An audio engineering rule of thumb is that individual electrodynamic drivers provide quality performance over at most about three octaves. Multiple drivers (e.g., subwoofers, woofers, mid-range drivers, and tweeters) are generally used in a complete loudspeaker system to provide performance beyond three octaves.
[edit]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 (7.6 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 also to the lack of crossover components. Detractors typically cite wide-range drivers' limited frequency response and modest output abilities, together with their requirement for large, elaborate, expensive enclosures—such as transmission lines, or horns—to approach optimum performance.[citation needed]
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.[citation needed]
Limited-range drivers are typically used 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 these applications, 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.[citation needed]
[edit]Subwoofer
A subwoofer is a woofer driver used only for the lowest part of the audio spectrum: typically below 120 Hz. Because the intended range of frequencies in these is limited, subwoofer system design is usually simpler in many respects than for conventional loudspeakers, often consisting of a single speaker enclosed in a suitable box or enclosure.[citation needed]
To accurately reproduce very low bass notes without unwanted resonances (typically from cabinet panels), subwoofer systems must be solidly constructed and properly braced; good ones are typically extraordinarily heavy. Many subwoofer systems include power amplifiers and electronic sub-filters, with additional controls relevant to low-frequency reproduction. These variants are known as "active subwoofers".[citation needed] "Passive" subwoofers require external amplification.
[edit]Woofer
A woofer is a driver that reproduces low frequencies. Some loudspeaker systems use a woofer for the lowest frequencies, making it possible to avoid using a subwoofer. Additionally, some loudspeakers use the woofer to handle middle frequencies, eliminating the mid-range driver. This can be accomplished with the selection of a tweeter that responds low enough combined with a woofer that responds high enough that the two drivers add coherently in the middle frequencies.[citation needed]
[edit]Mid-range driver
A mid-range speaker is a loudspeaker driver that reproduces middle frequencies. Mid-range drivers can be made of paper or composite materials, or they can be compression drivers. If the mid-range driver is cone-shaped, it can be mounted on the front baffle of a loudspeaker enclosure, or it can be mounted at the throat of a horn for added output level and control of radiation pattern. If it is a compression driver, it is invariably mated to a horn.[citation needed]
[edit]Tweeter
A tweeter is a high-frequency driver that typically reproduces the highest frequency band of a loudspeaker. Many varieties of tweeter design exist, each with differing abilities with regard to frequency response, output fidelity, power handling, maximum output level, etc. Soft-dome tweeters are widely found in home stereo systems, and horn-loaded compression drivers are common in professional sound reinforcement. Ribbon tweeters have gained popularity in recent years, as their output power has been increased to levels useful for professional sound reinforcement, and their pattern control is conveniently shaped for concert sound.[citation needed]
[edit]Coaxial drivers
A coaxial driver is a loudspeaker driver with two or several combined concentric drivers. Coaxial drivers have been produced by many companies, such as Altec, Tannoy, Pioneer, KEF, BMS, Cabasse and Genelec.[12]
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