a high frequency signal, and then route the low and high frequencies into two power amplifiers, each of which send their powered signal to different speaker enclosures. One power amp (usually of higher power) handles the low frequencies, which are sent the larger drivers (at lower frequencies), and a less powerful amp amplifies the high frequencies, which are sent to the horn. For bass players seeking a pure, transparent sound, biamplification may produce a "cleaner" sound. For bass players in hard rock or heavy metal who are using an overdriven sound, biamplification may be safer for the horn or tweeter; while a clipped, distorted signal can be handled by a heavy-duty woofer, the same clipped signal will come much closer to damaging a horn driver or a tweeter. Biamping allows a bassist to have the "dirty" overdriven sound through their woofer(s) while keeping the signal sent to the horn clean, thus protecting the horn. At the high onstage volume levels used in large rock and metal concerts, a powerful, overdriven bass signal poses a higher risk of horn damage in non-biamped systems. Often what is referred to as a "guitar amp" is in fact a combo amplifier: a cabinet with speakers and a built-in amplifier. Combo amplifiers may be referred to by their speaker cabinet configuration plus the word "combo", so that "4x10 combo" means a guitar amplifier built into a 4x10" speaker cabinet. Since the popular configurations are limited in variety, cabinet configurations are often written abbreviated without ambiguity: For example, 4x10" may be written 410, and 112 refers to a single cabinet housing a 12" speaker. The speaker cabinets, which hold these drivers can be closed-back or open-back, along with variations such as a semi-open back 4x12 in cabinet, which may have a baffle deflecting two of the four speakers. Closed back cabinets may be acoustic suspension or bass reflex. Bass cabinets are usually closed-back or use a bass reflex port or vent to boost low frequency response. The purpose of the cabinet is match the acoustic impedance seen by the driver to the driver's own electrical/mechanical impedance. Cabinets are best used when they are matched to the driver(s) being used; casual substitution of another driver which can be mounted in a cabinet will only accidentally make changes in a beneficial direction. The sound of the speaker and cabinet is crucial to the sound of the electric guitar,