Bruel & kjaer 4215 User guide

Artificial Voice Type 4215

This

instrument

is

an

acoustically

well-defined

sound

source,

which

may

be

used

for

free-field

measurements

as

wel

l as

for

measurements

under

c

onstant

sound

pressure

conditions.

BHUEL&KJ&R

Nif!rum,

Denmark

•

Phone

80

05 00

Telegrams:

BRUKJA,

Copenhagen

BB

421!5

ARTIFICIAL

VOICE

TYPE

4215.

August

1959

Description

General

Description

Operation

Contents

General

.

.........

..

........

.

.........

.

..

.

.....

.

......

...

..

. . .

Recording

th

e

Frequen

cy

Response

of

Mic

rophones

.

..

. .

.. ..

.

...

.

Determin

ati

on

of

Mi

c

rophone

Se

nsitivity

...........

...

.......

..

.

Specification

3

4

10

11

13

15

Description.

General.

The

Artificial

Voice

Type

4215 is

designed

for

use

in

laboratories

and

pro-

duction

lines

where

a

well

defined

sound

source

is

required,

and

covers

the

frequency

and

pressure

range

that

is

normally

covered

by

the

human

voice.

The

apparatus

is

of

cy

lindrical

shape,

and

it

differs

from

the

artificial

voices

normally

used

for

telefon

measurement

by

its

provision

for

automatic

regulation

of

th

e

sound

level.

It

consists

of

a

small

loudspeaker

mounted

in

a

metal

housing

,

provided

with

a

co

upler

and

with

sockets

for

the

mounting

of

a

regulating

microphon

e

with

Cathode

Follower.

Damping

material

Coupler

\

Gold

covered

contact

Socket

for

regulating

microphone

Guard

ring

Loudspeaker

connect

Gold

covered

contact

l.:j1l~~~-~~f-

Guard ring

contact

for

follower

Fig.

1.

Sectional

view

of

the

Artificial

Voice.

3

Description.

The

sound

producing

element

of

the

Artificial

Voice

is a

small,

dynamic

type

loudspeaker,

the

diameter

of

which

is 90

mm.

It

is

mounted

in

an

aluminum

housing

with

rigid

walls

and

of

cylindrical

shape,

as

shown

in

Fig.

1.

In

front

of

the

loudspeaker

is

placed

a

special

coupler

(mouth

open-

ing)

which

is

made

removeable,

in

order

to

make

it

possible

for

the

user

to

insert

couplers

for

particular

purposes.

The

coupler

is

fastened

by

means

of

a

union

ring,

which

can

also

be

used

lo

fasten

a

lightning

ring,

thus

ensuring

an

airtight

connection

to

the

microphone

under

t

est.

The

special

coupler

supplied

with

the

Artificial

Voice

h

as

an

opening

dia-

meter

of

38

mm.

It

may

be

used

for

measurements

under

constant

sound

pressure

conditions

(provided

th

at

th

e

microphone

can

be

mounted

directly

at

the

opening)

as

well

as

for

free

field

measurements.

Microphone under

test

Regulating

microphone

type

4132

Fig. 2.

Artificial

Voice

with

regulating

microphone

and

test

object

mounted

for

pressure

calibration.

In

the

opening

is

placed

a

socket

for

mounting

of

a

regulating

microphone,

i.e.

the

standard

Condenser

Microphone

Cartridge

Type

4132. As

seen

from

Fig.

2,

lhe

front

of

the

microphone

cartridge

is

exactly

in

level

with

the

opening

of

the

coupler,

whereby

is

obtained

a

sound

pressure

regulation

in

the

very

front

of

the

Artificial

Voice.

By

employing

the

B & K

standard

microphone

the

sound

pressure

can

be

kept

constant

to

within

2

db

in

the

frequency

range

100

cfs

to

7

kc

/s.

The

socket

w'

hich

is

placed

in

th

e

mouth

opening

is

connected

to

another

socket

placed

on

the

side

of

the

housing.

To

thi

s

socket

a

Ca

thod

e

Follower

4

Type

2612

or

2613

can

be

fastened.

By

means

of

a

screened

cable

the

cathode

circuit

potential

of

the

cathode

follower

is

connected

to

the

guard

ring

seen

on

Fig.

