acustica1985 marshall&meyer

7/25/2019 Acustica1985 Marshall&Meyer

1/11

The

Directivity

and

Auditory

Impressions

f

Singers

by A. H. Marshall * and J. MeYer

*

University

of Auckland,

New Zealand

Information

from

the Physikalisch-Technische

Bundesanstalt,

Braunschweig

Dedicated

to Prof.

Dr.-Ing.

L. Cremer

on the occasion

of

his 80th

birthday

S

u m m a r y

The

directivity

of the

professional singers

voice

was measured

in

anechoic

conditions

for a

male

(Baritone) ind

two iemales

(Soprano

and

Alto). In

each

case he

range

of

notes

sung

was

t;;.

and'comprised

3

vowels

and two

vocal styles.

Resllts_are

given

at

20o

intervals

in

to.irontut

and

vertical

planes

down

to

40o depression

below

the

singers,mouth.

Particular

atten-

iio"

ir

giu"n to the

'singer's

formant'

and con-clusions

re drawn

regarding

the

important

direc-

tions

for

reflecting

surfaces.

tn

ttre

second

art

of the

paper

experiments

are

described

which explore

the

auditory

impres-

sion ofsingers in vocal ensemblesand as soloistsby exposingthe singers o qynthetic sound fields

in

tremi-aiectroic

conditions.

The

singer's

auditory

impression

is dominated

by

reverberation

rather

than

the early

reflections

which

are so

important

to

instrumentalists.

An adverse

com-

bination

of discrete

iarly

reflections

and

reverberation

occurs

when

the reflection

delay

approxi-

mates

o

40

ms.

Ric

htc harakteristik

und Gehiirseindruc

k beim Sdnger

Z u s a m m e n f a s s u n g

In

einem

reflexionsarmen

Raum

wurde die

Richtcharakteristik

von

professionalen

Siingem

ge-

messen,

und

zwar bei

einer

Miinnerstimme

(Bariton)

und

zwei

Frauenstimmen

(Sopran

*9

{t):

Der

untersuchte

Tonumfang

reichte

jeweiis

iiber

zwei

Oktaven,

alle

TOne

wurden

mit

drei

Vokalen

und

zwei

verschie&nen

Stimmtechniken

gesungen.Die Ergebnisse

werden

mit

einer

eunOsung

von 20o

in der

horizontalen

sowie

zwei

vertikalen

Ebenen

bis zu

einem

Neigungs-

winkel

v6n

40o unter

dem

Mund des

Siingers

angegeben.

Besondere

Aufmerksamkeit

ist

dabei

dem

sog.

,,siingerformanten"

gewidmet, und

es

werden Riickschliisse

auf

die fiir Reflexions-

fl ichen wichtigen Abstrahlrichtungen gezogen.

Im

zweiten-Teil

der Arbeit

wird tibir einige

Experimente

berichtet,

die der

Untersuchung

des

Gehiirseindrucks

von Chorsingern

und

Gesangssolisten

gelten;

dabei

wurden

die

raumakusti-

r.tr.n

S"aingungen

fiir

die Siin-ger

n einem

Halbfreifeldraum

durch

ein synthetisches

Schallfeld

simuliert.

Dir Gehtirseindruck-der

Siinger

wird

mehr durch

Nachhall

geprbgt

als

durch

die

ersten

Reflexionen,

wlhrend diese

bei

Instrumentalspielern

vorrangige

Bedeutung

besitzen.

Ein

ungiinstiger

Bereich

fiir die erste

Reflexion

(bei

Schallfeldern

mit Nachhall)

liegt

bei

Verziige-

rungszeiten

um

40 ms.

Directiviti

et impressions

auditives

des chanteurs

S o m

m a i

e

On

mesure

dans

des conditions

anchoiques

a directivit6

de la

voix de chanteurs

profession-

nels:

un

homme

(baryton), et deux femmes

(soprano

et

alto). Chacun

chante

des

notes

reparties

sur

deux

octaves,

en

pronongant

3

voyelles

selon

deux

styles de

voix

diffrents.

Les rsultats

sont

donn6s

ous

les

20' dins

les

plans

horizontaux

et

verticaux,

en

descendant

usqu'A

{O

"

en dessous

de la bouche du chanteur. Le

7/25/2019 Acustica1985 Marshall&Meyer

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reflection

level

and delay,

the

frequency

dependence

of instrument

directivity,

and identify

the

frequency

region

of

particular

importance

for on-stage

com-

munication

between

musicians.

Amongst

other

results it is clear that reverberation does not con-

tribute

significantly

to

ease

of ensemble

or instru-

mentalists

but

that

appropriate

early reflections

are

essential.

The

present

work

is

intended

to

provide

similar

information

for the

singer's

environment,

or at

least

to

address

he

questions

of

singing

comfort

and

ease

of

ensemble.

It is

a

common

experience

amongst

singers that

rooms

differ

markedly

in the

support they

provide.

In some

here

is a stimulating

feedbackwhich

links

singer, listener

and space

and

promotes

artistic

communication.

