Microphones are basically transducers that convert changes in air pressure (sound waves) into electrical signals. In practice, the microphone is the input point for the signal and is in fact the most important and expensive part of the sound level meter. The main feature of a microphone is its sensitivity. Although there are different types of microphones, the most suitable for a sound level meter is usually a condenser microphone.
Delta OHM microphones are of the polarised or pre-polarised condenser type, with a standard diameter of ½” or ¼” and optimised for free field or diffuse field measurements depending on the model.