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AUDITORIUM ACOUSTICS

AUDITORIUM ACOUSTICS. REFERENCES: Science of Sound, 3 rd ed., Chapter 23 Springer Handbook of Acoustics, 2007, Chapters 9, 10

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AUDITORIUM ACOUSTICS

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  1. AUDITORIUM ACOUSTICS REFERENCES: Science of Sound, 3rd ed., Chapter 23 Springer Handbook of Acoustics, 2007, Chapters 9, 10 Principles of Vibration and Sound, 2nd ed., Chapter 11 Concert Halls and OperaHouses, 2nd ed.,Leo Beranek, 2004

  2. pvsr log p vs log r SOUND FIELD OUTDOORS AND INDOORS Free field Reflections

  3. DIRECT AND EARLY SOUND SOUND TRAVELS AT 343 m/s. THE DIRECT SOUND REACHES THE LISTENER IN 20 to 200 ms, DEPENDING ON THE DISTANCE FROM THE SOURCE TO THE LISTENER. A SHORT TIME LATER THE SAME SOUND REACHES THE LISTENER FROM VARIOUS REFLECTING SURFACES, MAINLY THE WALLS AND THE CEILING. THE FIRST GROUP OF REFLECTIONS, REACHING THE LISTENER WITHIN ABOUT 50 to 80 ms, IS OFTEN CALLED THE EARLY SOUND. EARLY REFLECTIONS FROM SIDE WALLS ARE NOT EQUIVALENT TO EARLY REFLECTIONS FROM THE CEILING OR FROM OVERHHEAD REFLECTORS. IF THE TOTAL ENERGY FROM LATERAL REFLECTIONS IS GREATER THAN THE ENERGY FROM OVERHEAD REFLECTIONS, THE HALL TAKES ON A DESIRABLE “SPATIAL IMPRESSION.”

  4. PRECEDENCE EFFECT RATHER REMARKABLY, OUR AUDITORY PROCESSOR DEDUCES THE DIRECTION OF THE SOUND SOURCE FROM THE FIRST SOUND THAT REACHES OUR EARS, IGNORING REFLECTIONS. THIS IS CALLED THE PRECEDENCE EFFECT OR “LAW OF THE FIRST WAVEFRONT.” THE SOURCE IS PERCEIVED TO BE IN THE DIRECTION FROM WHICH THE FIRST SOUD ARRIVES PROVIDED THAT: 1. SUCCESSIVE SOUND ARRIVE WITHIN 35 ms 2. SUCCESSIVE SOUNDS HAVE SPECTRA AND ENVELOPES SIMILAR TO THE FIRST SOUND 3. SUCCESSIVE SOUNDS ARE NOT TOO MUCH LOUDER THAN THE FIRST

  5. GROWTH AND DECAY OF REVERBERANT SOUND SOUND SOURCE SOUND AT LISTENER

  6. GROWTH AND DECAY OF REVERBERANT SOUND RT = K (volume / area) RT = 0.161 V/A(V in m3; A in m2 ) If room dimensions are given in feet, the formula may be written: RT= 0.049 V/A (V in ft.3 ; A in ft.2 )

  7. SOUND DECAY Sound decay Sound decay in a 400 m3 classroom Sound pressure level as a function of time for that room

  8. DECAY OF REVERBERANT SOUND

  9. CALCULATING REVERBERATION TIME

  10. CALCULATINGREVERBERATION TIME

  11. CRITERIA FOR GOOD ACOUSTICS ●ADEQUATE LOUDNESS ●UNFORMITY ●CLARITY ●REVERBERANCE ●FREEDOM FROM ECHOES ●LOW LEVEL OF BACKGROUND NOISE

  12. ACOUSTIC PARAMETERS (Gade, 2007) Reverberance (RT, EDT) Clarity (C) Sound strength (G) Spaciousness apparent source width (ASW) listener envelopment (LEV) Timbre or tone color (balance between hi, med, low freq) Ease of ensemble Early support Speech inteligibility

  13. Desirable reverberation times for various sizes and functions Variation of reverberation time with frequency in good halls

  14. Avery Fisher Hall (New York)

  15. McDermott ConcertHall (Dallas)

  16. Orchestra Hall(Chicago)

  17. MeyerhofSymphony Hall(Baltimore)

  18. Walt Disney Concert Hall

  19. Disney

  20. Kimmel Center Auditorium (Philadelphia)

  21. BING CONCERT HALL (Stanford) Named in honor of donors Helen and Peter Bing ´55, this 842-seat concert hall opened in 2013.

  22. BING CONCERT HALL (Stanford) Architect: Ennead Acoustical consultant: Nagata Acoustics Seats: 842 Room Volume: 17,000 m3 V/N = 19 m3 RT=2.6 s (empty), 2.4 s (occupied)

  23. BING CONCERT HALL (Stanford) (From Nagata Acoustics website)

  24. BACKGROUND NOISE CRITERIA

  25. Important criteria for concert halls: • Spatial impression • Intimacy • Early decay time • Clarity • “Warmth”

  26. Concerthallsthroughoutthe World

  27. CHURCHES CHURCHES AND SYNAGOGUES ARE NOT PRIMARILY CONCERT HALLS, BUT THEY SHARE MANY OF THE SAME REQUIREMENTS FOR GOOD ACOUSTICS OLD CATHEDRALS HAVE LONG REVERBERATION TIMES, AND THE SPOKEN WORD IS NOT AS IMPORTANT AS IN CONTEMPORARY WORSHIP. MUCH ORGAN MUSIC WAS COMPOSED FOR THESE SPACES BACKGROUND NOISE SHOULD BE VERY LOW ELECTRONIC REINFORCEMENT OF SOUND SHOULD BE USED ONLY WHEN NECESSARY!

  28. CLASSROOMS NEED FOR GOOD ACOUSTICS: STUDENTS MUST BE ABLE TO UNDERSTAND THE TEACHER AND EACH OTHER MUST CONROL: • REVERBERATION • HEATING, VENTILATION, AND AIR CONDITIONING • NOISE FROM OUTSIDE THE CLASSROOM ANSI STANDARDS: NC-25 to NC-30

  29. WALLS AND NOISE BARRIERS The transmission coefficient is the ratio of transmitted to incident intensity: τ = IT/I0 and the transmission loss is: TL = -10 log τ. At low frequency, the sound transmission loss follows a mass law, increasing with increasing frequency and mass density M of the wall: Transmission loss for a wall may fall below that predicted by the mass law, due to any of the following: 1. Wall resonances 2. Excitation of bending waves at the critical frequency where they travel at the same speed as certain sound waves in air 3. Leakage of sound through holes and cracks

  30. TRANSMISSION LOSS THE EFFECT OF A HOLE ON TRANSMISSION LOSS

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