Bruel & kjaer 4152 User guide

Artificial Ear Type 4152

For measurement on earphones as

used in hearing aids and telephone

communication systems. Provided

with couplers made in accordance

with the lEG Recommendation

126

,

and various American and German

Standards.

Artificial

Ear

Type 4152

December

1970

Contents

Page

I. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..

3

General

.....

.

....................................................

3

2

em

3

Coupler

...........

..

.......................................

4

6

~m3

Coupler

....................................................

6

2. Operation

......

.......

.

..

....

....................

.......

......

.

..

9

Operation

of

the

Artificial

Ear

. .

......

.....

.................

9

Operation

of

a

Complete

Arrangement

for

the

Testing

of

the

Earphone

10

Artificial

Ear

in

Connection

with

the

Precision

Sound

Level

Meter

..

13

3. Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..

16

Automatic

Recording

of

Harmonics

in

Earphones

.

..

. . . . . . . . . . . . . . . . . 16

Some

Typical

Examples

of

Coupler

Adaptation

. . . . . . . . . . . . . . . . . . . . . . 17

4.

Appcndix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..

20

Influence

of

Vibration

............

..

.

.......

..

........

.

...

.....

20

Use

of

protecting

cover

in

the

6

cm

3

Coupler

...

........

.....

......

..

22

1.

Description

General.

The

Artificial

Ear

Type

4152 is

designed

to

enable

acoustical

measurements

on

earphones

to

be

carried

out

under

well-defined

acoustical

conditions

.

It

consists

basically

of

a

replaceable

acoustical

coupler,

and

two

sockets

for

the

mounting

of a

Condenser

Microphone

Cartridge

Type

4144,

and

a Micro-

phone

Preamplifier

Type

2619

or

the

Sound

Level Meter

Type

2203.

Fig. 1.1.

The

Artificial Ear

Type

4152.

A

spring

arrangement

is

provided

to

fulfil

certain

Standards

requirements

regarding

the

force

applied

to

the

object

under

measurement.

It

can

be

adjusted

to

apply

a

force

of

200

grammes

to

an

earphone

when

using

the

2

cm

s

Coupler,

as

prescribed

in

the

earlier

American

Standard

ANSI

Z.

3

24

.-9.-1949 (

but

not

in

the

pr

ese

nt

3.3-1960 ANSI

Standard

),

and

the

German

Sta

ndard

DIN 45600,

and

when

using

the

6

cm

s

coupler,

the

force

may

be

a

dju

sted to 500 gra

mm

es as

prescribed

in ANSI

Standard

Z. 24.-9.-1949

Figs. 3

and

4.

Retaining

arrangement

Coupler

Adopter i

(000111)

Mi

crophone

Cartridge

Coupl.r

M

ic

rophone

Preomplifier(2619)

Adju

st

able

retaini

ng

spring

support

163761

Pig

. 1.2. Sectional view

of

the Artificial Ear and

the

Condenser Microphone.

Fig. 1.2 show.s a

sectional

view

of

the

socket

with

the

mounting

arrangement

for

the

condenser

microphone.

The

guard

ring

(internal

shield)

principle

used

in

the

Mi

c

rophone

Preamplifier

Type

2619 is ex

tended

to

include

the

socket

which

keeps

th

e

effective

transmission

loss

of

the

4152

as

low

as

approximately

0.1 dB.

As

indi

ca

ting

met

er,

the

Microphone

Preamp

lifier

Typ

e 2619

and

the

Measur-

ing A

mplifi

er

Typ

e 2606

can

be

used

as well as

the

Sound

Lev

el Meter T

ype

2203. See Fig. 1.3.

The 2 em3 Coupler.

One

of

the

couplers

supplied

with

the

Artificial

Ear

Type

4152 is a 2

cm

3

Coupler

(DB 0138)

which

fulfils

the

requirement

of

International

Standard

(I.E.C.

Recommendation

Publication

126). A

sectional

view

of

the

Coupler

is

shown

in

Fig

. 1.4.

