21. 1'' Lownoise Microphone System- G.R.A.S. 40HF

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.


More details

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


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.


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.


Measure beyond the threshold of human hearing


Back to G.R.A.S. Product List

Related Products