Frequency analysis
Shock metrology
Piezoelectric transducers
Signal conditioning

Measuring microphones


The condenser microphone is to-day accepted as the standard acoustical transducer for all sound and noise measurement because of its very high degree of accuracy; an accuracy which is higher than what is possible with any other acoustical transducer.

Not only is the condenser microphone an accurate laboratory tool used by standards laboratories, it is also used for a broad range of field measurements under many different and often severe environmental conditions.

Microphone Measurement Range

The reason for the high degree of acceptance is that the condenser microphone has the following properties which are essential for a standard transducer:

  • High stability under various environmental conditions.
  • Flat frequency response over a wide frequency range.
  • Low distortion.
  • Very low internal noise.
  • Wide dynamic range.
  • High sensitivity.

    In order to attain the microphone’s high standard, considerable care is required in both design and production. This includes advanced clean-room techniques, very tight mechanical tolerances, a special diaphragm construction and artificial ageing techniques.

    Microphones and Preamplifiers

    The condenser microphone converts the acoustical pressure electrical signal which thereafter is amplified in a preamplifier. always be connected very close to the microphone since its convert the very high impedance of the microphone into a low permitting use of long cables and connection to instruments impedance. The low impedance ensures very little pick up of and this is especially important when using long cables.

    Types of Microphones

    Microphones are divided into 3 types according to their response in the sound field: free field, pressure, and random incidence.

    Free field microphones have uniform frequency response for the sound pressure that existed before the microphone was introduced into the sound field. It is of importance to note that any microphone will disturb the sound field, but the free field microphone is designed to compensate for its own disturbing presence as discussed later.

    The pressure microphone is designed to have a uniform frequency response to the actual sound level present. When the pressure microphone is used for measurement in a free sound field, it should be oriented at a 90° angle to the direction of the sound propagation, so that the sound grazes the front of the microphone.

    The random incidence microphone is designed to respond uniformly to signals arriving simultaneously from all angles. When used in a free field it should be oriented at an angle of 70° - 80° to the direction of propagation.

    In the following we will have a closer look at the reason for the difference between the microphones and when each type should be used.


    Before measurements are undertaken, it is important to calibrate the microphone and instrument together. This will check the function of the measurement system and ensure that high accuracy can be obtained allowing comparison to be made between measurements taken at different times. Calibration ought therefore to be made before each series of measurements and it is recommended that the calibration is repeated after a series of measurements as a double check.

    Acoustic Calibration

    Acoustic calibration is normally to be preferred, since the whole system from microphone to indicating device will be checked. To carry out acoustic calibration, fit the calibrator on the microphone, making sure it fits snugly. Switch on the calibrator and adjust the read out on the indicating device to the sound level produced by the calibrator being used. Two different calibrators are available for acoustic calibration: a pistonphone and an acoustical calibrator.