Type 40HH

Type 40HH
The ½" Low-noise Level Microphone System Type 40HH can measure noise levels well below the threshold of human hearing.
It is amply suitable for acoustic measurements on even very quiet products, e.g. disk drives and other computer products, as well as in quiet rooms.
It has a wide dynamic range which enables measurements from below -2 dBA re. 20µPa (in 1/3-octave bands) in a frequency range from 20 Hz to 20 kHz.
The Type 40HH comprises the following two specially-designed components:
  • a high-sensitive ½" microphone (Type 40AH)
  • a low-noise ½" microphone preamplifier (Type 26HH)
The microphone and its preamplifier are an individually matched combination.
The system can be switched to operate either for pressure measurements or free-field measurements.
To complete the measuring system, one of the following special power modules is required and is available from G.R.A.S., i.e.
  • Type 12HF for single-channel measurements
  • Type 12HM for multi-channel (1 to 10) measurements
The chosen power module provides all necessary voltages for powering the preamplifier(s) as well as polarising the microphone(s). It also has a two-position switch for selecting which microphone operation to use, i.e. pressure or free-field.
The following high-quality extension cables are available for the preamplifier:
  • AA0046 3m
  • AA0047 10m
  • AA0048 30m
Specifications Type 40HH
Specifications Type 40HH (with a power module)
Nominal sensitivity:
System 0.75 V/Pa

Microphone 75 mV/Pa
Frequency range:
12.5 Hz – 10 kHz ± 1 dB
10 Hz – 16 kHz ± 2 dB

6 Hz – 20 kHz + 2 dB, –3 dB
Dynamic range:
6.5 dBA to 113 dB re. 20µPa
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