19. 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.

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More details

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

Design

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

G.R.A.S

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).

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Microphone

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.

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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.

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Measure beyond the threshold of human hearing

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