BRUEL & KJAER 2206 User manual

Instruction Manual
Precision Sound Level Meter Type 2206
033-0120
2206
Small, lightweight, Precision Sound Level
Meter fulfilling requirements of IEC 1 79 .
+ Bri.iel & Kj~r

PRECISION SOUND LEVEL METER
TYPE 2206
Revision October 1 977

CONTENTS
1. INTRODUCTION AND SPECIFICATIONS (PRODUCT DATA) ................................................. 1
2. CONTROLS .................. .. .. .. .... ........ .... .... ........ .... .......... .. .. .............................. .. .................... 5
3. OPERATION . ........ .... .... .. .. .. ... ........ . .. .............. .. .. ...... .......... .. ........ .. ...................................... 7
3.1. GENERAL CONSIDERATIONS ............. ........................................... . ........... 7
3.2. BATIERY CONSIDERATIONS .... ................................................. . .............. . 7
3.3. MOUNTING OF MICROPHONE ....... . ...................................................... .. .. . 7
3.4. CALIBRATION .... .. . ....... . ........................................................................... 8
General ............ . .......................................................................... . .. ......... 8
Calibration with Microphone Type 4148 ..................................................... 8
3.5. SOUND MEASUREMENTS ......................................................................... 8
General ................................................................................................... 8
Procedure
for Sound Measurements ........................................................... 9
3.6. LOCKING OF CONTROLS .......................................................................... 9
Locking
the Attenuator .......................................................................... .... 10
Locking the Weighting Networks ................................................................ 11
3. 7. CHARACTERISTICS ....... . .......................................................................... 12
Use
of A & C Weighting Networks ............................................................. . 12
Output Socket .......... ...... ............................. ; ............................................ 13
Frequency Response ............................ . ..................................................... 13
Influence of Reflections ..... . .............................................................. . ........ 13
Directional Characteristics ......................................................................... 13
Effect
of Vibrations .. .. . .............................................................................. 15
3.8. USE WITH PINK NOISE TEST RECORD OR 2011 ................................ ......... 15

FEATURES 2206:
• Fulfils IEC R 1 79 and
ANSI S 1.4 - 1971 Type 1
for precision sound level
meters
• Special B &K 1 /2"
Condenser Microphone
• A and C-weighting
networks
• Linear position
FEATURES 2208:
• Hold circuit for maximum
A-weighted noise level
• Store
for held value
•
Fulfils IEC R 1 23 and
ANSI S 1.4-1971 Type 2
for general purpose sound
level meters
• B & K 1" Piezoelectric
microphone
• A-weighting network
• Easy conversion for
"Precision" measurement
COMMON FEATURES:
• Fast and Slow meter
damping
• Dynamic range up to
140 dB SL ( 130 for 2208)
• 0 utput for Tape Recorder,
or Level Recorder
• Light weight approximately
0,8 kg (28 oz)
• Large tilted meter for easy
reading
USES:
• Sound
measurements in
industrial work areas to
check for health hazards
• Traffic noise measurement
16-085
types 2206 and 2. 208
Miniature Sound Level Meters
2206
• Building noise, insulation
and distribution surveys
• Community noise surveys
• Product noise
measurements for
development and quality
control
•
Measurements on
electroacoustic systems
These miniature sound level me-
ters provide a quick and reliable
method of determining noise level.
They are the ideal tools for noise
abatement engineers, traffic police,
2208
industrial hygienists, public health
inspectors and others whose con-
cern it is to keep noise at a toler-
able level in our modern industrial
society.
Portable sound level meters can
be used
profitably for an initial sur-
vey of noisy environments and
then , where necessary, a more de-
tailed analysis can be made using
more complex instrumentation . The
big advantage·
of these miniature
meters however, is that their simple
operation makes them suitable for
use ·by people without the technical
knowledge to handle the more com-
plex equipment.

