The acoustic guitar's extremely broad frequency spectrum presents a special challenge to loudspeaker designers. Whereas the electric guitar sounds we have come to know and love are partly the product of speakers that are very poor by hi-fi standards, acoustic guitar amplifiers aim to reproduce the entire spectrum evenly.
To this end, many acoustic amps take the same approach as most hi-fi speakers and PA systems - the signal is split into two or more frequency bands with a separate speaker for each, the typical arrangement involving low, mid and high-frequency units in a single cabinet. As with PA and hi-fi speakers though, there is generally a trade-off between flat response and phase coherence, because each frequency band of the signal must pass through different circuitry, and the variously sized drivers employed each have different response times.
Broadband speakers aim to reproduce the entire spectrum with a singe driver, and are commonly found in televisions and car hi-fis. The simultaneous presence of deep bass and high treble frequencies often causes distortion, and it's difficult to design a single speaker that reproduces the whole frequency range well. The use of broadband speakers in acoustic amplifiers therefore relies on particularly high quality components, but carries many advantages including improved phase coherence and reduced interference. Broadband speakers are used by AER, a leading innovator in acoustic amplification.