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Thread: REW and DSP help - Acoustical vs Electrical crossover.

  1. Back To Top    #21

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    In a couple days I'd be curious to get your input about the differences between sine sweeps vs pink noise. I'll share some pictures once I have re-tuned everything to pink noise.

    Question(s) of the day:
    So sine sweeps can bring out phase issues, as well as resonance issues, right? So at what point should I use sine sweeps to double-check my measurements and what exactly should I be looking for? Where is the happy medium?

  2. Back To Top    #22

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by DirtyBumOAK510 View Post
    In a couple days I'd be curious to get your input about the differences between sine sweeps vs pink noise. I'll share some pictures once I have re-tuned everything to pink noise.

    Question(s) of the day:
    So sine sweeps can bring out phase issues, as well as resonance issues, right? So at what point should I use sine sweeps to double-check my measurements and what exactly should I be looking for? Where is the happy medium?
    Use pink noise, rta, and moving mic averaging to measure and tune, if something isn't acting right (xovers not summing correctly or other weirdness) then use sweeps to diagnose problems. In short, take both types of measurements and use rta for tuning.

  3. Back To Top    #23

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by Justin Zazzi View Post
    The important thing is can you make the measurements reapeatable? Like if you make a "measurement" using whatever method you want, can you make a second (separate) measurement and then compare the traces and have them agree really nicely? That is when you know you're moving slow enough, measuring for long enough, and doing it "right".
    Thanks again for all the help. I had an issue I was having a hard time wrapping my head around. I am on round 5 of tuning. In Round 1 I checked for polarity of the speakers, and everything was as it should have been. I did this using the IASCA test CD. At the end of rounds 1-4 I verified polarity by reversing polarity on my mids and looking for the major gulch around the crossover. Everything was normal. I just completed round 5, and I got the crossovers to almost perfectly match the house curves. But when I ran the entire left side (subwoofer, mid-bass, and horns), all of a sudden I'm getting a major dramatic dip exactly at the crossover, and if I flip the phase of my horns, the gulch becomes almost completely flat.

    So my question of the night...
    1. If my crossover between my mids and horns (tweeters/midrange) is out of phase ... and its fixed by reversing the polarity of the horns ... does that mean that the entire range of my horns are now out of phase? Or does it just mean that I'm out of phase near my crossover? (800hz).
    2. Do I just flip the polarity of my horns to fix this?
    3. Or what do I do to fix the phase issue at my crossover point?

  4. Back To Top    #24

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by DirtyBumOAK510 View Post
    So my question of the night...
    1. If my crossover between my mids and horns (tweeters/midrange) is out of phase ... and its fixed by reversing the polarity of the horns ... does that mean that the entire range of my horns are now out of phase? Or does it just mean that I'm out of phase near my crossover? (800hz).
    2. Do I just flip the polarity of my horns to fix this?
    3. Or what do I do to fix the phase issue at my crossover point?
    1. If your crossover region is better one way, go with it.
    2. Sure.
    3. If you want to make the crossover sum together well then use the combination of settings that result in the best summing.

    This is about the best you can do with REW that I know of, however John is constantly adding new features so maybe there's cool stuff I haven't seen yet : )
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Do it for them.

  5. Back To Top    #25

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by Justin Zazzi View Post
    1. If your crossover region is better one way, go with it.
    2. Sure.
    3. If you want to make the crossover sum together well then use the combination of settings that result in the best summing.

    This is about the best you can do with REW that I know of, however John is constantly adding new features so maybe there's cool stuff I haven't seen yet : )
    I need to learn more about phase...
    I started off my tune and double checked (even triple checked) that all my speakers were in phase. I played phase tests and it was night and day. I was 100% confident that everything was in phase. After massive EQ work, adjusting levels, matching my measurements to house curves ... sure enough, I get pronounced -10db dips ~where my crossovers are. I reverse phase on my horns and the dips turn ~perfectly flat with my house curve. I played the same "phase test" sample tracks and again, it sounds night and day 100% correct ... but now my horns are reversed from where they started from.

    As a small update:
    My measurements with pink noise (I dare not go back to sweeps lest I ruin my sanity) are measuring within ~1.5 db of my house curve from 30-18khz. I am fixing a few small issues that came up during my 31 band pink noise tests. The main issue was that at certain points the right would be 1.5db the opposite direction as the left, and vice versa, thus throwing off the imaging @ 160hz, 1200hz and 2000hz. I'm going to try and dial those closer to center this week as I have ~5-6 hours of drivetime this weekend to add my "subjective" notes.
    I'm having a small issue where my subwoofer is playing flat from 80hz-160hz which is adding a baby bump in my curve @ ~ 125 hz. It's only ~5db below where my mid-bass come in, so it is showing up on my RTA measurements. I don't know that I can really hear it. It may also be less noticeable because due to the -14db generated pink noise I'm using from REW, the subwoofer flat spot is @ 75db, and my whole system is tuned to 80db (as this is where the pink noise gets me). My normal listening levels are higher than that.
    I had a post on DIYMA about trying to eliminate the flat spot on the subwoofer. I tried making cuts using my JL Twk88 DSP, however even with a variety of -12db (max) cuts, it only made a very small ~ -3db difference. The LPF on the amp seemed to make a bigger difference, but the problem is that the -12db/oct slope from the LPF would start to cut into my 60-80hz range. I did set my gains on the subwoofer amp to -10db attenuated tones, so likely I could afford to dial back the gains a bit. The only problem with that is that I'm using a pair of low sensitivity (~83db) 6.5" subwoofers, and right now my measured RTA readings (which match my house curve) goes to +10db from 30hz-60hz (and at f3 of +7db @ 20hz) in a dual sealed box. I like the extra room on my attenuation knob because some music that I listen to frankly lacks sub-bass. I'd rather attenuate than be looking for more.
    I'm still confused as to where that flat spot from 85hz-160hz is coming from on my subwoofers...
    Last edited by DirtyBumOAK510; 1 Week Ago at 12:01 AM.

  6. Back To Top    #26

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by DirtyBumOAK510 View Post
    I need to learn more about phase...
    If you want to learn more about phase, a good place to start is to learn the difference between phase and polarity. Anytime you make an adjustment that is labeled as a positive or negative, or a 0 vs 180 degrees, or normal vs. reversed, these are all polarity changes. These are the same as if you took the positive and negative wires on the speaker and reverse them. Polarity means any time the cone should move forward it moves backwards instead and vice versa. Polarity has the same effect at every frequency.

    Everything else that you think is phase, probably is, unless it's polarity.

    For your other questions, it would be easier with screenshots since we don't know what you're seeing.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Do it for them.

  7. Back To Top    #27

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Heres a few pictures of subwoofer RTA measurements.

    Unfortunately these aren't labeled well, but they represent a mix of electronic crossovers from 60hz-90hz, some with EQ where I tried to eliminate the flat spot at 85-140hz with -12db spikes ... the main reason I show these photos is to demonstrate the flat spot is present no matter how I change my crossovers or EQ cuts.
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  8. Back To Top    #28

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    That doesn't seem too strange. You have a dip around 110hz and a peak around 140hz so if you want to straighten then out you might need one filer for each: a little boost at 110hz and a little cut at 140hz (or whatever the frequencies are).

    If you try to fix it with only a crossover filter, then you'll still have that squiggle but it'll be moved up or down as a whole since the crossover filter won't separate that dip and peak that as so close together.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Do it for them.

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