Battery 1.5 Vo------<rr
On
OQff
'2206 ----------,
I Condenser
I Microphone Polarization Voltage
Adapter
(Source
follower)
~~ (Type~4-1_48_) ...__-1
L- -- - _...._____. J
~ Pl.,oeloct~ ~ - - - -~
Microphone
I (Type 4117) I
I I
l220!_ _______ j
Meter
Voltage Voltage
Converter Regulator
~~-----
Hold
1
I L-----'
I
lsi ow
I
I
2206
l._f
208
only _j Rectifier
Output
740632
Fig.1. Block diagram for the miniature sound level meters
Description
The Type 2206 Precision Sound
Level Meter and Type 2208 Noise
Event
Meter are two variations of
the same basic instrument. Both
meet the internationally apprbved
standards
for general purpose
sound level meters, while the Type
2206 also satisfies the require-
ments for precision sound level me-
ters.
Various special features have
been
included in the two instru-
ments so that a sound level meter
can be obtained with only those fea-
tures necessary for its particular
use. This gives an instrument that
is both inexpensive, and simple to
operate. Reference to the block dia-
gram in Fig.1 shows the similarities
and differences between the instru-
ments.
The microphone normally sup-
plied with the Type 2208 is the 1"
diameter Piezoelectric Microphone
Type 4117. This is a high quality,
low cost measuring microphone de-
signed primarily for use in general
purpose sound level meters. Its
high capacitance allows it to be
used
with amplifiers having moder-
ate input impedance to give ade-
quate
low frequency performance.
The high capacitance also permits
the use of relatively long connection
cables between the microphone and
the
sound level meter (reducing the
2
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Briiel & Kj(8r Potentiometer Ronge, __ dB Ro<tilier, __ L- lim. Froq. :_Hz 'VIr . Spoed: __ mmf- . Popo< Spoed:_....,..c.
C-hogon 50 25 , 10 75
dB dB Condenser Microphone 4148:=f dB dB
860
Moosuring Obj.:
Microphones Piezoelectric Microphone 4117
~~u~~n~:~;~ 30 15
Meters
()0 Free Field
---2010
---·105
~
o.u:._
Sign.: 0 0
430
10dB
2 15
Qp 1124 10
20 Hz 50 100
200
500 1000 2000 5000 0 0
10000 20000 40000 D A B C lin.
Multiply Fre<{vency Scole by
Z.ro t.....l:
1612/2112 A B C lin. 17 2221
Fig.2. Typical frequency response curves for the microphones
possibility of reflections from the op-
erators body) without serious loss of
sensitivity. A typical frequency re-
sponse
curve is shown in Fig.2. The
performance of the 2208 with this
microphone is in accordance with
IEC R1 23 for general purpose
sound level meters.
The Type 2206 features a special
8 &K condenser microphone sys-
tem, and the drcuitry for 2208 has
also been designed to accept this
system. The Type 4148 1 /2" Con-
denser Microphone requires 28 V
polarization voltage, and was devel-
oped for these miniature instru-
ments. It is mounted on the meter
by means of the UA 0208 Adaptor,
and when fitted, the requirements
of IEC, ANSI and DIN for precision
sound level meters are met. The
Adaptor contains a source follower
(FET) to transform the high imped-
ance of the condenser microphone
into a low output impedance. A typi-
cal frequency response curve for
the 1 /2" Condenser Microphone is
also shown in Fig.2. When fitted
with the 1 /2" Condenser Micro-
phone and Adaptor, the 2208 be-
comes a Precision
Sound Level Me-
ter in accordance with IEC, ANSI
and DIN.
The Piezoelectric Microphone, or
Condenser Microphone and Adap-
tor, can be replaced by a JJ 0037
Adaptor, which permits connection
with miniature coaxial cables, thus
allowing the sound level meters to
be used as indicating instruments
for 8 & K accelerometers. It should
be noted however, that when the

