G.R.A.S. Low-noise measuring systems can measure noise levels below the threshold of human hearing, e.g. from disk drives, computer equipment in general and in quiet rooms.
A quiet location can easily be subjected to intrusive noise when many otherwise "inaudible" devices are in use.
It therefore becomes important to know in advance (through accurate measurements) the noise contribution of quiet products when many of these are to be placed in quiet working environments.
| Type | 40HF | 40HH | 40HT | 40HL | ||||
| Size | 1" | ⅛" | ½" | ½" | ||||
| Nom. sensitivity - System | 1.1 V/Pa | 0.75 V/Pa | 0.75V/Pa | 0.75 V/Pa | ||||
| - Microphone [mV/Pa] | 110 | 75 | 75 | 75 | ||||
| Frequency range [Hz] | 12.5-4k ± 1dB | 12.5–10k ± 1dB | 12.5–10k ± 1dB | 12.5–10k ± 1dB | ||||
| - | 10–10k ± 2dB | 10–16k ± 2dB | 10–16k ± 2dB | 10–16k ± 2dB | ||||
| - | 6–12.5k + 2dB, –3dB | 6–20k + 2dB, –3dB | 6–20k + 2dB, –3dB | 6–20k + 2dB, –3dB | ||||
| Dynamic range [dB] | –2dBA-110dB re. 20µPa | 6.5dBA-113dB re. 20µPa | 6.5dBA-113dB re. 20µPa | 6.5dBA-113dB re. 20µPa |