Typical applications and use
- Building-acoustics measurements
- Acoustic-transfer measurements
- Sound-intensity measurements
It has the following signal-conditioning settings:
- High-pass filtering
Whichever one is selected is applied to both channels.
The G.R.A.S. 12AA can be powered either by internal standard batteries or an external DC supply (12 V-18 V), e.g. a mains/line adapter. It is built into a sturdy anodized aluminium cabinet. The polarization voltage for the microphone fitted to the preamplifier can be set to 0 V for prepolarized microphones, or 200 V for externally polarized microphones. The voltage supply for the preamplifier can be set to 120 V for maximum dynamic range, or 28 V for minimum power consumption. The G.R.A.S. 12AA will run for up to 10 hours on fresh standard alkaline batteries. A Battery meter indicates the condition of the batteries.
The inputs are two 7-pin LEMO sockets (A and B) on the front panel which are wired up for G.R.A.S. microphone preamplifiers, e.g. 26AB, 26AC, 26AJ and 26AK, but are also compatible with other available makes of similar microphone preamplifiers.
The outputs are two standard BNC connectors (A and B) on the rear panel. Both channels have an overload indicator. The gain in each channel can be set individually from – 20 dB to + 40 dB in steps of 20 dB.
The standard A-weighting filter in each channel complies with IEC Standard 60651: Sound level meters Type 0. The high-pass filter in each channel is a 3-pole Butterworth filter with a – 1 dB cut-off at a frequency of 20 Hz. These filters are for reducing unwanted low-frequency signals, e.g. caused by wind-induced noise on the microphone.
For intensity measurements, which require extremely good phase matching, the preamplifier signals can be coupled directly to the outputs of the 12AAby selecting direct output. This makes the output of each preamplifier available free of any signal conditioning.
A built-in precision 1 kHz oscillator enables a complete check of each measuring channel when used with G.R.A.S. preamplifiers 26AH, 26AJ or 26AL, which include SysCheck. The oscillator can be activated directly via a push-button on the front panel or remotely via a mini-jack connector on the rear panel. The output level of the oscillator can be individually adjusted in each channel using a small screw driver on potentiometers accessible via holes in the front panel.