I just need one HPF for my aux-fed subwoofer

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This topic contains 11 replies, has 5 voices, and was last updated by Profile photo of Andreas Andreas 5 years, 3 months ago.

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  • #54014
    Profile photo of Ratchet
    Ratchet
    Participant

    I just want to (4th order) filter the subsonic frequencies below 35Hz from my MIX send feeding my subs. I realize this isn’t specifically a “Qu” question, but what piece of gear would give me this single capability without paying for all the extras that come with a DBX DriveRack, for instance? Or is that my only option?

    It’s just that my racks are all full, and I’d need to buy another rack and reconfigure things to add a driverack now. It just seems like a waste to just use one function of a DRPA for one channel too. I could use it for my mains, but then I couldn’t run my subs AUX-FED, (MIX-FED?) and that’s not really ideal for me. Any suggestions? Thanks.

    #54016
    Profile photo of Art
    Art
    Participant

    Why not use the High Pass Filter in the PEQ for the mix?

    #54017
    Profile photo of Ratchet
    Ratchet
    Participant

    Because there isn’t one. There is a shelving shape to cut some, that wouldn’t work as well though. It looks to be about 6dB per octave and really digs into the surrounding frequencies too much. Thanks for the suggestion though.

    #54018
    Profile photo of GCumbee
    GCumbee
    Participant

    You could build a passive RC filter inside a male/female barrel connector. I did years ago. Can’t remember the values

    #54020
    Profile photo of Ratchet
    Ratchet
    Participant

    Thanks for the suggestions. I decided to overcompensate and just ordered a DriveRack PA+, because they’ve been discontinued and they were blowing them out for $219. I might just go ahead and run my subs off the L/R main mix now as well, just to get more use out of this thing. I also realized my Furman could be mounted on the rear rails of my rack, since I don’t touch it once it’s on, so it should work out okay. It just felt weird buying some digital piece of gear when I have such a capable mixer, that already does many of the things the DBX DRPA+ does (redundancy) – and to go through extra DAC. I’m hoping it won’t hurt my sound quality too much.

    #54022
    Profile photo of GCumbee
    GCumbee
    Participant

    Or you can feed your mains with the LR or another mix. Then do a mix for subs feed that into the PA+ and just set it up and use the low out. I have done that on one install many years ago where they already had a dig console. Just a thought.

    #54079
    Profile photo of Gordon
    Gordon
    Participant

    “I just want to (4th order) filter the subsonic frequencies below 35Hz from my MIX send feeding my subs.”

    You can get pretty close to this with the PEQ on the Mix channel. Simply set the LF band to the following settings…

    Q Width = 1/9th Octave (or adjust to taste)
    Frequency = 20 Hz
    Gain = -15 dB

    According to the on screen graph, the roll-off starts somewhere between 30 and 40 Hz and ends deep at 20 Hz. Even the standard HPF doesn’t slope that abruptly.

    #54081
    Profile photo of Andreas
    Andreas
    Moderator

    PEQ with narrow Q is still a notch filter not a HighPass. You just don’t see whats left out of the display.

    #54082
    Profile photo of Gordon
    Gordon
    Participant

    “You just don’t see whats left out of the display.”

    Are you saying that there is content below 20 Hz that is not being filtered out? (Not being snide or smart-ass. Just making intelligent discussion.)

    I realize that a well-designed HighPass would make deeper (dB) cuts than an EQ notch and probably remove all content below the slope, but this trick should at least get audible results without spending any money.

    The OP wants to reduce level between 20 Hz and 35 Hz. Whether it’s a notch or a shelf, the EQ is still making significant cuts to that area. Is it not? I chose a notch because you can vary the slope.

    #54097
    Profile photo of Andreas
    Andreas
    Moderator

    The OP didn’t want to reduce level between 20 and 35Hz, he needs to cut everything below 35Hz (which totally makes sense since this region isn’t recognizable by our ears and simply eat power from the Amp and force sub speakers to extraordinary movement, except you have subsonic-able speakers, then you can feel this inside your body…).
    If you set a notch filter at 20Hz which is on unity gain one octave higher (40Hz), that it will be unity also on one octave below, which is 10Hz. Next octave below would be 5Hz, then 2.5Hz, then 1.25Hz and so on. Such frequencies may be created by wind, for example.
    A notch filter is a notch filter, not a high pass.
    And, no, there should be no reasonable content below some 30Hz which is worth to be fed to your subs, that’s why the OP asks for a steep low cut (4th order would be 24dB/Oct). Technically there are many factors which normally would eliminate such low frequencies, like capacitors within the signal path. But such first order “highpasses” only cut with 6dB/Octave which isn’t much.

    #54154
    Profile photo of Ratchet
    Ratchet
    Participant

    The OP wants to reduce level between 20 Hz and 35 Hz.

    Close, but not exactly. I wanted to cut everything below 35Hz, with a steep 4th order (24dB/octave) Linkwitz Riley slope.

    Are you saying that there is content below 20 Hz that is not being filtered out?

    Yes, many movies have extremely low (useless) frequencies < 10Hz, that instantly put my amp into protect-mode. The driver’s resistance goes below 2Ω with these subsonic frequencies, triggering the amp’s protection circuit. I use my mixer for everything, including my “home theater”, so I can get my money’s worth from it.

    The OP didn’t want to reduce level between 20 and 35Hz, he needs to cut everything below 35Hz (which totally makes sense since this region isn’t recognizable by our ears and simply eat power from the Amp and force sub speakers to extraordinary movement, except you have subsonic-able speakers, then you can feel this inside your body…).

    Thank you! I see all kinds of people on the home-theater forums chasing the < 20Hz dragon, and it seem so futile. They give up so much efficiency, and claim it makes all the difference for their listening pleasure. I won’t even mention my 35Hz x-over point on those forums, because they wouldn’t even begin to understand. They have huge threads with waveform pictures touting the merits of movies that go as low as 5Hz – I put an alien movie from their list on my video-monitor and instantly regretted it. My woofers surpassed their physical limits and my amp went into protect-mode, within the first minute of that movie.

    I got a DriveRack PA+ for $219 delivered, on closeout, because they’re discontinued, which was the pièce de résistance of my rig, in effect. 99% of its functions are already covered by the Qu-16, but I really needed that 1%, so I bought the thing. The newer, replacement, the DriveRack PA-2, adds wireless iPad control, so people can ring-out their monitors from the stage and so forth, but I can already do all that with the Qu-16, so I didn’t need any of the cool new features, and saved a grip on the deal. I’m basically just using it as a crossover with subsonic filtering at this point, but I still like it.

    #54193
    Profile photo of Andreas
    Andreas
    Moderator

    Now that you have the DriveRack, you could feed the range below 35Hz into a rotary woofer. 😉
    http://www.eminent-tech.com/main.html

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