G.R.A.S. 40HF User manual

Instruction Manual
Single-channel Low-noise Measuring
System consisting of:
1-inch Low-noise Level Microphone
System Type 40HF and
Power Module Type 12HF
G.R.A.S.
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark Tel. [phone] Fax [phone]
Type 12HF
Type 40HF

Revision 19 10 2015
Single-channel
Low-noise Measuring System
consisting of:
1-inch Low-noise Level Microphone System Type 40HF
Power Module Type 12HF

G.R.A.S. Sound & Vibration
CONTENTS
1. Introduction and Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Microphone Type 40EH .............................................3
1.2 PreamplierType26HF .............................................3
2. Power Module Type 12HF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Rear Panel .......................................................8
2.3 Battery Pack ......................................................9
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Based on System Sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Pistonphone ............................................................10
3.2 Measurements ...................................................11
4. Specications ..................................................12
4.1 1-inch Low-noise Microphone System Type 40HF . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2 Single-channel Power module Type 12HF (separate order).................12
4.3 Common . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 4
1. Introduction and Description
Fig. 1.1 shows a 1-inch Low-noise Level Microphone System Type 40HF which comprises:
• 1-inchMicrophoneType40EH.
• 1-inchPreamplierType26HFwithtwobuilt-incompensationltersandanoverload-warn-
ing LED.
To complete the system, a special single or 10-channel power module is required and is avail-
able from G.R.A.S., i.e.
• Type12HFforsingle-channelmeasurements,seeFig.1.2(left).
Or
• Type12HMformulti-channel(1to10)measurements,seeFig.1.2(right)
Thechosenpowermoduleprovidesallnecessaryvoltagesforpoweringthepreamplier(s)as
well as polarising the microphone(s).
Fig. 1.3 shows a Single-channel Low-noise Measuring system (as described in this document)
and consists of:
• 1-inchLow-noiseLevelMicrophoneSystemType40HF.
• PowerModuleType12HF.
Note: the power module must be ordered separately and the tripod and tripod adapter are
optional extras.
1.1 Microphone Type 40EH
The Type 40EH is a special high-sensitive 1-inch pressure microphone with a nominal sensitivity
of110mV/Pa.Itisexternallypolarisedwithaspeciallyreducedinherentnoiseoorinorderto
achieve a high dynamic range and wide frequency range.
1.2 PreamplierType26HF
Thebodyofthepreamplierhasanoverload-warningLED,(Fig.1.1),whichisrepeatedonthe
front panel of the chosen power module (Fig. 2.1).
Thesignalofthemicrophoneisampliedby20dBinthePreamplierType26HF.
Thetwocompensationltersgivethesystemtwoparalleloutputswhichcorrespondto:
a) linear pressure-frequency response.
b) linearfree-eldfrequencyresponseatanangleof0°incidence.
The choice of which frequency response to use is made via a two-position switch marked Pres-
sure / Free Field: on the front panel of the power module (see Fig. 2.1).
Fig.1.4showstheresponsesofthetwocompensationltersaswellasthefree-eldresponse
for0°incidence.Note:free-eldcorrectionsareaddedtothelowestcurve.
Fig.1.5showsthewhatthesefree-eldcorrectionsareforvariousanglesofincidence.
Fig.1.6shows,foracompletelow-noisemeasuringsystem,atypicalnoiseoorin⅓-octave
bands for both the linear and A-weighted cases.
Fig. 1.1 1-inch Low-noise Measurement Microphone System Type 40HF
Overload-warning LED indicates when the measured
sound pressure level overloads the system’s electronics

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 5
Fig. 1.3 A Single-channel Low-noise Measuring System as described
in this document, shown here with Tripod and Tripod Adapter
(both available from G.R.A.S.)
Fig. 1.2 Power modules available from G.R.A.S. for Type 40HF,
Left: Single-channel Power Module Type 12HF
Right: 10-Channel Module Type 12HM
Tripod
Adapter
RA0093
Tripod
AL0006
1-inch Low-noise Level Micro-
phone System Type 40HF
Single or 10-chan-
nel power module
(here single chan-
nel Power Module
Type 12HF)

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 6
Fig. 1.4 Typical frequency response curves of Type 40HF
Fig. 1.5 Free-eld corrections for various angles of incidence on the 1-inch Microphone Type 40EH.

