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Thread: Crossover question

  1. Back To Top    #11

    Re: Crossover question

    Quote Originally Posted by Souths1der View Post
    I'm with Big Al up above, if you have that sub maxed out, there may not be much signal left to filter. But if you're worried, I would just use the built in crossover and leave the Helix in bypass for your sub channel, but invert the polarity. Set the crossover on your sub to 80Hz. Change the highpass on your woofers to 80 12db slope in Helix.
    I'm rather new at this, but it was my understanding that you typically want to use 24dB LR slopes for everything in an active configuration (I think it was the easiest way to keep phasing intact?) - and also to avoid any "humps" at the crossover frequency. So I have been setting all of the crossovers to 24dB LR. Is that really not a "hard and fast" rule? Would switching everything to 12dB slopes cause more issues that it solves with the sub crossover? Or does it just "all depend"?

    I'm also curious about the polarity inversion for the sub - why would you do that (again, just trying to learn what I can, where I can along the way). :-) Right now, I definitely get better bass with normal polarity, but maybe that would change if I went to 12dB slopes all around?

    Please don't take my questions the wrong way - just trying to get a better understanding of this stuff.

    Thank you!

  2. Back To Top    #12

    Re: Crossover question

    Quote Originally Posted by Jdunk54nl View Post
    In the output area of the helix software, you will have to turn your gain down on those channels to make it max 2v. Then set gains on sub amp accordingly. IIRC doubling/halving the voltage is +-6db, so to cut by 1/3, it should be around -9db..Someone correct me if I am wrong. But I would personally attach a DMM to the output and check the level to be sure.
    Ok, thank you! So what would happen otherwise - I would just get no sound on the sub (if I didn't reduce gains on the sub channels in the Helix)?

  3. Back To Top    #13
    Noob Jdunk54nl's Avatar
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    Re: Crossover question

    Quote Originally Posted by jtrosky View Post
    Ok, thank you! So what would happen otherwise - I would just get no sound on the sub (if I didn't reduce gains on the sub channels in the Helix)?
    You risk overdriving your inputs and clipping them which could do a lot of harm to all parts of the amp/sub. The amp might go into protect mode due to being overdriven or you might fry some circuitry by sending too much voltage through it, you might fry a voice coil, etc. You will still get sound.

    Now, that is what could happen, whether it does or not is dependent on how loud you listen if the music actually ever sends that much of a signal to the amp. With subs, it probably will.

  4. Back To Top    #14

    Re: Crossover question

    Quote Originally Posted by Jdunk54nl View Post
    You risk overdriving your inputs and clipping them which could do a lot of harm to all parts of the amp/sub. The amp might go into protect mode due to being overdriven or you might fry some circuitry by sending too much voltage through it, you might fry a voice coil, etc. You will still get sound.

    Now, that is what could happen, whether it does or not is dependent on how loud you listen if the music actually ever sends that much of a signal to the amp. With subs, it probably will.
    Thank you. This higher-voltage stuff is new to me since I'm used to inexpensive equipment that is usually 2V max. :-) I appreciate the warning. I need to do a little more research on input/output voltages before I damage something! :-)

  5. Back To Top    #15
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    Re: Crossover question

    With the crossovers, if you use 24 db slopes for both you are still in phase. If you use 12 db slopes you're 180 degrees out of phase, hence the flip. Since you can only do 12 with the sub I would do 12 for the woofer highpass rather than a 36. I personally have never done such a thing. I believe the math works out, but the sound might be crap.

  6. Back To Top    #16

    Re: Crossover question

    Ah - I understand what you are saying now. I'll do some experimenting. I think I'll first try just setting both the sub itself and the DSP sub channel to the same xover freq, with both set to 12dB slopes - which will then "combine" to put the sub at a 24dB slope, which matches everything else. Sounds like a simple-enough solution - assuming I understand properly. :-)

    I still have a lot to learn about phasing....

    Thanks for all of the assistance, everyone!

  7. Back To Top    #17
    Noob Jdunk54nl's Avatar
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    Re: Crossover question

    Quote Originally Posted by jtrosky View Post
    I still have a lot to learn about phasing....
    I think most (including me) have a lot to learn about phase. REW does not make seeing this super easy. Some other $1000 programs like systune or smaart do.

    Phase is super important to get a well balanced and centered sound stage. Ultimately that is all we are impacting at the listening position via our time alignment adjustments. Some other things that impact phase are: Crossovers impact phase, IIR filters impact phase with EQ adjustments, All pass filters impact phase, etc. All of this is happening, but we don't really pay much attention to it when we should be, and we should have a better understanding of it and how the changes we make are impacting the phase.

  8. Back To Top    #18

    Re: Crossover question

    Yeah, with REW, the only way to see phase information is via the "Measure" sweeps, correct? I'll be honest, I haven't even messed with that yet. I've just done pink-noise-based measurements and tuning (using IIR filters for EQ) - so I'm sure I have plenty of phase issues that I am completely unaware of. I'm pretty new at this stuff, so one step at a time. Need to "master" time-alignment, xovers, level matching and EQ first - they I'll move on to working on phase, I guess! :-) Had no idea how "involved" this stuff could be - but I definitely have a better sounding system than I started with, so I *am* making progress, thanks to you all more experienced folks that are so willing to help!

  9. Back To Top    #19
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    Re: Crossover question

    Ya, you have to do the sweeps, which I find hard to get to repeat on tweeters if you move the microphone and average a bunch of sweeps (I normally set it to 8 repeats). That limitation is odd to me because smaart lets you run Periodic Pink Noise via its generator and can tell you the impulse, the phase, and the magnitude all in real time on a screen and can do it with a bunch of microphones. Systune looks like it can do that too but i haven't experienced it. It truly is a beautiful setup.

  10. Back To Top    #20

    Re: Crossover question

    This is easy to do and setup with rew start off with your under seat subwoofer set to 80hz ish, dsp set flat, now take a measurement and you will see the response including that of the crossover, set it so it’s -3db is 80hz... remember you’re after an actual crossover point of 80hz, you can also put it into auto eq with your chosen crossover applied to the room curve of your choosing and compare the two, play with your dial until the roll off matches the slope created by rew in auto eq

    once this is correct now add in the dsp at 12db and change your auto eq crossover to 24db slope, now adjust the dsp crossover so the measured slope matches the prediction from rew also

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