Electroacoustic Devices

If the spoken word or a program of music is to be transmitted electrically, some electroacoustic device must either convert the sound waves into electric energy or permit the sound waves to control the electric power supplied by a source such as a battery. Such an electroacoustic device is defined¹ as a telephone transmitter, "a device whereby sound waves produce substantially equivalent electric waves." The familiar word microphone is¹ "a term frequently used as a synonym for telephone transmitter, particularly in radio and sound picture fields."

A telephone transmitter (or microphone) is a special form of electro-acoustic transducer, defined¹ as "a transducer by which power may flow from an electric system to an acoustic system or vice versa." The term transducer is defined¹ as "a device by means of which energy may flow from one or more transmission systems to one or more other transmission systems". There are two types of transducers, a passive transducer, containing no source of power, and an active transducer, containing a source, or sources, of power.¹ Accordingly, telephone transmitters (or microphones) that contain no source of power but which convert acoustic energy into electric energy are passive or generator-type transmitters and sometimes are called passive electro-acoustic transducers.² Similarly, telephone transmitters that use sound waves to control the flow of power from a battery are active or modifier-type transmitters and are sometimes called active electro-acoustic transducers.³