Loudspeakers play an important role in a public address system (or for that matter any sound reproduction system) as the final link in the signal processing chain.

They convert electrical energy from the power amplifier into acoustic energy in air that travels as sound waves to the listeners. Regardless of the quality of the preceding signal processing chain, if the loudspeakers are of poor quality or incorrectly connected or operated, the result will be poor quality sound.

Typically, the performance of loudspeakers is orders of magnitude (ie, multiples to the power of 10) worse than what we would accept from other audio processing devices.

At some time or other, we have all struggled to understand a public speaker in a church or school hall amplified with the typical "column" or horn loaded public address loudspeaker system. In fact, most people have concluded that high-quality vocal reproduction in a reverberant environment is difficult, if not impossible.

So what exactly are the requirements for a public address loudspeaker?

Well, it must reproduce acoustically the electrical input signal at an adequate level to be heard, without introducing distortion or colouration. The loudspeaker must accurately match the ‘timbre’ of the voice or instrument it is reproducing. The sound should be clear and intelligible for each listener, even though the listeners may be widely dispersed in three dimensions. If used inside an enclosed space, it must do this with the added encumbrance of the superimposed room acoustics.

The loudspeaker should not be prone to feedback or howl-around, when used with open microphones. From a practical point of view, it should be small, light and visually unobtrusive. It should be physically constructed in such a way that it can be installed in optimal positions, both acoustically and aesthetically. Finally, it must connect and function reliably.

There are many methods of converting electrical energy into acoustical energy (including some esoteric ones) but the overwhelming majority of loudspeakers use electrodynamic transducers constructed with voice coils in permanent magnet fields driving a moving diaphragm. Electro-
dynamic transducers have so far proven to offer the best balance of performance and ruggedness at an affordable price.

To achieve the performance ideals listed above, the following areas of loudspeaker system performance are important:

• Time Alignment and Source Coincedence,
• Controlled Directivity, and
• Stored Energy.