1

whereby

the

input

to

ground

capacity

of

the

cathode

follower

is

reduced

to

a

minimum.

The

centre,

spring

loaded

contact

in

both

sockets

are

covered

with

gold

to

ensure

the

best

possible

electrical

connection

and

low

noise

conditions.

When

used

wit.h

the

control

microphone

the

apparatus

is

essentially

a

co

nstant

sound

pressure

source*)

with

an

extremely

low

internal

impedance,

equivalent

to a

constant

voltage

generator

in

electrical

circuitry.

The

sound

pressure

is

constant

in

the

mouth

opening

and

along

the

axis

of

symmetry

of

the

artificial

voice

when

no

reflections

are

present.

The

use

of

the

Artificial

Voice

under

closed

condition

does

not

offer

other

problems

than

those

encountered

through

wave

'

motions

in

the

coupler

volume,

and

those

due

to l

eakage

to

the

outside.

The

coupler

volume

should

consequently

be

kept

small

and

too

much

leakage

may

be

avoided

through

a

light

and

simple

packing

between

the

L

est

object

and

the

Artificial

Voice

.

The

packing

is

easily

obtained

by

the

use

of

a

foamed

ruhber

pad

(see

Fig.

2}

.

The

two

small

holders

on

s

id

e

of

the

housing

normally

offer

a

convenient

support

for

a

spring

arrangement

used

to

keep

the

test

object

in

place

if

this

is

desireable.

To

provide

frequency

independent

regulation

at

higher

frequencies

the

sensitive

part

of

the

test

object

should

be

placed

as

close

to

the

regulating

microphone

as

possible.

Thereby

the

same

sound

pressure

level

is

present

at

both

microphones.

At a

frequency

of

5ooo

c/s

f.

ex.

the

wavelength

2

in

air

will

be

approximately

6.8

em.

The

distance

between

the

diaphragm

of

the

regulating

microphone

and

the

sensi

tive

part

of

the

test

object

should

now

be

<<

2

/4

"'

l.7

em.

The

pressure

response

curve

shown

in

Fig. 3 is

obtained

with

a

distance

of

o.6

em

between

the

two

diaphragms.

a9u.9,

o

~e

1

£,

0

o

~

o o o o o o o o o o,

9.R.O

•.

Oo o o o o o o o o o

o

,g.,

~,q,,o

o o o o o

o

,~~.

o

.,

.........

CIIiil-=

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=·

.....

Artificial

Vnic• Type 4

215

Condenser

Mjcrophonp

Type

4132

:::~

=~--k=

D

- •

..50dh.

- ·

...l1.:..1.:..5

--;"~~~

·~~

"'

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"'

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~

ooo

oo

~o

oo

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o"&'8~o

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oo

0

o

0

~DoD

f!f9276

Fig. 3.

Typical

pressure

response

curve

of

the

Artificial

Voice

with

regulating

microphone

emp

l

oyed.

*)

A

constant

sound

pressure

source

is

here

defined

as

a

source

which

, by

means

of

a

utomatic

regulation,

keeps

constant

th

e

sound

pressure

in

front

of

itself

when

the

frequency

and

the

lo

ad

is

varied.

5

The

Artificial

Voice

may

also

be

used

under

closed

conditions,

but

without

regulation.

The

pressure

response

curve

without

regulation

is

shown

in

Fig.

4.

0~000000000000000000000000000000000000000000000

BrUe~)c.r

......

:

lrt•l

•

I.,

lrhl

•

I.,

::::

:

-"""'

·

..

.........lllO..d.b._,_.,_.,

_J__

"-

IJIL

,

~

__2Q__

......

H..l

--

0

- .

.5ll..d.b.

.....

~

w-

.,_.

,

.1Cll_

.,.

,

___E_E_

o

o o o o o o o o o o o

"'

o o o o

"'

o o

rr'o

o

'tf'

o o o

'8'

o o 'g' o

o

~

o o o

IDOOO

0 0 0

10

D

0 0 0

'8

0 0 0 0 0 0 0 0

Fig. 4.

Pressure

response

curve

of

4215

without

regulation

(regulating

micro-

phone

inserted

but

not

us

ed

for

regulation)

.

Free

field

measurements

can

furthermore

be

very

conveniently

car

ried

out

by

means

of

the

Artificial

Voice.