=:j~il~l:i.:r

'--+--(E~~)

"'"--

i-

_~

-

-~-~I:

2606 2619

o.

4152

b.

1637+9

Fig.I.3.

a)

The

Artificial Ear

Type

4152, MiCl'ophone Preamplifier

Type

2619 and

the

Measuring

Amplifier

Type

2606.

b)

The

Artificial Ear

and

the

Sound

Level Meter

Type

2203.

It

consists

of

a

housing,

a

standardized

18

mm

ear

mould

s\lbstitute,

and

an

airtight

screw

seal.

The

housing

is

supplied

with

threads

for

mounting

a

Microphone

Cartridge

4144

in

one

end

and

for

the

screw

seal

in

the

other.

The

screw

seal

is

made

airtight

by

means

of

a

rubber

ring,

which

is

also

used

as a

lock

arrangement

for

the

nub

of

the

earphones

for

hearing

aids.

The

18

mm

ear

mould

substitute

is

made

removable

to

allow

other

adapters

to

be

used, if

required,

as

shown

on

p. 18.

When

the

Condenser

Microphone

cartridge

is

screwed

into

the

coupler

the

effective

volume

(including

the

equivalent

volume

of

the

cartridge)

is 2 ems,

within

the

tolerances

permitted

by

the

standard.

To

enable

pressure

equalization

a

capillary

tube

arrangement

is

included

in

the

coupler,

as

shown

in

Fig. 1.2

and

1.4.

If

desired

the

couplers

can

also

be

used

screwed

directly

onto

a

Condenser

Microphone

as

shown

in

Fig. 1.5. Fig. 1.5

shows

also

the

exact

dimensions

of

the

ear

mould

substitute

for

the

convenience

of

the

user

who

may

wish

to

make

his

own

special

substitutes.

Airtight rubber

seal

O,Smm-D.020"

wire to fill

capillary partially

Airtight

seal'----fJ!:=:;::::::;:==I=::;::::;;:;~1J

Standard pressure

microphone

Pressure equalisation

capillary

O,6mm-O,024"

1

59259

Fig. 1.4.

The

"normal"

2

cm

3 Coupler DB 0138.

The

6

cm

3

Couplers.

To

enable

acoustical

tests

to

be

made

on

headphones

used

in

audiometers

and

in

telephone

systems,

two

6

cm

3

couplers

are

available

for

the

Artificial

Ear

Type

4152.

One

of

these

couplers,

the

one

normally

included

in

the

4152

ear,

fulfils

the

requirements

of

th

e N.B.S.

9A

Coupler

and

ANSI

Z. 24.5-1951,

the

other

being

in

accordance

with

the

requirements

of

the

ANSI

Z.

24.9-1949

Type

1

Coupler

.

Sectional

views

of

the

couplers

are

shown

in

Fig. 1.6.

According

to

the

standards

the

couplers

should

be

used

in

connection

with

microphones

supplied

with

a

front

cavity

.

As

the

Microphone

Cartridge

Type

4144 is

made

with

a

flat

front,

a

Coupler

Adapter

Ring DB 0111 is

supplied

with

the

couplers.

By

unscrewing

the

normal

protection

cover

from

the

microphone

cartridge

and

mounting

the

coupler

adapter

ring

instead,

measurements

can

be

mad

e

in

complete

agreement

with

the

standards.

However,

the

openings

of

the

couplers

are

big

enough

that,

by

accident

a

small

object

might

be

dropped

into

the

cavity

and

damage

done

to

the

unprotected

microphone

diaphragm

.

To

avoid

this

risk

of

damaging

the

6

Ear mould

Condenser

Microphone

Adapter for 2 cm3 coupler '592<1

Fig. 1.5. Dimensional drawing

of

the 2

ems

Coupler.

diaphragm

it

is

recommended

to

place

the

microphone

with

its

normal

protecting

cover

in

the

coupler.

