The microphone of a sound level meter is the input device. The processing section is where the sound from the microphone is analyzed. The processing section typically includes a weighing network, where the signal is passed through without modification. Filters then divide the sound into separate frequency bands. Next, the root mean square detector amplifies the signal and determines the RMS value of the signal. This value is based on the amount of energy in the signal. Finally, the display unit shows the sound level in decibels, or dBs.
Basic sound level meters are divided into two categories: F Characteristic and S Characteristic. F Characteristic sound level meters feature a fast reacting display that will change rapidly based on incoming levels of sound. These meters are ideal for measuring sounds that are relatively constant. For constantly changing sound levels, it is advisable to use an S Characteristic sound level meter. The display unit of these meters will react more slowly, averaging out the fluctuating sound levels.
Impulse sound meters are used to measure isolated, high-impact sounds that are too short in duration to be accurately read with an F or S Characteristic sound level meter. Impulse sound meters will display the peak value of sounds received by the microphone, regardless of length. Noise Dose meters are useful for gauging the daily noise exposure of workers throughout a day. These meters calculate the amount of noise heard by a person over time in order to prevent hearing loss.
Sound level meters are extremely useful in a variety of situations. They're commonly used by sound engineers before live performances, especially when planning multistaged events. Recording engineers will also use sound level meters while micing a recording session. This can be a useful practice when ensuring the quality of a recording or live performance, as well as the hearing integrity of the performers and audience members.
The accuracy of a sound level meter is entirely dependent upon its calibration. Improperly calibrated units will give inaccurate readouts, and are basically useless. Be sure to calibrate your sound level meter before and after each measurement session by situating an acoustic calibrator, like a sound level calibrator or Piston Phone, above the sound level meter's microphone.