In others

control of the

voice

and

the achievementof ensemble s much more difficult

though

of

course,

as the following

experience

llus-

trates,

the

professional

singer

can still

sing

even in

such

extreme

environments

as anechoic

conditions.

For

amateur

choirs

"difficult"

rooms

may

affect

performance

acutely.

The

objective

in

designing

stages

and rooms

is

to

provide

an acoustical

environment

for the

singers

n

which

the

complexity

of tone

and

timbre,

musical

structure,

expressive

uances,

nsemble

and

the like

are achieved

effortlessly in

the

act of artistic

com-

munication

between

performer

and listener.

Singers

usually refer

to

such acoustical

conditions

as'room

resonance'.

'Room

resonance'

can be

usefully considered

as

modal

effects,

'early'

reflections

from

individual

surfaces,

and

reverberation.

It is assumed

in

this

paper

that the

rooms

concerned

are too large

for

pronounced

modal

behaviour

in the

frequency

range

of the

singers.

Reverberation

comprises

the

statistical

decay of

sound energy

level in

the

space

as

a

whole.

The

early individual

reflections

depend

upon

the location

of

surfaces relative

to the

singer

and the

directivity

of the voice

when

singing.

We

start therefore with

a set of measurements

of

the

directivity

of

the human voice

comprising

hree

vocal ranges, two styles of voice production and

three

different

vowels.

The

second

part

of

the

paper

addresses

he

questions

of singing

comfort

and ease

of ensemble

for

soloists,

a

quartette

and a

small

choir in

a

variety

of

synthetic

acoustical

environ-

ments.

2.

Review of the

literature

The

directional

characteristics

of the

human

voice

in

the literature

[5-8]

refer

almost

exclusively

to

measurements

on speech.

Most

frequently

cited

A.H MARSHALL and J MEYER:DIRECIIVtt AND AUDITORY IMPRESSIONS

131

are the

results

of

Dunn

and

Farnsworth

(1939)

mea-

sured

with

a microphone

at

a distance

of

only

60

cm.

These

show,

n

the

horizontal plane

a steady

level

reduction

from

front

to

back which

is

more

marked at higher frequencies. In the vertical plane

rather

weaker

secondary

maxima

occur

which

just

exceed

the

level

in

the

forward

direction.

Niese

(1956)

obtained

similar

results

(deviations

up to

2

dB) with

running

speech

using

a

microphone

distance

of 2

m. It

appeared

that with

some

test

persons

he

level

in the

forward

direction

was

about

I dB

below

the maxima.

Finally

it

is worth

noting

that

Trendelenburg (1929)

showed

that

the

.reduc-

tion

to

the

back

of the

head

s

greater

han

is found

in

the shadowing

of

a

point

source

by

a spherical

surface.

He

ascribed

this

to

the

projecting

effect of

the

mouth

and

showed

also

differences

with

altered

mouth shapes. It follows that one cannot assume

that

speech

directivity

data are

applicable

without

further question

to

the sung

radiation

patterns.

3. The

directivity

ofsingers

The

measurements

on

singers were

carried out

in

an

anechoic

room in

the

horizontal

and

two vertical

planes.

The

singer

stood

sufficiently

high

to

permit

the

radiation pattern

to

be measured

down to 40o

below

the horizontal plane

at head

height.

Measure-

ments generallywere made at 20o intervalsbut in

part

at l0o intervals

in the

horizontal

plane.

The

range

of sung

notes was

Baritone

(G2

to

Ga), Alto

(G3

to G5), Soprano

(Ca

to

C6). The

programme

included

test

syllables

with

three vowels

sung n two

vocal

styles

"full

voice"

and the

so called

"Rand-

stimme"

(or

half voice).

Evaluation

was

made after

octave

iltering.

3.L

Basic results

Figs. I

and 2

show

the

polar

diagrams for the

7

flequency

bands

and

in two

planes.

These

results

were

derived

from the

"full voice"

measurement

on

the Baritone and values are averagedover the three

vowels

and

all

pitches

within

each

octave

band.

Reference

level,

0 dB is

the level

in the

horizontal

plane

in

front

of the

singer.

It should

be noted

that

the

singer inclined

his head

forward

approximately

l0o

to

achievea relaxedposture.

In the horizontal plane

it is immediately

clear

that

the

maximum

level

occurs

at 0o

only above

4kHz.

At lower

frequencies

the maxima

shift

to the

sides.

Up to 500

Hz the

effect is relatively

small and

is

comparable

with

the

profile

indicated

by Niese. t

is worth

noting

that in

the

1000Hz

band the

level

7/25/2019 Acustica1985 Marshall&Meyer

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Fig. l.

Directivity of a singer

n

the

horizontal

plane.

remains

above

the

reference

evel at 0o back

to

I l5o. The

greatest

ncrement of about 3

dB occurs

at

2000H2

and at about

40o. To the

rear. as

ex-

pected,

he shading effect of the

head is clear and

increasing

with

frequency.

