Acoustical assessment of the Jack Singer Concert Hall

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Acoustical assessment of the Jack Singer Concert Hall

NATlONAt RESEARCH COUNCIL OF CANADA

*

DIVISION OF BUILDING RESEARCH

DBR INTERNAL REPORT NO. 508

ACOUSTICAL ASSESSMENT OF THE JACK SINGER CONCERT

HALL

by J.S. Bradley

ANALYZED

Clmcksdby: A.c.C.W. Approved by:

L

.

W. GO ld Data: April 1986

Pnpuodfor: Calgary Centre for the Performing Arts

AB STRAC T

Extensive acoustical measurements were made to evaluate the Jack Singer Concert Hall in accordance with the most recent international research knowledge. The hall was found to be very good for

orchestral music, but not as suitable for other types of performances. This lack of adaptability is due to the variable acoustics devices in the hall producing only relatively small changes in the acoustical character of the hall.

I n t r o d u c t i o n

The a c o u s t i c a l q u a l i t y of a c o n c e r t h a l l o r a u d i t o r i u m i s c r i t i c a l t o

t h e s u c c e s s o f ' p r o d u c t i o n s performed i n i t . The i n f l u e n c e of a c o u s t i c a l

q u a l i t y c a n v a r y from q u i t e s u b t l e e f f e c t s t o more d i s a s t r o u s s i t u a t i o n s . While t h e laore extreme problems a r e e a s i l y i d e n t i f i e d and r e c t i f i e d t h e more s u b t l e d e f e c t s may b e a t t r i b u t e d by t h e a u d i e n c e t o t h e p e r f o r m e r s r a t h e r

t h a n t o t h e h a l l . 'Ihe s c i e n c e of a u d i t o r i u m a c o u s t i c s h a s made c o n s i d e r a b l e

p r o g r e s s o v e r t h e p a s t 20 y e a r s , and i t i s now p o s s i b l e t o make d e t a i l e d

o b j e c t i v e measurements u s i n g s e v e r a l t y p e s of new a c o u s t i c a l measures t h a t

have been shown t o r e l a t e t o s u b j e c t i v e a s s e s s m e n t s of h a l l s . Such newer

measuremnts a r e t h e only r e l i a b l e method of e v a l u a t i n g a h a l l , and t h e y a r e p a r t i c u l a r l y u s e f u l t o u n d e r s t a n d i n g t h e e f f e c t s of v a r i o u s v a r i a b l e

a c o u s t i c s d e v i c e s . The p r o p e r t i e s of such d e v i c e s a s moveable r e f l e c t i n g

p a n e l s a r e n o t w e l l u n d e r s t o o d i n a q u a n t i t a t i v e manner, and i t i s o n l y a f t e r

v e r y thorough e v a l u a t i o n s t h a t one can be s u r e of how t h e y s h o u l d be u s e d f o r optimum e f f e c t .

Although much p r o g r e s s h a s been made, t h e r e a r e s t i l l a number of a r e a s

where r e s e a r c h i s r e q u i r e d . D e t a i l e d s t u d i e s of e x i s t i n g h a l l s a r e

p a r t i c u l a r l y u s e f u l i n t h i s r e g a r d , p e r m i t t i n g much t o be l e a r n e d from t h e

comparison of t h e r e s u l t s from d i f f e r e n t h a l l s . A s c u r r e n t wisdom s u g g e s t s

t h a t a r e c t a n g u l a r h a l l i s a good s t a r t i n g p o i n t t o a c h i e v e a n a c o u s t i c a l l y s u c c e s s f u l c o n c e r t h a l l , i t i s of some c o n s i d e r a b l e r e s e a r c h i n t e r e s t t o s t u d y t h e r e c t a n g u l a r J a c k S i n g e r H a l l . It i s hoped t h a t t h e s e and s i m i l a r s t u d i e s w i l l a l l o w u s t o p r o v i d e Canadian c o n s u l t a n t s w i t h b e t t e r i n f o r m a t i o n f o r t h e d e s i g n and e v a l u a t i o n of a u d i t o r i a . I n t h i s r e p o r t , t h e s e c t i o n f o l l o w i n g t h i s i n t r o d u c t i o n b r i e f l y

d e s c r i b e s t h e t y p e of measurements t h a t were made, and t h e f o l l o w i n g s e c t i o n

d e s c r i b e s t h e key r e s u l t s . The l a s t s e c t i o n summarizes t h e p r i n c i p a l r e s u l t s

and g i v e s some recommendations f o r f u t u r e c o n s i d e r a t i o n s . A l l d a t a and

t e c h n i c a l r e s u l t s have been i n c l u d e d i n t h r e e a p p e n d i c e s s o t h a t t h e main

body of t h e r e p o r t i s more c o n c i s e and n o t t o o encumbered w i t h t e c h n i c a l

terms. Appendix A p r e s e n t s r e s u l t s f o r t h e b a s i c h a l l i n what was termed t h e

s t a n d a r d c o n c e r t c o n f i g u r a t i o n f o r o r c h e s t r a l performances. Appendix B g i v e s

r e s u l t s t h a t e v a l u a t e t h e e f f e c t of t h e sound a b s o r b i n g b a n n e r s and c u r t a i n s .

Appendix C p r e s e n t s r e s u l t s t o e v a l u a t e t h e performance of t h e moveable

over-s t a g e canopy.

U n f o r t u n a t e l y i t was n o t p o s s i b l e t o e v a l u a t e t h e h a l l a s c o m p l e t e l y a s

would be d e s i r a b l e because i n - h a l l measurement t i m e d u r i n g o u r v i s i t t o

Calgary was l i m i t e d t o a few hours. Thus t h e r e s u l t s of Appendix C a r e much

more l i m i t e d t h a n i s d e s i r a b l e t o f u l l y e v a l u a t e t h e moveable o v e r - s t a g e

canopy, and no a t t e m p t was made t o a s s e s s t h e a c o u s t i c a l c h a r a c t e r i s t i c s o f t h e o r c h e s t r a p i t .

Measurements

The measurement s y s t e m h a s e v o l v e d o v e r a number of y e a r s of s t u d i e s o f

v a r i o u s h a l l s . Its development h a s been h e a v i l y i n f l u e n c e d by t h e p r a c t i c a l

problems of making a broad range of measurements a t a l a r g e number of

accommodate t h e u s u a l c o n s t r a i n t s e x p e r i e n c e d i n r e a l h a l l s . Measurements a r e m d e by t a p e r e c o r d i n g p i s t o l s h o t s produced by a c a l i b r a t e d b l a n k

p i s t o l . The r e c o r d e d p i s t o l s h o t s a r e d i g i t i z e d and p r o c e s s e d by computer t o p r o d u c e v a l u e s of 1 2 d i f f e r e n t q u a n t i t i e s e a c h i n o c t a v e bands from 1 2 5 t o

8000 _{Hz. I n o r d e r t o p r o p e r l y r e p r e s e n t t h e s e a t - t o - s e a t v a r i a t i o n s i n t h e}

h a l l and t h e i n f l u e n c e of s o u r c e p o s i t i o n , measurements must b e made f o r a

l a r g e number of s o u r c e and r e c e i v e r p o s i t i o n s . I n t h e J a c k S i n g e r C o n c e r t H a l l measurements were made f o r t h e 36 c o m b i n a t i o n s of 3 s o u r c e p o s i t i o n s and