When

the

regulating

microphone

is

em-

ployed

,

the

frequency

response

of

the

Artificial

Voice is

flat

within

the

limits

given

by

the

pressure

response

of

the

regulating

microphone.

The

output

pressure

will

,

however,

be

inversely

proportional

t'O

the

variation

in

sensitivity

of

the

regulating

microphone.

The

free

field

correction

for

the

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OrUe~)CIIr

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4215

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response

bistancp

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measuring

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,_

....,,

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..

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Fig.

5.

Free

field

response

of

Type

4215

with

regulating

microphone

employed.

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...

~~~~~~~~

1

":•'1'1'

1

••~~~~~~~~~~

1

'1'"1'

~~~~-~·~~~~~:IS

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....__,a.,-.

.......

Artificial

Voice

Type

4215

Fig.

6.

Free

field

response

without

regulation

(microphone

inserted,

but

not

employed).

6

Ylicrophone

Cartridge

Type

4132

with

pwtection

grid

for

·180°

incidence

is

less

than

1

db

up

to

9

kc

/s,

thus

giving

a

free

field

response

of

the

Artificial

Voice

as

shown

in

Fig.

5. (

Further

information

about

the

free

field

correction

of

the

microphone

is

found

in

the

instruction

manual

Type

4131-32

and

in

the

B. & K.

Technical

Reviews

No. 1

and

2 1959.

In

Fig.

6

the

free

field

response

is

shown

for

the

Artificial

Voice

used

without

regulation.

\Vhen

measuring

c

lose

talking

microphones

such

as

those

used

in

telephone

21U

a.

Fig.

7.

Measuring

arrangements

used

to

obtain

the

curves

shown

in

Fig. 5

and

6

respectively.

7

systems

and

megaphones,

the

distance

between

the

mouth

opening

and

the

microphone

is

so

small

that

interaction

between

the

nearfields

around

the

test

object

and

the

Artificial

Voice

will

influence

the

frequency

response.

The

influence

on

the

sound

pressure

in

the

mouth

opening

caused

by

a

cylindrical

obstacle

with

a

diam

eter

of

40

mm

and

placed

in

a

distance

of

4

em

from

the

opening

does

not

excee

d ± 2

db

at

frequencies

be

low

5ooo

cjs.

(This

counts

with

regulation

as

well

as

without

regulation

).

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1

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lolol

o

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o

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4115 • •

........

Sound

fje!

d L

em

tOto

• • •

from

mouth

openjng

~S928f

Fig.

8.

Curve

showing

the

influence

of

a 24

mm

microphone

with

flat

front

placed

in

a

distance

of

4

em

from

the

mouth

opening.

C

urve

II

shows

the

frequency

response

as

taken

with

th

e 24

mm

microphone

and

curve

I

shows

the

frequency

response

as

obtained

with

a

microphone

which

has

negligible

effect

on

the

sound

field.

In

Fig.

8 is

shown

the

influence

of

a 24

mm

microphone

with

flat

front

placed

in

a

distance

of

4

em

from

the

mouth

opening.

Fig.

9 s

hows

the

variation

in

fr

e

quen

cy

respon

se

with

di

s

tan

ce

as

m

eas

ured

with

the

above

mentioned

24

mm

mi

c

rophon

e (B. &

K.

Type

4131 ).

The

curve

shown

in

Fig.

10

indicates

the

decrease

in

so

und

pr

ess

ure

level

oooooooooooooooooooooooooooooooooooooooooooc

BrUe~Jatr

....

lrlel

6

ll•r

lr

..

l

a.

ll•r

db

-"'-"'

------.

Frequency

response

120

of

4215

measured

with

4131 -

24mm

em

Condenser

microphone

vmgn"J\

regulation

-----------'

00

_________

90

z..

....,,

__so__

--

·- - -

'-

.....

'"

2..Q__

._

...

,- --

- ._2.5__

"'""~

w;'~

~

';;'~~~o

o o o

"'

o o

~

o

'8'

o o o

'8'

o

~

o

~

o o

o

~

o o

""'&

'8

~

/)""

o c

fS9282

Fig.

9.

The

variation

of

the

frequency

response

with

distance

when

measur

-

ing

the

nearfield

with

the

above

mentioned

24

mm

microphone.

8

BRUEL & KJAER 4215 User guide

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