1. STUDIOS AND LISTENING ROOMS
ACOUSTICS OF CONCERT HALLS AND ROOMS
STUDIOS AND LISTENING ROOMS
Principles of Vibration and Sound, Chapter 11
Science of Sound, Chapters 25, 29
Sound System Engineering (Davis & Davis, 1987)

2. THREE SOUND FIELDS IN A ROOM:
DIRECT SOUND,
EARLY REFLECTED SOUND,
REVERBERANT SOUND
IN A SMALL ROOM, WALLS AND CEILINGS ARE SO CLOSE THAT MANY REFLECTIONS ARRIVE WITHIN A FEW MILLISECONDS
ACHIEVING “INTIMACY” (WHICH DEPENDS UPON A SHORT DELAY BETWEEN DIRECT AND FIRST REFLECTED SOUND IS NO PROBLEM AT ALL

3. NORMAL MODES IN CAVITIES
THE WAVE EQUATION IN THREE DIMENSIONS:
IN RECTANGULAR COORDINATES, THIS BECOMES:

4. MODE FREQUENCIES FOR A RECTANGULAR ENCLOSURE:
DISTRIBUTION OF MODE FREQUENCIES FOR 2 ROOMS
l : w : h = 2 : 2 : 2
l : w : h = 3 : 2 : 1

5. CONTOURS OF
EQUAL SOUND
PRESSURE IN A
RECTANGULAR
ROOM
a) (2,0,0) axial mode
b) (3,2,0)
tangential mode

6. SOUND IMAGES FROM MULTIPLE SOURCES
AT LOW FREQUENCY WE DETERMINE THE DIRECTION OF A SOUND SOURCE MAINLY BY INTERAURAL TIME DIFFERENCE (ITD) CUES
AT HIGH FREQUENCY WE DETERMINE THE DIRECTION OF A SOUND SOURCE MAINLY BY INTERAURAL INTENSITY DIFFERENCE (IID) CUES

7. LOCATION OF SOUND IMAGES FROM TWO SOURCES SL AND SR
WITH THE SAME PROGRAM MATERIAL
(c) One source delayed by increasing the dis-
tance from source to
listener
Identical
sources
(b) Same signal
at different levels

8. THE ANGLE OF THE IMAGE ΘI CAN BE ESTIMATED FROM THE EQUATION
WHERE ΘA IS THE ANGLE OF EACH SPEAKER WITH THE MID-PLANE, AND pL and pR ARE THE SOUND PRESSURES AT THE LISTENING POINT DUE TO THE TWO SPEAKERS

9. TIME – INTENSITY TRADING RATIO
WITHIN CERTAIN LIMITS IT IS POSSIBLE TO TRADE AMPLITUDE FOR TIME DELAY WHEN IT COMES TO LOCALIZING THE IMAGE OF A SOUND SOURCE
THE TRADING RATIO IS FREQUENCY-DEPENDENT
THE TRADE-OFF IS NOT COMPLETE
THE TRADING RATIO DEPENDS ON SEPARATION: IT VARIES FROM 125 μs/dB FOR 1 m TO ABOUT 70 μs/dB FOR 2.5 m.
THERE IS SOME DISAGREEMENT AMONG VARIOUS EXPERIMENTS

10. TIME/INTENSITY TRADING AND APPROXIMATE RANGE OF TIME AND INTENSITY DIFFERENCES OVER WHICH THE PRECEDENCE EFFECT APPLIES

11. LOCATION OF SOUND IMAGES FROM TWO OUT OF PHASE SOURCES

12. BROADENING OF SOUND IMAGE BY FREQUENCY EMPHASIS

13. SOUND FIELD IN LISTENING ROOMS
TO ACHIEVE REALISM IN REPRODUCED SOUND:
THE FREQUENCY RANGE SHOULD BE SUFFICIENT
THE SOUND SHOULD BE FREE OF DISTORTION AND NOISE
THE DYNAMIC RANGE SHOULD MATCH ORIGINAL SOUND
THE SPATIAL PATTERN SHOULD BE REPRODUCED
THE REVERBERATION CHARACTERISTICS (SPACE AND TIME) SHOULD BE REPRODUCED
THE EXTENT TO WHICH THE SOUND-REPRODUCING SYSTEM IS ABLE TO SATISFY THESE DETERMINES ITS FIDELITY

14. TOP LEVEL, THRESHOLD LEVEL AND DYNAMIC RANGE FOR MUSIC IN ROOMS OF VARIOUS SIZES

15. FAVORABLE STEREO LISTENING AREAS FOR THREE DIFFERENT LOUDSPEAKER ARRANGEMENTS IN A RECTANGULAR ROOM WITH DIMENSION IN THE RATIO 3:2
SPEAKERS SHOULD SUBTEND AN ANGLE BETWEEN ABOUT 40O AND 90O
THE HATCHED AREA IS CALLED THE “SWEET SPOT”

16. ACOUSTICS OF LISTENING ROOMS
FOR MOST ACCURATE IMAGING, A LISTENING ROOM SHOULD BE SYMMETRICAL ABOUT THE VERTICAL PLANE ALONG THE PRINIPAL LISTENING AXIS.
SMALL ROOMS CAN PRODUCE SIGNIFICANT COLORATION AND POOR SPATIAL IMAGING OF REPRODUCED SOUND. TO MINIMIZE THIS, RESONANCES AND REFLECTIONS SHOULD BE SUPPRESSED WITH BROADBAND ABSORBING MATERIAL. AVERAGE ABSORPTION COEFFICIENTS IN EACH OF THE ROOM’S PRINCIPAL AXES ARE ABOUT THE SAME, PREFERABLY AT LEAST 0.5.

