Full-range Speaker - Typical Designs

Typical Designs

Typically, a full-range drive unit consists of a single driver element, or voice coil, used to move and control a diaphragm. Often the cone structure includes optimizations to enhance high-frequency performance. For example, a small low-mass horn or whizzer cone can be mounted where the voice coil and diaphragm meet, thereby increasing the output at high frequencies. The shape and materials used in the cone and whizzer are highly optimized.

Another arrangement, uses a radiating dome in place of the usual dust-cap; it is acoustically active. In most speaker drivers such dust-caps are constructed so as to be relatively acoustically inert. Sometimes the dust cap takes the form of a small conical shape, claimed to improve dispersion at higher frequencies. Yet other designs simply modify the diaphragm and dome/whizzer materials instead of compliantly coupling the diaphragm to achieve full-range operation.

In some designs, the main diaphragm may be coupled to the voice coil using a compliant bond such that high frequency vibrations are not transmitted into it, but instead move the whizzer cone. The technique of using a compliantly coupled (or modified) diaphragm for the low frequencies and auxiliary whizzer or modified dust-cap (dome) for the high frequency response of a speaker is a mechanical implementation of an audio crossover.

Since the requirements of a full-range driver include both good low and high frequency response (which are contradictory in terms of physical construction), a full-range driver is usually limited to covering the audio spectrum above perhaps 100Hz—leaving lower frequencies to be handled / augmented by a separate sub woofer or by a special cabinet design for low frequency reinforcement. These requirements usually mean that the full-range must have good sensitivity (for lower frequencies) with a light voice coil (for high frequencies) – these speakers commonly use a larger or more powerful magnet than usual, which improves sensitivity and thus lowers the power requirement at low frequencies as well as allowing a lighter voice coil. In addition, many have limited maximum excursions, requiring special enclosures which do not require large excursions at low frequencies for reasonable low end output.

There are rare exceptions that use multiple elements to drive a common diaphragm, but these should not be confused with coaxial speakers that use separate and concentrically aligned elements to achieve the desired range of reproduction, and are not, strictly, classified as full-range drivers.

Full-range drivers are seen in applications ranging from televisions and computer speakers, to superb hi-fi speaker systems. The performance of the driver is substantially affected by their enclosure, and enclosures vary from mundane beige plastic boxes, at the low end of the scale, to large horn loaded enclosures with spectacular audio performance.