In the vertical plane the polar diagramsshow a

sharp maximum at high frequencies,

and directed

downwards at 20

o

as their

most conspicous eature.

The maximum

value

is about 4 dB

in the 2000Hz

octave.

This maximum though

weaker remains ap-

parent

at the low frequencies

(in

comparison

with

the

results n the horizontal

plane where

as

we

saw

the high frequency maxima are directed

outwards

at about 45" and virtually disappear below

l000Hz). Other note-worthy features are the sec-

ondary maximum

above and

to the rear at 1000Hz

and 2000Hz and the sharp reduction

n level

below

the

horizontal

plane

at the back.

The intermediate

vertical plane (not shown in this figure) gives a

smooth transition

in level between he

maxima

just

described in the horizontal and

vertical

planes

without

any other

noticeable

secondary

maxima.

The

principal

directional

properties

of the sung

voice are summarized in Table I which shows the

direction of maximum radiation, the range from

this maximum to the

minimum

value measuredand

the angular extent of the 3 dB-down

region in the

horizontal and vertical

planes.

Fig. 3

gives

the 3 dB- and l0 dB-down

regions

graphically.

Note in

the

horizontal the doubling

of

the 3 dB region

below

1000Hz and the

gap

at

2000Hz due to the

downward

direction

of the

maximum

at

this

frequencyand

above.The narrow-

nessof the 4000Hz

3 dB

radiation

pattern

(+

35")

is

particularly

significant since

this is the region of

the

so-called

"singer's

formant",

which

gives

the

trained voice its

carrying

power

and brilliance

[9,

l0]. At

8000

Hz

the

pattern

again

broadens but

one

should note that the radiation in

this

band

com-

prises

he

high

frequency

partials

of the sung

vowels

rather

than the consonantswhich dominate mea-

surements

on speech n this octave. Niese's mea-

surements, or

example,'onspeech onsonants

ive

a

much narrowerpattern (+ 30').

The

pronounced

downward inclined maximum

in

the vertical

plane

indicates he

great

importance of

floor reflections to

singers.

There is also a markedly

smaller

vertical

dispersion than horizontal

which

suggests hat reflectors

to the

sides of a singer are

likely to be rd6re useful

han

thoseoverhead.

Fig.

4

gives

a-colnpariion of the

intensity in

the

three most important

d{rections,

referred to the

radiation

to the front 6f the singer

(0").

Overhead,

the level'drops about

I

dB/Octave

with increasing

frequency.

To

the

side the

level is lower at low fre-

ig. 2. Directivity

of a singer n the

vertical

plane.

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Table .

Characteristical

alues

f the singer's

irectivity.

133

Centre Direction of the

frequency maximum

of

the

octave

band

[Hz]

AZ*"

3 dB-down region

dB

horizontal

vertical

125

250

500

1000

2000

4000

8000

6 . 0

7 . 5

9 . 5

11

20.5

23.5

3 1 . 5

+45

(front)

+40

(frOnt)

} 20

(side)

-40

cFront)

-20

(frOnt)

-20

(frOnt)

-20

(frOnt)

- 45

Ec

+ 45

- 80

E

c

+ 80

- 9 0

Ec

+ 9 0

\

H 5

Ec

+ H 5

} 20

EEE

} 60

- 35

Ec

+359

and }

70

Ec

}

80

- 50

E

c

+ 50

(-40 )c

E

+120

(-40

)c

E

110

(-40 )c

E

75

(-40 )c

E

60

- 3 2 c - 8

- 35 c

+35

- 35 c

+25

0 ]3dB n

0 ]10 dB

Fig.3. Principal

radiation directio ns of a singe r in the

different octave

bands.

quencies

but reaches + 2

dB at 1000

Hz

-

about

5 dB higher than the level overhead.Apart from the

pronounced peak

at 1000Hz,

the sideways

level

remains

constant at about 3 dB below the frontal

level

until the high frequency

drop-off above

about

2000 Hz. By

comparison the level to the rear falls

steadily at about

2.5 dB/Octave. The

peak

at

1000

Hz may be ascribed to the

diffraction

around

the singer'shead.

3.2.

nfluence

ofvoice

production

technique

Fig.4

also

indicates

the effect of dynamics

on

directivity. Results for

forte

(full

voice)

and

piano

(half voice) singing are plotted. Overhead and

behind the singer he

curvesare close

ogether.Pro-

jection

to

the side is markedly weaker with

piano

singing

in the

frequencies above 1000Hz, the differ-

ence being about 3 dB in the important region

for

vocal

timbre. That means that

to the side of

the

singer an

exaggerated dynamic

can

be expected

with

significant ossoftone colour in

piano passages.

Apart from this,

size and location of the

principal

radiation regions

change

insignificantly during

transition

between "full

voice"

and "half

voice".

-

the variation being only in the order of

5

o.

3 . 2 .. C o m p a r i s o n o f m a l e v o i c e s

a n d f e m a l e v o i c e s

Analysis

of results for the

female

voices

showed

substantive

agreement n the radiation

patterns

with

those obtained

for the Baritone

differences being

smallest n the

8000Hz region. The

only significant

deviation

was

in the 2000 Hz

octave

where

for

the

female voices

the sharp maximum

downwards

to

the front

(Fig.

