G.R.A.S. 40HF 1'' Lownoise Microphone System

Freq range: 10 Hz to 10 kHz
Dyn range: -2 dB(A) to 110 dB
Sensitivity: 1.1 V/Pa

Typical applications and use

  • Very Low Sound pressure measurements
  • Lownoise product measurements
  • Lowlevel Sound power measurements
  • Measurements on hard-disk drives, computer products, quiet rooms etc.


The G.R.A.S. 40HF comprises:

  • a special high-sensitive 1-inch (23.77 mm) Condenser Microphone Type 40EH
  • a special 1-inch (23.77 mm) Low-noise Preamplifier Type 26HF

The preamplifier and microphone are an individually-matched combination. To complete the measuring system, a special power module is required and is available from G.R.A.S., i.e. G.R.A.S. 12HF for single-channel measurements or G.R.A.S. 12HM for multi-channel (1 to 10) measurements. The chosen power module provides all necessary voltages for powering the preamplifier(s) as well as polarizing the microphone(s).


The G.R.A.S. 40EH is an externally polarized microphone with a specially reduced inherent noise floor in order to achieve a high dynamic range and wide frequency range. Its diaphragm is specially tuned to yield high sensitivity coupled with low internal-noise generation.


The G.R.A.S. 26HF Preamplifier has a built-in overload indicator (which is repeated on the chosen power supply) and a frequency correction facility for both pressure-microphone operation as well as free-field microphone operation.

Dehumidifier RA0095 (optional)

For use when humidity is high and only with a rear-vented version of the G.R.A.S. 40EH Microphone. Order only at the time of ordering a Type 40HF.

Frequency response and noise floor

The chosen power supply has a two-position switch for selecting which microphone operation to use, i.e. pressure or free-field. A typical free-field response for an angle of incidence of 0 ° is shown in the data sheet when the G.R.A.S. 40HF is switched to free-field operation. Also shown in the data sheet is a complete low-noise measuring system, a typical noise floor in 1/3-octave bands for both the linear and A-weighted cases.

Frequency range (±1 dB) Hz 12.5 to 4k
Frequency range (±2 dB) Hz 10 to 10k
Frequency range (±3 dB) Hz 6 to 12,5k
Dynamic range lower limit (microphone thermal noise) dB(A) -2
Dynamic range upper limit dB 110
Set sensitivity @ 250 Hz (±2 dB) mV/Pa 1100
Polarization voltage V 200 V / Traditional
Microphone venting Rear
Output impedance Ω 47
Temperature range, operation °C / °F –20 to 60 / -4 to 140
Temperature range, storage °C / °F -40 to 85 / -40 to 185
Connector type BNC
CE/RoHS compliant/WEEE registered Yes/Yes/Yes
Weight g / oz 620 / 22

Typical frequency response

Typical noise floor shown in ⅓-octave bands for both the linear and A-weighted cases



High sensitive 1" microphone

Lownoise 1" preamplifier

Optional items

G.R.A.S. 12HF

1-Channel Power Module for Lownoise Systems

G.R.A.S. 12HM

10-Channel Power Module for Lownoise Systems

G.R.A.S. AM0363

Windscreen for 1" Microphones

G.R.A.S. 42AA

Pistonphone, Class 1

G.R.A.S. RA0090

Pistonphone Coupler

G.R.A.S. AL0006


G.R.A.S. RA0093

Adjustable, high quality, stainless steel tripod adapter

G.R.A.S. RA0095

Dehumidifier for 1” microphones

G.R.A.S. AA0046

3 m LEMO 7-pin - LEMO 7-pin Cable for Low-noise measuring system

G.R.A.S. AA0047

10 m LEMO 7-pin - LEMO 7-pin Cable for Low-noise measuring system

G.R.A.S. AA0053-CL

Customized length LEMO 7-pin - LEMO 7-pin Cable for Low-noise measuring system