Typical applications and use
- Very low sound pressure measurements
- Very low sound power measurements
G.R.A.S. 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 ⅓-octave bands) from 20 Hz to 20 kHz.
It comprises a special high-sensitive ½-inch Condenser Microphone G.R.A.S. 40AH, a ¼-inch High-impedance Preamplifier G.R.A.S. 26HG with adapter G.R.A.S. GR0010 for the ½-inchmicrophone, special Gain and Filter Unit G.R.A.S. 26HT
The Gain and Filter Unit and Microphone are an individually-matched combination. To complete the system, a special single or 10-channel power module (available from G.R.A.S.) is required, i.e. G.R.A.S. 12HF for single-channel measurements or G.R.A.S. 12HMfor 1 to 10 channel measurements
Each channel provides all voltages required for 40HT and polarizing its microphone.
Gain and Filter Unit G.R.A.S. 26HT
This has a built-in overload indicator (which is repeated on the chosen power supply) and a frequency correction facility for both pressure-microphone operation as well as free-field microphone operation.
The G.R.A.S. 40AH icrophone 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 switchfor 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 40HT is switched to free-field operation. Also shown is a complete low-noise measuring system, a typical noise floor in ⅓13-octave bands for both the linear and A-weighted cases.
|Frequency range (±1 dB)||Hz||TBD|
|Frequency range (±2 dB)||Hz||TBD|
|Frequency range (±3 dB)||Hz||TBD|
|Dynamic range lower limit with G.R.A.S. preamplifier||dB(A)||TBD|
|IEC 61094 designation||TBD|
|Temperature range, operation||°C / °F||-30 to 70 / -22 to 158|
|Temperature range, storage||°C / °F||-40 to 85 / -40 to 185|
|Temperature coefficient @250 Hz||dB/°C / dB/°F||TBD / TBD|
|Static pressure coefficient @250 Hz||dB/kPa||TBD|
|Humidity range non condensing||% RH||TBD|
|Humidity coefficient @250 Hz||dB/% RH||TBD|
|Influence of magnetic field @80 A/m, 50 Hz||dB re 20 µPa||TBD|
|Influence of axial vibration @1 m/s²||dB re 20 µPa||TBD|
|CE/RoHS compliant/WEEE registered||No/TBD|
|Weight||g / oz||/ TBD|