Full-range
From Wikipedia, the free encyclopedia
A Full-range loudspeaker drive unit is defined as an acoustic driver that attempts to reproduce as much of the audible frequency range possible, with high-fidelity, within the boundaries imposed by the physical limitations of the specific design.
Typically the full-range drive unit consists of a single driver element, or voice coil, used to actuate the acoustic interface, or diaphragm. Often the diaphragm includes optimizations to enhance high-frequency extension. For example a small low-mass horn or whizzer cone is mounted where the voice coil and diaphragm meet thereby increasing the efficiency (and hence frequency range) at high frequencies. The larger (or main) diaphragm may be coupled to the voice coil using compilant material so that high frequency vibrations of the coil are transferred only to the whizzer and not to the diaphragm.
Another arrangement, which doesn't employ a whizzer, uses a dome in place of the dust-cap – it looks like a dust cap but the material used is acoustically active. In contrast a dust-cap is constructed (or made of a material) such that it is as acoustically inert as possible, i.e., it does not contribute anything to the speaker's frequency responseǂ. Some times the dome takes the form of a small conical shape to improve dispersion. Yet other designs may simply modify the diaphragm and dome/whizzer materials instead of compliantly coupling the diaphragm to achieve full-range operation.
This arrangement 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 constitutes a mechanical crossover.
Since the requirements from a full-range are both good low and high frequency response (which tend to be contradictory in terms of physical construction) a full-range usually covers the audio spectrum from about 200Hz and above - often augmented by a separate subwoofer or special cabinet design for the lower end. 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 use a larger or more powerful magnet which improves sensitivity and thus lowers the power requirement for low frequencies as well as allowing a lighter voice coil.
There are exceptions that utilize multiple elements to drive a common diaphragm, but these should not be mistaken for units that utilize separate and concentrically aligned elements to achieve the desired range of reproduction. The latter are commonly referred to as coaxial drive units, and are not strictly classified as Full-range.
Full-range drive units may be found in applications ranging from inexpensive multimedia loudspeakers to costly esoteric constructions, the latter often utilizing large transmission line or horn loaded enclosures to increase the low frequency output.
ǂ – In practice, the dust cap will always add its own bit to the overall frequency response since it is also a part of the moving system of a speaker. However its contribution is controlled by making the dust-cap very small, light and dense enough to just stop dirt from entering the voice-coil gap. Indeed, a dust cap can be modified to also double up as a high frequency radiator or dome.