2) almost disappears

and

the 3 dB

region is

spread o approximately

30o upwards.

An

additional secondary

maximum occurs for

female

voices at 60o upwards

n both the 2kHz and

4kHz

@

@

@

@

@

E

P

@

@

@

@

P

@

@@

@

@

E

Q

P

E

B

C

B

R

B

v

B

O

v

v

O

O

~

R

WS

_

B_

\oerrino

R

_

125 ?50 500 1000 2000

1000Hz 8000

FreQuency

Fig.4.

Sound

pressure

evel

in

three directions

referred

to

the

front

as a function of vocal technique:

a< forte,

O-t

piano.

7/25/2019 Acustica1985 Marshall&Meyer

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octaves.

An

interesting

deviation

occurred

in the

1000Hz

octave

to

the side

where the female

voices

showed

similar

tendency

o the

"half

voice" of the

Baritone.

It is

quite possible

however that

these

differences

are

due as

much to

the

quality

of

voice

production as

to voice type, since the female test

persons were far

less experienced

than the Baritone

and

found

singing

in

anechoic

conditions

much

more difficult.

3.3.

Effect

of dffirent

vowels

A similar

comparison

was made for the

three

vowels o, a,

e. Differences

were

most marked

to the

side of

the singer

as

indicated in Fig. 5. Up to

500

Hz the radiation

of all three

vowels is identical,

from 500

to 2000

Hz

there is a sharp deviation

with

a subsequent

eduction

in difference above

4000 Hz.

Fig. 6 presents he polar diagrammes for thesethree

vowels in the

2000

Hz octave

band.

Note that the

40o sideways

maxima

evident

with

"o" and "a"

are

missing

with "e"

in the horizontal

plane.

In the

vertical

plane,

o and

a radiate strongly forward and

down

with "e"

again

much weaker.

In this context

it is noted that Slavik and Tichy

[8]

found

differences

in the directivity,

particularly

to

the side, for

different

vowels. A

possible

explana-

tion for this

phenomenon

could be

phase

cancella-

tion across

he

openings similar to that known

in

the

radiation

from

airflow

across

ipe

openings l].

An influence

of

pitch

on

directivity

is

discernible

only at

the highest notes

n each

of the

individual

vocal ranges.

Above the singer

these

tones

were

2

"'

4 dB

less attenuated

than

the other tones

and

this further

strengthened

the

upwards

secondary

maxima. The effect was strongest n the top Sopra-

no c

in which the upward

secondary

maxima

were

8 dB stronger

than the

middle-

and low-frequency

tones.

To the

rear

of

the singer some

sound

components

are less attenuated

-

by

as much

as

4

"'

5 dB be-

tween 500

to

1000

Hz

with

"o"

and "a"

and from

500

to 2000 Hz

with

"e".

At high

frequencies

there

is no difference between

them.

Sideways

however

the components

at 4000

Hz in "a"

and "e" suffer

3

"'

5

dB

greater

attenuation

han

the

other sounds.

The consequence

s that the

"singer's

formant"

is

less

prominent

to the side

of a singer

for these

vowels.

3.4. Summary

of conclusions

We

can summarize

the

results of this

section as

follows:

l) Noticeable differences

in

vocal timbre

will follow

if the singer

turns more than

40" from the

normal

position.

Beyond 80o the

problem

will become

acute. Reflectors

should be

designed

to minimize

this effect.

2) The floor reflection

is a

particularly

important

component of the

radiation

pattern

to the lis-

teners.The area 2 "'5 m in front of the singer s

the most

significant region.

Carpet

on this region

of floor

is to be avoided.

3)

Stage design should exploit

the side

reflections

rather than overhead

reflections,

particularly

with

surfaces

within

an

angle

of 60o to the

view

direction.

4) To avoid occlusion

of one

row of choristers by

another

a steep step between

rows

is necessary.

The rake should be I

: I

(45o)

minimum.

5) Microphone

placement

right and

left of the

singer

gives

richer high

harmonics

than overhead

but also

eads to weaker low

frequencies.

\

O

C

O

R

O

v

O

O

x

v

O

O

/

_

M

_

_

15

1 2 5 2 5 0 5 0 0 1 0 0 0 2 0 0 0 4 0 0 0 H 2 0 0 0 0

Frequency \

Fig.5,Sound pressure level to the side referred to the front

For three vowels.

4. The singer's

acoustical

environment

We describenow the experiments

imed at

termining

preferred

acoustical

environments

singers.

4.1.

Procedure

The singers

performed

n hemi-anechoic

ondi-

tions it being recognized

hat

virtually all stages

Fig. 6. Directivity

in the 2000

Hz octave band

for

3

vowels.

