STUDIOS AND

LISTENING ROOMS

ACOUSTICS OF CONCERT HALLS AND ROOMS

Principles of Vibration and Sound, Chapter 11Science of Sound, Chapters 25, 29Sound System Engineering (Davis & Davis, 1987)

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

NORMAL MODES IN CAVITIES

THE WAVE EQUATION IN THREE DIMENSIONS:

IN RECTANGULAR COORDINATES, THIS BECOMES:

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

a) (2,0,0)axial mode

b) (3,2,0)tangential mode

CONTOURS OF EQUAL SOUND PRESSURE IN ARECTANGULARROOM

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

LOCATION OF SOUND IMAGES FROM TWO SOURCES SL AND SR

WITH THE SAME PROGRAM MATERIAL

(a) Identical sources

(b) Same signalat different levels

(c) One source delayed by increasing the dis-tance from source to listener

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

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

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

LOCATION OF SOUND IMAGES FROM TWO OUT OF PHASE SOURCES

BROADENING OF SOUND IMAGE BY FREQUENCY EMPHASIS

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

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

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”

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.

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)

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

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

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

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

SOUND RECORDING STUDIOS

MAY VARY IN SIZE FROM 300 m3 to 2000 m3 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.

SOUND RECORDING STUDIO (Newcastle, UK)

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

NOVA MUSICRECORDING STUDIO

EXAMPLE OF THE USE OF AN ISOLATED ROOM

CONTROL ROOM

BOWLING GREEN UNIVERSITY RECORDING STUDIO

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”

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