(See

Appendix).

Both

the

6

ems

and

2

ems

couplers

may

be

used

directly

on

the

Artificial

Ear

Type

4152,

but

if

it

should

be

desired

to use

the

couplers

directly on

a

microphone

without

the

art

ifici

al

ear,

this

may

be

done

by

employing

the

method

described

in

the

following.

The

method

of

mounting

the

2 ems

coup

l

er

is

described

above,

but

to

mount

the

two 6

cm

3

coupuers,

the

micro-

phone

cartridge

is

screwed

off

the

preamplifier

and

the

stop

collar

YO

2340,

which

is delivered

with

the

coup

l

ers

DB 0160

and

DB 0161

but

not

wiih

the

Artificial

Ear

Type

4152, is

placed

on

top

of

the

preamplifier

so

that

the

preamplifier

is recessed

in

the

ring.

By

replacing

the

microphone

cartr

idge

on

th

e

preamplifier

th

e

stop

collar

is

fixed

in

its

position,

and

th

e respective

coupler

can

be

placed

on

the

microphone

as

show

n

in

Fig.

1.7

.

When

th

e

7

Sec

ASA Type 1

=

I

Packing Washer

--------;,~

CoupLer

Adapter

Ring

F

Stop

CoLLar

I

159262

Fig. 1.6. Sectional views

of

the 6

cm

3 Couplers.

couplers

are

used

directly

on

the

microphon

e

it

is

recommended

to

use

one

of

the

B & K

microphone

stands.

,----

Packing

Washer

,---

CoupLer

Adopter

Condenser

Microphone

Cartridge

6 cc

CoupLer

ASA

Type

1

Stop

Collar

----

Preamplifier

Fig.

1.7.

Sketch

showing

how

the

6

cm

3 Couplers are

mounted

directly on

the

Condenser Microphone.

8

2.

Operation

To

carry

out

meas

ur

eme

nt

s

by

me

ans

of

the

Artificial

Ear

Type

4152,

it

must

be fitted

with

a

Microphone

Cartridge Type 4144, a Microphone

Preamplifier

Type

2619

and

an

indicating

instrument.

It

is possible

to

us

e

the

Sound

Level

Me

ter

Type

2203

instead

of

th

e

pr

eam

plifier a

nd

the

indic

ating

instrument

.

To

ma

ke

th

e Artificial

Ear

ready

for

use,

proc

eed as follows:

Operation

of

the

Artificial

Ear.

1.

Unscrew

the

coupler

and

if

mounted,

the

Coupler

Adaptor

Ring.

2.

Screw

the

Microphone

Cartridge

Type

4144,

without

protection

grid, to

the

microphone

socket.

2 ems

Coupler

6 ems

Coupler

3.

If

it

is

desir

ed to use

an

adapter

other

than

the

standardized

18

mm

ear

mould

substitute,

then

this

should

be

replaced

by

the

desired

one

, see

page

18

.

4.

Screw

the

Coupler

onto

the

micro-

phone.

NBI

Take

great

care

not

to

damage

the

diaphragm.

3a. Screw

the

Coupler

Adapter

Ring

onto

the

microphone

.

*)

4a.

Screw

the

Coupler

to

the

Coupler

Socket.

5.

Mount

the

earphone

to

be

tested

on

the

top

of

the

Artificial

Ear

.

6.

If

the

spring

arrangement

is

used,

adjust

the

height

of

this

arrangement

until

the

correct

force

to

the

earphone

can

be

read

on

the

scale.

Now

the

Artificial

Ear

is

ready

for

use,

and

the

indi

ca

ting

instrument

and

signal

to

the

earphone

must

be

connected.

*)

If

des

ir

ed,

the

Fron

t

Cover

DD

00

15 may

be

screwed

onto

the

Co

upler

Adapter

Rin

g.

(See Appendix).

Operation

of

a Complete Arrangement for the Testing

of

the Earphone.

