AUDIO REPRODUCTION DEVICES

2-30 Figure 2-29.—Simple crystal frequency synthesizer. Q25. What is the primary function of an afc circuit? Q26. What is frequency synthesis? AUDIO REPRODUCTION DEVICES The purpose of audio reproduction devices, such as loudspeakers and headphones, is to convert electrical audio signals to sound power. Figure 2-30 shows you a diagram of a loudspeaker called the PERMANENT MAGNET SPEAKER. This speaker consists of a permanent magnet mounted on soft iron pole pieces, a voice coil that acts as an electromagnet, and a loudspeaker cone connected to the voice coil. The audio signal has been previously amplified (in terms of both voltage and power) and is applied to the voice coil. The voice coil is mounted on the center portion of the soft iron pole pieces in an air gap so that it is mechanically free to move. It is also connected to the loudspeaker cone; as it moves, the cone will also move. When audio currents flow through the voice coil, the coil moves back and forth proportionally to the applied ac current. As the cone (diaphragm) is attached to the voice coil, it also moves in accordance with the signal currents; in so doing, it periodically compresses and rarefies the air, which produces sound waves. Figure 2-30.—Permanent magnet speaker.