance is a continuation, protraction, prolongation, continuation, or extension of the original sound.  Room Acoustics Qualities Theater Planning Acoustic Defects  Room Acoustics Qualities Theater Planning Acoustic Defects You hear flutter echo as the repetitive “wa‐wa‐wa‐wa‐wa,” when clapping in a room or corridor with two parallel walls. Canting or splaying one of the walls by at least five degrees (so they are no longer parallel), applying absorption to one of the walls, or texturing one of the walls for diffusion remedies  Room Acoustics Qualities Theater Planning Acoustic Defects  Room Acoustics Qualities Theater Planning Acoustic Defects  Room Acoustics Qualities Theater Planning Acoustic Defects  Room Acoustics Qualities Theater Planning Acoustic Defects  Room Acoustics Qualities Theater Planning Acoustic Defects  Room Acoustics Qualities Theater Planning Acoustic Defects Avoid concave‐curved surfaces, whether on the rear wall of a theater or the dome of a lobby that will hold music performances. Reflective curves like these focus sound the way a curved mirror or lens focuses light. The multiple reflections arrive at the focal point simultaneously, an echo is heard, and the areas not in the focal point fail to get reflections, generating acoustical dead spots. The simultaneously arriving reflections from a curved surface can produce a reflection louder than even the direct sound. Room Acoustics Qualities Design Checklists Design Checklists Rooms for Unamplified Music Performance Checklist  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist When making rooms for music, designers should prioritize: 1. absence of background noise, 2. absence of echo and other acoustic defects, 3. appropriate reverberance, 4. sufficient loudness, 5. enhanced spatial impression, 6. robust warmth, and 7. limited seat count. The most consistent performers are rectangular rooms with shoebox proportions, although other, more experimental, forms have also done well. The best halls prioritize strong, low‐ frequency, early‐arriving lateral sound reflections.  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist Room Shaping 1. Include the musicians and audience in the same geometric volume. Avoid the kind of outcroppings that occur with deep under‐balcony spaces and spatially distinct stage areas. (Loudness, spatial impression). 2. Define a room geometry to bring strong early sound reflections to the audience. (Loudness, clarity). 3. Shape the room to deliver lateral reflections from the side walls or, in the case of a vineyard arrangement, terrace walls. (Spatial impression) 4. Limit the width of the room so first‐order lateral sound reflections arrive early to the seated audience. For rectangular rooms, widths generally shouldn’t exceed 90 feet. (Loudness, spatial impression, clarity, intimacy, absence of acoustic defects) 5. Limit the audience size. Take special care designing rooms with more than 2,000 seats to  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist 6. Limit the length of the room. Get as many people as close to the source as reasonable. Position seats no farther than 100 feet from the stage on the main level, and no farther than 130 feet to the farthest balcony seat. (Loudness, intimacy) 7. Utilize balconies. They bring the listeners closer. In the case of side balconies, they direct sound otherwise destined for the ceiling back toward the main‐level audience block. Limit side balconies to one or two rows of seats, because deeper side balconies often cannot provide clear stage sightlines for the third or fourth row. (Loudness, spatial impression) 8. Size the room to achieve the appropriate reverberation time. Because the width and length of the room are limited by other acoustic considerations, often the ceiling height must be adjusted to ensure proper room volume. For unamplified music rooms, plan on employing high ceilings. Several of the most respected concert halls have height‐to‐width ratios greater than 0.7. (Reverberance)  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist 9. Limit absorption in the room, outside of that brought by the absorptance of audience and performers. (Reverberance, loudness, warmth) 10. Shape the sending end to provide beneficial reflections and increase directivity. This should happen in both plan and section. (Loudness, clarity) 11. Rake the seating plane. Because the ears sit at about the same level on the head as the eyes, a clear line of sight to the source also ensures direct sound access. Use stepped seating for rooms with more than 100 people. Know that too‐steeply‐raked seating absorbs more of the direct sound because the source “sees” more of the absorptive seating plane. (Loudness, reverberance) 12. Treat the rear wall. It is the most likely source of echo, and should therefore be minimized in height with balconies, diffusion, or sloped ceilings. (Absence of acoustic defects) 13. Avoid concave curves. Domes and other concave curved surfaces produce sound creep and sound focusing. (Absence of acoustic defects)  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist 14. Consider the overhead plane. This might involve shaping the ceiling or hanging a suspended sound‐reflective canopy. Overhead reflections are important for loudness, but the high ceiling height needed