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.