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 7
Fig. 1.6 Typical noise oor of Type 40HF for system and microphone. Shown in ⅓-octave bands for
both the linear and A-weighted cases

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 8
Fig. 2.1 Front panel of the Power Module Type 12HF
2. Power Module Type 12HF
SincethemicrophonesignalisampliedinthePreamplierby20dB,thenominalsystem
sensitivity at the output of the Power Module corresponds to 1.1 V/Pa. In other words when the
measured output voltage from the Power Supply is 1.1 V RMS, the microphone is being sub-
jectedto94dBre.20μPa.
The actual sensitivity is quoted on the individual calibration chart supplied with each Type 40HF.
Important!
The Single-channel Power Module Type 12HF (available from G.R.A.S.) is a dedicated module.
Under no circumstances should any other Power Module (apart from the multi-channel Power
Module Type 12HM - also available from G.R.A.S.) be used with the 1-inch Low-noise Level
Microphone System Type 40HF.
2.1 Front Panel
The front panel has the following features (see Fig. 2.1):
• PowerswitchwithtwoLEDs:green“OK”,red“Batt.Low”.
If the power supply is correct, the green LED lights up. If the red LED lights up, either the
batteries are low and should be changed (see section 2.3) or the external DC supply volt-
age is too low.
• Two-positionswitchforselectingfrequencyresponse,Pressure microphone operation or
Free Field microphone operation:
Pressure-toselecttheoutputofthecompensatinglterwhichgivesthesystemalinear
pressure-frequency response.
Free Field-toselecttheoutputofthecompensatinglterwhichgivesthesystemalinear
free-eldfrequencyresponseat0°incidence.
• Overload-warningLEDsynchronisedwiththeoneonthePreamplierType26HF(see
Fig. 1.2)
Power switch
Green LED
powerOK
Red LED Batt.
Low
Input 7-pin
LEMO socket
Output BNC
socket
Overload LED indicates
when the measured
sound pressure level
overloads the system’s
electronics
Switch for
selecting either
pressure micro-
phone opera-
tionorfree-eld
microphone
operation

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 9
Fig. 2.2 7-pin LEMO EGA 307 1B input socket
(external view)
Fig. 2.3 Rear panel of the Power Module Type 12HF
• 7-pinLEMOEGA3071Binputsocketforthemicrophoneandpreampliersignal.Wiring
diagram shown in Fig. 2.2.
• BNCoutputsocketfortheselectedcompensatedoutputsignal
2.2 Rear Panel
The rear panel has the following features (see Fig. 2.3)
• Twist/releaseholderfor315mAfast-blowfuse.
• Inputsocketforanexternalvoltagesupplyof6V-20VDC;centrepin+terminal.Usethe
Mains/line Adapter AB0005 supplied with the system.
• Lockingscrew
Unscrew to remove base plate and gain access to the battery pack (see section 2.3).
Input for external
Power Supply
6V-20VDC
Fuse 315 mA fast
blow
Locking screw for
base plate

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 10
Fig. 2.4 Showing the battery pack of the Power Module Type 12HF
2.3 Battery Pack
To gain access to the battery pack, unscrew the locking screw on the rear panel (Fig. 2.3) and
slide the base plate off towards the rear. Pull out the battery pack See Fig. 2.4.
Thebatterypackconsistofabatteryholderand4xLR14(C)standardalkalinecells.When
replacing the batteries, replace all of them making sure that the polarity is as indicated on the
battery holder.