for proper reverberance may delay first‐order ceiling reflections such that they come after the 80 millisecond threshold required for integration with the direct sound. These reflections are useful both for audience and musicians on stage, who need to hear one another. A suspended canopy over the stage and first rows of the audience can simultaneously allow for a high ceiling and early overhead sound reflections. The importance of a canopy is not universally accepted in the field, and there is some debate as to its usefulness. (Loudness, reverberance) 15. Vary the sizes of reflecting surfaces. Large surfaces are needed to reflect low‐frequency sound. (Warmth, diffusion)  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist Surfaces 1. Design the audience plane with acoustics in mind. Reverberation and loudness requirements often dictate that the only meaningful absorbing surfaces in a room for music are the seats and the people who occupy them. Note that seats and absorption coefficients vary considerably from one upholstered condition and seating configuration to another. Seating densities should fall between 6.5 and 9.0 square feet per person, and seats that excessively absorb bass should be avoided. (Loudness, reverberance, warmth) 2. Reflect low‐frequency sound. Specify smooth, high‐mass reflecting surfaces, flush‐ mounted and absent air spaces. Use plaster (minimum one inch thick), painted concrete block, or poured concrete for side‐wall construction. Wood, wood veneers, and lightweight stud assemblies are notorious for disproportionally absorbing low‐frequency sound and robbing a room of bass response. (Warmth)  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist Surfaces 3. Detail for surface irregularities. Convex curves, pyramids, coffers, canted and angled surfaces, protruding pilasters, piers, and other craggy surfaces with varying dimensions generate diffuse reflections. Diffusion protects against echo, flutter echo, creep, sound focusing, and “acoustical glare” associated with flat surfaces. It is especially helpful near the sending (stage) end and on surfaces, such as rear walls, that are most likely to create echo problems. The relative importance of diffusing surfaces is not universally agreed upon in the field. (Diffusion) 4. Provide for variable acoustics. Retractable sound‐absorbing banners or curtains allow for a wider range of reverberation times, and therefore a wider range of performance types. Curtains are also helpful in simulating the reverberance of a full hall during a rehearsal with unoccupied audience seats. (Reverberance)  Room Acoustics Qualities Design Checklists Rooms for Unamplified Music Performance Checklist General 1. Limit background noise. Specify quiet air‐conditioning systems, and locate machinery far from the performance space. Design vestibules as sound and light locks separating lobbies, loading docks, backstage areas, and other ancillary spaces from the performance room. Background noise from outdoor sources should be inaudible. (Loudness, clarity, absence of acoustic defects) 2. Consider subtle electronic sound reinforcement. (Loudness, reverberance)  Room Acoustics Qualities Design Checklists Other Types of Rooms Checklist When designing any acoustically sensitive space, many of the rules established for unamplified music halls still apply. These cover: 1. Ensure an absence of acoustic defects like excessive background noise and echo, 2. Maximize early sound reflections, and 3. Ensure appropriate reverberation times. Room Acoustics Qualities Design Checklists Opera Houses 1. Use architecture to help maintain the balance of orchestra and vocalist. 2. Right‐size the reverberance. Because of its reliance on both symphonic music and tonguetwisting librettos, opera performance demands more reverberance than a theater, but less reverberance than a symphony hall. Appropriate reverberation times range between 1.2 seconds and 1.8 seconds (mid‐frequency, unoccupied). When opera is performed in the language of the audience, as is often the case in Europe, the lower end of that range allows for more intelligibility of the vocal content and story dialog. In other places, where the audience typically doesn’t understand what is sung, the higher end of that range is more appropriate. 3. Provide lateral sound reflections. Researchers find spatial impression to be vitally important to opera as well. Room Acoustics Qualities Design Checklists Theaters 1. Provide clear sightlines to the stage and limit the distance to the farthest seat. This may necessitate steep audience seating rakes that absorb wanted sound. 2. Design buffer zones (storage rooms, corridors, etc.) between the theater house and noisy spaces such as the wood shop, loading dock, exterior areas, bathrooms, lobbies, and mechanical rooms. 3. Shape the ceiling and walls to provide strong early sound reflections—and prohibit strong late sound reflections. 4. Recognize that theater lighting will occupy much of the ceiling surface that would otherwise be used for overhead sound reflections. Also, the stage house fly loft will reroute much of the sound energy intended for the audience to a death above the stage.  