Fig. 2.1

shows

a

typical

measuring

arrangement

used

to

check

the

frequency

characteristic

of

earphones.

4152

t7o¥<%'

Fig

. 2.1. Typical measuring arrangement for the production check

of

earphone

characteristics.

It

consists

of

a

Beat

Frequency

Oscillat

or

Type

1022 toge

ther

with

a Level

Recorder

Type

2305

and

a Meas

urin

g

Amplifier

Type

2606.

The

adjustment

of

the

different

ins

trum

e

nts

are

made

as

follows:

Adjustment

of

the Oscillator.

1.

Turn

the

toggle

switch

marked

POWER

to

"On"

and

adjust

the

frequency

scale

as

described

in

the

Instruction

Manual

for

the

Type

1022

under

"Operation".

2.

Set

the

frequency

scale

pointer

to

1000

Hz.

10

3.

Turn

the

switch

AUTOMATIC

SCANNING

to

"Off"

.

4.

Turn

FREQUENCY

INCREME

T

knob

until

the

pointer

of

the

incre·

mental

frequency

scale

is

at

"0

Hz

".

5.

Set

MODULATION

FREQUENCY

to

"Mod.

Off"

.

6.

Set

the

COMPRESSOR

SPEED

switch

to

"Comp.

Off".

7.

Turn

OUTPUT

LEVEL

until

the

pointer

of

the

indicating

meter

is

positioned

at

"12"

at

the

upper

scale.

8.

Set

MATCHING

IMPEDANCE

switch

to

"AU.".

9.

Set

ATTENUATOR

to

"120

mV",

or

another

desired

value

.

Connect

the

aUenuator

output

to

the

input

terminals

of

the

earphone

under

test.

Asse

mbl

e

th

e

Artificial

Ea

r

as

described

under

"Op

era

tion

of

the

Arti·

fic

ial

Ea

r

page

10, a

nd

u

se

th

e

co

upl

er

suted

for

th

e

ea

rphone

.

Adjustment

of

the

Measuring

Amplifier.

1. Co

nn

ec

t the

Condenser

Microphone

of

the

Artificial

Ear

to

th

e

Measur·

ing

Amplifier,

as

shown

in

Fig.

2.1.

2.

Set

th

e

co

ntrols

of

th

e

Measuring

Amplifier:

INPUT

"

Preamp.

"

METER

FUNCTION

"RMS

Fast

"

IN

PUT

SECTION

ATTEN

UA

TOR

"0.1 V"

OUTPUT

SECTION

ATTE

UATOR "x 1"

Select

th

e

pushbuUons

"

Ref

50

mV

RMS"

"2

2.4

Hz

HP"

"2

2.4

kHz

LP

"

No weig

hting

network

should

be

selectel

and

th

e

RECORDER

output

s

wit

ch

should

be

in

position

"AC".

3. S

witch

POWER

"

On

"

and

allow

30 sec

to

warm

up.

4.

Determine

th

e

microphone

Op

en

Circuit

Se

nsitivity

from

its

calibration

c

hart.

5. W

ith

met

er

scale

SA

0039

fitt

ed,

th

e

met

er

defl

ec

tion

pr

o

du

ce

d

by

th

e

reference

vo

lta

ge

should

be

adjusted

to

indicate

the

op

en

circuit

sensitivity

of

th

e

mi

c

rophon

e

in

u

se

on

th

e a

uxilliary

red

scale

"Micr

.

Sens

> (Note

that

if

a

preamplifier

other

th

an

th

e 2619 is

us

e

d,

it

is

necess

a

ry

to

correct

th

e mi

cro

phon

e

sensitivity

for

th

e

pr

ea

mplifier

gain

and

th

e

capacitive

loadin

g

of

the

pr

ea

mplifi

er

as

described

in

the

instruction

manual

for

th

e

pr

ea

mplifier).

6.

Cancel

th

e

selection

of

"

Ref

50

mV

RMS»

and

the

Measuring

Amplifier

is

ready

for

use.

