Transducers Electronics Meets Acoustics
Transducers are devices for converting one type of signal into another. Microphones convert sound (acoustic) signals into electronic signals. Speakers do the reverse; they convert electronic signals into sound. In audiology, the tiny speakers used in hearing aids are called receivers: They receive the electronic signal and provide sound to the ear canal. (Be aware that in acoustics literature, microphones, not speakers, are classified as receivers since microphones receive the incoming acoustic signals; speakers are classified as transmitters.)
Intensity Level and Sound Pressure Level
Before beginning your study of transducers it is important to develop a firm understanding of how sound is quantified. As sound propagates through the air, it carries energy that enables it to activate a response
in a microphone or in your own tympanic membrane. Since a certain amount of energy is carried during each unit of time, you can think of the sound as carrying power (energy per unit time). Also, as sound propagates through open spaces (is not confined to pipes), it spreads out, covering larger and larger areas. Very sensitive sound detection systems can be made by means of large parabolic reflectors able to intercept very faint sounds and direct the sound toward a microphone. The larger the area of the reflector, the more sensitive the device becomes. Because the power in a sound wave is spread over an area, the intensity of sound is defined as the power per unit area.