1 2 r e c e i v e r p o s i t i o n s i n c l u d i n g one measurement p o s i t i o n a t t h e podium. T h i s i s t h o u g h t t o b e a minimum number of measurement p o s i t i o n s t o p r o p e r l y assess

t h e a c o u s t i c a l q u a l i t y of a l a r g e h a l l . The s o u r c e and main f l o o r r e c e i v e r p o s i t i o n s a r e shown on F i g u r e 1 . Measurement p o s i t i o n s i n t h e f i r s t and second b a l c o n i e s were d i r e c t l y above t h o s e i n row D a t t h e rear of t h e main f l o o r . Complete sets of measurements were made f o r two c o n d i t i o n s of t h e h a l l : normal c o n c e r t c o n f i g u r a t i o n w i t h a l l b a n n e r s and c u r t a i n s withdrawn and t h e o v e r - s t a g e canopy f u l l y r a i s e d , and f o r t h e c a s e of t h e same r a i s e d canopy p o s i t i o n and w i t h a l l b a n n e r s and c u r t a i n s exposed. A t h i r d

c o n f i g u r a t i o n was p a r t i a l l y measured w i t h t h e canopy lowered. Each p i s t o l s h o t was r e p e a t e d f o u r times s o t h a t a v e r a g i n g would minimize s h o t - t o - s h o t v a r i a t i o n s . I n t o t a l 336 s h o t s were r e c o r d e d and p r o c e s s e d and from e a c h of t h e s e 84 _{octave-band a c o u s t i c a l measures were c a l c u l a t e d . Because of t h e}

l a r g e q u a n t i t y of d a t a t h a t was o b t a i n e d many r e s u l t s a r e p r e s e n t e d as t h e mean o v e r v a r i o u s s e a t i n g g r o u p s o r o v e r a l l a u d i e n c e s e a t i n g p o s i t i o n s .

Although 1 2 d i f f e r e n t measures were c a l c u l a t e d , t h e r e a r e o n l y f o u r d i f f e r e n t t y p e s of q u a n t i t i e s t h a t must be c o n s i d e r e d . Many of t h e o t h e r q u a n t i t i e s a r e v e r y s t r o n g l y r e l a t e d t o 5 p r i n c i p a l measures and a r e n o t d i s c u s s e d i n t h i s r e p o r t . C o n v e n t i o n a l l y r e v e r b e r a t i o n t i m e , RT, h a s been used a s t h e major q u a n t i t a t i v e o b j e c t i v e measure of a h a l l ' s a c o u s t i c a l

q u a l i t y . We now know t h a t t h e e a r l y decay time, EDT, i s more c l o s e l y r e l a t e d t o t h e s u b j e c t i v e l y p e r c e i v e d r e v e r b e r a n c e o r l i v e n e s s of a h a l l . Both

q u a n t i t i e s a r e p r e s e n t e d i n t h e s e r e s u l t s . Of v a r i o u s e a r l y - t o - l a t e a r r i v i n g sound e n e r g y r a t i o s , C g O , where t h e d i v i s i o n between e a r l y and - l a t e a r r i v i n g

r e f l e c t i o n s i s t a k e n a s 0.08 _{s e c o n d s a f t e r t h e a r r i v a l of t h e d i r e c t sound,}

h a s been most w i d e l y a c c e p t e d a s a measure of c l a r i t y . The g r e a t e r t h e C B O , t h e g r e a t e r t h e p e r c e i v e d c l a r i t y o r d e f i n i t i o n a s s o c i a t e d w i t h music i n t h e h a l l . Very low C g O v a l u e s would l e a d t o a muddy sound. The o v e r a l l s t r e n g t h of t h e sound i n a h a l l , G, r e l a t e s t o how loud a g i v e n sound s o u r c e w i l l be i n t h e h a l l . H a l l s w i t h h i g h e r G v a l u e s have been found t o b e p r e f e r r e d i n s u b j e c t i v e t e s t s . F i n a l l y t h e l a t e r a l f r a c t i o n , L F , measures t h e f r a c t i o n of t h e e a r l y sound t h a t a r r i v e s from t h e s i d e a t a p a r t i c u l a r measurement

p o s i t i o n . S t r o n g e a r l y s i d e w a l l o r l a t e r a l r e f l e c t i o n s a r e p r e f e r r e d and l e a d t o t h e i m p r e s s i o n of b e i n g immersed i n o r s u r r o u n d e d by t h e sound r a t h e r t h a n j u s t " l o o k i n g a t it". I n t h i s r e p o r t o c t a v e band m e a s u r e s of KT, EDT, C B O , G, and W a r e p r e s e n t e d t o e v a l u a t e t h e a c o u s t i c a l q u a l i t y of t h e h a l l . These q u a n t i t l e s a r e m a t h e m a t i c a l l y d e f i n e d i n Appendix D.

Very low background n o i s e l e v e l s a r e a l s o e s s e n t i a l t o o b t a i n a h i g h q u a l i t y c o n c e r t h a l l . One s h o u l d make d e t a l l e d measurements of background n o i s e l e v e l s t o c o m p l e t e l y e v a l u a t e t h e a c o u s t i c a l q u a l i t y of a h a l l . U n f o r t u n a t e l y t i m e d i d n o t p e r m i t s u c h measurements.

Figure 1

P r i n c i p a l R e s u l t s

The r e s u l t s p r e s e n t e d i n Appendix A i n d i c a t e t h a t t h e t h e a c o u s t i c a l q u a l i t y of J a c k S i n g e r C o n c e r t Hall i s q u i t e good f o r o r c h e s t r a l music

performances. W i t h i n t h e l i m i t s of o u r p r e s e n t knowledge, t h e mean v a l u e s of RT, EDT, C a O , and LF a r e a l l w i t h i n t h e r a n g e of a c c e p t a b l e v a l u e s f o r t h i s t y p e of music. The o v e r a l l mean mid-f requency RT v a l u e was 2.2 s e c o n d s w i t h t h e EDT s l i g h t l y l o n g e r . The o v e r a l l mean mid-frequency C a O was -0.3 dB, G +5.0 dB, and LF was 0.23. The mid-frequency RT and EDT v a l u e s a r e p e r h a p s a

l i t t l e l o n g e r t h a n i s n e c e s s a r y and t h i s c o n t r i b u t e s t o t h e CaO b e i n g

s l i g h t l y l o w e r t h a n might b e i d e a l f o r optimum c l a r i t y . Optimum c l a r i t y i s

t h o u g h t t o c o r r e s p o n d t o C a O v a l u e s between 0 a n d +5 dB. The measured G v a l u e s a r e g r e a t e r t h a n found i n t h e A l b e r t a J u b i l e e A u d i t o r i a and i n t h e m i d d l e of t h e r a n g e of v a l u e s found i n s e v e r a l European s t u d i e s . An o v e r a l l mean v a l u e of +5.0 dB would a p p e a r t o r e p r e s e n t q u i t e a c c e p t a b l e o v e r a l l s t r e n g t h f o r t h i s h a l l . The r e l a t i v e l y h i g h l a t e r a l f r a c t i o n v a l u e s i n d i c a t e t h a t p r e f e r r e d s t r o n g e a r l y l a t e r a l r e f l e c t i o n s a r e p r e s e n t and would g i v e t h e d e s i r e d s p a t i a l i m p r e s s i o n of b e i n g immersed i n t h e m u s i c a l sounds. The s e a t - t o - s e a t v a r i a t i o n and t h e e f f e c t of t h e s o u r c e p o s i t i o n o n t h e s e

q u a n t i t i e s i s r e l a t i v e l y small, i n d i c a t i n g t h a t t h e a c o u s t i c a l q u a l i t y i s

q u i t e u n i f o r m t h r o u g h o u t t h e h a l l . F i n a l l y t h e s i m i l a r i t y between EDT and RT v a l u e s i n d i c a t e s t h a t t h e r e i s a h i g h d e g r e e of d i f f u s i o n i n t h e e a r l y

r e f l e c t i o n s i n t h i s h a l l t h a t i s a g a i n s u i t a b l e and d e s i r a b l e f o r p e r f o r m a n c e s of o r c h e s t r a l music.

