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

Instruction Manual
Single-channel Low-noise Measuring
System consisting of:
½-inch Low-noise Level Microphone
System Type 40HH and
Power Module Type 12HF
G.R.A.S.
Sound & Vibration
Skovlytoften 33, 2840 Holte, Denmark Tel. [phone] Fax [phone]
12HF
40HH

Revision 17 September 2017
Single-channel Low-noise Measuring System
consisting of:
• ½″ Low-noise Level Microphone System Type 40HH
• Power Module Type 12HF

G.R.A.S. SOUND & VIBRATION
CONTENTS
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Microphone Type 40AH .............................................3
1.2 Preamplier Type 26HH .............................................3
2 Power Module Type 12HF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Rear Panel .......................................................8
2.3 Battery Pack ......................................................9
3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Based on System Sensitivity.........................................10
3.2 Level Calibratinon using a Pistonphone ................................10
3.3 Frequency Response Calibratoin ..................................... 11
4 Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 Specications ..................................................12
5.1 ½″ Low-noise Microphone System Type 40HH. . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 Single-channel Power module Type 12HF (separate order).................12
5.3 Common . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6 What to Order ..................................................14

G.R.A.S. SOUND & VIBRATION
Single-channel Low-noise Measuring System consisting of: Type 40HH and Type 12HF - Page 4
1 Introduction
Fig. 1.1 shows a ½″ Low-noise Level Microphone System Type 40HH which comprises:
• ½″ Microphone Type 40AH.
• ½″ Preamplier Type 26HH with two built-in compensation lters and an overload-warning
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 polarizing the microphone(s).
Fig. 1.3 shows a Single-channel Low-noise Measuring system (as described in this document)
and consists of:
• ½″ Low-noise Level Microphone System Type 40HH.
• Power Module Type 12HF.
Note: the power module must be ordered separately, and the tripod and tripod adapter are
optional extras.
Fig. 1.1 ½″ Low-noise Measurement Microphone System Type 40HH
1.1 Microphone Type 40AH
The Type 40AH is a special high-sensitive ½″ microphone. It is externally polarized with a spe-
cially reduced inherent noise oor in order to achieve a high dynamic range and wide frequency
range.
1.2 Preamplier Type 26HH
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 (see Fig. 2.1).
The signal of the microphone is amplied by 20 dB in the Preamplier Type 26HH.
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
Pressure / Free Field on the front panel of the chosen 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 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.
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 40HH 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 40HH,
Left: Single-channel Power Module Type 12HF
Right: 10-Channel Module Type 12HM
Tripod
Adapter
RA0093
Tripod
AL0006
½″ Low-noise Level Microphone
System Type 40HH
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 40HH and Type 12HF - Page 6
Fig. 1.4 Typical frequency response curves of Type 40HH
Fig. 1.5 Free-eld corrections for various angles of incidence on the ½″ Microphone Type 40AH
100 kHz10 kHz1 kHz100 Hz
Decibels re. level at 250 Hz
- 6
- 4
- 2
0
2
4
6
8
10
180 º
Random incidence
150 º
120 º
0 º
30 º
60 º
90 º
0 º
90 º
120 º
- 8
14
12

G.R.A.S. SOUND & VIBRATION
Single-channel Low-noise Measuring System consisting of: Type 40HH and Type 12HF - Page 7
Fig. 1.6 Typical noise oor of Type 40HH 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 40HH and Type 12HF - Page 8
2 Power Module Type 12HF
Since the microphone signal is amplied in the Preamplier Type 26HH by 20 dB, the nominal
system sensitivity at the output of the Power Module corresponds to 0.8 V/Pa. In other words
when the measured output voltage from the Power Supply is 0.8 V RMS, the microphone is
being subjected to 94 dB re. 20 μPa.
The actual sensitivity is quoted on the individual calibration chart supplied with each Type 40HH.
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 ½″ Low-noise Level Micro-
phone System Type 40HH.
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 voltage
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 26HH
(see Fig. 1.2).
Fig. 2.1 Front panel of the Power Module Type 12HF
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 40HH and Type 12HF - Page 9
• 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 (Pressure / Free Field) 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 AB0010 supplied with the Type 12HF.
• Locking screw
Unscrew to remove base plate and gain access to the battery pack (see section 2.3).
Fig. 2.2 7-pin LEMO EGA 307 1B input socket
(external view)
Fig. 2.3 Rear panel of the Power Module Type 12HF
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 40HH and Type 12HF - Page 10
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.
Fig. 2.4 Showing the battery pack of the Power Module Type 12HF