17. SURROUND SOUND MOST COMMONLY USED IS THE 5.1 SYSTEM
FANATASOUND (USED BY DISNEY IN FANTASIA, 1940)
QUADRAPHONIC SOUND
HAFTER STEREO
AMBISONIC SURROUND SYSTEM (GERZON)
POSITION-INDEPENDENT (PI) STEREO (PHILIPS)
VIRTUAL MULTICHANNEL SURROUND SOUND (DOLBY)

18. VIRTUAL MULTICHANNEL SURROUND SOUND (DOLBY)
INCLUDES CROSSTALK CANCELLATION
ATTEMPTS TO REPRODUCE IMPULSE RESPONSE OF ROOM
CAN BE USED IN REFERENCE MODE OR WIDE MODE
TRANSFER FUNCTION OF ACOUSTICAL CROSSTALK MEASURED FOR EACH EAR (EXPRESSED AS 2x2 MATRIX)
SYSTEM (INCLUDING FILTER AND CANCELLER) IMPLEMENTED AS A REAL-TIME PROGRAM ON A PC OR A DSP CHIP

19. VIRTUAL SURROUND SOUND CANCELLER (from Davis and Fellers, 1997)

20. SPATIALIZATION AND VIRTUAL ACOUSTICS
SPATIALIZATION CUES INCLUDE:
AZIMUTH CUES INCLUDE ITD (INTERAURAL TIME DELAY), IID (INTERAURAL INTENSITY DIFFERENCE), AND IED (INTERAURAL ENVELOPE DIFFERENCE OR FRANSSEN EFFECT)
ELEVATION CUES COME MAINLY FROM THE PINNA
DISTANCE CUES: FOR FAMILIAR SOUNDS (SUCH AS SPEECH), THE DIRECT SOUND DROPS 6 dB FOR DISTANCE DOUBLING; FOR UNFAMILIAR SOUNDS, IT IS MORE LIKE 10 dB FOR DISTANCE DOUBLING
REVERBERATION CUES (INCLUDING “EARLY REFLECTIONS” OCCURING 30 to 80 ms AFTER DIRECT SOUND) DETERMINE IMPRESSION OF SIZE, SHAPE, AND QUALITY OF THE ROOM
MOTION CUES INCLUDE TIME-VARYING DIRECTION, DISTANCE, AND DOPPLER EFFECT

21. MODELING DIRECT SOUND AND FIRST ORDER REFLECTIONS
EACH OF FOUR LOUDSPEAKERS IN LISTENING ROOM RECEIVES DIRECT SOUND (HEAVY LINES) AND REFLECTED SOUND (DASHED LINES).
GEOMETRY OF VIRTUAL ACOUSTIC SPACE DETERMINES DISTANCES FOR ALL DIRECT AND REFLECTED PATHS

22. SOUND RECORDING STUDIOS
MAY VARY IN SIZE FROM 300 m3 to 2000 m WITH RT FROM 0.9 to 2.4 s
A DIFFUSE SOUND FIELD IS VERY IMPORTANT
NOISE ISOLATION IS VERY IMPORTANT
“RULE OF THREE”: DISTANCE TO ANY OTHER MICROPHONE SHOULD BE AT LEAST 3 TIMES GREATER THAN TO THE MUSICIAN’S OWN MIKE
ISOLATED ROOMS MAY BE USED FOR VOCALS, DRUMS, etc.

23. SOUND RECORDING STUDIO (Newcastle, UK)

24. ACOUSTICS OF RECORDING STUDIOS
A GOOD STUDIO SHOULD BE QUIET, ON THE ORDER OF NC 10 to 15
IT SHOULD BE WELL ISOLATED FROM EXTERNAL NOISE
IT SHOULD BE FREE OF ACOUSTICAL DEFECTS SUCH AS FLUTTER
IT SHOULD HAVE REASONABLE DIFFUSION
BASS REVERBERATION SHOULD BE WELL CONTROLLED
GOOD VISUAL COMMUNICATION WITH THE CONTROL ROOM

25. EXAMPLE OF THE USE OF AN ISOLATED ROOM
NOVA MUSIC
RECORDING STUDIO

26. CONTROL ROOM
BOWLING GREEN UNIVERSITY RECORDING STUDIO

27. ACOUSTICAL DESIGN OF CONTROL ROOM
QUIET (NC 10 to 15), WELL ISOLATED FROM STUDIO
MONITOR LOUDSPEAKERS CAREFULLY PLACED
EARLY REFLECTIONS CAREFULLY CONTROLLED
LIVE-END-DEAD-END DESIGN (Davis & Davis, 1987): FRONT HALF OF STUDIO REFLECTION-FREE ZONE
CONTRARY OPINION BY TOOLE (1990): TOTALLY DIFFUSING REAR WALL CREATES “FOG OF SOUND”

28. CREATING A REFLECTION-FREE ZONE BY SHAPING RELATIVE SURFACES TO DIRECT SOUND AWAY FROM THE MIXES