Room Acoustics Qualities Design Checklists Multipurpose Spaces 1. Know that it is generally impossible to achieve excellent acoustics for music and speech when both are performed in the same room. (Think of a single stadium used for two sports.) Multipurpose spaces include the infamous “cafetoriums” in schools; the divisible halls in hotel conference centers that house banquets, meetings, and dances; and the medium‐sized‐city multipurpose auditoria intended to host every imaginable type of performance from dance to opera to Broadway musical to stand‐up comedy. Music requires reverberation times on the order of two seconds, and speech calls for reverberation times less than half that. 2. Consider an adjustable acoustic environment to bridge the yawning range of appropriate reverberation times needed for the venue’s different uses. This could include kinetic absorptive surfaces, such as panels that slide and flip, or curtains/banners that deploy and retract. Room Acoustics Qualities Design Checklists Lecture Halls 1. Design fan‐shaped rooms to bring the audience closer to the stage (less than 125‐ degree angle), or rectilinear rooms to promote lateral reflections and keep the audience in clear view of the screen at the front of the room. 2. Splay the surfaces near the sending end (ceiling and at least one wall) so that the opposite sides are nonparallel and less likely to build up flutter echo. 3. Position absorptive materials on the back wall and the upper‐rear portions of the side walls as needed to optimize reverberation time. This has the added advantage of absorbing what might otherwise be echo reflections, while allowing the surfaces most likely to deliver earlyarriving first‐order reflections to remain sound reflective. 4. Rake the audience at least 7 degrees, and put the source on a raised stage to maintain clear Room Acoustics Qualities Design Checklists Lecture Halls 5. Keep the ceiling sound‐reflective and low enough so that the room volume is between 80 and 150 cubic feet per seat. 6. Know that speech is not audible more than 35 feet from the source without careful acoustic design or amplification. Rooms with more than 100 seats should have electronic sound reinforcement. 7. Use automatic door closers without latches to minimize the disruption by latecomers. Room Acoustics Qualities Design Checklists School Classrooms 1. Install sound‐absorbing material equal in area to approximately the floor area. This does not all have to be on the ceiling. 2. Ensure sound‐reflecting surfaces in the middle of the ceiling and the wall surfaces nearest to the source to provide beneficial early first‐order reflections. 3. Run walls from structural deck below all the way to structural deck above. Avoid partial height walls separating classrooms. 4. Locate the mechanical room as far as possible Room Acoustics Qualities Design Checklists Conference Rooms 1. Detail the ceiling over the table so that it is sound reflective. 2. Limit the ceiling height over the table to less than ten feet. Room Acoustics Qualities Design Checklists Worship Spaces 1. Identify the music‐speech balance. Worship services often include a measure of both speech and music, but the weighting between the two varies across congregations. Organ requires very long reverberation times; music requires long reverberation times; and speech requires short reverberation times. Added reverberance may also save the congregant from a feeling of “singing alone” during group chants or “speaking alone” during group prayers and responsive readings. 2. Design a space with a long reverberation time for music and an excellent amplification system for speech in cases where neither speech nor music dominates the service. 3. Size rooms to be 180 to 300 cubic feet per person if speech dominates the service, and 200 to 400 cubic feet per person if music dominates. Room Acoustics Qualities Design Checklists Worship Spaces 6. Maintain a singular room volume. Avoid deep balconies, convoluted room shapes with deep occupied alcoves, concave surfaces, and deep recesses for organs. 7. Use automatic door closers without latches to minimize the disruption of latecomers. Room Acoustics Qualities Design Checklists Amphitheaters 1. Recognize that without drastic measures (i.e., burying a busy rail line, relocating an industrial plant, or moving a roadway), some sites are just too noisy to locate an amphitheater, period. 2. Angle band shell surfaces and outbuildings to bring early‐arriving first‐order sound reflections to the front of the audience. 3. Use amplification when the audience is large or the site is noisy. This may require an array of many loudspeakers suspended high above the ground throughout the audience. So that listeners adjacent to the loudspeaker aren’t blown away, and listeners remote from the loudspeakers an still hear, make the far‐throw distance of each loudspeaker no more than double the near‐throw distance. 4. Put loudspeakers on a delay so that the direct sound from the source on stage arrives before the amplified sound from the loudspeaker. 5. Examine the geometry of the site for large building surfaces positioned so that they might deliver unwanted late‐arriving echoes.  