Lownoise Microphone System 1″ Gras 40HF Class 1

Typical applications and use

• Very Low Sound pressure measurements
• Lownoise product measurements
• Lowlevel Sound power measurements
• Measurements on hard-disk drives, computer products, quiet rooms etc.

Design

The GRAS 40HF comprises:

• a special high-sensitive 1-inch (23.77 mm) Condenser Microphone Type 40EH
• a special 1-inch (23.77 mm) Low-noise Preamplifier Type 26HF

The preamplifier and microphone are an individually-matched combination. To complete the measuring system, a special power module is required and is available from GRAS, i.e. GRAS 12HF for single-channel measurements or GRAS 12HM for multi-channel (1 to 10) measurements. The chosen power module provides all necessary voltages for powering the preamplifier(s) as well as polarizing the microphone(s).

Microphone

• The GRAS 40EH 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.

Preamplifier

• The GRAS 26HF Preamplifier 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.

Dehumidifier RA0095 (optional)

• For use when humidity is high and only with a rear-vented version of the GRAS 40EH Microphone. Order only at the time of ordering a Type 40HF.

Frequency response and noise floor

• The chosen power supply has a two-position switch for 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 GRAS 40HF is switched to free-field operation. Also shown in the data sheet is a complete low-noise measuring system, a typical noise floor in 1/3-octave bands for both the linear and A-weighted cases.