Editing Subwoofer (section)

=====End-fire array=====
[[File:End-fire Subwoofer Array.png|thumb|End-fire array using three rows of subwoofers. Each row is delayed a few milliseconds more than the previous row.]]

The end-fire subwoofer method, also called "forward steered arrays",<ref name="ForwardSteered" /> places subwoofer drivers co-axially in one or more rows, using destructive interference to reduce emissions to the sides and rear. This can be done with separate subwoofer enclosures positioned front to back with a spacing between them of one-quarter wavelength of the target frequency, the frequency that is least wanted on stage or most desired in the audience. Each row is delayed beyond the first row by an amount related to the speed of sound in air; the delay is typically a few milliseconds. The arrival time of sound energy from all the subwoofers is near-simultaneous from the audience's perspective, but is canceled out to a large degree behind the subwoofers because of offset sound wave arrival times. Directionality of the target frequency can achieve as much as 25&nbsp;dB rear attenuation, and the forward sound is coherently summed in line with the subwoofers.<ref name=Kamlet2004 /> The positional technique of end-fire subwoofers came into widespread use in European live concert sound in 2006.<ref name=Stevens2006 />

The end-fire array trades a few decibels of output power for directionality, so it requires more enclosures for the same output power as a tight-packed, flat-fronted array of enclosures. Sixteen enclosures in four rows were used in 2007 at one of the stages of the [[Ultra Music Festival]], to reduce low-frequency interference to neighboring stages.<ref name=Brill2007 /> Because of the physical size of the end-fire array, few concert venues are able to implement it. The output pattern suffers from comb-filtering off-axis, but can be further shaped by adjusting the frequency response of each row of subwoofers.<ref name="ForwardSteered"/>
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