microphone

A transducer that converts acoustical waves into electrical signals. The most common instrumentation microphone uses a capacitive sensing element, hence, the name condenser microphone.

Tips on Microphone Use
The following tips can help you make better measurements with microphones:

1. For the most accurate measurements, use precision condenser microphones that are individually calibrated.
2. For measurements in a free field (a sound field with no major nearby reflections), use a free-field microphone pointed at the source of sound.
3. For handheld measurements, keep the microphone as far as way from you body as possible to prevent it from creating undesirable reflections or shadow. A goose neck (microphone extension arm) is useful.
4. For measurements where the microphone is mounted on a tripod, the tripod can give reflections at higher frequencies (above 5 kHz). If these frequencies are critical, use of a gooseneck is again advisable.
5. For measurements in a diffuse field, such as inside in a highly reverberant room, where sound is coming from all directions, use a random incidence microphone.
6. For measurements inside a closed chamber, or when the microphone is part of the surface of a room or of the object being measured, use a pressure microphone.
7. To select one sound source out of many, use a directional microphone pointed directly at the source of the sound. Note that directional microphones may not have as flat frequency response as omnidirectional microphones. In addition, some types of directional microphones exhibit what is called a "proximity effect", where the frequency response is greatly accentuated at lower frequencies when measuring close to the sound source. A more advanced technique (and significantly more expensive) uses "acoustic imaging" or "acoustic holography" using an array of microphones.
8. For outdoor measurements, the microphone should be fitted with suitable protection against the environment. This may include rain caps, anti-bird spikes, built-in heaters to prevent condensation.
9. For measurement in corrosive environments, check that with the manufacturer of the microphone for recommendations. Most condenser microphones have nickel diagphragms and can be very sensitive to corrosion.
10. To prevent vibrations from influencing the measurement, shock mounting of the microphone may be necessary. Check the microphone specifications for vibration sensitivity.
11. For reproducible measurements, make sure the microphone is mounted firmly and at a precisely reproducible location, both compared to the unit being tested and to the environment.
12. Always calibrate the entire measurement chain, including the microphone, before starting the measurement. For highly critical measurements, as an extra precaution, you may want to perform a new calibration immediately after the measurements are completed to make sure the system is still within tolerances.
    

Helpful Web Sites:

• Acoustic Test Chambers and Environments
  
  

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