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Archictectural Acoustics

Archictectural Acoustics. Reverberation Time Room Characteristics Problems Control of Reverberation Time Design of Auditoriums, classrooms, music rooms, etc. Reverberation Time. Sounds bounce off walls, ceiling, floor, etc. before reaching the ear. Also arrive directly.

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Archictectural Acoustics

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  1. Archictectural Acoustics • Reverberation Time • Room Characteristics • Problems • Control of Reverberation Time • Design of Auditoriums, classrooms, music rooms, etc. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  2. Reverberation Time • Sounds bounce off walls, ceiling, floor, etc. before reaching the ear. • Also arrive directly. • Sound decreases • As distance travelled increases • At each bounce. • Reverberation time is time for energy to drop by 60 dB • i.e. to decrease by factor 106) Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  3. Reverberation Time • For example, a short sound results in a series of short sounds decreasing in intensity. • Or a prolonged sound produces an envelope of sound as the intensity dies down. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  4. What is a Good Reverberation Time? • This depends on the type of effect desired. • Is determined by • volume of the room, • nature of construction materials, etc.. • Some guidelines for a “good design” do exist, however: Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  5. Room Qualities • Liveness: • Longer reverberation time  more “liveness” • Intimacy: • Determined by time for first reflected sound to reach listener • less than approximately 20 ms is “intimate”. • Fullness: • Ratio of reflected sound to direct sound. • The more reflected sound relative to direct, the greater the “fullness”. • Clarity • Opposite to “fullness”. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  6. Room Qualities Reverberation time depends somewhat on frequency, usually diminishing from 0-500 Hz. • Warmth • Low-frequency sound reverberation time is longer than higher frequency • Brilliance: • The reverse of “warmth”. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  7. Room Qualities • Texture: • All reflections arrive in uniformly decreasing intensity • Blend • Sound is well diffused around the room – not focussed. • Ensemble • Members of an orchestra hear each other “quickly”. No peaks in time. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  8. Problems • Focussing: • Reflections are focussed on a spot in the room • Shadows • External Noise • Resonances Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  9. How Do We Control Reverberation Time • Reverberation time depends upon the volume of the room and on the material that makes up its walls, ceiling, floor, etc. • A working formula is • Here, V is volume and A is the “effective area” of “open window” in the walls, ceiling, etc.. • Units for A are “Sabins” Volume of room in ft3 Area of floors, walls, etc. in Sabins Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  10. How Do We Control Reverberation Time • To compute the value to use for A, we need to know • the absorption coefficients a1 , a2 , a3 , etc. • and the areas A1 , A2, A3 , etc. for the various materials used in the room: Values for ai At various Frequencies. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  11. How Do We Control Reverberation Time • Number of Sabins for other materials and objects in a room: Values for ai x Ai in Sabins - ie ft2 of open window equivalents at various frequencies. Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  12. An Example – Our Auditorium Check performance at 250 Hz: • Rough dimensions are 50’ x 30’ x 10’  V = 15,000 ft3 • Using table for 250 (Hz): • TV = 0.050 V/A = 0.050 x 15,000 / 1,101 ~ 0.7 s Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

  13. What is a Good Reverberation Time? • This appears to be within the bounds for such a room !! X Much of the content of these slides is acknowledged to come from “Physics of Sound” By R.E.Berg and D.G.Stork, Pearson, 3rd Edition

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