The d e s i g n h a s made l i t t l e compromise t o accommodate t h e n e e d s of o t h e r t y p e s of performances. For o p e r a , chamber music, s p e e c h , o r v a r i o u s

a m p l i f i e d p e r f o r m a n c e s t h e h a l l i s t o o r e v e r b e r a n t . T h i s c o u l d i n p r i n c i p l e be s o l v e d by t h e u s e of v a r i a b l e a b s o r p t i o n d e v i c e s s u c h a s t h e b a n n e r s and c u r t a i n s t h a t a r e i n s t a l l e d i n t h e h a l l . U n f o r t u n a t e l y t h e i r e f f e c t i s v e r y s m a l l and c e r t a i n l y n o t enough t o r e d u c e t h e r e v e r b e r a t i o n t i m e t o v a l u e s a c c e p t a b l e f o r t h e s e o t h e r t y p e s of performances. The r e s u l t s of Appendix B i n d i c a t e t h a t t h e mid-frequency RT i s a b o u t 2.2 seconds and i s r e d u c e d t o 2.0 s e c o n d s w i t h a l l b a n n e r s and c u r t a i n s exposed. A more i d e a l g o a l would b e t o have a n i n i t i a l RT of 2.0 s e c o n d s t h a t c o u l d be reduced t o 1.5 s e c o n d s w i t h t h e a d d i t i o n of b a n n e r s and c u r t a i n s . O t h e r h a l l s s u c h a s t h e Opera of t h e N a t i o n a l Arts C e n t r e i n Ottawa have s i m i l a r l y i n e f f e c t i v e b a n n e r s w h i l e Hamilton P l a c e h a s much more e f f e c t i v e sound a b s o r b i n g b a n n e r s . The

measurements of t h e o t h e r q u a n t i t i e s showed c o r r e s p o n d i n g s m a l l changes a s a r e s u l t of a d d i n g t h e a b s o r p t i o n of t h e c u r t a i n s and b a n n e r s t o t h e h a l l . None of t h e measured c h a n g e s i n d i c a t e d t h a t t h e a c o u s t i c a l l y a b s o r b i n g b a n n e r s and c u r t a i n s would produce s u b s t a n t i a l a c o u s t i c a l c h a n g e s t o t h e h a l l .

The p u r p o s e of t h e moveable o v e r - s t a g e r e f l e c t o r i s l e s s c l e a r .

Presumably l o w e r i n g i t i s i n t e n d e d t o p r o v i d e s t r o n g e r e a r l y r e f l e c t i o n s t h a t a r r i v e a l i t t l e s o o n e r a t l i s t e n e r s e a r s . There a r e i n d i c a ~ i o n s t h a t t h i s e f f e c t d o e s o c c u r , and s m a l l i n c r e a s e s i n e a r l y sound e n e r g y a r e i n d i c a t e d by c o r r e s p o n d i n g s m a l l i n c r e a s e s i n C a O and G v a l u e s and s m a l l d e c r e a s e s i n EDT v a l u e s a t s e a t s on t h e main f l o o r when t h e canopy was moved from i t s h i g h e s t t o i t s l o w e s t normal p o s i t i o n . The magnitude of t h e s e c h a n g e s i s t h o u g h t t o be t o o s m a l l t o be s u b j e c t i v e l y very u s e f u l . The most s i g n i f i c a n t changes o b s e r v e d when t h e canopy was lowered were l a r g e r i n c r e a s e s i n t h e e a r l y sound e n e r g y i n t h e 250 Hz o c t a v e band. T h i s was o b s e r v e d f o r b o t h CBO and G

v a l u e s a t i s o l a t e d s e a t s on t h e main f l o o r . These l a r g e r low f r e q u e n c y e f f e c t s a r e t h o u g h t t o be due t o m o d i f i e d e a r l y r e f l e c t i o n s from t h e canopy changing t h e dominance of p a r t i c u l a r low f r e q u e n c y i n t e r f e r e n c e e f f e c t s .

Although t h e s e measurements i n d i c a t e t h a t t h e a c o u s t i c a l e f f e c t of moving t h e canopy from one extreme t o t h e o t h e r a r e v e r y s m a l l , c o n s i d e r a b l y more

e x t e n s i v e measurements a r e r e q u i r e d t o more c o m p l e t e l y a s s e s s i t s performance

and t o d e t e r m i n e how i t c a n b e used most e f f e c t i v e l y .

C o n c l u s i o n s and Recommendations

The measurements d e m o n s t r a t e t h a t t h e J a c k S i n g e r C o n c e r t H a l l

s u c c e s s f u l l y meets t h e r e q u i r e m e n t s f o r o r c h e s t r a l music w i t h i n t h e l j m i t s of

c u r r e n t r e s e a r c h knowledge. It i s a l s o n o t e d t h a t t h e r e i s no compromise i n

t h e d e s i g n t o accommodate t h e a c o u s t i c a l needs of o t h e r t y p e s of p e r f o r m a n c e s

such a s chamber music, o p e r a , s p e e c h o r v a r i o u s a m p l i f i e d performances. The

moveable sound a b s o r b i n g b a n n e r s and c u r t a i n s c o u l d p o t e n t i a l l y p r o v i d e t h i s

a d a p t a b i l i t y b u t t h e y do n o t produce l a r g e enough changes t o meet t h e

a c o u s t i c a l needs of t h e s e o t h e r t y p e s of performances. Although t i m e d i d n o t

p e r m i t a s c o m p l e t e a s t u d y of t h e moveable o v e r - s t a g e canopy, i t a p p e a r s t o

p r o d u c e o n l y small o v e r a l l changes w i t h i s o l a t e d l a r g e r low f r e q u e n c y

e f f e c t s .

A b e t t e r o v e r a l l compromise f o r t h e h a l l d e s i g n , t o accommodate t h e

n e e d s of o t h e r t y p e s of p e r f o r m a n c e s a s w e l l a s o r c h e s t r a l music, would b e t o

have a lower mean r e v e r b e r a t i o n t i m e , and t h e p o s s i b i l t i y of g r e a t e r v a r i a b i l i t y from a r e v i s e d s y s t e m of a c o u s t i c a l banners.

These measurements a r e n o t e n t i r e l y c o m p l e t e , and t h e r e a r e a number o f

a r e a s where f u r t h e r t e s t s would be of c o n s i d e r a b l e value. The most o b v i o u s

a d d i t i o n a l measurements, would b e a much more e x t e n s i v e e v a l u a t i o n of t h e

o v e r - s t a g e canopy. These s h o u l d i n c l u d e complete measurements f o r t h e . f u l 1

c o m b i n a t i o n of s o u r c e and r e c e i v e r l o c a t i o n s f o r s e v e r a l p o s i t i o n s of t h e

canopy. It i s o n l y from t h e r e s u l t s of such t e s t s t h a t one would l e a r n

unambiguously t h e p r o p e r t i e s of t h e canopy and how t o u s e i t f o r optimum

a d v a n t a g e . F u r t h e r measurements a r e a l s o d e s i r e a b l e t o e v a l u a t e t h e combined

e f f e c t s of t h e canopy and b a n n e r s , t o e v a l u a t e t h e o r c h e s t r a p i t , and t o d e t e r m i n e t h e c h a r a c t e r i s t i c s of t h e h a l l when o c c u p p i e d w i t h a f u l l

a u d i e n c e . F i n a l l y a complete e v a l u a t i o n of t h e h a l l s h o u l d i n c l u d e

background n o i s e l e v e l measurements.