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Fig.7. Plan of the hemi-anechoic

oom showing

the

arrangement f the

vocal

quartette,

he microphones nd

the oudspeakers:

S

=

side

eflections,

R

=

rear

eflections,

C

=

ceiling eflections,

Rev,

Rev'

reverberation.

have.a

reflective floor. Side, overhead

and

rear re-

flections

corresponding to a

variety of

stage

sizes

were simulated with a digital delayline, feeding

back directly

to the singers

via cardioid micro-

phones

at

0.5

m from each singer's

mouth, and

loudspeakers at a

distance of

about

3 m,

see

Fig. 7.

Levels

were

calculated

according

to spherical

diver-

gence

with some correction

for vocal directivity.

Reverberation

was

generated

on the two inco-

herent

feeds from an

EMT Goldfoil

reverberation

plate

and radiated

to the ensemble

rom three loud-

speakers arranged

to simulate

the reverberance of

the auditorium,

see Fig. 8 a for

schematic

synthetic

sound fields and

Fig. 8 b for simulated

stage sizes.

Table II

gives

the delay applied

through

the

delay-

line plus the delaycausedby the 3 m dimension be-

tween the singing

group

and

the respective

loud-

speakers.

The music

chosen consisted

of unaccompanied

chorales

and choruses

from the J.

S. Bach "St Mat-

thew Passion"

and

"Elijah"

by Mendelssohn.

Ex-

cerpts approximately

30

s long

were

sung

for each

trial and then the

musicians

were

asked

to rate the

conditions

on

7-point scales for

"ease

of

singing"

and

"ease

of

ensemble",

before

the

next

presenta-

tion. Fourteen

presentations

wer made in

random

order in each series.

A.H.MARSHALL and J.MEYER:DIREC

YW AND AUDITORY IMPRESS10NS

~ m g

| c A A c

m u

135

@

Fig.

8.

a) Temporal

structure of

the test sound

fields.

b) Schematic

of the simulated stage

plans.Simulation code:

lst letter:

ceiling and rear

reflections,

2nd letter:

side reflections.

Table II.

Delay of

reflections and reverberation.

Code

AKG delay] Total dday Appro

mate

line surfa

distance

E

B

E

E

E

N

X

no reflection

A 6.25

ms

B

12.5ms

C

18.75 s

D 2 5 m s

E 31.25

s

F 37.5

ms

G 5 0

Rever-

75

beration

16.25 ms

22.5 ms

28.75 ms

35 ms

41.25 ins

47.5 ms

60

85

2.75m

3.82m

4.89m

5.95m

7 . 0 1 m

8.07m

10.2 m

(13 .6o

7/25/2019 Acustica1985 Marshall&Meyer

7/11

l, 1.5 and

3s, The

onset time

of the

reverberated

signal

was

varied

through

60, 85 and

ll0

ms and for

asymmetrical stage

simulations

(i.e.

side "walls"

at

a different distance rom

simulated

rear and over-

head

"surfaces")

preference

for

wide or deep

stages

wasexplored,seeFig. 8b.

Fig.9. Photograph

f

the vocal

quartette

n the anechoic

room.

The

greatest

number

of experiments

were

per-

formed by the

quartette,with the choir of 14

voices

and the

soloists

each

available on only one

occasion.

To

maximize

dependence

on the "reflected"

sound

singers

faced

away

from

each other on the

hemi-

anechoic

pace.

See

Fig.

9.

5. General

observations

It had b'een

observed

in the field that singers,

both

solo and

choral,

are sensitive

o

the

reverberant

conditions.

The

first

question

was, then,

whether it

would

be

possible o sing

in

ensemble

n anechoic

conditions at all. To start with, the quartette stood

back

to back

in

the large anechoic

room

at

PTB. To

everyone's

surprise

singing in ensembleunder

such

conditions

was

quite possible

though observers

noted some

difficulties

in intonation. Of

the four

subsequent

occasions

on

which

the

quartette

sang,

in the hemi-anechoic

oom, the first

was

used

o test

the consistency

of

judgements.

Consistent

udge-

ments

were

found

to be

possible.

The results re-

ported

here however,

are derived from the

last three

sessions

nly. The choir

results

were

less clear. Not

only

were the singers

relatively

inexpert

(i.e.

un-

practiced)

at

making the

experimental

judgements

but some, notably the upper parts, proved quite

unable

to

respond

consistently

at all. The

raw

choir

results

were thus

rather smeared.

A

procedure

to

purge

the unreliable

udgements

was

adopted and

is

described

n the Appendix.

Finally, the results rom

only

7

of the

14choir

singers

were ncluded.

6.

Experimental

variables

In addition to

reflection

delay and level,

reverbera-

tion time was

varied in the

presentations

through

0,

7. Results

7.1.

Correlation

between ease

of singing"

and

"ease

of ensemble"

For

all

groups

here is a high

correlation

between

the

judgements

of ease

of singin

and ease

of en-

semble.

Correlation coefficients

lie between

0.82

and 0.90

for all trials. Fig.

l0 shows

he dependence

of the correlation

coefficients

on

the four reverbera-

tion times presented for the quartette. The correla-

tion

was even higher for

the choir

(0.92).