It

The Level Recorder.

50 dB

potentiometer

is

used.

1.

POWER

and

MOTOR toggle

switches

to

"On".

2.

POTENTIOMETER

RANGE

to

"50".

3.

RECTIFIER

RESPONSE

to

"RMS".

4.

LOWER

LIMITING F'REQUENCY

to

"

20

Hz".

5.

WRITING

SPEED:

160

mmlsec

(large figures)

with

50

mm

paper,

or

315

mm/sec

(small

figures)

with

100

mm

paper.

6.

PAPER

SPEED

to

"3

mm/sec"

(small figures).

7.

Set

the

Synchronizing

Gear

Lever

X

in

its

outer

position

.

Make

sure

that

the

Lever

is

pulled

completely

to

the

out

position

by

moving

the

grooved

finger

wheel

Z

to

a

nd

fro

at

the

sa

me time

as

pulling. (

The

actual

paper

drive

speed

now

corresponds

to

the

small

figures

marked

around

the

PAPER

SPEED

knob).

See

Fig

. 2.

2.

Drive

Shofts

pI 5

Fig. 2.2.

Front

and

side

view

of

the

Level

Recorder

Type

2305.

pI

8.

PAPER

DRIVE

to

"Start"

and

"Forward"

commencing

the

paper

to

run,

this

will

continue

until

the

built-in

automatic

single

chart

stop

switch

declutches

the

drive

mechanism

(one

chart

length

or

less).

9.

By

means

of

the

finger

wheel

Z (Fig. 2.2)

adjust

the

paper

until

the

recorder

stylus

is

on

the

mark

20 Hz

of

the

pre-calibrated

recording

paper.

10.

Lower

the

pen.

Adjust

the

knob

OUTPUT

LEVEL

on

the

Beat

Frequency

Oscillator

until

a

sound

pressure

level

of

100 dB

in

the

Coupler

call

be

measured

on

the

Measuring Amplifier.

By

means

of

INPUT

POTENTIOMETER

and

INPUT

ATTENUATOR

of

the

12

Level

Recorder,

the

deflection

of

the

pen

is

adjusted

to

the

40

dB

line

of

the

recording

paper.

Turn

the

frequency

scale

pointer

of

the

Oscillator

to

20 Hz,

that

is

to

a

position

corresponding

to

the

position

of

the

recorder

stylus

on

the

pre-

calibrated

recording

paper,

and

set

AUTOMATIC SCANNING

switch

to

"On".

Now

the

recording

can

be

started

by

pressing

down

the

SINGLE

CHART·

CONT. RECORD.

pushbutton

for

a

short

while

and

then

release

it,

and

the

frequency

characteristic

will

be

recorded

automatically

on

the

paper

strip.

Normally

earphones

are

measured

under

the

conditions

described

above

which

are

constant

voltage

conditions

.

However,

by

connecting

a

resistor

in

series

with

the

earphone

and

using

the

voltage

drop

across

this

resistor

to

control

the

compressor

circuit

of

the

1022

constant

current

conditions

can

be

obtained

for

the

test.

Artificial

Ear

in

Connection

with

the

Precision

Souud

Level

Meter.

As

amplifier

and

indicating

meter

it

is

possible

to

use

the

Precision

Sound

Level Meter

Type

2200.

The

Artificial

Ear

and

2203

make

a

very

handy

combination

for

audiometer

control,

and

the

measuring

set

up

must

be

adjusted

in

the following

way

: Assemble the Artificial Ear

as

described

under

"Operation

of

the

Artificial

Ear"

page

10

and

use

the

coupler

suited

for

the

earphone.

Feed

the

signal

to

the

earphone,

for

example

from

an

audiometer

Fig. 2.3,

or

another

generator.

Connect

the

Artificial

Ear

to

the

Sound

Level

<>

(; 0

00

0 0 0

udiometer 2203

-163752

Fig. 2.9. Measuring set-up used for audiometer control.

