EQ'ing a sub mix on an AUX with the TM16

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  • Hello all - so we've recently started running out subs (4 x KW181's) on an Aux in an effort to keep lower frequency instruments where they need to be. I found this page on the QSC site, which is informative enough:

    http://qscservice.com/howto/touchmix/mi ... ubwoofers/

    But no mention is made of EQ settings - are they simply not that important given that the KW's already have a low-pass filter built in? I set up a gradual curve using the Aux EQ that gradually drops off everything above 100hz for that aux, and then we only put the kick, bass, and our track into that sub mix. It does assist in being able to regulate the sub volume independently of the mains, but I just wonder if its actually necessary to make the EQ adjustment at all or if it should just be left flat. Thoughts?
    pir8matt
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  • pir8matt wrote:Hello all - so we've recently started running out subs (4 x KW181's) on an Aux in an effort to keep lower frequency instruments where they need to be. I found this page on the QSC site, which is informative enough:

    http://qscservice.com/howto/touchmix/mi ... ubwoofers/

    But no mention is made of EQ settings - are they simply not that important given that the KW's already have a low-pass filter built in? I set up a gradual curve using the Aux EQ that gradually drops off everything above 100hz for that aux, and then we only put the kick, bass, and our track into that sub mix. It does assist in being able to regulate the sub volume independently of the mains, but I just wonder if its actually necessary to make the EQ adjustment at all or if it should just be left flat. Thoughts?


    Use the filters and not only chop off everything above, but also everything BELOW what your sub is capable of. Depending on the way you run your tops, you might cut off everything below 100hz that goes to the tops, so cut off everything above 100hz that is going to the sub. In addition, you should cutoff everything below 40hz (KW181s can go down to 34hz, so you could cutoff everything below that, but 40 should be low enough).

    The reason is, if you end up with any frequencies below what the sub can produce going to the sub, the speaker will "try" reproduce anyway ends up making the sub work harder than it needs to. The subs will work a lot more efficiently by sending them only the frequencies they are actually able to reproduce.

    YMMV

    I hope this helps,

    Steph
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  • Thanks Steph, that's useful info. Do you think just completely zeroing out those freqs is the way to go? Or just have a gradual tapering off from 100 on?
    pir8matt
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  • Actually, the KW sub, the K-Sub, and the KLA Sub all have built-in LP/HP filters to start with. They cannot produce signals above or below their intended frequency ranges. You can send them UNprocessed full-range audio, the subs will simply "know" what to do with those frequencies. In fact, it is actually undesirable to pre-process the HP or LP filters inside another upstream device (such as the TouchMix) only because you could easily end up with unintended interactions of the mixer's crossover points and the sub's crossover points. A "double filter" at 100 Hz, so to speak, and that might not be good.

    Just send audio to the subs with higher and lower frequencies than the sub is intended to produce (again, such as full-range audio). The sub will internally figure it out.

    Note that all of this advice is for our POWERED subs, since they have internal DSP processing. Non-powered subs, fed by a traditional power amp, would likely need pre-processed HP/LP filtered audio.

    Note, too, that either way you can still EQ the subs to taste, within their frequency band of course.
    Fred Thomke
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  • Hmm, ok well then - is there even any point in putting the subs on an aux at all? Other than to be able to control the volume independently of the mains?


    Fred Thomke wrote:Actually, the KW sub, the K-Sub, and the KLA Sub all have built-in LP/HP filters to start with. They cannot produce signals above or below their intended frequency ranges. You can send them UNprocessed full-range audio, the subs will simply "know" what to do with those frequencies. In fact, it is actually undesirable to pre-process the HP or LP filters inside another upstream device (such as the TouchMix) only because you could easily end up with unintended interactions of the mixer's crossover points and the sub's crossover points. A "double filter" at 100 Hz, so to speak, and that might not be good.

    Just send audio to the subs with higher and lower frequencies than the sub is intended to produce (again, such as full-range audio). The sub will internally figure it out.

    Note that all of this advice is for our POWERED subs, since they have internal DSP processing. Non-powered subs, fed by a traditional power amp, would likely need pre-processed HP/LP filtered audio.

    Note, too, that either way you can still EQ the subs to taste, within their frequency band of course.
    pir8matt
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  • Hi pir8matt,

    " is there even any point in putting the subs on an aux at all? "

    Yes. With only instruments producing low frequencies going to the subs, you clean up your mix.
    Think about a mic on a stand on a hollow stage that is resonating at a low frequency, and some of that sound is getting in to the mic.
    Since that mic's channel isn't going to the sub, there is no way for that low frequency noise to come out of the sub.

    Somebody drops a mic with a big low frequency boom going to the channel, but again, the channel isn't assigned to the sub so no LF boom is heard.(The higher frequencies are heard through the tops, but the overall effect isn't so obnoxious.)

    Additionally, I work a couple venues that might start an evening with 100 patrons, go up to 300, and down to 100 near the end of the evening.
    I have found that quite a bit of sub energy is absorbed by a lot of bodies on the dance floor, and as the crowd grows it is easy enough to bump up everything in the subs a few dbs with the aux master, and later lower the subs.

    The biggest downside to aux-fed-subs is the fact that it requires an aux. If you absolutely need all your auxes for other sends, then you are back to using crossovers in a rack or self-powered speakers. Or going to a mixer with more auxes.

    Good health, Weogo
    Weogo
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  • You beat me to the punch, Weogo. Your answer is spot on!
    Fred Thomke
    NO PRIVATE MESSAGES, PLEASE (use email address)
    Application Engineering Team
    Systems Support - Senior
    QSC Audio Products, LLC
    +1-800-QSC-AUDIO Tech Support
    +1-800-854-4079 Sales
    fred.thomke@qsc.com

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    Fred Thomke
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