Room Acoustics Qualities Design Checklists Night Clubs and Small Rock Music Venues 1. Maintain a “flat” reverberation time, one that doesn’t rise in the 63‐Hz and 125‐Hz octave bands, as many rooms for music do. This takes work because standing audience members absorb five times more in the mid- and high octave bands than the low octave bands, so measured empty‐room reverberation times must dip down in the low frequencies to account for the audience impact. 2. Keep reverberation times low. For room volumes ranging from 30,000 to 200,000 cubic feet, reverberation times should lie between 0.6 and 1.2 seconds. Reviewers judge the best halls as “crisp” (least reverberant), and the least‐liked rooms generally are described as “boomy” (most reverberant). 3. When adding digital reverberance to an amplified track, use a filter to target only the mid- and Room Acoustics Qualities Design Checklists Cinemas 1. Place sound absorption on virtually every surface except the floor. 2. Isolate one cinema from the adjacent cinema. Room Acoustics Qualities Design Checklists Recording Studios 1. Achieve very low reverberation times. This requires ample absorption on most surfaces. 2. Avoid room resonance. Small rooms with parallel sound‐reflective walls produce standing waves, so if a surface is sound reflective, splay, apply diffusion, or apply absorption on the opposite surface. This includes the floor‐ceiling surfaces. 3. Maintain excellent noise isolation, both from the inside to out, and from the outside to in. The audible conversation in the hallway can ruin the recording track. 4. Start big. The sound isolation and absorption measures will eat up considerable room height. Room Acoustics Qualities Sound System Design Sound System Design  Room Acoustics Qualities Sound System Design Electronic Sound Reinforcement Often loudspeakers are exposed, in plain sight, but you too have likely been unknowingly in the presence of amplified sound from hidden equipment. Masking noise commonly plays over hidden speakers in open‐plan offices to preserve some of the privacy of conversations; loudspeakers amplify speech in lecture rooms; and digital reverberance radiates from hidden equipment, enhancing the extant reverberance in rooms for music. Room Acoustics Qualities Sound System Design Effective amplification systems preserve localization, the listeners’ sense that the sound they’re hearing is approaching from the original source, rather than approaching from the nearest loudspeaker. This typically necessitates loudspeakers in the vertical plane above the source, with the amplified sound arriving to the ear after the direct sound, and amplifiers set not‐too‐loud. It is common, but misguided, to design two separate loudspeaker groupings, one to each side of the source, to achieve a “stereo” effect. This destroys localization. Room Acoustics Qualities Sound System Design Because one’s ears are on either side of the head, the human auditory system is better at locating sound in the horizontal plane than in the vertical plane. For this reason, amplified sound arriving from the vertical plane common to the source is more easily recognized as emanating from the direction of the source. For tall rooms this translates to central cluster loudspeaker groupings high above the middle of the stage, 20 to 40 feet above, and slightly in front of the source. Amplified sound arrives after the direct sound because it’s traveled farther. Because it doesn’t come from either side, the system maintains proper localization. (Electronic reverberation systems and other digital effects may require loudspeakers in multiple locations throughout a room. Room Acoustics Qualities Sound System Design In long, low rooms, a single cluster fails to bring appropriate sound levels to both the front and back of the room simultaneously. Alternately, many smaller loudspeakers may be integrated into the seatback in front of each row of listeners. For those spaces, a loudspeaker array with digitally delayed signals allows the amplified sound to arrive after the direct sound. Room Acoustics Qualities Sound System Design In amplified spaces, aim the loudspeakers to fully cover the audience, but not so close to the edges that sound spills over to the walls and other non‐audience surfaces of the room. (Loudspeakers have narrow directivity in higher frequencies, and approach omni‐directionality with decreasing frequency.) When amplified sound reflects off room surfaces, it becomes muddled. Besides, if reverberance is required, it can be added electronically, baked into the signal upstream of the loudspeaker rather than delivered by the room. For this reason, amplified spaces require much shorter reverberation times and more absorbent room surfaces. Room Acoustics Qualities Sound System Design Finally, the technicians who mix and signal shape (with an equalizer) in real time during a show require an environment that sounds like the room they’re mixing for, and it is best to locate them in the room itself. It’s part art and part science; the sound engineers can best hear and react to the effects of the sound equipment if they are within the same space as the audience. Sacrifice some audience seats (50 square feet or more) for a remote mixing station in the house, which will typically communicate to a semi‐enclosed sound booth in the back of the house, behind the last row of seats on one or more of the levels. Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design Room Acoustics Qualities Sound System Design