Meter. See Fig. 2.4. Remove

one

of

the

rubber

feet

from

the

Artificial

Ear

and

screw

it

under

the

Sound

Level

Meter

(see Fig. 1.3b).

Adjust

the

Sound

Level Meter

as

follows (Fig. 2.5):

1.

Pull

out

knob

1

and

turn

it

to

position

"Batt".

The

meter

pointer

should

now

deflect

to

within

the

red

area

marked

BATTERY

indicating

that

the

batteries

are

alive.

If

it

does

not,

replace

the

batteries.

2.

Turn

knob

to

"Lin".

3.

Turn

knob

2

fully

anti

clockwise.

13

Fig. 2.4. Artificial Ear and Precision Sound Level Meter

in

combination.

4.

Turn

knob

3

fully

clockwise

.

The

mark

"Ref"

appears

in

the

red

circle

to

the

right.

5.

The

meter

pointer

should

now

deflect

to

a value,

on

the

upper

red

scale,

equal

to

the

k-value

obtained

from

the

microphone

ca

libration

chart.

If

it

does

no

~

,

adjust

the

SENSITIVITY

ADJUSTMENT

by

means

of

a

screwdriver,

until

the

said

condition

is

obtained

.

NOTE:

The

in

s

trument

should

warm

up

for

ap

pro

ximate

ly 15

seconds

before

calibration.

6.

Turn

knob

2

clockwise

until

th

e

meter

pointer

deflects

between

0-10

dB,

a

nd

the

so

und

pressure

level in the Artificial

Ear

is

measured.

7.

If

th

e

meter

pointer

does

not

deflect

when

knob

2 is fully clockwise,

then

turn

knob

3

counter

clockwise,

until

th

e

point

er

defl

ects

between

0--10

dB,

and

the

sound

pressure

level

can

be

mea

s

ur

ed.

14

Further

it

is

possible

to

us

e

the

Sound

Le

vel Meter

in

connection

with

the

Level

Recorder

Type

2305

for

automatic

recording

of

the

frequency

characteristic

of

an

ea

rphone

.

The

Sound

Level

Meter

must

be

adjusted

as

described

above

item

1

to

5,

and

knob

2 (

Fi

g.

2.

5)

is

turned

clock-

wise

until

100

appears

in

th

e

red

circle

to

th

e

ri

g

ht.

Operation

s

of

the

Beat

Frequency

Oscillator

Type

1022 a

nd

th

e Level

Recorder

Type

2305

are

described

under

"

Operation

of

a Complete

Arrangement

for

the

Testing

of

the

Earphone".

Sensitivity

Red

Circle

Adjustment

Knob 2

(black knob)

Knob 3

(transparent knob)

MeterLight

Fi

lter

Input Output Socket

Filter

Output

Pilot

Lamp

(flashing

when

on)

Knob 1 f6(7d>1

Fig. 2.5. The Sound Level Meter

with

identification

of

knobs.

16

3.

Application

Automatic Recording

of

Harmonics in Earphones.

By

using

the

Artificial

Ear

Type

4152

together

with

an

oscillator

with

a

low

distortion,

such

as

the

B & K

Beat

Frequency

Oscillator

Type

1022,

and

the

Audio

Frequenc

y

Spectrom

eter 2113,

an

equipm

e

nt

is

obt

a

in

ed

for

me

asuring

harmonics

produ

ced in

earphones.

If

the

Spe

ctrometer

a

nd

th

e B.F.

O.

are

16

2113

2619 4152

Fig. 3.1. Measuring arrangement for automatically measuring frequency

characteristics and harmonic distortion of earphones.

c

ombin

ed

with

th

e B & K Level Re

cord

er Type 2305

the

me

asuring

arrange-

me

nt

ca

n

now

autom

a

ti

ca

lly r

ec

ord

th

e ha

rmoni

cs

of

th

e device

under

test

on

frequ

ency

ca

librat

ed paper. A ve

ry

c

ommon

us

e

of

thi

s

combination

is

in

the

tes

tin

g

of

fr

eue

nc

y char

ac

te

ri

stics

with

ass

oci

ated ha

rmoni

cs

produced

in

ear

ph

ones. A m

eas

urin

g

se

t-up

s

uit

a

bl

e

for

this

purpo

se

is

sk

e

tched

in

Fig. 3.1.