2208 is used for viQration measure-
ment , the weighting network will
influence the readings making accu-
rate calibration extremely difficult.
Nevertheless, the accuracy is suffi-
cient for quick estimates of vibra-
tion level.
Two attenuator stages are pro-
vided, and these are connected to-
gether so that the 10 dB steps in
range are obtained with the best
possible signal to noise ratio. To
simplify readout, the range selected
is displayed in a window on the me-
ter scale . On the 2206 a separate
push-button switch operates in the
first amplifier stage. This can be
used
to increase the measuring
range quickly by 10 dB, regardless
of range setting, to allow for sud-
den high levels. The range control
switch on both instruments can be
locked internally , in any of its ten
positions (30 to 120 dB), to prevent
inadvertent range changes when
the instrument is to be used by in -
experienced personnel . The use of
the "+ 10dB" button is retained
while the range selector is locked.
Type 2206 is equipped with the
A and C-weighting networks and
has, in addition, a linear position.
The 2208, being equipped with a
maximum hold circuit, has only the
widely used A-weighting network.
The network selector switch can
also be locked to prevent accidental
changes which could cause false
readings. The A and C-weighting
characteristics are shown in fig . 3.
The second amplifier stage feeds
the rectifier and an AC output termi-
nal. The output is used with Tape
Recorders
or Level Recorders. (See
Fig.4) .
The rectifier gives correct RMS
values within 5% for signals with
crest factors up to 3 at full scale me-
ter deflection . The internationally
standardized "Fast" and "Slow " me -
ter damping characteristics are pro-
vided. The meter is a DC moving
coil instrument with ribbon suspen-
sion . The angled meter scale is eas-
ily read, with graduations from
-1 0 dB to + 10 dB over a 5, 5 em
(2,25 in) scale length .
In
the Type 2208, a special cir-
cuit can hold the maximum meter
deflection that occurs during a
measurement. This feature is partic-
ularly useful for measurements of
rapidly changing levels such as traf -
Bruel & Kj mr Bruel & Kjmr Bru el & Kjaer
oo ooooooooo o ooooooooooooooooooooooooooooooooooooo
ruei&Kjcer Potenti ome te r Rang e: -- dB Re ctifier:- - Low er Lim Fr e q. :- Hz Wr Sp eed :- mm / s ec Pape rSpeed :- mm /sec.
Cop e nhag en 50 25 10 75
+
dB dB
dB dB
40 20
8 60
M e asur i ng Ob j .: f== f:= C
--- 3015
6 45
- -- 2010
4 30
10 dB
-- - 10
2 15
R ec . No .:
Dat e __ = f:= A
Sign .: __ 0 0
10 20 Hz 50 100
200 500 1 000 2000
Qp 11 24
M ul ti pl y Fre qu en cy Sca le by Zero Level:
Fig.3. Typical A and C-weighting characteristics
74 0634
Miniature Sound
Level Meter
2206 or 2208 Level Recorder 2306
Fig.4. Portable set-up for recording
levels
fie noise. When the METER RESET
button is depressed the meter de-
flection is cleared, and the instru-
ment is ready for the next measure -
ment. In addition , a held level can
be
stored, to prevent loss of the
reading if subsequently a higher lev-
el
occurs . This is achieved by turn-
ing the Function Selector to
"Store", which grounds the incom-
ing signal to prevent it from reach-
ing the meter . The hold circuit can
be by-passed
allowing the Type
2208 to be used as a general pur-
pose sound level meter.
Another version, the Precision
Sound Level Meter Type 5606 is
available on special order for vehi-
cle noise measurements to ISO
R 362 (moving vehicles) and the pro-
posed ISO method for noise meas-
urements on stationary vehicles.
+ 1
dB 0
- 1
c - 2
0
· ;;
Deflection in
Similar to a Type 2208 with a Con-
denser Microphone, the Type 5606
features a speical max . hold circuit
that can be externally controlled.
This enables a tachometer to trigger
the hold function when a preset en-
gine speed is reached .
The curves in Fig.5 show the rela-
tive meter deflections to be ex-
pected
on the 2208 in position
"Fast" with MAX. RMS HOLD
switched to "On" and "Off" for dif -
ferent impulse durations. The dot-
ted line indicates that in position
"fast", HOLD "Off'' , the meter de-
flection will return to the real value
for a steady state signal with dura-
tion longer than about 1 second.
The overshoot in position "Fast",
Hold "Off" is as specified by IEC
R 179.
Calibration may be performed
with either the Type 4230 Sound
Level Calibrator (94 dB at 1000Hz).
or with the Type 4220 Pistonphone
(1 24 dB at 250Hz) . Because the
2208 sound level meter registers
the . weighted sound level, a correc-
tion factor must be applied when
using the Pistonphone with this in -
strument .
------
- ........ ._
~-----
~
~
./
~
- 3
't
-4
pos . " Fast", Hold "on" ,
~
0
Q)
- 5
~
- 6
~
- 7
· ~
-8
Q;
a: - 9
-10
- 11
- 12
- 13
-14
~v
//
/A
//
"
//
Ma x. deflection in pos . "Fa st ", Hold "off"
//
//
//
/V
//
ff'
20
50 100 200 500
msec . 1
sec .
171007
Impulse Duration
Fig.5 . The relationship between Impulse Duration and Relative Meter Deflection for the 2208
3

