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Subwoofer Integration Basics

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  • Subwoofer Integration Basics

    Most of what we assume is a "boomy" subwoofer is just poor alignment between it and the main speakers. Getting the bass system adjusted right is 90% of the goal of superb bass performance. Here's how.

    Assuming the standard 80Hz crossover, the trick is to get an overlap without amplitude ripple - irregularities in the frequency response and that lumpy, subwoofer-forward sound we want to avoid. Since the main and bass speakers each have their own unique response shapes in both amplitude and phase, ideally we have to get all of that aligned.

    The ideal way for a fairly conventional, fairly plug-and-play sub/main pairing is to use 1) a standard 80Hz-and-below subwoofer - they're usually set in either the speaker itself or the AVR but ideally not both - and 2) a main speaker with a natural, acoustical 80Hz highpass function plus another complimentary electronic highpass crossover - also an AVR setting, such as "small speaker".

    The usual lowpass (subwoofer) function is 4th order, or attenuation of 24dB for each octave above 80Hz - remember, we can't brickwall either speaker, so we have to overlap them correctly instead. Meanwhile the acoustical speaker response in a sealed main speaker is 2nd order, half that rate, or -12dB with each descending octave. To get to our desired -24dB main speaker function, which matches our standard subwoofer function, hopefully our AVR has a -12dB electrical highpass function.

    Let's simplify:

    Subwoofer function: -24dB per octave @ 80Hz.
    Final bass lowpass response; 80Hz @ -24dB per octave attenuation

    Acoustical main speaker function for a sealed speaker: -12dB per octave @ 80Hz
    Added electrical crossover main speaker function: -12dB per octave @ 80Hz
    Final main speaker highpass response; 80Hz @ -24dB per octave attenuation

    Assuming some other aspects of this arrangement aren't terribly misaligned - crossover Q, relative speaker distances to the big chair, and level - the symmetry puts the two systems into good agreement with one another and the subwoofer acoustically disappears - the main speakers sound like they're going all the way to 20Hz. That's the effect we want.

    The Chane A5/A5rx-c/A5.4 has a bass reflex, open-port response down to about the mid 40's and because it's vented, an aggressive rate of attenuation that approaches our -24dB/octave by itself. As a stopped-port, sealed speaker, however, its cutoff rises to 80Hz, but the response shape becomes that gradual, -12dB/octave acoustical response that forms half of our desired combined response. Does the AVR have the other -12dB/octave electrical highpass in it? Is everything set to 80Hz? If so, the stopped-port A5.4 is a natural setup.

    In open-port mode things get a little more complicated. We'd assume the extra bass reach would add to the subwoofer's output in the same region however phase rotation accompanies any speaker or analog crossover attenuation. When it does the combined response ends up fighting itself - we get response "ripple" and that detached woofer sound we're trying to avoid. In some cases if the phase disagreement is too much the two halves of the combined system actually defeat one another and we get a hole in the response.

    One recourse is to try a roughly 45Hz crossover point, again using similar rules, but this time because of the faster ported-speaker attenuation, the main speakers need no electrical attenuation. The issues with this are that lacking an electrical highpass on the mains they get no power and cone excursion protection and they may be overloaded. At the same time the subwoofer is now crossed so low that it's natural deep bass cutoff and this much lower lowpass crossover point overlap such that the sub never reaches sufficient output. It's own internal responses on either end of its very limited range become conflicted.

    Try stopping the A5's ports, dial in a -12dB/octave electrical highpass at 80Hz, give the sub one crossover at 80Hz too, tune a few things by ear, and enjoy. Any similar speaker, which includes our A series range of models, follows the same rule.

  • #2
    Thanks for the tutorial on sub integration Jon. If I remember correctly You are working on some quality self powered subs at a nice price point. It would be good to just purchase subs that integrate perfectly with the Chane products as I know that must be part of your goal. Looking forward to see what the future holds. Always want that goodsound.

    Goodsound

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