Acknowledgements

The a s s i s t a n c e of Mr. K e l l y Kruger of A l b e r t a P u b l i c Works i n making t h e

APPENDIX A

C h a r a c t e r i s t i c s of t h e B a s i c H a l l

D i s c u s s i o n s w i t h t h e s t a f f a t t h e Jack S i n g e r C o n c e r t Hall i n d i c a t e d t h a t i n t h e b a s i c c o n c e r t c o n f i g u r a t i o n of t h e h a l l f o r o r c h e s t r a l

p e r f o r m a n c e s t h e o v e r - s t a g e canopy was f u l l y r a i s e d and a l l a b s o r b i n g b a n n e r s and c u r t a i n s were withdrawn from t h e h a l l . R e s u l t s i n t h i s Appendix a r e f o r t h i s b a s i c c o n d i t i o n o n l y , measured a t c o m b i n a t i o n s of 3 s o u r c e p o s i t i o n s and 1 2 r e c e i v e r p o s i t i o n s .

R e v e r b e r a t i o n t i m e , RT, h a s h i s t o r i c a l l y been r e g a r d e d a s t h e k e y

o b j e c t i v e d e s i g n p a r a m e t e r f o r a u d i t o r i a . I n s p i t e of t h e newer developments and newer a c o u s t i c a l m e a s u r e s , r e v e r b e r a t i o n t i m e i s s t i l l a u s e f u l i n d i c a t o r of t h e a v e r a g e a c o u s t i c a l p r o p e r t i e s of a h a l l and measurements of RT make p o s s i b l e comparisons w i t h t h e l a r g e amount of p u b l i s h e d v a l u e s from o t h e r h a l l s . F i g u r e A-1 p l o t s t h e mean measured RT v a l u e s v e r s u s o c t a v e band f r e q u e n c y o b t a i n e d from t h e measurements a t t h e 33 c o m b i n a t i o n s of t h e 3

s o u r c e p o s i t i o n s and t h e 1 1 a u d i e n c e r e c e i v e r p o s i t i o n s . The mean 1 0 0 0 Hz RT was 2.2 s e c o n d s which i s a l i t t l e l a r g e r t h a n some o l d e r r e f e r e n c e s would recommend. For example, Knudsen and Harris1 recommend mid-frequency RT v a l u e s up t o 1.95 s e c o n d s f o r a h a l l of t h i s volume b u t t h i s e x t r e m e i s onSy i n d i c a t e d f o r "church" music. Newer work s u g g e s t s t h a t t h e p r e c i s e v a l u e of t h e RT i s n o t a s c r i t i c a l a s p r e v i o u s l y t h o u g h t and t h a t t h e r e i s a r a n g e o f a c c e p t a b l e v a l u e s . G o t t l o b ' s r e s u l t s 2 i n d i c a t e a n optimum r a n g e a r o u n d a v a l u e of 2.0 s e c o n d s RT. Of c o u r s e t h e measured RT v a l u e s would b e r e d u c e d somewhat w i t h a n a u d i e n c e p r e s e n t .

While t h e c l a s s i c a l RT s t i l l h a s i m p o r t a n c e , t h e e a r l y d e c a y t i m e , EDT, r e l a t e s more c l o s e l y t o s u b j e c t i v e judgements of a h a l l s r e v e r b e r a n c e . Mean EDT v a l u e s v e r s u s o c t a v e f r e q u e n c y a r e a l s o p l o t t e d o n F i g u r e A-1 and a r e s e e n t o a g r e e q u i t e c l o s e l y w i t h RT v a l u e s . 1Jp t o 2000 Hz EDT v a l u e s a r e a l i t t l e l a r g e r t h a n t h e c o r r e s p o n d i n g RT v a l u e s . Comparisons of s i m i l a r measurements from a number of h a l l s s u g g e s t t h a t t h e d i f f e r e n c e between t h e RT and EDT v a l u e s i s r e l a t e d t o t h e d e g r e e of d i f f u s i o n of t h e e a r l y

r e f l e c t i o n s i n a h a l l . For m u s i c a l p e r f o r m a n c e s s u c h d i f f u s i o n i s t h o u g h t t o be d e s i r e a b l e . I n t h i s c a s e , where t h e EDT and RT v a l u e s a r e v e r y s i m i l a r , t h e s u b j e c t i v e i m p r e s s i o n w i l l be s i m i l a r t o t h a t i n d i c a t e d by t h e measured RT v a l u e s .

C a O h a s become a c c e p t e d a s a measure of t h e c l a r i t y of music. _{When % 0} v a l u e s a r e h i g h , h i g h c l a r i t y o r d e f i n i t i o n w i l l be e x p e r i e n c e d . A t t h e o t h e r e x t r e m e when Cao v a l u e s a r e low, music c o u l d i n t h e e x t r e m e sound muddy. F i g u r e A-2 p l o t s t h e mean, minimum, and maximum C v a l u e s v e r s u s o c t a v e band f r e q u e n c y . S t u d i e s s u c h a s t h o s e by R e i c h a r d t g s u g g e s t t h a t a c c e p t a b l e c l a r i t y c o r r e s p o n d s t o C e O v a l u e s between a b o u t 0 a n d +5 dB. The mean 1 0 0 0 Hz v a l u e s i n t h i s h a l l a r e s l i g h t l y below t h e bottom of t h i s range. The mean mid-frequency C e O i n t h i s h a l l i s s i m i l a r t o t h a t i n Elassey H a l l i n T o r o n t o b u t lower t h a n t h a t measured i n e a c h A l b e r t a J u b i l e e Auditorium. Massey Hall i s a p p a r e n t l y w e l l l i k e d f o r m u s i c a l p e r f o r m a n c e s and t h e h i g h e r C e O v a l u e s i n t h e J u b i l e e A u d i t o r i a a r e more s u i t e d t o t h e i r m u l t i - p u r p o s e use. Thus a l t h o u g h C a O v a l u e s a r e a t t h e bottom of t h e a c c e p t a b l e r a n g e , t h e y r e l a t e t o good c o n d i t i o n s f o r many t y p e s of msir-.

FREQUENCY,

Hz

Figure A-1

Mean RT,

---

,

and Mean EDT,

-

,

versus frequency.

FREQUENCY,

Hz

Figure A-2

Mean,

---

,

Minimum,

-

,

and Maximum,

-.-.-

C80 versus frequency.

The r a n g e of CaO v a l u e s , (between t h e minimum and t h e maximum), shown o n F i g u r e A-2 i s c o n s i d e r a b l y less t h a n found i n t h e o t h e r two above mentioned h a l l s . Thus t h e q u a l i t y of t h e sound a s i n d i c a t e d by CaO i s more u n i f o r m t h r o u g h o u t t h e J a c k S i n g e r H a l l . ' h i s u n i f o r m i t y i s f u r t h e r d e m o n s t r a t e d i n F i g u r e A-3 which p l o t s mean CaO v a l u e s v e r s u s f r e q u e n c y f o r e a c h of t h e t h r e e s o u r c e s s e p a r a t e l y . The a v e r a g e r e s u l t s f o r t h e t h r e e d i f f e r e n t s o u r c e

p o s i t i o n s a r e remarkably s i m i l a r , i n d i c a t i n g t h a t a v e r a g e d o v e r a l l a u d i e n c e r e c e i v e r p o s i t i o n s t h e a c o u s t i c a l q u a l i t y i s i n d e p e n d e n t of t h e p o s i t i o n of t h e s o u r c e on t h e s t a g e .