DODDOODOD

OD

OOQODOOODOODDQDOOOODODDODoaOOOOOOODDOOO

--

Measuring

Of

"

..

fundamentgl

CI

..

in

egrl}hooe

·2nd. harm.'

3nd. harm.

1

00

1000

Fundamental

-

Noise

Level

",

_",

e

u.,.

10000 1,,

1(2111

)'" c

u..

,

-163751"

Fig.

9.2. Typical recording

of

frequency characteristics

("Fundamental")

Wld

harmonic signals

in

earphones.

In

Fig.

3.2

are

given

the

recorded

results

of

measuring

the

fundamental

together

with

the

harmonics

produc

ed

in

an

e

arphone

measured

by

setting

the

filter

switch

on

the

Spectrometer

so

that

it

runs

ah

e

ad

of

the

frequency

scanning

of

the

BFO,

the

selected

space

difference

being

in

accordance

with

the

harmonic

which

is

going

to

be

measured.

By

means

of

the

facility

included

in

the

Level

Rec

order

Type

23(}5,

which

allows

th

e

recording

paper

to

be

reversed

by

one

chart

length

without

loosing

the

synchronization

between

the

BFO

a

nd

th

e

Spectromet

e

r,

the

harmonics

are

readily

recorded

on

the

same

chart

as

the

fundamental.

Some

Typeical

Examples

of

Coupler

Adaptation.

As

mentioned

previously

the

ear

mould

substitut

e

of

the

normal

2

cm

3

coupler

may

be

repl

a

ced

by

special

arrangements

.

Figs

. 3.3

to

3.6

show

some

ty

pical

exa

mpl

es

of

thi

s kind

of

adap

tat

ion.

Fig.

3.3

makes

use

of

the

ear

mould

substitute

such

as

is

used

for

the

measurement

of

hearing

aids

with

coupling

pieces.

The

hearing

aid

shown

is

of

the

type

fitted

into

sp

e

ctacle

frames

.

In

Fig.

3.4

the

rubb

er

seal

is

replaced

by

a

special

fitting

for

measurements

on

hearing

aids

wh

en

the

coupling

pieces

are

removed

.

When

hearing

aid

coupling

pi

e

ces

are

provided

with

ear

inserts

an

arrange·

ment

as

shown

in

Fig

. 3.5,

may

be

used

for

the

measurement.

17

2

em'

coupler used for

fr.e

field measurement

on

spectacle-type hearing

aid

Fig. 3.3. Coupler

mounting

for measurements on hearing aid earphones

with

coupling pieces.

/$8231

Flexible connecting

tube

mounted

on adapter.

The

adopter is

in

this

case

replacing

the

ear

insert

Fig.

3.4. Coupler

mounting

for measurements

on

hearing

aids,

speelable tl/pe,

coupler directly attached

to

the

sound tube.

18

Fig. 3.6

shows

how

another

type

of

ear

insert

can

be

fitted

to

the

coupler

.

The

var

ious special

adap

ters sh

own

in

Fig. 3.4

to

3.6 are

not

supplied

by

B &

K,

but

can

easily

be

made

by

the

user

for

his

own

special

purposes.

Adopter provided

with

hole

for

ear

insert

Fig.

3.5. Coupler mounting for measurements

on

hearing aid earphones with

special rubber insert

s.

Example of

mounting

of

earpiece

in

2cm

3

coupler

Fig. 3.6. Coupler mounting for measurements

on

hearing aid earphones with

moulded ear insert.

1-9

BRUEL & KJAER 4152 User guide

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