G.R.A.S. Sound & Vibration
Single-channel Low-noise Measuring System consisting of: Type 40HT and Type 12HF - Page 4
* Tripods and Tripod adaptors are available from G.R.A.S.
1.
Introduction and Description
The ½-inch Low-noise Microphone System Type 40HT (Fig. 1.1) can measure noise levels
below the threshold of human hearing.
Its specifications are similar to the Type 40HH but can also be used in confined spaces, e.g.:
•
in the KEMAR Head Type 45DA
•
in the Hearing-protector Test Fixture Type 45CA
when these are to be used for measuring very low noise levels.
The Type 40HT comprises:
•
½-inch High-sensitive Microphone Type 40AH.
•
¼-inch High-impedance Preamplifier Type 26HG
•
¼ to ½-inch Adapter GR0010 (included with Type Type 26HG)
•
Gain and Filter Unit Type 26HT with two built-in compensation filters and an overload-
warning LED.
To complete the system, a special single or 10-channel power module is required and is avail
-
able from G.R.A.S., i.e.
•
Type 12HF for single-channel measurements, see Fig. 1.2 (left).
Or
•
Type 12HM for multi-channel (1 to 10) measurements, see Fig. 1.2 (right)
The chosen power module provides all necessary voltages for powering the preamplifier(s) as
well as polarizing the microphone(s).
Fig. 1.1 ½-inch Low-noise Measurement Microphone System Type 40HT
Gain and Filter Unit Type 26HT.
With overload-warning LED to
indicate when the measured
sound pressure level overloads
the system’s electronics
Front end comprising:
• ½-inch High-sensitive Micro
-
phone Type 40AH
• ¼ to ½-inch Adapter GR0010
• ¼-inch High-impedance
Preamplifier Type 26HG
Tripod Adapter
RA0096 *
To Power Module Type 12HF
(or Type 12HM for multi-chan-
nel set-ups). see Fig 1.3
Preamplifier’s
LEMO connector