The u n i f o r m i t y of C a o v a l u e s t h r o u g h o u t t h e h a l l i s a l s o c o n s i d e r e d i n F i g u r e A-4 which p l o t s C a O v e r s u s f r e q u e n c y f o r each of f i v e s e a t rows. Thus t h e r e s u l t s measured a t t h e two s e a t s i n e a c h row and f o r a l l t h r e e s o u r c e p o s i t i o n s were a v e r a g e d t o produce e a c h curve on t h i s f i g u r e . The lower f r e q u e n c y r e s u l t s v a r y a l i t t l e a s would be e x p e c t e d b e c a u s e a t t h e s e

f r e q u e n c i e s t h e r e s u l t s c a n be s t r o n g l y i n f l u e n c e d by i n d i v i d u a l i n t e r f e r e n c e e f f e c t s . A t medium and h i g h e r f r e q u e n c i e s o n l y one s e a t row h a s s l i g h t l y d i f f e r e n t CaO v a l u e s . I n row B of t h e f i r s t b a l c o n y , mid-frequency CaO

v a l u e s a r e about 1 dB h i g h e r t h a n t h e o t h e r s e a t rows. These r e s u l t s a g a i n . i n d i c a t e q u i t e uniform CsO v a l u e s t h r o u g h o u t t h e h a l l .

F i g u r e A-5 p l o t s t h e mean, minimum, and maximum v a l u e s of o v e r a l l s t r e n g t h , G, v e r s u s o c t a v e band f r e q u e n c y . The mean 1000 Hz G v a l u e i s a p p r o x i m a t e l y +5.0 dB. Other s t u d i e s have shown G v a l u e s between 0 and +10 dB, and t h u s a mid-frequency G of +5.0 dB p r o b a b l y i n d i c a t e s q u i t e good c o n d i t i o n s where m u s i c a l g r o u p s c a n produce sounds t h a t a r e a d e q u a t e l y loud. There i s n o t much p u b l i s h e d i n f o r m a t i o n c o n c e r n i n g t h e r a n g e of G v a l u e s i n o t h e r h a l l s . The A l b e r t a J u b i l e e A u d i t o r i a e x h i b i t lower mean G v a l u e s and l a r g e r s e a t - t o - t o s e a t v a r i a t i o n s i n G v a l u e s i n comparison t o t h e J a c k S i n g e r Concert H a l l .

F i g u r e A-6 p l o t s mean G v a l u e s v e r s u s f r e q u e n c y f o r e a c h of f i v e d i f f e r e n t s e a t rows. Recent ,European r e s e a r c h s t u d i e s 4 s 5 have r e p o r t e d

t h a t G v a l u e s d e c r e a s e w i t h i n c r e a s i n g d i s t a n c e from t h e s o u r c e . Although t h i s was n o t a n t i c i p a t e d from c l a s s i c a l room a c o u s t i c s c a l c u l a t i o n s , t h e r e s u l t s of F i g u r e A-6 c o n f i r m t h i s b e h a v i o u r of G v a l u e s . From t h i s f i g u r e i t i s s e e n t h a t G v a l u e s a r e h i g h e s t f o r t h e c l o s e s t row of t h e main f l o o r , row J , and l o w e s t f o r s e a t s i n t h e b a l c o n i e s . Thus a performance w i l l sound l o u d e r a s one moves t o t h e f r o n t of t h e h a l l .

S t r o n g e a r l y r e f l e c t i o n s from t h e s i d e w a l l s g i v e t h e s u b j e c t i v e

i m p r e s s i o n of b e i n g immersed i n t h e sound and n o t j u s t " l o o k i n g a t i t " from a remote p o s i t i o n . Some have compared t h i s t o t h e d i f f e r e n c e between

monophonic and s t e r e o p h o n i c sound systems. It i s w e l l e s t a b l i s h e d t h a t h a l l s w i t h s t r o n g l a t e r a l r e f l e c t i o n s are p r e f e r r e d f o r m s i c , b u t t h e r e i s l i t t l e p u b l i s h e d i n f o r m a t i o n from measurements of t h e s e p r o p e r t i e s i n r e a l h a l l s . F i g u r e A-7 p l o t s measured l a t e r a l f r a c t i o n s , LF, v e r s u s f r e q u e n c y f o r e a c h s o u r c e p o s i t i o n s e p a r a t e l y . There i a l i t t l e d i f f e r e n c e between s o u r c e

p o s i t i o n s , b u t t h e c e n t r e s o u r c e , which was f u r t h e s t from t h e s i d e w a l l s , l e d t o s l i g h t l y lower LF v a l u e s . The mean mid-frequency LF v a l u e s a r e h i g h e r t h a n t h e A l b e r t a J u b i l e e A u d i t o r i a , b u t s t u d i e s i n Denmark by ~ a d e ' s u g g e s t t h a t LF v a l u e s a r e , l a r g e l y d e t e r m i n e d by t h e mean w i d t h of t h e h a l l . Thus t h e Jack S i n g e r H a l l b e i n g a r e l a t i v e l y narrow h a l l , h a s r e l a t i v e l y h i g h e r LF v a l u e s and more p r e f e r r e d c o n d i t i o n s f o r music.

Figure A-3

Mean C e O versus frequency f o r each source, + + c e n t r e ,

k-rt l e f t , 0 - 0 r i g h t .

FREQUENCY, Hz

Figure A-4

Mean Ceo versus frequency by s e a t row. Main f l o o r row

J

-,

R

---,

and D - - - * - , f i r s t balcony row B

...,

second row D

+-+.

1 2 5

250

500

1.OK

2.OK

4.OK

8.OK

FREQUENCY,

Hz

Figure A-5

Mean

---

,

minimum -

,

and maximum - * - * - G versus frequency.

FREQUENCY, Hz

Figure A-6

Mean G versus frequency by seat row. Main floor row J

-,

row R

---

,

row D

- - -

,

first balcony row B a * . , second

APPENDIX B

E f f e c t s of t h e Sound Absorbing Banners and C u r t a i n s

Moveable sound a b s o r b i n g . m a t e r i a l s have been i n c l u d e d i n many h a l l s s o t h a t a form of v a r i a b l e a c o u s t i c s c a n be a c h i e v e d t o p e r m i t t h e h a l l t o meet

a v a r i e t y of a c o u s t i c a l needs. C o n v e n t i o n a l l y moveable a b s o r b i n g s y s t e m s

h a v e been d e s i g n e d t o v a r y t h e RT of t h e h a l l . It i s d i f f i c u l t t o d e s i g n

t h e s e s y s t e m s s o t h a t t h e y produce a s u f f i c i e n t l y l a r g e change i n RT v a l u e s .

A change of RT of 0.2 seconds i s a b o u t t h e s m a l l e s t change t h a t i s r e a d i l y

s u b j e c t i v e l y n o t i c e d , and a change of a b o u t 0.5 s e c o n d s would b e a more

d e s i r e a b l e d e s i g n g o a l f o r a v a r i a b l e a b s o r p t i o n system. I n t h i s s t u d y we

have a l s o e v a l u a t e d t h e e f f e c t of t h e a b s o r b i n g c u r t a i n s and b a n n e r s w i t h r e s p e c t t o t h e v a r i o u s newer a c o u s t i c a l measures b e c a u s e t h e s e have been more

c l o s e l y r e l a t e d t o s u b j e c t i v e a s s e s s m e n t s . The measurements were a g a i n

c a r r i e d o u t a t c o m b i n a t i o n s of 12 r e c e i v e r p o s i t i o n s and 3 s o u r c e p o s i t i o n s

and i n t h i s Appendix t h e r e s u l t s a r e compared w i t h measurements made a t t h e

same l o c a t i o n s w i t h o u t t h e a b s o r b i n g m a t e r i a l exposed. Only t h e two e x t r e m e

c o n d i t i o n s were c o n s i d e r e d ; t h e b a n n e r s and c u r t a i n s were e i t h e r c o m p l e t e l y

exposed o r c o m p l e t e l y withdrawn.

