GEOMETRICAL DESIGN STUDIES

GEOMETRICAL DESIGN STUDIES

ACOUSTICS OF CONCERT HALLS AND ROOMS

Handbook of Acoustics, Chapter 9

Long, Architectural Acoustics, Chapter 19

THE LISTENING ENVIRONMENT

• STRONG LATERAL REFLECTIONS SO AUDIENCE FEELS ENVELOPED

• A STRONG REVERBERANT FIELD

• CLARITY AND DEFINITION FOR RAPID MUSICAL PASSAGES

• ADEQUATE LOUDNESS THROUGHOUT THE HALL

• ROOM MUST NOT COLOR THE NATURAL INSTRUMENT SPECTRA

• LOW BACKGROUND NOISE (NC 20 OR LESS)

•SMOOTH DECAY WITHOUT ECHOES

• PERFORMERS SHOULD BE ABLE TO HEAR EACH OTHER (ENSEMBLE)

HALL SIZE

SEATING CAPACITY PAYS THE RENT

HOWEVER THE “BEST LIKED” CONCERT HALLS HAVE CAPACITIES OF ABOUT 1800-1900 SEATS

“LEAST LIKED” HALLS AVERAGED 2800 SEATS

BASIC ROOM SHAPES

FAN-SHAPED GREEK/ROMAN THEATER

CIRCUS OR ARENA

SIMPLE PLAN FORMS FOR

CONCERT HALLS IN NORMAL AND SURROUND

CONFIGURATIONS

NORMAL SURROUND

DIRECTIONS OF SIDE-WALL REFLECTIONS

DEPENDING ON ROOM

SHAPE

RECTANGULAR FAN-SHAPE

GRAZING INCIDENCE (LESS THAN 5O)

FOR REFLECTION AT A HARD SURFACE, REFLECTED WAVE IS IN PHASE WITH INCIDENT WAVE AND PRODUCES AN INCREASE (OR DECREASE) IN SOUND LEVEL

10-20 dB IN FOR REFLECTION AT A SOFT SURFACE (SUCH AS THE HEADS OF THE AUDIENCE) REFLECTED WAVE IS 180O OUT OF PHASE WITH INCIDENT WAVE AND WAVE INTERFERENCE CAN AMOUNT TO 10--20 dB IN THE 100--800 Hz RANGE (GADE, 2007)

SEATING ARRANGEMENT

GRAZING INCIDENCE ATTENUATES NOT ONLY THE DIRECT SOUND BUT ALSO THE FIRST-ORDER REFLECTIONS FROM THE SIDE WALLS. THIS RESULTS IN WEAKER EARLY REFLECTIONS AND REDUCED CLARITY, INTIMACY and WARMTH IN THE ORCHESTRA SEATS (“STALLS”)

NORMALLY A CLEARANCE OF 8 cm WILL SUFFICE TO AVOID GRAZING-INCIDENCE ATTENUATION, BUT SIGHT LINES WILL STILL BE UNSATISFACTORY (UNLESS SEATS ARE STAGGERED), INCREASING THE CLEARANCE TO 12 cm WILL MAKE BOTH ACOUSTIC AND VISUAL CONDITIONS SATISFACTORY, BUT THIS IMPLIES A STEEPER FLOOR SLOPE.

CALCULATION OF A FLOOR SLOPE WITH CONSTANT CLEARANCE

A CURVED FLOOR SLOPE WITH CONSTANT CLEARANCE MAY PREVENT EXCESS CLEARANCE IN SEATS CLOSE TO THE SOURCE

SECTION OF A HALL WITH A REAR BALCONY AND CONSTANT CLEARANCE. THE RESULT IS AN INCREASED

SLOPE FOR THE ELEVATED BALCONY

FOR SAFETY THE SLOPE SHOULD NOT EXCEED ABOUT 35O

IMPORTANT PARAMETERS FOR MAINTAINING PROPER SOUND IN SEATS OVERHUNG BY BALCONIES

FOR THEATERS, H>2D

FOR CONCERT HALLS H>D

(GADE, 2007)

UNDER BALCONY EARLY DECAY TIME EDT (Barron, 1993)

VOLUME AND CEILING HEIGHT

VOLUME INFLUENCES BOTH REVERBERANCE AND LOUDNESS. FOR HALLS OF HIGH CAPACITY, A LOW VOLUME PER SEAT HELPS PRESERVE ACOUSTICAL ENERGY.

THOSE WHO PREFER THE MODEL OF BOSTON SYMPHONY HALL PREFER AROUND 9 m3 (320 cu ft) PER SEAT. HALLS SUCH AS McDERMOTT AND BIRMINGHAM (WITH OPENABLE REVERBERATION CHAMBERS) ARE AT OR ABOVE 11 m3 (400 cu ft). THESE HALLS INCLUDE A LARGE MOVEABLE REFLECTOR ABOVE THE ORCHESTRA WHICH OFFSETS SOME OF THE EFFECTS OF A HIGH VOLUME (Long, 2006)

VOLUME PER SEAT FOR SEVERAL HALLS (Long)

ECHO ELIPSES DRAWN WITH SOURCE AND RECEIVER POINTS AT THE FOCI, AND THE SUM OF DISTANCES FROM THE FOCI EQUAL DISTANCE BETWEEN FOCI PLUS 17 m. IF A SURFACE OUTSIDE AN ELLIPSE REFLECTS SOUND TO A LISTENER, IT SHOULD BE MADE ABSORBING (Gade, 2007)

RESHAPING OF CEILING PROFILE TO AVOID FOCUSING AND PROVIDE MORE EVEN SOUND

DISTRIBUTION

DIFFUSION BY GEOMETRIC SHAPES:

TRIANGULAR RECTANGULAR

PROTRUSIONS SEMI-CYLINDRICAL

SURFACE

CROSS SECTION OF A PHASE GRATING (QUADRATIC RESIDUE) SOUND DIFFUSER, AS

SUGGESTED BY SCHROEDER (1975)

MAXIMUM DEPTH OF THE WELLS DETERMINES THE LOW-FREQUENCY LIMIT OF THE DIFFUSER. WELL DEPTH SHOULD BE 12 TIMES WAVELENGTH AT THE LOWEST FREQUENCY.THE HIGHEST FREQUENCY IS DETERMINED BY WELL WIDTH, WHICH IS A HALF WAVELENGTH AT THE HIGHEST FREQUENCY.

SYMPHONYHALLBOSTON

V =18,750 m3

39 m x23.6 m x18.6 m

2625 seats

Furthest seat: 40.5 m

T60 = 1.85 s

V/N = 7.14 m3

NEUES GEWANDHAUS

LEIPZIG

CONCERTGEBAUW

AMSTERDAM

BERLIN PHILHARMONIC HALL

CHRISTCHURCH TOWN HALL, NEW ZEALAND BUILT 19722662 seats, V = 20,000m3, T = 2.4s

SEGERSTROM HALL, ORANGE COUNTY

Seats 2900Acoustic Design, Marshall, Hyde, Paoletti

STANFORD MEMORIAL CHURCH