From this

we conclude hat essentially

nly

one

udgement

was

being

made.

The only exception

was a combination

of a

long

reverberation time and unfavoured

reflection delays.

In this situation,

"ease

of ensemble"

seemed o be

little

worse han "easeof singing".

7.2.

Early

reflections

for

the ensembles)

Although it

was

quickly

appatent

that the

princi-

pal

conclusion

to

be

drawn from

the experiments

concerned the importance of reverberation to

singers, approximately

half the

presntations to the

subjects

comprised only

early

reflections

without

reverberance.

The results are

very straight forward

and

will be

presented

lrrst.

Fig. I I summarises

hese

results. t

is

a cumula-

tive

plot

of

normalised

preference

against

he rela-

tive

energy

of

early

reflections

which as noted above

0 1 2 s 3

Reverberoi ion

ime

+

Fig. 10. Correlation coefficient between "ease

of ensemble"

and

"ease

of singing"

for

different

reverberation times

presented.

@

O

E

U

x

O

E

Q

O

P

E

E

X

E

E

E

E

O

O

b

O

O

v

v

O

\

.

7/25/2019 Acustica1985 Marshall&Meyer

8/11

'

( -o )

-12

- t 0 -8

-6

-1 -?

dB

0

Re lo t i ve nergYev l

Fig. I

l. Normalised

preference (ensemble)

or the

quartette

for reverberation-lree simulated refl ections.

approximate to

spherical divergence

relative

to the

strongest reflections

(situation

code

AA:

0 dB). This

reference

evel is about 16dB lower

than

the sound

power

evel

of the singer.

It is

clear that there

is

a simple dependenceof

preference

n the

level

ofthe early

reflections.

7.

3. Reverberation

or

ensembles

In the sound fields

presented

without early reflec-

tions but with reverberation the reverberation time

seems o have no systematic effect on

preference

n

the

range

of the 3 reverberation imes

presented 1,

1.5

and 3s respectively) o the

quartette

and the

choir.

7 . 3 . 1 .

f f e c t o f s o u n d fi e l d s c o n s i s t i n g

o f e a r l y

r e f l e c t i o n s a n d

r e v e r b e r a t i o n f o r t h e e n s e m b l e s

The most

striking

result is the

generalpreference

for the sound fields

with

reverberation

for both the

ensembles. ig. 12 s a typical

plot

of results

or the

quartette and shows that with the exception of

situation EE

(delay

about 40 ms) the fields with

reverberationare strongly

preferred.

Similar results

were obtained with the

choir.

Fig. 13 shows the

sharpnessof the

interaction between the early re-

flections and the reverberant field by

plotting

the

difference in

preference

between the

reverberated

and dry reflections. All the

presentations

to

the

choir and

quartette

involving reverberationsettings

of 1.5s and

85

ms delay are included. Some

of the

fields

presented

were

"symmetrical"

while others

were

"asymmetrical"

as shown n Fig. 8 b.

A.H.MARSHALL and J.MEYER:DIREC

Y AND AUDmRY IMPRESS10NS

137

Both

for long

delays

(and

corresponding low

reflection

levels),

and

for short

delays

with

relative-

ly

more

energetic

early reflections

the

improvement

in

preference

for

the fields

including reverberation

is significant and about the same. This improve-

ment

disappears

quite

sharply

at

about

40 ms delay

relative

to the direct.

The

effect is so

strong

and

independent

of

group

size

(choir

or

quartette)

or

whether

the

presentations

were

symmetrical or

EnsemblP

A

m _ ' R

D A

O

@

@

@

@

E

P

P

@

@

\

B

B

B

v B

E

B

v

v

O

O

n

d

v

O

Q

E [

Fig.

12. Normalised

preference

for the

quartette

for sound

fields with

(dark

areas)

and

without

(ight

areas)

everber-

ation component.

CodelX X GG

36 CC

E E D E M0 0 0 6 8 0 B A C C A A A

( -o )

- ' 12 -10

-8 -6

-1 -?

dB 0

ne lo l i v

nergyeve l

Fig.

13.

Difference

in normalised

preference

between

sound

fields

with

and without

reverberation component as a

function of relative reflection

level.

Reverberation

ime

1.5s. onsetdelav

85

ms.

Code: A

.

quartette,

sym.

Iields,

o

quartette,

asym. ields,

r choir,

sym. fields,

o choir,

asym. -relds.

O

C

W

O

E

U

O

C

S

O

B

e

s

h

h

P

O

O

O

v

O

O

v

@

n

n

x

O

n

O

v

O

U

7/25/2019 Acustica1985 Marshall&Meyer

9/11

A.

H.

MARSHALL

nd J.