F i g u r e B-1 p l o t s t h e o v e r a l l mean RT v a l u e s f o r b o t h c o n d i t i o n s . The

change i n RT

is

g r e a t e s t a t 1000 Hz, where i t i s s l i g h t l y less t h a n 0.2

seconds. As _{one would e x p e c t t h e b a n n e r s and c u r t a i n s a r e a l i t t l e less}

e f f e c t i v e a t lower f r e q u e n c i e s b e c a u s e of t h e a b s o r b i n g p r o p e r t i e s of t h e m a t e r i a l s i n v o l v e d . The change i n RT v a l u e s a r e s m a l l e r a t h i g h f r e q u e n c i e s b e c a u s e of t h e d o m i n a t i n g e f f e c t of a i r a b s o r p t i o n , and t h e b a n n e r s and c u r t a i n s r e p r e s e n t a s m a l l e r f r a c t i o n of t h e t o t a l sound a b s o r p t i o n i n t h e h a l l a t t h e s e f r e q u e n c i e s . T h i s maximum p o s s i b l e change i n RT v a l u e s w i l l o n l y p e r m i t r e l a t i v e l y s u b t l e changes i n t h e p e r c e i v e d r e v e r b e r a n c e of t h e

h a l l . While some o t h e r h a l l s have s i m i l a r l y u n s u c c e s s f u l v a r i a b l e a b s o r p t i o n

s y s t e m s , o t h e r s have been mesured t o be more s u c c e s s f u l . The Opera of .the

N a t i o n a l A r t s C e n t r e i n Ottawa i s a n example of t h e former where t h e banners

change t h e RT by a s i m i l a r amount t o t h a t measured i n t h e J a c k S i n g e r Concert

Hall. On _{t h e o t h e r hand t h e a b s o r b i n g b a n n e r s i n Hamilton P l a c e change t h e}

mid-frequency RT by a p p r o x i m a t e l y 0.5 s e c o n d s .

Because t h e EDT i s known t o be more c l o s e l y r e l a t e d t o s u b j e c t i v e

judgements, i t i s of p a r t i c u l a r i n t e r e s t t o a s s e s s t h e performance of t h e

v a r i a b l e a b s o r p t i o n w i t h r e s p e c t t o EDT v a l u e s . The r e s u l t s of F i g u r e B-2

i l l u s t r a t e t h a t changes i n EDT v a l u e s a r e very s i m i l a r t o t h e changes i n RT

v a l u e s s e e n i n t h e p r e v i o u s f i g u r e . T h i s i s p e r h a p s n o t s u r p r i s i n g , b e c a u s e

i n t h i s c a s e t h e EDT and RT v a l u e s a r e q u i t e s i m i l a r f o r t h i s h a l l . These

r e s u l t s i n d i c a t e t h a t t h e s u b j e c t i v e l y p e r c e i v e d v a r i a t i o n i n t h e

r e v e r b e r a n c e of t h e h a l l w i l l be t h e same a s i n d i c a t e d by t h e RT v a l u e s . One would e x p e c t t h a t e a r l y - t o - l a t e a r r i v i n g sound c n e r g y r a t i o s would d e c r e a s e w i t h t h e a d d i t i o n of a b s o r p t i o n , b e c a u s e a b s o r b i n g b a n n e r s and

c u r t a i n s a r e e x p e c t e d t o mainly a b s o r b t h e l a t e r a r r i v i n g sound. F i g u r e B-3

shows t h a t t h i s i s indeed t r u e f o r t h e mean C a O v a l u e s , b u t t h a t t h e change

i s o n l y a p p r o x i m a t e l y 0.5 dB a t mid-frequencies. Changes of t h e o r d e r of

1.0 dB i n C a O v a l u e s c a n o c c u r when t h e m e a s u r i n g microphone i s moved a s m a l l

amount t o r e p r e s e n t t h e movement of a l i s t e n e r s head f r o m one s i d e of h i s

FREQUENCY,

Hz

F i g u r e A-7 Mean l a t e r a l f r a c t i o n v e r s u s f r e q u e n c y by s o u r c e p o s i t i o n . C e n t r e

-

,

l e f t

---,

r i g h t - * - - - .

Hz

F i g u r e B-1 E f f e c t of b a n n e r s and c u r t a i n s on RT. Withdrawn

---,

exposed

-.

Figure B-2

E f f e c t of banners and c u r t a i n s on EDT. Withdrawn

---,

exposed

-.

Hz

Figure B-3

E f f e c t of banners and curtains on C e o - Withdrawn

---,

exposed

-.

of t h e b a n n e r s and c u r t a i n s , t h e c o r r e s p o n d i n g i n c r e a s e i n p e r c e i v e d c l a r i t y would be q u i t e n e g l i g i b l e .

F i g u r e B-4 p l o t s G v a l u e s v e r s u s f r e q u e n c y f o r b o t h a b s o r b i n g a n d

non-absorbing c o n d i t i o n s of t h e h a l l . . Mtd-frequency G v a l u e s were changed by

o n l y a f r a c t i o n of a d e c i b e l . If t h e b a n n e r s and c u r t a i n s were a b l e t o

d o u b l e t h e t o t a l amount of sound a b s o r p t i o n i n t h e h a l l G v a l u e s would be

e x p e c t e d t o change by 3 dB. T h i s would be v e r y d i f f i c u l t t o a c h i e v e and i t

i s t h e r e f o r e thought t h a t l a r g e changes i n G v a l u e s a r e n o t l i k e l y w i t h

v a r i a b l e a b s o r p t i o n systems.

The change i n t h e o v e r a l l mean LF v a l u e s between a b s o r b i n g a n d

non-absorbing c o n d i t i o n s i s i l l u s t r a t e d i n F i g u r e B-5. m e r e i s v e r y l i t t l e

change i n d i c a t e d . T h i s i s n o t unexpected b e c a u s e t h i s measure o n l y r e f l e c t s

changes i n t h e e a r l y r e f l e c t i o n s , and b a n n e r s and c u r t a i n s a r e i n t e n d e d t o a b s o r b t h e l a t e r a r r i v i n g sound.

The changes t h a t were r e c o r d e d were f o r c o n d i t i o n s w i t h o u t a n a u d i e n c e

p r e s e n t . With a n a u d i e n c e p r e s e n t t h e t o t a l amount of sound a b s o r b t i o n i n

t h e h a l l would be i n c r e a s e d and hence t h e f r a c t i o n a l change due t o t h e

a d d i t i o n of t h e c u r t a i n s and banners would be smaller. Thus w i t h a n o c c u p i e d

Hz

Figure B-4

Effect of banners and curtains on G. Withdrawn

---,

exposed

-.

FREQUENCY, Hz

Figure B-5

Effect of banners and curtains on

LF.

Withdrawn

---,

exposed

-.

APPENDIX C

E f f e c t s of t h e Over-Stage Canopy

The moveable o v e r - s t a g e canopy was e v a l u a t e d i n two d i f f e r e n t p o s i t i o n s

t h a t were s a i d t o r e p r e s e n t t h e e x t r e m e s of normal use. The normal c o n c e r t

p o s i t i o n f o r o r c h e s t r a l g r o u p s c o r r e s p o n d e d t o a s e t t i n g of 1166 on t h e

canopy c o n t r o l i n d i c a t o r w i t h t h e canopy f u l l y r a i s e d . T h i s c o n d i t i o n was

a s s e s s e d a t t h e complete set of c o m b i n a t i o n s of 3 s o u r c e p o s i t i o n s a n d 1 2

r e c e i v e r p o s i t i o n s . The canopy was i n t h i s r a i s e d p o s i t i o n f o r a l l of t h e

measurements p r e s e n t e d i n t h e p r e v i o u s two a p p e n d i c e s . As a second canopy

p o s i t i o n , measurements were a l s o made w i t h t h e canopy lowered t o a p o s i t i o n

of 823 on t h e canopy c o n t r o l i n d i c a t o r . T h i s was s a i d t o r e p r e s e n t t h e

.

l o w e s t p o s i t i o n f o r normal use. U n f o r t u n a t e l y t i m e d i d n o t p e r m i t a f u l l

e v a l u a t i o n of t h i s c o n d i t i o n , n o r any measurements of o t h e r p o s i t i o n s of t h e

canopy. Measurements a t t h e lower p o s i t i o n were made f o r combinations of t h e

3 s o u r c e p o s i t i o n s and 4 r e c e i v e r p o s i t i o n s on t h e c e n t r e l i n e of t h e main

f l o o r of t h e h a l l . The r e c e i v e r p o s i t i o n s i n c l u d e d one a t t h e podium which

was t h o u g h t t o b e i m p o r t a n t b e c a u s e of i t s p r o x i m i t y t o t h e canopy.