Specifications
B & K Type Number
2206
220B
Measuring Range:
39 to 135 dB(A)
32 to 1 30 dB(A)
51
to 135 dB(C)
58 to 135 dB(Lin)
Signal to Noise Ratio:
Better than 5 dB for the lower limit .
Weighting Networks:
A and C plus Linear
A
(20Hz to 16kHz(± 3 dB))
Meter Scale:
Graduations from -10 dB to+ 10 dB. Range displayed in window
Meter Damping:
Fast and Slow to IEC standard 179, ANSI S1. 4-1971 and DIN 45 633
Rectifier Accuracy:
± 5% for signals with crest factors less than 3
Hold Circuit Accuracy:
Held
meter deflection
corresponding
to
maximum
RMS "Fast" response ± 2 dB
Better accuracy with durations longer than 1 s (see
Fig.5)
Hold Decay:
Less than 1 dB in 5 minutes at 25°C (77°F)
Store:
Any held value can be stored
Reset: Push button resets meter
Input Impedance: > 2000 MO / I 40 pF
10 MO / / 140 pF
output Impedance: Less than 50 0
Minimum Load Impedance :
50000
Output Voltage:
Approximately 2,5 V RMS for full scale meter deflection
Maximum Output :
20V peak to peak
Distortion:
Less than 1% for full scale meter deflection
Noise: (A-weighted) Less than 3,1 t-N relative to input with 17 pF across Less than
1,2/.N
relative to
input with 4000 pF
input
across input
Microphone Type: B & K 1/ 2" Condenser Type 4148
B & K 1" Piezoelectric Type 4117
(28 V DC polarization Voltage)
Microphone Frequency Linear ± 2 dB between 4Hz and 16kHz for incidence
Linear ± 3 dB between 4Hz and 10kHz for incidence
Response: perpendicular to the diaphragm in a free field perpendicular to the diaphragm in a free field
Individual calibration curve supplied Individual calibration curve supplied
Microphone Sensitivity: Approx . 14 mV per N/ m2
Approx . 3 mV per N/ m2
Microphone Capacitance:
17 pF 4000 pF
Microphone Temperature
- 0,015 dB/ °C (-0,0083 dB /° F)
Coefficient :
Battery Type: Single " C" cell, IEC R 14 . (B & K order number QB 0009)
Battery Life: 10 hours continuous operation
5 hours continuous operation
Operating Temperature :
-10 to+ 50°C (+ 14 to+ 122°F)
Storage Temperature (battery
-20 to + 70°C (-4 to + 1 58°F)
removed):
Humidity Range:
Up to 90% relative humidity
Dimensions: Length:
235 mm (9,2 in)
186 mm (7,3 in)
Width: 84 mm (3,3 in)
84 mm (3,3 in)
Height:
51 mm (2,0 in) 51
mm (2,0 in)
Weight: 0,83 kg (29 oz) including battery
0,8 kg (28 oz) including battery
Accessories Included : Condenser Microphone 4148
Piezoelectric Microphone 4117
Microphone Adaptor UA 0208
Windscreen UA 0207
Windscreen UA 0237
Carrying Case KE 0060, Pistolgrip Handle DH 0129, Wrist Strap DH 0128 , Screw Driver QA 0001
1,5 V Battery IEC type R 14 ("C" size) QB 0009
Accessories Available:
Set of 6 spare Windscreens UA 0254
Set of 6 spare Windscreens UA 0253
3 m Extension Cable AO 0063 6 m Extension Cable AO 0061
Input Adaptor for accelerometer cable JJ 261 5
Condenser Microphone 4148
Microphone Adaptor UA 0208
Set of 6 Windscreens for 1/ 2" Microphone UA 0254
Sound Level Calibrator 4230, Pistonphone 4220 , 1,2 m Output Cable AQ 0037, Tripod UA 0049
Input Adaptor for accelerometer cable JJ 0037
4

