GENERAL RADIO COMPANY I559-B User manual

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TYPE I559-B
MICROPHONE
RECIPROCITY CALIBRATOR
GENERAL
A
RADIO COMPANY

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TYPE I559-B
MICROPHONE
RECIPROCITY CALIBRATOR
Form 1559-01'10-A
July,1965
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Copyright 1965 by General Radio Company
West Concord, Massachusetrs, U.S.A.
GENERAL RADIO COMPAN
WEST CONCORD, MASSACHUSETTS, USA

TABL ECONTENTS
Section 1' INTRODUCTION'
1.1 PurPose . .
L.2 Description'
1.3 Accessories Required
Section 2. OPERATING PROCEDURE
2.I Preliminary Control Settings '
2'2 Piezoelectric Microphone Calibration
2.3 Calibration of W E 640AAandB a K4131
MicroPhones
2.4 Precision Accoustic Source
2.5 Comparison With Standard Microphone
2.6 Sound-Level Calibrator'
2'7 CalibrJion of Type 1565-A Sound-Level Meter
anO fype 1560-P40K Microphone Preamplifier
2.8 MicroPhone ResPonses '
2.9 Ambient Noise Level
2.10 Deviations in Microphone Calibration
Section 3. PRINCIPLES OF OPERATION
3.1 PrinciPle of ReciProcitY
3,2 Microphone Calibration by the Reciprocity
Technique
3'3 The Auxiliary Transducer''
g.4 Ratio and Product of Sensitivities
3'5 CouPling ImPedance' Z4
3.6 Current SamPler ' '.
g.7 Resistive-Insert Technique
3.8 The Analog ComPuter
3.g Explanatio:n of Calibration Procedure '
Section 4. SERVICE AND MAINTENANCE'
4.I WarrantY
4.2 Service .
4.3 Removal of Instrument From Cabinet
4.4 Trouble-Shooting '
4.5 Resistance Measurements '
Appendix I
L4
T6
L6
I
1
I
J
4
4
6
9
t0
11
11
11
12
13
T7
18
18
20
20
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22
22
25
25
25
26
26
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27
30
Appendix 2

SPECIFICATIONS
I'tICR,OPHONE CAIIBRATOR
Ronse:-Direct -reading for microphone sensitivities between
-35 dB and -75 dB re I Y /pbar.
Fre^quency Ronge: 20 c/s to 6 kc/s direct reading, with correetions
to 8 kc,/s.
Accurccy: 10.2 dB + (0.1 db X_fleque-ngy -lg kc) up to 2.5 kc/s.
Trpn 1560-PB and Tipp ts60-p4: io.Z"aS at""i z.ff.c7-'io
7 kc/s.
Typr 156O-P5 and Tvpn 1b60-p6 | t0.Z dB above 2.8 kc/s to
'Western Electric 640-4A I -O. l.Ur,- ai.u"t -."aiirrgl
or equivalent J with coire"iio", to S k.7?l
lype t55t.Ptt: +0.7 dB above 2.5 kc/s to b kc/s.
PRECISION ACOUSTICA1 SOURCE
Frequency Ronge: 20 c/s to Z kc/s.
Output: 92 dB re 0.0002 pbar for excitation of 50 V.
Accurocy: At 92 dB, +0.1 dB f error in determining microphone
sensitivity.
SOUND.IEVEI CATTBRATOR
Frequency Rcnge: 20 c/s to 2.8 kc/s.
Output: 92 dB re 0.0002 pbar for excitation of 50 V.
Accurocy: +0.7 dB at standard atmospheric pressure.
GENER.At
Mcximum Sofe lnput Vohoge: S0 V behind 600 O.
ACCESSORTES
Required: Generator anddetector. Generator to supply 5 volts
or more into a 2000-pF load, and 2.5 V or more into a OfftlO toaa.
.l,ower voltage can be used,rvith a resul.tant lowering of signal_io_
ambient-noise ratio. The - Ty^pr_ _t qo+.B _Be,atF;;4"*"cf A"dio
Generator, the Tvpn t2t0-C Unit-n-COJritt ti., "id--t'iri'-
Tv-pr_t3tb-A Audio Oscillaio"-u.e fu;m]iint"ed. The Tvpn
1551-8 or -C Sound-Level Meter is recomme;a;al;; tfre aitecio..
Supplied: Trpn 27rt-NP P_atch Cord and an extension cable for
connection to generator and detector; and adaptors for recioroc_
lty^_elg comparison calibration_ of the Typp l560_pb, ivpn
1560-P6, and Western Electric 640-AA o. bqulvale"i-l..oirfr""ur.
IiECHANICAI DATA: Ftip-Tilt Cobtnet
*o*, Width Heisht Depth Net Shinnino
Weight Weisht"
in ?nn1, in tntn in n1,nx Ib kg lb ks
Portable lO 2SS I2OS 7V2 190 13 622 t0
Ra,clc 19 185 1OV2 27O SI r 30 14 6.5 29 13.5
t Bebiod panel.
U.S. Patent No. 2,966,257.
General Radio Experimentet reference: Vol 37, No. 4, 5, April-May L963.