R e s u l t s are f i r s t p r e s e n t e d f o r a v e r a g e s of a l l main f l o o r a u d i e n c e

s e a t s f o r e a c h of t h e t h r e e c o n f i g u r a t ' i o n s t e s t e d . C o n d i t i o n A c o r r e s p o n d s

t o t h e measurements of Appendix A where t h e canopy was r a i s e d and t h e

a b s o r b i n g b a n n e r s and c u r t a i n s w e r e withdrawn. C o n d i t i o n B c o r r e s p o n d s t o

t h e measurements p r e s e n t e d i n Appendix B where t h e canopy w a s r a i s e d and t h e

sound a b s o r b i n g b a n n e r s and c u r t a i n s were exposed. F i n a l l y c o n d i t i o n C

c o r r e s p o n d e d t o h a v i n g t h e canopy lowered and t h e a b s o r b i n g b a n n e r s and

c u r t a i n s withdrawn. There were fewer measurement p o s i t i o n s on t h e main f l o o r

f o r t h e l a t t e r c o n d i t i o n . These main f l o o r a v e r a g e r e s u l t s a r e f o l l o w e d by

r e s u l t s i n d i c a t i n g t h e e f f e c t of t h e canopy a t i n d i v i d u a l s e a t s . It i s

n e c e s s a r y t o examine i n d i v i d u a l s e a t r e s u l t s b e c a u s e t h e a d d i t i o n o r movement of a r e f l e c t i n g s u r f a c e would be e x p e c t e d t o change p a r t i c u l a r r e f l e c t i o n s t h a t would be d i r e c t e d t o p a r t i c u l a r a r e a s of t h e h a l l .

F i g u r e C-1 compares t h e mean measured RT v a l u e s v e r s u s f r e q u e n c y f o r a l l

t h r e e c o n d i t i o n s a t t h e main f l o o r s e a t s . While t h e a d d i t i o n of t h e c u r t a i n s

and b a n n e r s h a s t h e e f f e c t d i s c u s s e d i n t h e p r e v i o u s a p p e n d i x , t h e movement

of t h e o v e r - s t a g e canopy h a s no m e a s u r e a b l e e f f e c t on RT v a l u e s . One would

n o t e x p e c t t h e movement of a r e f l e c t i n g p a n e l t o change t h e RT of t h e h a l l . Only changes t o t h e amount of sound a b s o r b i n g m a t e r i a l o r t o t h e volume of t h e room would be e x p e c t e d t o change t h e measured RT v a l u e s .

I n F i g u r e C-2 i t i s s e e n t h a t t h e l o w e r i n g of t h e canopy d o e s h a v e a n

e f f e c t on t h e measured EDT v a l u e s , b u t t h i s e f f e c t i s very s m a l l and probably

n o t s u b j e c t i v e l y n o t i c e a b l e . There i s a t e n d e n c y toward lower EDT v a l u e s

when t h e canopy i s lowered.

A t . t h e main f l o o r r e c e i v e r s C a O v a l u e s i n c r e a s e d w i t h t h e a d d i t i o n o f t h e b a n n e r s and c u r t a i n s a s o b s e r v e d f o r t h e c o m p l e t e h a l l i n t h e p r e v i o u s

appendix. F i g u r e C-3 a l s o shows t h a t t h e l o w e r i n g of t h e canopy l e a d s t o

v e r y s m a l l i n c r e a s e s i n mid- and h i g h f r e q u e n c y C a O v a l u e s and somewhat

l a r g e r i n c r e a s e s p e a k i n g a t 250 Hz. _{T h i s} 250 _{Hz i n c r e a s e w i l l l a t e r b e s e e n}

FREQUENCY,

Hz

Figure C-1

RT v e r s u s frequency f o r main f l o o r r e c e i v e r s . Condition A

---,

B -

,

and C - * - * - .

FREQUENCY,

Hz

Figure C-2

EDT v e r s u s frequency f o r main f l o o r r e c e i v e r s . Condition A

---,

One would n o t e x p e c t t h e movement of a r e f l e c t i n g p a n e l t o g r e a t l y

change G v a l u e s . F i g u r e C-4 i n d i c a t e s t h a t a t medium and h i g h e r f r e q u e n c i e s

G v a l u e s d i d n o t change s i g n i f i c a n t l y when t h e canopy was lowered. However

a t t h e l o w e s t two o c t a v e bands t h e r e were s m a l l i n c r e a s e s i n G v a l u e s when

t h e canopy was lowered.

LF v a l u e s v e r s u s f r e q u e n c y f o r t h e t h r e e c o n d i t i o n s a r e shown o n

F i g u r e C-5. For t h e s e main f l o o r s e a t s t h e a d d i t i o n of t h e b a n n e r s and

c u r t a i n s reduced

LF

v a l u e s by a small amount and t h e lowering of t h e canopy

produced a l a r g e r r e d u c t i o n i n LF v a l u e s . Presumably LF v a l u e s a r e reduced

b e c a u s e t h e r e l a t i v e p o r t i o n of non l a t e r a l e a r l y sound e n e r g y i s i n c r e a s e d

by t h e lower p o s i t i o n of t h e canopy. The a p p a r e n t r e d u c t i o n i n LF v a l u e s may

a l s o have been i n f l u e n c e d by n o t i n c l u d i n g measurement p o s i t i o n s n e a r t h e s i d e w a l l s f o r t h e c o n d i t i o n w i t h t h e canopy lowered.

If one c o n s i d e r s t h e r e s u l t s a t i n d i v i d u a l s e a t s , mid-frequency v a l u e s

of RT, EDT, C e O , and G do n o t v a r y much w i t h t h e change i n p o s i t i o n of t h e

canopy

.

However t h e r e i s a g a i n evidence of q u i t e pronounced changes a t

l o w e r f r e q u e n c i e s and i n p a r t i c u l a r i n t h e 250 Hz o c t a v e band a t s e v e r a l main

f l o o r l o c a t i o n s . A s s e e n i n F i g u r e C-6 f o r measurements a t s e a t J-8 w i t h t h e

c e n t r e s o u r c e p o s i t i o n , 250 Hz CBO v a l u e s were i n c r e a s e d by a p p r o x i m a t e l y

4.5 dB when t h e canopy was lowered. F i g u r e C-7 shows G v a l u e s were s i m i l a r l y

i n c r e a s e d when t h e canopy was lowered. This e f f e c t was n o t o b s e r v e d f o r a l l

s o u r c e - r e c e i v e r combinations. F i g u r e C-8 shows v e r y l i t t l e change i n C

v a l u e s w i t h t h e change i n canopy h e i g h t when measured a t s e a t D-22 a t t

to

e

r e a r of t h e main f l o o r . Although l o w e r i n g t h e o v e r - s t a g e canopy would be

e x p e c t e d t o i n c r e a s e t h e s t r e n g t h of r e f l e c t e d sound o n - s t a g e , F i g u r e C-9

i n d i c a t e s no s i g n i f i c a n t change t o G v a l u e s on-stage as measured a t t h e

podium.

