1. L 18 Auditorium and Room Acoustics

4. Dekelbaum Concert Hall at the U MD Smith Center

6. Paths of sound in room

8. Intensity vs. time for pulse

10. We define the reverberation time T as the time the sound intensity takes to decay to one millionth of its original steady-state intensity. This is the time taken the sound level to decay by 10 log(1,000,000)= 60 db

13. Average Intensity vs. Time for a constant tone

15. To calculate T, consider a room with a hole in one wall of area A. Call the reverberation time T. T ˜ volume V, 1/A T= K V/A It has been worked out that, for V in m 3, A in m 2 T= 0.16 V/A

16. Let us now replace the open window area with an absorbing material of area S and absorption coefficient a. Then A= Sa. If there is more than one type of absorbing material, the A= S 1 a 1 +S 2 a 2 +S 3 a 3 +… If you prefer, we can write T= 0.16 V/(ΣS i a i )

17. For a window, a=1 For a totally absorbing material, a=1 also. For a perfectly reflecting surface, a=0. For real materials, a lies between 0 and 1.

18. We call this new “area” A the “total room absorption”, measured in sabins (same unit as area, but a somewhat different meaning)

20. If we wish to calculate T, we need to calculate the total room absorption- from the walls, floor, ceiling, furniture, drapes, people, etc.

21. An empty room with totally reflecting walls, ceiling, floors, etc. has a a) shorter T than one (empty) of comparable dimensions with perfectly absorbing walls, ceiling, floors, etc. b) shorter T than one(empty) of comparable dimensions with open windows c) shorter T than one (empty) of comparable dimensions with no windows and with carpets covering the walls d) a longer T than one of comparable dimensions with perfectly reflecting walls, but with people inside.

22. Examples of Reverberation Times One way to respond to the question "What is a good range of reverberation times for concert halls?" is to give examples of some of the most famous halls in the world. For the overall average reverberation times:reverberation times Vienna, Musikvereinsaal : 2.05 seconds Boston, Symphony Hall: 1.8 seconds New York, Carnegie Hall: 1.7 seconds But the overall average reverberation time does not tell the whole story. The variation of reverberation time with frequency is also important.

23. Ideal Reverberation Times

26. Search youtube for Notre Dame de Paris organ (try a Bach piece)

27. Intimacy Room said to be “intimate” when the first reverberation arrives within 20 ms of the direct sound.

28. Fullness vs. Clarity Refers to the amount of reflected sound relative to the amount of direct sound

29. Warmth vs. Brilliance Warmth increases with increasing T for low frequencies

30. Acoustical Design Problems 1.Focusing of sound 2.Echoes 3.Shadows 4.Resonances 5.External noise 6.Double-valued T

31. Focusing of Sound Occurs with use of parabolic surfaces either behind performers or at rear of auditorium

32. Echoes Highly reflective flat or parabolic wall shapes Flutter echos from parallel walls Standing waves between parallel walls

33. Resonances Rectangular practice rooms Parallel walls (flutter) Singing in the shower

34. Double-valued T Playback room with reverberation Concert halls with side areas

35. Auditorium Design

36. General Design Considerations 1.Visual 2.Ventilation 3.Acoustical a. seating b. stage c. room shape d. room walls

37. Absorptions (in sabins) Frequency (Hz) Material125 250 500 1000 2000 Unupholstered seat0.15 0.22 0.25 0.28 0.50 Upholstered seat3.0 3.1 3.1 3.2 3.4 Adult person2.5 3.5 4.2 4.6 5.0 Adult/upholstered seat3.0 3.8 4.5 5.0 5.2

38. Some Absorption Coefficients Frequency (Hz) Material1252505001000 2000 4000 Concrete/brick0.01 0.01 0.02 0.02 0.02 0.03 Glass0.19 0.08 0.06 0.04 0.03 0.02 Plasterboard0.020.20 0.15 0.10 0.08 0.04 Plywood0.45 0.25 0.13 0.11 0.10 0.09 Carpet0.10 0.20 0.30 0.35 0.50 0.60 Curtains0.05 0.12 0.25 0.35 0.40 0.45 Acoustical board0.25 0.45 0.80 0.90 0.90 0.90

39. Control of T R Let’s call it T T = 0.16 V / A Where: T = reverberation time in seconds V = room volume in cubic feet A = total room absorption in sabins

40. Estimate the reverberation time of this lecture hall

43. Should there be an enforced control of sound level in listening devices and public performance venues? a) yes b) no

44. CNN ping refraction or total internal reflection http://www.cnn.com/2014/04/11/t ech/innovation/mh-370- underwater- sound/index.html?hpt=hp_t1