Figure l-1. Type 1559-B Microphone Reciprocify Cqlibrotor.

INTRODUCTION
SEC"ION I
INTRODUCTION
l.l PURPOSE.
The Type 1559'8 Microphone Reciprocity Calibrator (Figure 1) can be
used ro calibrate microphones whose sensitivity is in the range from '75 dB
i" -l: aA re f volt/prbar. This inscrument will calibrate General Radio Types
UeO-p!,'P3,and'P4Microphonesand,withtheadaptorsupplied'theTypes
feO-p> and -P6 Microphones' In addition, it includes igtl-t::t permitting a
primary calibration to be perfotmed on w E 6404A' B & K 4I3L' M R103' and
other condenser microphones of this type' Because the National Bureau of
Standards also uses th" ...ip,ocity method to calibrate these microphones,
thereisnowadirectlinkbetweenNBsandthisnewversionoftheGRMicro.
phoneReciprocityCalibrator.Thehighaccuracyoftheinstrumentmakesit
suitable for standardization measurements, while its ease of operation makes
it useful for daily checks on sensitivity'
Theinstrumentcanalsobeusedasasoufceofconstantacoustlcout.
Putoverawidefrequencyrange'tomakerapidcalibrationchecksonmicro.
pion." and sound-lerr"l ,"t"r", or ro ser rhe reference level of analyzing
systems.
I.2 DESCRIPTION.
l.2.lGENERAL.Thereciprocitycalibratorincludesthecircuitandthestruc.
ture required for the .to".d-.oopler (cylindrical-cavity) reciprocity calibra-
tion procedure, which is widely recognized as the preferred method of per-
forming the absolute calibration of laboratory standard microphones' The

TYPE 1559.8 MICROPHONE RECIPROCITY CALIBRATOR
instrument also includes an analog computer, which performs the calculations
necessary to determine microphone sensitivity. The reversible transducer
necessary for the calibration procedure is the cartridge of a Type I560'P3
PZT Microphone which is built into the coupler. The auxiliary transducer is a
PZT cylinder, which forms the cylindrical wall of the coupler. The insert
voltage is varied in 10-dB steps, to extend the calibration range while main'
taining high resolution. The coupler has a volume of. L7.74 cubic centimeters
and is designed to yield the random-incidence resPonse of the microphone
over an extended range without the use of helium.
The PZT cylinder used in che reciprocity calibration also serves as a
stable acoustic source when the instrumentis usedas a sound-levelcalibrator.
A merer, calibrated in terms of the sound-pressure level produced, indicates
the absolute value of the signal applied to the PZT cylinder.
I.2.2 CONTROLS AND CONNECTORS. Table 1 liscs the controls and con-
connectors on the panel of the Type 1559-B Microphone Reciprocity Cali-
brator.
1.2.3 ACCESSORIES SUPPLIED. Supplied with the reciprocity calibrator are
aType 274-NP Patch Cord, a 30-inch output cable for connection to the sound-
level meter, and adaptors for WE 64OAA-type microphones, Type 1560-P5 Mi-
crophone, and Type 1560-P6 Microphone Assembly.
TABLE I
CONT RO LS AND CONN ECTOR S
Fis. 1-11
R"l I
Type Futtction
2
)
INPUT
92DB-84DB
Microphone coonector
Tran sfer-function switch
(R,EAD.ADJ)
SENSITIVITY LEVEL
MICROPHONE CUR.
RENT
OUTPUT TO SLM
SENSITIVITY LEVEL
Slide pins (2)
Phillips-head screws (4)
Binding post pair
3-position toggle switch
3-terminal Cannon Type
XLR locking connector
9-position selector switch
Continuous rotary control
Continuous rotary control
3-terminal Cannon Type
XLR locking connector
4-position selector switch
Input connection from oscil-
lator to Type f559-8,
Selects $eter range.
Receives microphone to be
calibrated.
Sets necessary electrical
transfers.
Adjusts value of resistance
attenuato!.
Controls level of driving cur
rent of reversible transducer.
Output connection to sound-
level meter.
Sets insert voltage level.
Lock the cabinetin the cover.
Lock the insuument in the
cabinet.
8
9
10