2. CONTROLS
The controls of the Precision Sound Level Meter Type 2206 are shown in Fig. 2.1.
Power__..
switch
Battery
___ ..
housing
MICROPHONE:
PROTECTION GRID:
MICROPHONE ADAPTOR:
Microphone
Microphone
adaptor
Range indicator
Fig. 2. 1. Controls of the 2206
Half inch Condenser Microphone Type 4148.
173265
Sensitivity
adjustment
Protects the diaphragm of the microphone from physical damage. This
grid should not be removed except when the microphone is to be fitted
with a Nose Cone or Rain Cover or for inspection of the diaphragm.
DO NOT TOUCH THE DIAPHRAGM WITH ANY OBJECT.
The Condenser Microphone screws directly onto the Microphone
Adaptor Type UA 0208, which in turn screws directly into the main
body of the instrument. (See section 3.3).
5

SOCKET &
INSULATING WASHER:
POWER SWITCH:
WEIGHTING NETWORK:
SELECTOR:
RANGE SWITCH:
+ 10 dB BUTTON:
OUTPUT SOCKET:
SENSITIVITY
ADJUSTMENT:
TRIPOD BUSHES:
6
See Section 3.6.
The functions of this four position switch are :-
"Off.". No power is supplied to the instrument with the switch in this
position.
"Batt.". Provides a battery check. If the deflection of the meter needle
be below the region marked "Battery" then the battery must be re-
placed. (See
section 3.1.).
"Fast" & "Slow". Give the "fast" and "slow" meter responses respec-
tively.
"A", "C". Selects one of the standardized frequency weighting net-
works . (See section 3.7.).
"Lin . ". Gives a linear frequency response within the range limits of
the instrument.
A ten position switch controlling the gain of the input amplifier in
10 dB steps from 30 dB to 1 20 dB. The RANGE SWITCH setting ap-
pears
in the "RANGE INDICATOR" window on the meter scale.
Depressing this button adds a further 10 dB to the measuring range.
When used, 10 dB must be added to all readings.
A standard microsocket accepting B & K cables fitted with microplugs
(e.g. AO 0037) (see section 3.7.).
An adjustable screw potentiometer used for calibration purposes, pro-
viding a change in the gain of the amplifier of 12 dB (see section 3.4.).
Two quarter inch bushes permit the 2206 to be attached to a tripod, a
pistol grip or a wrist strap.

