GRAS 40HT 1/2'' Lownoise Microphone System for Confined Spaces
Freq range: 10 Hz to 16 kHz
Dyn range: 6.5 dB(A) to 113 dB
Sensitivity: 800 mV/Pa
Technology
Introduction
GRAS 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) from 20 Hz to 20 kHz.
Typical applications and use
40 HT is for low sound pressure measurements and very low sound power measurements.
Design
40HT comprises a special high-sensitive ½-inch Condenser Microphone GRAS 40AH, a ¼-inch High-impedance Preamplifier GRAS 26HG with adapter GRAS GR0010 for the ½-inch microphone, and special Gain and Filter Unit GRAS 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 GRAS) is required, i.e. GRAS 12HF for single-channel measurements or GRAS 12HM for 1 to 10 channel measurements.
Each channel provides all voltages required for 40HT and polarizing its microphone.
The Gain and Filter Unit GRAS 26HT 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.
Microphone
The GRAS 40AH microphone 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 1/3-octave bands for both the linear and A-weighted cases.
Specifications
Typical frequency response
Typical noise floor
GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.
Ordering info
Included items
| GRAS 40AH |
High sensitive 1/2" microphone |
| GRAS 26HT |
Gain and filter unit |
| GRAS 26HG |
Lownoise 1/4" preamplifier with adapter for the 1/2" microphone |
Optional items
| GRAS 12HF |
1-Channel Power Module for Lownoise Systems |
| GRAS 12HM |
10-Channel Power Module for Lownoise Systems |
| GRAS AM0069 |
Windscreen for 1/2" Microphones |
| GRAS 42AA |
Pistonphone, Class 1 |
| GRAS RA0090 |
Pistonphone Coupler |
| GRAS AL0006 |
Tripod |
| GRAS RA0096 |
Adjustable, high quality, stainless steel tripod adapter |
| GRAS AA0046 |
3 m LEMO 7-pin - LEMO 7-pin Cable for Low-noise measuring system |
| GRAS AA0047 |
10 m LEMO 7-pin - LEMO 7-pin Cable for Low-noise measuring system |
GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.