INTRODUCTION
1.2.4 CARRYING CASE. The Type L559'B is mounted in a General Radio
Flip-Tilt case. The captive protective cover serves as a mounting base when
the instrument is in use. The friction of the rubber seal keeps the instrument
at any convenient angle, from horizontal to vertical. The cables and instruc-
tion book are carried in the cover, in a protective polyurethane compartment.
I.3 ACCESSORIES REQUIRED.
1.3. I OSCILLATOR. An audio oscillator is required to drive the Type L559'B
Microphone Reciprocity Calibrator. Ideally, this oscillator should have an
output impedance of 600 ohms and should be able to deliver one watt into a
600-ohm load. The Type fl04-B Beat-Frequency Audio Generator fufills these
requirements and, in addition, is readily coupled to a recorder such as the
Type I521-B Graphic Level Recorder. The Type 1310-A Oscillator is also
recommended. Although the Type I559-B Microphone Reciprocity Calibrator
is designed to use a GdB change in output voltage when a 600-ohm source is
matched and is effectively unloaded, oscillators of other impedances can be
used. Two such oscillators are the Type I3IL-A Audio Oscillator, which
supplies 11 fixed frequencies between 50 and 10,000 c/ s, and the Type L2L0'C
Unit R-C Oscillator, which is continuously adjustable over the audio spectrum.
The Type L3I7-A should be used on the 30 v output position and the Type
I2I0-C on the 0-7 v output position. The need for the 600-ohm generator
impedance is most evident when the Type 1559-8 Microphone Reciprocity
Calibrator is used for sound-level calibrations. The output impedance of both
the Type L3II-A Audio Oscillator and the Type L2L0'C Unit R-C Oscillator
can be made equal to 600 ohms by adjustment of their resPective outPut-
level controls or by the addition of series resistance.
I.3.2 DETECTOR. The detector required to measrue the output signals of the
Type 1559-B Microphone Reciprocity Calibrator should have an input imped-
ance of at least 5 megohms and should be capable of measuring a signal of
several millivolts with a signal-to-noise ratio of at least 20 dB. In addition,
the detector should have a scale suitable for observing l'percent changes
in signal level. The detector can be a Type I551'C Sound-Level Meter, a
Type 1558-A Octave-Band Noise Analyzer, or a Type L564'A Sound and Vibra-
tion Analyzer. One of these is usually the instrument whose microphone is to
be calibrated.

TYPE 1559.8 MICROPHONE RECIPROCITY CALIBRATOR
BAROMETEN PRESSURE
CORRECTED TO
SEA LEVEL
INCHES
OF
MERCURY
3t
ALTITUDE OF STATION
IN
FEET ABOVE SEA LEVEL
BAROMETRIC PRESSURE
AT
STATION
MILLIMETERS
OF
MERCURY MILLIBARS
700
MILLIBARS
r o50
30
:"
2A
27
26
z5
24
23
zt
I OOOO
9000
8000
7000
6000
5000
zrooo
3000
2000
r 000
o
-tooo
I OOOO
9000
8000
7000
6000
5000
4000
3000
2000
r ooo
o
-t o00
Figure 2-l. Nomogroph for opplying oltitude correction to boro'
melric ptessure. Ploce stroight'edge ocross ProPer points on
center ond left-hond scoles ond reod ocluol pressure on righf'
hond scole. See Appendix 2 lot oltitudes obove seo level for
mony cities in fhe U.S. ond Conodo.

OPERATING PROCEDURE
SECTrcN 2
OPERATING PROCEDURE
2.I PRELIMINARY CONTROL SETTINGS.
2. l.l METER-ZERO CHECK.vith the instrument off' set the meter pointer to
zeto,ifnecessary'bymeansofthescrewdriveradjustmentonthemeterface.
2.l.2BARoMETRlcPRESSUREcoMPENsATloN.Formaximumaccuracy'
SCt thc BAROMETRIC PRESSURE MILLIBARS CONTTOI tO iNdiCAtC thc ACTUAI
barometric Pressure at your location'
Thepressure"gioenbytheUnitedStatesWeatherBureauandbyvarious
flighr facilities are ."orr".t"d pressures, i.e., pressures referred to sea level'
Most barometers are similarly calibrated to read Pressures corrected to sea
level. The actual barometric pressure can be specifically requested of your
local weather sration, or you.un.orr.., the published barometric reading for
yourownlocation.Thiscorrectionis4Junctionofaltitude,temperature,and
pressure, but the principal factor is ttb altitude correction of one inch of
'.,..,ryper1000f.et.bo,,esealevel.Figure2-lincludesanaltitudecor-
rection chart and a conversion nomograph for inches of mercury to millibars'
while the pressure set on the BAROMETRIC PRESSURE indicator should be
reasonablyaccurate,anerrorofafewmillibarswillnotgteatlyaffectthe
accuracy of measuremenr. An effor of 34 millibars (one inch of mercury) in
barometric pressure will cause an error of approximately 0.15 dB in micro-
phone calibrations and 0-3 dB in sound-level calibrations'