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 11
Fig. 3.1 Pistonphone without its normal coupler and ready to accept the
Coupler RA0090
3. Operation
3.1 Calibration
3.1.1 Based on System Sensitivity
SincethemicrophonesignalisampliedinthePreamplierby20dB,thenominalsystem
sensitivity at the output of the Power Module corresponds to 1.1 V/Pa. In other words when the
measured output voltage from the Power Supply is 1.1 V RMS, the microphone is being sub-
jectedto94dBre.20μPa.
The actual sensitivity is quoted on the individual calibration chart supplied with each Low-noise
Measuring System Type 40HF.
Based on this information, proceed as follows:
1. Connect the Type 40HF via its LEMO plug to the LEMO input socket of the Type 12HF.
2. Connect via a suitable cable the BNC output of the Type 12HF to the analyser to be used
and switch both Power Module and analyser on.
3. Adjusttheanalysertoindicate94dBre.20μPaforanRMSinputofSvolts;whereSis the
system sensitivity of the Type 40HF as quoted on the calibration chart.
3.1.2 Pistonphone
APistonphoneType42AAttedwithaCouplerRA0090(bothavailablefromG.R.A.S.)canbe
usedtoproduce94dBre.20μPaonthemicrophoneoftheType40HF.
Note:aPistonphonettedwithanormal1-inchcouplercannotbeusedbecausethiswillover-
loadthesystemwithalevelof114dBre.20μPa.
Proceed as follows:
1 Connect the Type 40HF via its LEMO plug to the LEMO input socket of the Type 12HF.
2. Connect via a suitable cable the BNC output of the Type 12HF to the analyser to be used
and switch both Power Module and analyser on.
3. Unscrew and remove the normal coupler of the Pistonphone.
4. Screw the Coupler RA0090 to the Pistonphone, see Fig. 3.1.
5. Mount the microphone of the Type 40HF in the Coupler as shown in Fig. 3.2 and switch the
Pistonphone on.
6. Adjusttheanalysertoindicate94dB*re.20μPa.
* Plusanycorrectionsforbarometricpressure.Seepistonphonemanual.

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 12
Fig. 3.2 Pistonphone tted with Coupler RA0090 and the microphone
inserted into the Coupler
3.2 Measurements
1. Assemble the system as shown in Fig. 1.3.
2. Connect the output from the Power Module to an analyser.
3. Switch both Power Module and analyser on.
4. Calibrate the set up via one of the methods described in section 3.1.
5. Select which microphone operation to use via the switch on the front panel of the Type
12HF marked Pressure / Free Field.
At this point you can make your measurements but keep an eye on the overload warning LEDs
to avoid overloading the system and invalidating the measurements.

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 13
4. Specications
4.1 1-inch Low-noise Microphone System Type 40HF
Low-noise Measuring System Type 40HF comprising:
1-inch Microphone: Type 40EH
Preamplier:  Type26HF(with3mcableandLEMOFGA.1B.307plug)
Frequency response:
12.5 Hz - 4 kHz: ±1.0 dB
10 Hz - 10 kHz ±2.0 dB
6Hz-12.5kHz:  +2.0dB,–3.0dB
Nominal sensitivity:
System: 1.1 V/Pa
Microphone: 110 mV/Pa
Microphone polarisation voltage:
200 V
Dynamic range:
Upper limit: 110 dB re. 20 µPa
Lowerlimit:  –2dBAre.20µPa(inherentnoise)
Microphone capacitance:
45 pF
4.2 Single-channel Power module Type 12HF (separate order)
Input channel:
7-pin LEMO EGA 1B connector
Outputs channel:
BNC socket
Output impedance:
30Ω
Polarisation voltage:
200 V
Power supply:
 internal:  6Vfrom4xLR14(C)standardalkalinecells
 external:  6V-20VDCviaincludedMainsAdapterAB0010
Dimensions:
 height:   132.6mm(5¼in)
 width:    34.6mm(1.3in)
 depth:   196.0mm(7.7in)

G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HF and Type 12HF - Page 14
Weight:
    620g(1.3lbs)
Accessories included:
Batteries: 4 x LR14 (C) standard alkaline cells
Mains/line Adapter: AB0010
Mains/line Adapter: AB0003 (US)
4.3 Common
Temperature range:
–20°Cto+60°C
Accessories available:
Power module (1 ch.): Type 12HF
Power module (10 ch.): Type 12HM
Windscreens(setof5): AM0363
Pistonphone: Type 42AA
Pistonphone Coupler: RA0090 (for 94 dB re. 20 µPa)
Tripod:   AL0006
Tripod Adapter: RA0093
3mExt.cable:  AA0046
10 m Ext. cable: AA0047
30 m Ext. cable: AA0048
WEEEdirective:
2002/96/EC
CE marking directive:
93/68/EEC
Manufactured to conform with:
RoHS directive:
2002/95/EC