3. OPERATION
3.1. GENERAL CONSIDERATIONS
When connecting or disconnecting to microphone be certain that the power is switched
off. In dry weather static electricity should be discharged from one's body before one fits
or removes the microphone. Only light finger torque should be applied when connecting
the microphone and extension rod together. Dust and foreign bodies should be kept off
the diaphragm, which must not be touched with any object. If the diaphragm must be
cleaned then the task should be done extremely carefully using cotton wool . Dry and
preferably warm conditions are recommended for storing the instrument.
3.2. BATTERY CONSIDERATIONS
The 2206 is powered by a single 1 ,5 V battery ("C" Cell, or Type RT4 in IEC publica-
tions). To insert the battery, unscrew the battery housing cover using a coin then place
the battery inside with the central (+) contact pointing outwards. Replace the housing
cover, but do not screw it back too tightly.
A good quality dry cell gives ten hours of continuous operation. The battery should be
removed, if the instrument is not going to be used for a long time, to prevent possible
battery leakage.
3.3. MOUNTING OF MICROPHONE
The condenser microphone normally supplied with the 2206 is the 4148. This micro-
phone has a nominal capacitance of 17pF.
A
high impedance Input Adaptor (UA 0208) is necessary to match the small capacitance
of the microphone to the rest of the circuitry. The UA 0208 contains a high impedance
(2000 M 0 in parallel with 50pF) field effect transistor (FET) input circuit. A special
cable,
AO 0063, is available for insertion between the meter and adaptor UA 0208 so
that the microphone can be used well away from the meter if required.
Cables cannot be used between the microphone cartridge and the adaptor because of
the large capacitance of a cable compared to that of the microphone. A flexible swan
neck extesion (UA 0196) can be used, however, after first removing the insulating
washer on the 4148, which is there to prevent the microphone from being inadvertently
connected to the wrong polarisation voltage via one of 8 & K preamplifers designed to
supply 200 volts polarisation. ·
In all
applications where there is a risk of water condensing inside the microphone a De-
humidifier UA 0308 should be inserted between the microphone and the Input Adaptor
UA 0208.
7

3.4. CALIBRATION
3.4.1. General
The meter and microphone are calibrated together before they leave the factory to give
correct readings. The calibration is stable with time but can change due to the effects of
impact or adverse conditions . Frequent calibration should not be necessary. Certain meas-
urement codes of practice, however, specify how often equipment should be calibrated.
The 2206 may be calibrated by placing over the microphone an acoustical source
which produces a steady, known sound pressure level.
Either the Sound Level Calibrator Type 4230 or Pistonphone Type 4220 is recom-
mended. The 4230 generates 94 dB (± 0,25 dB) at a frequency of 1000Hz while the
4220 generates 124 dB (± 0,2 dB) at a frequency of 250Hz. Detailed descriptions of
these calibrators are to be found in their respective Instruction Manuals .
3.4.2. Calibration with Microphone Type 4148
The calibration procedure when the 2206 is used with the microphone with which it is
normally supplied (Type 41 48) is as follows :
1. Attach the microphone, extension rods or cables and adaptors by screwing them to-
gether finger tight. (See section 3.3.). These must be included in the calibration as
they all affect the sensitivity.
2. Turn the POWER SWITCH to "Batt." and check the battery voltage: Then set the
switch to "Fast" and the WEIGHTING NETWORK SELECTOR to either "C" or "Lin." .
3 . Set the RANGE SWITCH to either "90"dB if the Sound Level Calibrator Type 4230
is being used or "120"dB if the Pistonphone Type 4220 is being used. Allow about
25 seconds for the circuits to charge up.
4. Fit the half inch adaptor onto the acoustic calibrator then place the calibrator snugly
over the microphone . Switch on the calibrator and hold it steady on the micro-
phone .
5.
Adjust if necessary the screw of the SENSITIVITY ADJUSTMENT with a small screw-
driver to give a meter reading of either "+ 3,8" (equivalent to 93,8 dB) for the 4230
or to give a reading of the value on the calibration chart (corrected if necessary for
barometric pressure) for the 4220. (See also the relevant Calibrator Instruction Man -
ual).
3.5. SOUND MEASUREMENTS
3.5.1. General
8
The accompanying booklet entitled Measuring Sound should be read through before pro-
ceeding with measurements as it contains much useful general information on the sub-
ject. One or two points should perhaps be emphasized. Ensure that the microphone has
the required dynamic range, frequency range and directional characteristics. Always use
a windshield for outdoor measurements and in a dusty environment.
Various nose cones are available for reducing wind noise as well as dehumidifiers. En- ·