MEYER:

DIRECTMTY

AND

AUDITORY

MPRESSIONS

ffiHli:i

2 d0 0

O

E

W

O

C

U

O

C

S

O

E

Q

O

E

OQ

P

B

B

B

v

B

E

B

v

O

B

B

Q

b

B

B

b

n

v

O

\

B

B

E

v

B

E

E

x

v

O

d

v

B

Q

Fig. 14.Differencen normalised

reference etween

ound

fields

with

and

without reverberation omponent.Rever-

beration

ime

1.0

s,

onset

elay

85

ms.

o

lst

series,

o

2ndseries.

asymmetrical

that

we

were convinced

it

is

a real

effect.

However

we addressed

this

question further

by

varying

the

reverberation

time and

by

varying

the

onset

delay

for

the

reverberated

signal.

7 . 3 . 2 .

e v e r b e r a t i o n

t i m e

v a r i a t i o n

Two series were conducted with the quartette

using

I s

reverberation

time

instead

of

the

l'5

s

adopted

as standard

with

onset

delay

85

ms.

Mask-

ing

of

the

early

reflections

by

reverberation

is

reduced.

Early

energetic

reflections

integrate

with

the

reverberation

so

that

preference for

the

rever-

berated

sound

is

negligible.

Only

for

delay

greater

than

about

40 ms

is

the reverberated

field

strongly

preferred

again.

See

Fig.

14.

This

result

gives a clue

as

to

what

is happening

n

Fig.

13.

The

pronounced

dip

occurs

at

the

point where

dependence

solely

on

the

reverberated

signal

takes

place

because

he

early

reflections

energy

is as

low

that

it

is negligible.

A

further variation with the quartette used 3.0s re-

verberation

time.

The

reverberant

signal at

3

s so

obviously

dominated

the

singing

experience

that

only

tests

with

the

reverberation

were run.

Apart

from

a

slight

improvement

in

preference for

the

earliest

and

most

energetic

discrete

reflections

preference

for

all

test

fields

was uniform

within

the

experimental

accuracy.

From

this

series

we

conclude

that the

shorter

the

reverberation

time,

the

more

important

the

earliest

reflections

are

for

ensemble.

However

after

about

35

ms

of reflection

delay the

statistical

reverberation

Fig.

15.

Normalised

preference

s

a function

of

relative

reflectionevel.Reverberationime l-5 s.

o

onset elay

60

ms,

o

onset elay

85 ms,

r

onset elay

l0 ms.

completely

dominates

the

singer's

perception

of the

performance environment,

irrespective

of the

pres-

ence

of

reflections.

7 . 3 . 3 . n s e t

d e l a y

t i m e

We

investigated

the

possibility

that

the

reduction

in preference for

the

reverberant

flreld

at

40 ms

could

have

been

an

artifact.

The

reverberation

signal

started

in

the experimental

set-up

at

a dis-

crete

time

-

virtually

like

a

reflection

at

85

ms

delay.

Accordingly

wc ran

a series

in

which

the

variable

was the onset

delay

time

for

the

reverbera-

tion.

The set-up

did

not

permit us

to include

the

unreverberated

field

for

comparison

as

would

have

given

us

directly

comparable

results

with

those

already

shown.

However

Fig.

15 shows

that

a

signilicant

dip

in

preference does

occur

with each

of

the onset

delays

at

the

40 ms

region

with a

reduc-

tion at smaller

onset delays

than

about

70 ms.

That

means, that the 40 ms effect is very important for

the design

of single

reflectors,

if the

other

reflecting

areas

have

distances

of more

than

about

l2

m.

7.4. Soloists

At the

conclusion

of

the

measuring

programme

described

in the first

section

of this

paper we asked

the singers

each

to

undertake

at

test

series

@ncern-

ing

"ease of singing"

comparable

to those

described

for

the

quartette

and

choir.

Fig.

16

gives

the

initial

plot of their

responses

while

Fig.

l7

gives the

preferences

plotted

against

reflection

energy

in the

-0,1

( - o

I

-10

-0

-6

-L

Relot ive

nerqy

evel

_0) ]

12 10 ]

8 ]

6 -4

7/25/2019 Acustica1985 Marshall&Meyer

10/11

Fig. 16. Soloists: Normalised

preference

(ease

of singing)

for sound fietds

with

(dark

areas) and

without

(light

areas)

reverberation

component.

Reverberation

time

1.5s, onset

delay

85 ms.

o

Baritone.

]

0 ]

]

]

Relotive Eneu

y tevel \

ACUSTICA

V 58 (1985)

(--) -12 -r0 -8 -6 -1 -? d8 0

nelotivenergy-evel

Fig. 17.

Soloists: Differences

n normalised

preference

between

ound ields

with

and

without reverberationom-

ponent.

Reverberation

ime 1.5

,onset elay

85ms.

o average,

r female

ingers,

o Baritone.

presentation.

Since

there

were only 3 subjects the

Baritone

is

plotted

separately

from

the two female

singers, ogether

with the average.

The striking features are the both extreme

variation in the

plots

and unanimity

between

voices.

The

strongly negative

response

o

"AC" and

"BG"

was coupled

to comment

from the singers that

having

the reverberation

arriving

from a distinctly

different

direction

from the early

sound

(overhead

and back)

was disturbing and

one should

not make

too much of

what is obviously

an artifact. As before

there is a clear

preference

for

reverberation

which is

complicated by

early energetic

reflections, especial-

ly if the side

reflections arrive

earlier

than the

overhead

eflection.

