ACOUSTICS AND THE PERFORMING ARTS

Russ CooperJaffe Holden Acoustics

Norwalk, CTFEBRUARY 14, 2012

ACOUSTICS 101

WHAT IS SOUND?

CompressionExpansion

POINT SOURCE PRESSURE WAVES

PRESSURE WAVES FROM TUNING FORK

THE HUMAN EAR

EAR DRUM RESPONSE TO PRESSURE WAVES

PROPERTIES OF SOUND

90 dB

75 dB

SOUND ABSORPTIVE MATERIALS

SOUND REFLECTIVE MATERIALS

THE SCIENCE OF ACOUSTICS• Wallace Clement Sabine, the father of acoustics

uses organ pipes as sound sources and seat cushions in a Harvard University lab in 1898 to measure the properties of sound.

• Sabine goes on to assist in the design of Boston Symphony Hall in 1900, considered the best acoustics for a concert hall in the world

BOSTON SYMPHONY HALL

TYPICAL REVERBERATION TIME DECAY CURVE

Rt60 = V 20 S

Reverb Time = Volume Sound Absorption

0 2

60

0

Open Window 0

Acoustical Ceiling Tile

¾” Plaster On Lath

MATERIAL % REFLECTED % ABSORBED & TRANSMITTED

SOUND ABSORPTION COEFFICIENT

()

30

93

100

70

7

1.00

0.70

0.07

ABSORBED - TRANSMITTED - REFLECTED SOUND

SCIENTIFIC ACOUSTIC TERMS

• Reverberation Time: RT60

• Early Decay Time: EDT• Clarity: C80

• Inter-aural Cross Correlation: IACC• Bass Ratio (Warmth): BR• Direction of Reflection: LF• Initial Time Delay Gap: ITDG• Gain (Loudness): G• Noise Criteria: NC

ACOUSTIC DESIGN OF PERFORMANCE HALLS

SCIENCE OF ACOUSTICS• We can predict and model how individual sources

of sound radiating equally in all directions with equal energy levels at all frequencies will react at a given receiver position in a hall.

SCIENCE OF ACOUSTICS

• However, most performances involve multiple sources in different locations with varying radiation patterns and different energy levels at different frequencies.

SCIENCE OF ACOUSTICS

Equal Energy at every Frequency for Acoustic Model

Actual Musical Instruments – Varying Energy at Different Frequencies

ARTISTIC APPLICATION OF ACOUSTICS

• The art is in the application of the science•Experience with how sound should behave on stage in musical ensemble • Acoustic “Listening” – how the room will sound on

the stage, in the pit, in the orchestra seats, in the

balconies• Intuitive Auralization – The acoustician

must “hear” the drawings• Tuning the Hall to achieve the acoustic goals• Interaction of artists with the hall

ACOUSTICS FOR MULTI-USE HALLS

• Program, program, program• Acoustic Designs:

– Proscenium Style– Platform Forward– Concert Hall “Shaper”

• Adjustable Acoustic Systems– Draperies, Banners, Panels

• Integration of acoustic reflectors, lighting and sound

PROSCENIUM STYLE

PLATFORM FORWARD

CONCERT HALL “SHAPER”

SKYPAC ACOUSTIC GOALS

1. Classical Music:

2. Theatre / Dance / Opera:

• Warm, rich, enveloping• Clear & present• Well defined – blended, but distinct• Quiet Room• Excellent on-stage hearing

• Dry, but warm• Articulate & intelligible

3. Amplified Events:• Not too loud, room won’t “Overload”• No Echoes• Bass Control

ACOUSTIC CHALLENGES WITH VARIABLE PROGRAMS

Speech is Directional

Music and Speech have different acoustic requirements

ACOUSTIC CHALLENGES WITH VARIABLE PROGRAMS

Music and Speech have different acoustic requirements

Music is Omni-Directional

ACOUSTIC SOLUTION FOR MUSIC

• Utilizes reverberant stage house coupling for low frequencieslow frequencies

• Uses reflective shell for mid and high mid and high frequency frequency sound projection to audience and performers

• Light weight demountable orchestra shell in a stage house

Music: Light Weight Orchestra Shell

ADJUSTABLE ACOUSTICS FOR

PERFORMANCE SPACES

When is it needed?– Variable acoustic systems allow hall to

have different reverberation times– Can be used to control echoes from

loudspeakers– Can be used to “tune” the room for

different programs

Lecture Drama

Opera/Ballet Symphony

1.0 sec.

2.0 sec.

0.8 1.0

1.4

2.0Liveness (Rt)

Mid-frequency

Preferred

Experience Shows That AcousticsDiffer For Each Type of Performance

TYPES OF ADJUSTABLE ACOUSTIC SYSTEMS

• Velour Drapes - 25 to 32 ounce material on track or drum or winch line

• Hung in space or against a wall• Hidden behind sound transparent material

or scrim or exposed• Fiberglass or Felt or wool panels tracked or

on drum• Low frequency panel absorbers

ACOUSTIC CURTAINS

FABRIC COVERED TRACKING PANELS

Vertically tracking acoustical panels

CONCEALED ADJUSTABLE ACOUSTIC SYSTEM

Acoustic banners hidden behind perforated metal

WOOL BANNERS

ADJUSTABLE ACOUSTIC SYSTEMS

ADJUSTABLE ACOUSTIC SYSTEMS

POPULAR MUSIC ACOUSTIC CHALLENGES

ECHO

ADJUSTABLE ACOUSTIC SYSTEMS

VO

LUM

E/S

EA

T (

CU

BIC

FEET P

ER

PER

SO

N) 300

200

100

400

305360

CARNEGIE

HALL

BASS H

ALL0

LARGE VOLUME-TO-SEAT RATIO IS A CHARACTERISTIC OF ACOUSTICALLY

EXCELLENT HALLS

300312

BOSTON

SKYP

AC

25 20 15 10 5

GOOD

BETTER

BEST

QUIET NOISE LEVELS ARE A CHARACTERISTIC OF ACOUSTICALLY

EXCELLENT HALLS

NC- NOISE CRITERIA

HA

LL Q

UA

LIT

Y L

EV

EL

POINT OF DIMINISHING

RETURN

SKYPAC

RE

VE

RB

ER

ATIO

N T

IME

(SE

CO

ND

S)

1.5

1.0

0.5

2.0

0%

ADJUSTABLE ACOUSTICAL DRAPES OPTIMIZE SKYPAC REVERBERATION TIME

PERCENTAGEOF ABSORPTION INTRODUCED INTO HALL

50% 100%0

??2.5

??

??

1.6

1.45

1.3M

easu

red

Measu

red

Measu

red

Calc

ula

ted

Calc

ula

ted

Calc

ula

ted

CONSTRUCTION ISSUES THAT AFFECT THE ACOUSTICS

Holes in walls reduce the sound isolation between spaces

Poor installation of acoustic devices

No coordination of utility requirements and acoustic requirements

ACOUSTICAL TUNING

• Listening to the various ensembles to determine the correct setting of the adjustable acoustical systems

• Working with the music directors for proper musician placement on stage

• Operating all adjustable systems in the hall• Measuring the reverberation time in unoccupied

condition• Listening to the ensembles with full audience to

confirm settings• Measuring the reverberation time in occupied

condition

SKYPAC