sure that the measuring pos1t1on, is suitable and hold the Sound Level Meter at arm's
length or mount it on a tripod pointing towards the sound source to minimize reflections
from the operator's body. Finally make sure that the background noise is not so high as
to make the measurements meaningless. For a full treatment of noise measurement
techniques, the reader is referred to B & K publication "The application of B & K equipe-
ment to Acoustic Noise Measurements".
3.5.2. Procedure for Sound Measurements
The 2206 is very simple to operate. To obtain an accurate sound level reading, it is only
necessary to follow this straight forward procedure .
1.
Screw pistol grip to the tripod bush
2. Check
that the microphone and Input Adaptor are firmly screwed onto the 2206 .
3. Turn the POWER SWITCH to position "Batt." and check that the pointer lies within
the red "Batt." region of the meter scale. If it does not, then the battery should be
replaced (see section 3.1.).
4.
Set the RANGE SWITCH to a high value, to avoid the possibility of overloading the
meter when switching on .
5.
Select a meter response time by turning the POWER SWITCH to either "fast" or
"slow".
6. Allow about 25 seconds for the circuits to charge up.
7.
If required, calibrate the meter as described in section 3 .4. Calibration is not nor -
mally required each time a reading is made,, unless the user's code of practise
states this explicitly.
8. Select the desired weighting ("A", "C" or "Lin . ") with the WEIGHTING NETWORK
SELECTOR.
9. Point meter at noise source and turn the RANGE SWITCH down until the meter
gives a reading on the Scale between the RANGE INDICATOR WINDOW and the
"1 0 dB" mark.
10 . The sound level is then the meter scale reading plus the figure in the window .
3.6. LOCKING OF CONTROLS
In some cases where measurements are to be taken by non-technical personnel, the in-
strument can be made more fool-proof by locking the controls . The attenuator RANGE
SWITCH and the WEIGHTING NETWORK SELECTOR may be locked in any desired posi-
tion, as described below .
For example, if measurements are always to be made with the A weighting network,
around 80 dB, the controls can be locked in these positions . The range of the meter will
then be 70dB (A). By pressing the " + 10dB" button, a further 10dB is added to the
range, i.e. the range with the button depressed would then be 80 dB (A)- 1 00 dB (A).
9.

3.6.1. Locking the Attenuator
10
" The procedure for locking the attenuator is as follows:
1. Unscrew and remove the microphone and adaptor.
2. Remove the screws which secure the front case of the instrument.(See Fig. 3.1 .).
Microphone c ~ mtact
__ __,.
Cover plate
Fig. 3. 1. Removal of Front Cover
3. Lift off the cover plate and spacing washer.
4. Remove the green front case of the instrument . Note that the "+ 10 dB" button fits
loosely into this case and that it could be lost unless due care is taken at this stage.
(Fig.3.2.).
~ocophooo Sockot
Elevated 0
Hexagon Screw
Spacing Washer
-- ..... ~ 4 ~
t._ _____ Range Knob Cover Fix i ng Screws ____ t.L......Jt
Fig. 3.2. Locking of Attenuators
17 11 86

5. Remove the knob of the RANGE SWITCH using a 1,5 mm hexa' gon ' key.
6.
Turn one of the hexagon screws two turns anticlock~ise. ·.
i· .
7. Set the RANGE SWITCH to the desired setting and position the knob of the RANGE
SWITCH so that the elevated hexagon screw engages the slot in the meter housing.
Lock the knob with the other screw. ·
8. Replace the front cover of the instrument, taking care that the "+ 10 dB" button is
correctly positioned.
9. Replace and secure the spacing washer and front cover plate.
10. Replace the microphone.
NOTE: It is advisable to mark by means of a self adhesive label that the RANGE SWITCH
of the instrument is locked. This will reduce the possibility of damage caused by forcing
the switch.
3.6.2. Locking the Weighting Networks
First follow the procedure in section 3. 6.1. for removing the outer cover. Having done
this, loosen the two nuts which hold the locking plate (Fig. 3.3.). Remove the locking
plate, select the network required and replace the locking plate with its pin set in the re-
spective slot. Fasten the nuts. Reassemble.
It may be advisable to put some adhesive tape over the switch to prevent it being forced
while it is locked.
Network Selector
Locking Plate
168226
Fig. 3.3. Locking of Weighting Network
11

