ACOUSTICS OF CONCERT HALLS AND ROOMS STUDIOS AND

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)

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 l: w: h=3: 2: 1

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

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 signal at different levels (c) One source delayed by increasing the distance 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 MIDPLANE, AND p. L and p. R 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/d. B FOR 1 m TO ABOUT 70 μs/d. B 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 40 O AND 90 O 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 2 x 2 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 d. B FOR DISTANCE DOUBLING; FOR UNFAMILIAR SOUNDS, IT IS MORE LIKE 10 d. B 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 m 3 to 2000 m 3 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

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

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