Bi-amping and tri-amping
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"Bi-amping" is the use of two channels of amplification to power each loudspeaker within an audio system. "Tri-amping" is the practice of connecting three channels of amplification to a loudspeaker unit: one to power the bass driver (woofer), one to power the mid-range and the third to power the treble driver (tweeter). The terms derive from the prefix bi- meaning 'two', tri- meaning 'three', and amp the abbreviation for "amplifier".
It differs from the conventional arrangement in which each channel of amplification powers a complete speaker. Bi-amping typically consists of a crossover network and two or more drivers. With ordinary loudspeakers, a single amplifier can power the woofer, mid-range and tweeter through an audio crossover, which filters the signal into high- medium- and low-frequencies (or high- and low-frequencies in 2-way speakers) – a mechanism that protects each driver from signals outside its frequency range. However, the passive crossover itself is inefficient, so splitting the frequencies electronically before these are amplified is a way to avoid this problem. In such a case, an amplifier each powers a frequency range determined by an active crossover to each of the drive units. The technique is primarily used in large-scale audio applications such as sound amplification for concerts, in portable powered speakers and by hi-fi enthusiasts.
A speaker system has to be wired to accommodate either configuration, typically with two sets of binding posts, one set for the bass and one set for the mid-highs. A single amplifier can usually power a woofer and a tweeter only through a crossover filter, which protects each driver from signals outside its frequency range.
Bi-amping of speakers requires double the channels of amplification and can be accomplished using two ordinary amplifiers in either a vertical or horizontal arrangement.
- Horizontal bi-amping uses one amplifier to power both bass drivers (woofers) and the second amplifier to power both treble drivers (tweeter) or the midrange and treble drivers together. Horizontal bi-amping has the advantage of allowing two different amplifiers that sound better than each other for bass or for treble.
- Vertical bi-amping uses two channels of an amplifier per loudspeaker, with a dedicated channel for the bass driver and a dedicated channel for the treble or the treble and the midrange together. Vertical bi-amping has the advantage of not having to use a single amp to power both bass sections, which can be very taxing on the amplifier, especially at higher volume or if the bass driver has a particularly low impedance at certain frequencies.
Most audible differences are subtle. If at all noticeable, benefits of bi-amping cannot be realized if passive crossover networks of a speaker system are not removed. Benefits include transients are less likely to cause amplifier overload (clipping) and/or speaker damage, and reduced intermodulation distortion, elimination of errors introduced by low frequency passive crossover, reduction of load to the load presented to the power amplifier, better matching of power amplifier and speaker driver and others.