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Message: <blockquote data-quote="Merlijn van Veen" data-source="post: 106100" data-attributes="member: 4708">Re: Endfire sub array under a stageI recommend staying clear, within reason, of any boundaries (except for the ground floor) in general when it comes to subwoofer configurations that rely on level and time interaction. Apparently there’s a preference for end-fired configurations over gradient or inverted stack configurations. As was already mentioned, end-fire has less rear rejection than gradient or inverted stack. It might be tempting to attenuate the rear speaker in gradient configurations for optimal cancellation at the microphone. This electronic offset however remains constant over distance, preventing the configuration from achieving maximum cancelation at greater distance. Without the electronic attenuation the difference in level caused by the physical displacement of the speakers becomes insignificant over distance, automatically increasing cancelation at greater distance when both levels become equal. The same can’t be said for end-fired. I’ve attached examples of a 4 element end-fire and a (2 element) gradient configuration, both optimized for an upper bandwidth limit of 100 Hz. The spacing is 1,13 and 1,24 meters respectively. Point of observation is 15 meters.[ATTACH]152806[/ATTACH] The end-fire bandwidth is indicated by the yellow markers. The right marker resides at the frequency equal to 1/3 wavelength spacing. At this frequency nothing is gained or lost. The left marker is its counterpoint. The black marker indicates the first cancelation and the red marker the critical frequency where all speakers add regardless of the amount of speakers. At 15 meters the front-to-back ratio within the bandwidth is 16 dB.[ATTACH]152807[/ATTACH] The gradient bandwidth is in indicated by the yellow and red markers. The yellow markers reside at the minus 3 dB points and the red markers at the minus 6 dB or 1/3 wavelength or 120 degrees phase difference points. The green marker indicates maximum summation. At 15 meters the front-to-back ratio within the bandwidth is 25 dB. For the sake of illustration, lets change the point of observation to 1 km. Now the front-to-back ratio for the same configurations becomes 14,5 dB and 63 dB for end-fire an gradient respectively. I’d also like to point out that end-fired configurations lack uniform coverage over frequency in contrast to gradient. As can be seen in the polar plots.[ATTACH]152808[/ATTACH][ATTACH]152809[/ATTACH] End-fired configurations of 3 or more elements require more real estate than gradient or inverted stack. At 5 or more elements one could speak of diminishing returns? When real estate is scarce gradient or inverted stack seems the lesser of two evils in contrast to putting the end-fired configuration under the stage. If vertical coverage is of concern and equal resources are available pile your subwoofers in a gradient configuration. And finally I’d like to point out that raising the level, for whatever reason, of an end-fired configuration over the mains comes “without” penalty. The same can’t be said of a gradient configuration. Raising the level of a gradient configuration over the mains brings into play the cancelled frequencies beyond the bandwidth. No amount of equalizing can restore this energy and if you try, you might end up blowing up your speakers. You’ll most likely hear no change due to the cancelation but each speaker individually is affected. The common emphasis of the subwoofers levels might account for the lack of impact that’s often associated with this kind of configuration. If you require more sub use a low-shelf on your processor input or mixer. Inverted stack is a poor derivative of gradient when real estate is an issue or flying is preferred because you hardly ever achieve true ¼ wavelength displacement. These plots are modeled with infinite small speakers without any physical dimensions but the trends should be clear…</blockquote>

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