Sound calibrator
114 dB 1 re. 20 µPa, 105.4 dBA re. 20 µPa
Meggitt Sensing Systems - Measurement Group
The model EM42AA is an extremely stable laboratory standard sound source which can also be used for field calibrations, retaining its high accuracy even under hostile environmental conditions. It is normally delivered for calibrating ½-inch microphones directly since these are most commonly used but can be delivered with a 1-inch coupler for calibrating 1-inch microphones directly if preferred.
The pistonphone works on the principle of two reciprocating pistons actuated by a precision-machined cam with a sinusoidal profile. The rotation speed of the cam is controlled to within 0.5% via a tachometer signal in a feed-back loop. The model EM42AA has a dual-colour LED above the ON/OFF switch to indicate both battery condition and stable operation. When the pistonphone is operating properly, the LED shows green, indicating that the speed of the cam is correctly locked to give 250 Hz. If it shows red while the pistonphone is switched on, the speed is incorrect; most likely because of low batteries.
The operating procedure is straight forward, simply fit the microphone into the coupler of the pistonphone and switch on. The pistonphone will now produce a constant sound pressure level on the diaphragm of the microphone. The model EM42AA is compatible with Endevco ½-inch, ¼-inch and 1/8-inch microphones and all other microphones having the same standard diameters. Adapters are included for calibrating ¼-inch and 1/8-inch microphones.
