Driver types

An audio engineering rule of thumb is that individual electrodynamic drivers provide quality performance over at most about 3 octaves. Multiple drivers (e.g., subwoofers, woofers, mid-range drivers, tweeters) are generally used in a complete loudspeaker system to provide performance beyond 3 octaves.


Full range drivers

A full-range driver is designed to have the widest frequency response possible, despite the rule of thumb cited above. These drivers are small, typically 3 to 8 inches (7 to 20 cm) in diameter to permit reasonable high frequency response, and carefully designed to give low distortion output at low frequencies, though with reduced maximum output level. Full range (or more accurately wide range) drivers are most commonly heard in public address systems, and in televisions, although some models are suitable for hi-fi listening. In hi-fi speaker systems, the use of wide range drive units can avoid undesirable interaction between multiple drivers, caused by non-coincident driver location, or crossover network issues. Fans of wide range driver hi-fi speaker systems claim a coherence of sound, said to be due to the single source and a resulting lack of interference, and likely to the lack of crossover components. Detractors typically cite the wide range driver's limited frequency response and their modest output abilities, together with their requirement for large, elaborate, expensive enclosures, such as transmission lines, or horns, to approach optimum performance.

Full range drivers often employ an additional cone called a whizzer: a small, light cone attached to the joint between the voice coil and the primary cone. The whizzer cone extends the high frequency response of the driver and broadens its high frequency directivity, which would otherwise be greatly narrowed due to the outer diameter cone material failing to keep up with the central voice coil at higher frequencies. The main cone in a whizzer design is manufactured so as to flex more in the outer diameter than in the center. The result is that the main cone delivers low frequencies and the whizzer cone contributes most of the higher frequencies. Since the whizzer cone is smaller than the main diaphragm, output dispersion at high frequencies is improved relative to an equivalent single larger diaphragm.

Limited-range drivers are typically noted in computers, toys, and clock radios. These drivers are less elaborate and less expensive than wide range drivers, and they may be severely compromised to fit into very small mounting locations. In this application, sound quality is a low priority. The human ear is remarkably tolerant of poor sound quality, and the distortion inherent in limited range drivers may enhance their output at high frequencies, increasing clarity when listening to spoken word material.