Subwoofers

A subwoofer is a type of loudspeaker dedicated to the reproduction of bass frequencies, typically from about 20 Hz to about 200 Hz. more...

It is difficult for small loudspeakers to reproduce frequencies below 40 Hz, especially above 100 dB, and so it is often advantageous to use a loudspeaker intended specifically for this task.

Overview

Subwoofers use drivers (woofer) with cones typically coming in 10" or 12" sizes, but can be as large as 34", and as small as 4". Larger diameters tend to be advantageous because low frequencies involve shifting a great deal of air; a recent trend has been for high excursion, i.e., how far the cone can linearly travel from its resting position; for example, some can move as much as 2.5" in or out, yielding an overall displacement of 5" (this is controlled movement range).

Subwoofers are usually powered by a high power amplifier, and often an electronic crossover with a Low-pass filter is used to ensure that higher frequencies will not be directed to the subwoofer.

The need to reproduce these frequencies has increased since older formats, such as vinyl records, have been replaced by digital formats, such as CDs, and particularly 5.1 formats such as Dolby Digital and DTS, in which the ".1" channel is dedicated solely to the subwoofer. The .1 channel is usually dedicated to extended bass frequencies, for example, the low frequencies of a gunshot, double bass, or thunder. This track is often used aggressively by mixing artists.

Applications

Professional audio

Subwoofers are found in professional applications such as live concerts, movie theatres, various other sound reinforcement applications (ranging from nightclubs to theme restaurants) and studios. Some of these applications require subwoofers designed for very high sound levels, such as the JBL 4645 or the Electro-Voice TL440 which use a larger than average 18" driver and are certified for use in THX movie theatres. THX Approved Cinema Equipment Most movie theatre speakers (situated behind a perforated screen) typically use 15" drivers, so the larger subwoofers are used only to reproduce the lowest frequencies at high sound pressure levels.

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