Type 40HT

Type 40HT
The ½" Low-noise Microphone System Type 40HT can measure noise levels well below the threshold of human hearing.
Its specifications are similar to the Type 40HH but can also be used in confined spaces.
The Type 40HT can measure sound pressure levels below the threshold of human hearing; and is amply suitable for sound-power measurements on even very quiet products. Its very, wide dynamic range permits measurements down to below – 2 dB re. 20 μPa (in 1/3-octave bands) in a frequency range from 20 Hz to 20 kHz.
The Type 40HT comprises the following components:
  • a special high-sensitive ½" Microphone (Type 40AH)
  • a high-impedance ¼" Microphone Preamplifier Type 26HG with adapter (GR0010) for the ½" Microphone
  • a special Gain and Filter Unit (Type 26HG)
The Microphone and the Gain and Filter Unit 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 Gain and Filter Unit:
  • AA0046 3m
  • AA0047 10m
  • AA0048 30m
Specifications Type 40HT
Specifications Type 40HT (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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