3.7. CHARACTERISTICS
3.7.1. Use of A 8t C Weighting Networks
12
The A & C, weighting networks give the meter the overall frequency characteristics
shown in Fig. 3.4. The A and C weighting curves are internationally standardized by IEC
Publications 1 23 and 1 79 for general purpose and precision sound level meters, respec-
tively. They are used to make the sound level meter respond in a similar way to the hu-
man ear, at low, medium and high sound levels respectively.
+ 20
+ 10
0
~
-
..,..
v
-10
1/
A/
1/
-20
-30
-40
/
-50
-60
v
-70
10 2 5
A
~
~
--...
r.:;::::
c
v
2 5 2 5
Frequency Hz
Fig. 3.4. Response of A & C Weighting Networks
~
........
2
168217/1
The weighting network used for making a measurement should always be stated (e.g.
Sound level A= xdB, or Sound level= xdB (A)).
The
difference between the two responses is most noticeable for low frequencies. Thus
if a considerable difference is noticed between the readings with different weighting net-
works, it can be assumed that there are strong low frequency components present . A
very rough frequency analysis is performed in this way, by observing the differences in
the readings with the weighting selector switch in positions A or C.
Attenuator Weighting
Network
Position A c Lin.
30 6 --
40
16 4 2
50
20
14 12
60 36
24 22
70 45 34
31
80 33 32 34
90 43 43
36
100 49 49 40
110 43 43
36
120 49 49
41
Table 3. 1. Typical output to noise ratio (dB) for full scale meter deflec-
tion

3.7.2. Output Socket
This is a standard microsocket accepting B & K cables with microplugs (e.g. AO 0037).
Tape recorders or level recorders can hence be connected when noise signals need to be
recorded
for later evaluation. The load impedance should be at least 5 kO. Output vol-
tage for full scale deflection on the meter is approx 2,5 V RMS. Maximum peak value
10 V. Typical signal to noise ratios at the output socket are shown in Table 3.1.
3.7.3. Frequency Response
A typical free-field frequency response for microphone Type 4148 at 0° incidence is
shown in Fig. 3. 5. This curve is for the microphone mounted on a preamplifier (261 9)
with a diameter equal to that of the microphone cartridge. A similar curve is supplied in
the calibration chart which accompanies each microphone, and is the free field response
of that particular microphone. Reflection of sound causes diffraction effects to be noticed
when the reflecting surfaces are close to the microphone.
Meaauring Obj.
dE d
160
31 15 Free Field Response
Pressure Response 4
~'
1~ 5
Roc. No.:
Date:
Sign
.: 0 0 0
10 20
Hz 50 100 200 500 1000 2000 5000 10000 20000 40000 D A 8 C l1n.
<P 1124 Muhiply Frequency Scole by:
Zorol- __ Frequency (Hzl (1112121121 A 8 C U'690651'
Fig. 3.5. Typical free-field response of 4148
3.7.4. Influence of Reflections
If. pure tones, narrow band noise, or highly directional sound is being measured, it may
be desirable to separate the microphone and meter with extension cable AO 0063 so
that the microphone is away from the influence of reflections from the observer.
3.7.5. Directional Characteristics
The microphone is of the omnidirectional type, with typical directional characteristics as
shown in Fig. 3.6. The random incidence response, representing the frequency response
to a diffuse field, is normally calculated conventionally at frequencies of 250, 500,
1000, 2000, 4000, 8000 and 12.500 Hz, according to the formula
where K1, K2 · · · K7 are constants (see IEC Recommendation 1 79) and
S0, S30 · · · S180 are the sensitivities (m V per N/m ) at 0°, 30° · · · 180°
13

14
Fig. 3. 6.. Typical directional characteristics of complete instru-
ment. (IEC Tolerances shown dotted)