As a conduit for the output of all electronically created sound, the loudspeaker is one of the most significant inventions of the past 150 years. Indeed, in one form or another loudspeakers have been at the heart of much of the technology that has since emerged—from telephone, radio, and television to hi-fi music systems.
It was Alexander Graham Bell (1847-1922) who patented the first electrical loudspeaker in 1876, as part of his telephone system. In conjunction with his assistant, Thomas A. Watson, Bell created a simple design. A drum was covered with a tightly stretched goldbeater's skin (diaphragm) and a magnetized free- floating armature was placed at its center. The armature was able to vibrate against the skin and responded to changes in a magnetic field. This device was connected to Bell's "liquid" transmitter into which he uttered words that were heard clearly by his assistant in the next room. It was an extremely rudimentary design, but in principle the device performed the same function as most contemporary audio systems: It turned electrical signals—those that had been derived and converted from an original source—into audible sound.
Bell himself was not specifically interested in the loudspeaker function, and he left it to others to make improvements to the device. A year later, German inventor and industrialist, Werner von Siemens (1816- 1892), patented a greatly more sophisticated idea—a loudspeaker cone with a diaphragm controlled by an electromechanical transducer. This would eventually evolve into the moving coil principle on which most loudspeakers have since been designed.