It i s known t h a t p a r t i c u l a r i n t e r f e r e n c e e f f e c t s s u c h a s t h e c o m b i n a t i o n o f a d i r e c t sound and a s t a g e f l o o r r e f l e c t e d sound can l e a d t o r e d u c t i o n s i n

t h e e a r l y sound a t p a r t i c u l a r s e a t s n e a r e r t o t h e s t a g e . I n a d d i t i o n a

phenomena known a s t h e s e a t d i p e f f e c t c a u s e s a marked a t t e n u a t i o n i n t h e sound p r o p a g a t i n g a t n e a r g r a z i n g i n c i d e n c e o v e r a u d i e n c e s e a t i n g a t l o w e r

f r e q u e n c i e s . It i s t h o u g h t t h a t t h e observed i n c r e a s e s a t 250 Hz a r e due t o

t h e canopy p r o v i d i n g i n c r e a s e d e n e r g y a t t h e s e f r e q u e n c i e s t h a t m o d i f i e s t h e

d e t a i l s of t h e e x i s t i n g d e s t r u c t i v e c a n c e l l a t i o n s . The canopy would

a p p a r e n t l y be p e r c e i v e d t o i n c r e a s e t h e s t r e n g t h of l o w e r f r e q u e n c y sounds a t

some s e a t s when i t i s moved t o i t s lowered p o s i t i o n . U n f o r t u n a t e l y i t i s n o t

p o s s i b l e t o g u e s s what e f f e c t t h e canopy would have a t o t h e r p o s i t i o n s o r

what e f f e c t s would o c c u r a t o t h e r s e a t s i n t h e h a l l where measurements were

FREQUENCY,

Hz

Figure C-3

C s O versus frequency f o r main f l o o r r e c e i v e r s . Condition A

---,

B

-

,

and C - * - - - .

FREQUENCY, dB

Figure C-4

G versus frequency f o r main f l o o r r e c e i v e r s . Condition A

---',

B -

,

and C - . - a - .

FREQUENCY, Hz

Figure C-5

LF versus frequency f o r main f l o o r r e c e i v e r s . Condition A

---,

B

-

,

and C - * - * - .

Hz

Figure C-6

C 8 0 versus frequency centre source, s e a t 5-8. Canopy up

-,

canopy down

---.

Hz

Figure C-7 G v e r s u s frequency c e n t r e s o u r c e , s e a t 5-8. Canopy up

-,

canopy down

---

.

Hz

Figure C-8 C a O v e r s u s frequency, c e n t r e s o u r c e , s e a t D - 2 2 . Canopy up

-,

canopy down

---.

Hz

Figure C-9

G versus frequency, centre source, a t podium, canopy up

-,

canopy down

---.

APPENDIX D D e f i n i t i o n of A c o u s t i c a l Measures

The v a l u e s of f i v e d i f f e r e n t q u a n t i t i e s e a c h measured i n s t a n d a r d o c t a v e

bands from 125 t o 8000

Hz

a r e p r e s e n t e d i n t h i s r e p o r t . Other q u a n t i t i e s

were measured b u t a r e n o t p r e s e n t e d b e c a u s e t h e y a r e h i g h l y c o r r e l a t e d w i t h

t h e p r i n c i p a l f i v e measures. The f i v e measures r e p r e s e n t f o u r d i f f e r e n t

t y p e s of q u a n t i t i e s , a l l of which c a n be c a l c u l a t e d from p u l s e r e s p o n s e s i n

r O O m s

.

Two d i f f e r e n t decay time measures were used. The c o n v e n t i o n a l

r e v e r b e r a t i o n t i m e , RT, i s t h e time c a l c u l a t e d f o r t h e sound energy t o

d e c r e a s e by 60 d e c i b e l s a f t e r t h e s o u r c e h a s stopped. RT v a l u e s -re

c a l c u l a t e d from s t r a i g h t l i n e f i t s t o t h e f i r s t 30 dB of decay u s i n g

S c h r o e d e r ' s i n t e g r a t e d impulse r e s p o n s e t e c h n i q u e . E a r l y decay times, EDT,

a r e a l s o measures of t h e t i m e r e q u i r e d f o r t h e sound energy t o d e c r e a s e by

60 dB, b u t are c a l c u l a t e d from s t r a i g h t l i n e f i t s t o t h e f i r s t 10 dB of t h e

decay.

E a r l y - t o - l a t e a r r i v i n g sound e n e r g y r a t i o s have been c a l c u l a t e d f o r

v a r i o u s temporal d i v i s i o n s between e a r l y and l a t e a r r i v i n g r e f l e c t i o n s . _C8,,

- w i t h a n 0.08 second e a r l y time limit i s c a l c u l a t e d as follows:

where p ( t ) i s t h e i n s t a n t a n e o u s p r e s s u r e response t o a n impulse source.

G, t h e o v e r a l l s t r e n g t h i n d i c a t e s t h e s t r e n g t h of t h e sound f i e l d r e l a t i v e t o t h a t f o r t h e same s o u r c e a t a d i s t a n c e of 10 m i n a n a n e c h o i c f i e l d . (Anechoic c o n d i t i o n s would be s i m i l a r t o o u t d o o r c o n d i t i o n s i n t h e a b s e n c e o f any r e f l e c t i o n s ) . G i s d e f i n e d a s f o l l o w s : where p A ( t ) i s t h e i n s t a n e o u s p r e s s u r e r e s p o n s e a t a d i s t a n c e of 10 m i n a n a n e c h o i c f i e l d . The l a t e r a l f r a c t i o n , LF, i s t h e f r a c t i o n of t h e e a r l y sound e n e r g y t h a t a r r i v e s from t h e s i d e ; i . e . , from l a t e r a l d i r e c t i o n s . It i s d e f i n e d a s f o l l o w s :

where p L ( t ) i s the instantaneous l a t e r a l pulse response measured with a figure-of-eight microphone pointed a t t h e s i d e w a l l s .

Ref e r e n c e e

I. Knudsen, V.O. and H a r r i s , C.M., " A c o u s t i c a l D e s i g n i n g i n A r c h i t e c t u r e , "

J o h n Wiley and Sons, Inc.

,

1965, p. 194.

2. G o t t l o b , D., "Comparison of O b j e c t i v e A c o u s t i c P a r a m e t e r s i n C o n c e r t

H a l l s w i t h R e s u l t s of S u b j e c t i v e E x p e r i m e n t s , " B r i t i s h B u i l d i n g R e s e a r c h L i b r a r y T r a n s l a t i o n 1 8 9 5 , ( t r a n s l a t i o n of o r i g i n a l t h e s i s i n German d a t e d G o t t i n g e n 1 9 7 3 ) .

3. R e i c h a r d t

,

W. and Lehman, U.

,

" O p t i m i e t u n g von Raumeindruck und

D u r s i c h t i g k e i t von M u s i k d a r b e i t u n g e n d u r c h Auswertung von I m p u l s s h a l t e s t s , " A c u s t i c a 4 8 ( 3 ) , 174-185 (1981).

4. Barron, M. and Lee, L-J., "Energy R e l a t i o n s i n C o n c e r t A u d i t o r i a , I,"

s u b m i t t e d f o r p u b l i c a t i o n i n J. Acoust. Soc. Am.

5. Gade, A.C., " O b j e c t i v e Measurements i n Danish C o n c e r t H a l l s , " P r o c e e d i n g s

of t h e I n s t i t u t e of A c o u s t i c s UK, 7 ( 1 )

,

9-16, Cambridge, F e b r u r a r y 1985.

6. S c h r o e d e r , M.R., "New Method f o r Measuring R e v e r b e r a t i o n Time," .J.