Crossover causing distortion? (audax center channel)

Discussion in 'Archived Threads 2001-2004' started by Rick Guynn, Apr 8, 2002.

  1. Rick Guynn

    Rick Guynn Second Unit

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    I built the audax HT set some time ago. All of the speakers sound great, with the center having a small problem.

    It sounds like there is a severe pocket of distortion in a narrow band of the upper vocal range (not suprano upper, normal dialog upper). I tried to duplicate the distortion using a signal generator, but could not. It only seems to occur with a combination of frequencies.

    The only thing I can figure is that I have a marginal component in the crossover somewhere. I am just at a loss on how to troubleshoot without completely rebuilding the crossovers from scratch.

    Anyone have any thoughts that might be able to help me out?

    Thanks,

    Rick
     
  2. rich r

    rich r Stunt Coordinator

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    Rick,

    I am in the process of building the Audax center channel!

    My project is not complete but I will finish it this week and post my results.

    Do you have a frequency range as to which you find the distorsion in?? This will greatly help in the troubleshooting process!!

    Also for L1 did you choose an Air core or iron core inductor??

    thanks

    Rich R
     
  3. Rick Guynn

    Rick Guynn Second Unit

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    I can't really isolate it to frequency numbers, as I was unable to duplicate it with the signal generator. The best I can do is to describe it as being in the upper vocals.

    I opted for the iron core. The air core was just too big and too expensive for me at the time.

    Others have been suggesting that perhaps this might be some sort of mechanical resonance rather than an electrical issue. I checked the dustcap on the driver and found no problems there (wasn't loose). I will be taking the drivers themselves out of the center pocket and checking for anything that might cause such a resonance.

    BTW, take note of the woofer polarities on the center channel. The schematic has them wrong, while the component layout has them correct.

    I don't think you'll be disappointed with the system though. I really like the sound. It's just this infrequent resonance that annoys me occasionally. Obviosly it's not hideous, because it has taken me almost two years to get around to asking about it....

    Rick
     
  4. rich r

    rich r Stunt Coordinator

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    Rick,

    Sorry about the delayed response, I have finished my cneter channel 2 days ago and wanted to give it a little break in before I sat down for a serious listen.

    As for listening results, all i can say is that this speaker meets my expectations and I am very satisified with the low end response. The lower end of the midrange seems to be tight and accurate, but the higher end of the vocal range seems to be a little cloudy, I dont really hear distorsion, but more of a (cloudy or muffled sound).

    I am not sue if this is the same range that you are refering to but I think this will clear up with more break in.

    I will be setting up a web site in the future with pics but it might take me a while -=-with all this warm weather its kinda hard-=-

    Anyway if you or anyone cant wait email me and ill send some pics!!!
     
  5. Greg Yeatts

    Greg Yeatts Second Unit

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    I have the same problem with the Audax HT center. I noticed the problem with movies, but not with music. On some movies, dialogue is fantastic, on others its so-so. I wonder if we are hearing poor recordings?
     
  6. Patrick Sun

    Patrick Sun Moderator
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    Rule of thumb: If the crossover is crossing over in the vocal range (over 1.5KHz), it's best to use aircore inductors. Ironcore inductors should be used in the upper bass region and below. Ironcore inductors tend to oversaturate when used in the range for vocals and above.
     
  7. Rick Guynn

    Rick Guynn Second Unit

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    Patrick, I wish that would explain it (still haven't had time to do any troubleshooting yet). The iron-core is used in the woofer Xover, which I think occurs at around 400Hz.

    The upper Xover occurs at 3.5kHz.... would this be considered upper vocals? Could a phase problem cause this kind of 'resonant' distortion? I built the thing to specs and even found all of the errors on the web-page schematics/layouts, so I don't know what the problem could be from an elctronic standpoint...

    Greg, the first time I ever really noticed the distortion was when I watched Iron Giant. It was a while back, but I think it was the scene when we first see the junkyard. There was a radio playing on the soundtrack. It was coming exclusively through the center and was very noticeably distorted. I thought maybe it was supposed to suond like that, so I let it go. But then I noticed on various other occasions. I guess it could be bad spots in the recordings.. The next time I have a really noticeable aoccurance on a DVD, I will replay it using headphones and see if I hear a distortion...

    Rich, I look forward to the pictures. I wish I could find all of the ones I took during construction...

    Rick
     
  8. Patrick Sun

    Patrick Sun Moderator
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    Sometimes, if the filter isn't done well, you get a resonance peak (high Q for the filter) which leads to a peak near its filter corner frequency. But if you are using a proven filter/crossover design, perhaps it's just a matter of the driver being faulty.
     
  9. James Mudler

    James Mudler Stunt Coordinator

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    Rick,

    I have the same CC. I am not using any passive x-o's all active. I do not hear anything you describe. Nor have heard any other complants when I started doing my research a year ago. I would lean toward something resonating. Tinsel leads hiting the cone, speaker wire, check the gaps around the surround both at the cone and basket, etc. Crossover parts securely mounted etc and speaker wire sealed properly entering the center cavity.

    Also disconnect the tweeter and see if that solves your problem.

    Hope it helps
     
  10. Rick Guynn

    Rick Guynn Second Unit

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    I'll have to go find something that it really resonates on to experiment with. This means some DVD watching (oh darn!) Now if I can just find the time to do it [​IMG]
    I will be sure to post up when/if I ever figure this out. Other than this somewhat minor glitch, I like the speakers.. I built them before Madisound had a kit for them [​IMG] So I have had them good while now. I absolutely love the mains, and if I thought I would really never use it for music, the rears are good enough that I might consider 4 of those in lieu of the mains.
    Rick
     
  11. Pete Mazz

    Pete Mazz Supporting Actor

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    Have you already tried wiring one of your mains as a temp center? This would rule out the possibility of a fault with the processor.

    Pete
     
  12. Rick Guynn

    Rick Guynn Second Unit

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    That was on my list of to do's Pete, as soon as I get time to find a good section in a movie that clearly shows the problem...

    I am hoping with all of the input I've had I will actually be able to narrow this down. Unfortunately I have been hella busy lately, and out of town on the weekends so I haven't really had a chance to try anything that has been suggested yet.. Very frustrating...

    Rick
     

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