G.R.A.S. 42AA Pistonphone, Class 1

Sound pressure level: 114 dB
Frequency: 250 Hz
IEC: 60942

Typical applications and use

  • Reference calibration source
  • Precision microphone calibrations
  • Microphone comparisons
  • P-I index measurement at 250 Hz

Design

With a microphone placed in the coupler of the pistonphone, the calibration level is:

  • 114 dB 1 re. 20 μPa
  • 105.4 dBA re. 20 μPa (with A-weighting applied)

At a static ambient pressure of 101.3 kPa, no further correction factors need be applied.

The 42AA is an extremely stable laboratory standard sound source which can also be used for field calibrations – it retains its high accuracy even under hostile environmental conditions.

The 42AA complies with all the requirements of IEC Standard 942 (1988) Sound Calibrators Class 1 when corrected with barometer ZC0002K as well as Class 0 when corrected with barometer RA0168. The 42AA includes ZC0002K.

The 42AA is normally delivered for calibrating ½" microphones directly since these are most commonly used, but can be delivered with a 1" coupler (RA0023) for calibrating 1" microphones directly if preferred. Please state preference when ordering.

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 42AA 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 Pistonphone 42AA is compatible with G.R.A.S. ½", ¼", and ⅛" microphones and all other microphones having the same standard diameters. Adapters are included for calibrating ¼" and⅛" microphones. Where applicable, the coupler RA0023 is also available for calibrating 1" microphones.

Each pistonphone is factory calibrated with an accuracy of ±0.09 dB re. 20 μPa and is supplied with an individual calibration certificate stating the exact value and test condition. The exact value is adjusted to be 114 dB within ±0.05 dB under reference conditions. Since the output level of a pistonphone depends on the static ambient pressure, the 42AA is delivered with a barometer which shows directly on a printed scale what must be added or subtracted to the output level of the pistonphone.

For use as a Class 0 calibrator, a precision barometer (not included) with an accuracy of ± 1 hPa or better should be used. The barometric correction at a given altitude very seldom varies by more than ± 0.2 dB.

Adapters for the G.R.A.S. 41AL Environmental Microphone and Outdoor Microphone Systems 41AM and 41CN are available for use with Pistonphone 42AA fitted with a 1" microphone coupler RA0023.

A two-port calibration coupler for ½" microphones (RA0024) is available for making comparison calibrations with a reference microphone . This can also be used for measuring the P-I (Pressure-Intensity) index of intensity systems at 250 Hz.

Octopus couplers are also available for simultaneously calibrating up to 8 microphones.

Frequency Hz 250
Sound pressure level dB 114 re. 20 μPa
Gain dB 1.5
ANSI standard S1.10
IEC standard 60942
Temperature range, operation °C / °F -10 to 55 / 14 to 131
Battery type 4 x AA alkaline (IEC LR 6)
Weight g / oz 325.00 / 11.464

Included

G.R.A.S. RA0049 Adapter for ¼" microphones
G.R.A.S. RA0069 Adapter for ⅛" microphones
G.R.A.S. ZC0002K Barometer
G.R.A.S. RA0048 Coupler for ½" microphones
G.R.A.S. EL0001 Four LR6-AA alkaline batteries

Optional

G.R.A.S. RA0009 Adapter for Outdoor Microphone System 1 41AM
G.R.A.S. RA0041

Adapter for Outdoor Microphone System 1 41CN

G.R.A.S. RA0010 Adapter for Environmental Microphone 1 41AL
 G.R.A.S. RA0157 Pistonphone adapter 1/2"  for KEMAR pinna
G.R.A.S. RA0024 Two-port calibration coupler
G.R.A.S. RA0023 Adapter for 1" microphones
G.R.A.S. RA0090 94 dB Pistonphone coupler
G.R.A.S. RA0168 Digital precision barometer