Calibration can be performed at either 250 Hz or at 1 kHz. Both frequencies have their advantages and disadvantages.

250 Hz is in the frequency range where the frequency response of almost all microphones is flat and will therefore give the most accurate calibration.

If, however, the microphone is used in connection with measuring equipment with weighting filters, for example a sound level meter with A-weighting, the 250 Hz signal will be attenuated by the weighting network. In this case it might be advantageous to use a 1 kHz calibration frequency.

At 1 kHz, the weighting filters have 0 dB attenuation and will therefore not affect the calibration.

GRAS 42AG Class 1 Sound Calibrator

The GRAS 42AG Multifunction Sound Calibrator is a portable, battery-operated precision microphone calibrator. The calibrator can be used directly on 1″ microphones. Adapters for calibrating 1/2″ (factory mounted), 1/4″ and 1/8″ microphones are included. It conforms to standard IEC 60942 for Class 1 sound calibrators

GRAS 90AA Audiometer Calibration System

The GRAS 90AA Audiometer Calibration System is configured to meet the requirements of modern audio-meter calibration. It is easy and fast to set up and control, fulfilling all regulatory requirements

GRAS 90CA-S2 Microphone Calibration System

The GRAS 90CA-S2 Microphone Calibration System provides for automated and reliable level and frequency response calibration of measurement microphones. The implemented calibration methods conform with relevant standards as listed in the specifications.

Pistonphones

Pistonphones are precision mechanically driven piston in a chamber to calibrate measurement microphones by generating a highly accurate and stable sound pressure level at 250 Hz. Many types of pistonphones are available from GRAS.