Fig. 18. String

quartette:

Differences n

normalised

pre-

ferencebetween ound ieldswith and without reverber-

ationcomponent.

o Response

o

"ease

f ensemble",

o

resporBe

o

"tone

quality".

7.5. nstrumentalists

For

comparison

with the

foregoing

work on

singers

we invited a string

quartette

to

play

in the

same experimental

set-up.

Within the

obvious

limitations concerning

instrument

directivity

we

found

confirmation that

the early

reflections are

critically

important for ease

of ensemble

while

re-

verberation is not. On the other hand the aesthetic

experience of

the instrumentalists was

clearly

not

highly correlated

with ensemble conditions

as

was

the case

with singers. Responses o a

question

about

ease

of achieving tonal

quality

showed

a consider-

able

dependence on

the reverberant

conditions.

These

esultsare

plotted

in

Fig. 18.

8. Conclusions

In addition

to measuring

the directivity

of the

sung

voice over

3 vocal ranges,

for 3 different

vowels and in two vocal styles we have conducted

experiments

with vocal

ensembles

o establish

pre-

ferred acoustical

conditions

on stage.

These experi-

ments show

that

"ease

of ensemble"

for singers

is

inseparable

from

questions

of singing

comfort and

that both

are controlled

by the

reverberant condi

tions. Energetic

early reflections do

contribute

posi-

tively

if

they

are early enough but at

about

40 ms

delay

reduce

preference

well below

that of a reflec-

tionJess

reverberant field.

This result is

in

direct

contrast

with

conditions

preferred

for

instrumental

ensemble n

which the early reflections are

essential.

139

P

V

P

P

P

x

O

v

v

O

n

d

v

O

\

\

\

\

\

\

]

n

n

v

O

O

v

v

u

n

b

v

O

Z

n

b

n

v

O

Z

O

C

S

B

O

E

O

E

Q

E

O

C

S

V

PPP

P

@

O

O

v

O

x

O

n

v

O

O

O

v

O

Z

7/25/2019 Acustica1985 Marshall&Meyer

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A c k n o w l e d g e m e n t s

The

authors

are most

grateful

to all the singers

who

participated

in the

work reported in this

paper,

particularly

to

Professor Claus

Ocker and Dr.-Ing.

Detlev Mencke.

The

project

was

supported

by

a

grant

from

the PTB

for Professor Marshall's

visit

and by

the Research

nd

Study eave

programme

of

the University

of Auckland

(NZ).

Appendix

Evaluation

of chamber-choir

esponses

During

the analysis

of

choir

members esponses

t

became

apparent

that their

individual reliability

varied considerably.

(Each

singer indicated

vocal

part

and

approximate

position

on the

form.)

Since

every

presentation was repeated at least

once

it

was

possible o test he individuals reliability and purge

inconsistent

esults

by comparing

the two responses.

Ideally

of course

each subject

should have made

an identical

response o

the repeated ield

when it

reappeared

n the series.

Subjective actors

such as

familiarity,

fatigue,

improving

listening

skills

and

confidence

would

prevent

that occurring

in

practice

but

if there

is

no consistent

change

in the assess-

ments reliable

rank

ordering

of the

results can be

achieved.

For

every test

subject

we determined

the differ-

ence or eachsound ield. Usually the rangewas ess

than three

preference

steps

but occasionally

there

were as

many as

five steps

difference

in the assess-

ment. Fig.

19 shows

3 examples.

Singer

(l)

judges

the

repetition

rather better.

Singer

(2)

judges

the

first

programme

about

the

same

yet

again

better on

the repetition.

(Perhaps

t took

the first three before

he

got

used to

it.) Singer

(3)

has such a broad

distribution

of results

hat

his responses

hould be

purged.

To test

reliability

we counted

the number of

repeated

ests n

which nearly

the same

result or at

least a

consistent

difference

occurred,

i.e. we

summed up the number of tests n that group of

three bars

containing

the

highest

number of tests.

Thesebars

are

hatched n

Fig. 19.

With 14

presenta-

tions in each

of

2 series

we had 28

possible

for a

perfect

score.

Results

ranged from

14 to

26. We

accepted

results

of 21 or

more. ln

practical

terms

that

meant

that for

at

least

75o/o f

judgements

he

difference

must be

no more

than

*

I step.Only

7 of

the

choir

of 14 achieved

his

result and

it is their

responses

hat

are

ncluded

n the

paper.

(Received

ebruary

1th, 985.)

R e f e r e n c e s

[]

Meyer, J., Akustik und musikalischeAuffiihrungs-

praxis. VerlagE. Bochinsky,

rankfurt a.M.,

2. Auf-

lage, 980.

[2]

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A. H., Gottlob,

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Progromme

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D i f i e r e n c e i n t h e i n d i v d u o l us u l l s

Fig. 19. Reliability of

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