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Is My Null Fixed?

Discussion in 'Acoustics' started by Zing, Nov 3, 2010.

  1. Zing

    Zing Retired Admin Famous

    The purple trace is the typical response I've been dealing with since moving the sub up front. A few different adjustments here and there have altered it in some fashion but I'm always left with some form of that W-shaped null between 35 and 90Hz.

    I had some time this afternoon to play around and the yellow trace is the result. I say that's a significant improvement. What say you?


    [​IMG]
     
  2. soundhound

    soundhound Well-Known Member

    Looks better. I use a Behringer Feedback Destroyer Pro to flatten out the output from my subs.
     
  3. Zing

    Zing Retired Admin Famous

    Once I get those traps up on the ceiling, I"ll see what kind of improvement they offer. If it's minimal, I may pick up one of those BFD's.

    I'll give you five dollars if you can correctly guess how I made the improvement between the purple and yellow traces. And I'll give you ten dollars if you're still talking to me after I tell you how I did it. :shifty:
     
  4. DIYer

    DIYer Well-Known Member Famous

    Zing, you tell us you did something but won't say the specifics. Is this a secret method you're about to patent and sell? :(
     
  5. Zing

    Zing Retired Admin Famous

    HA! I wish!

    You're another one whol'll likely have a :doh: moment when I tell you so I guess I'll give you ten dollars too if you don't resign your moderator position and run away screaming.
     
  6. DIYer

    DIYer Well-Known Member Famous

    Give a tip or two. Did you work with what you already have in that room?
     
  7. Zing

    Zing Retired Admin Famous

    I enabled the XO on the sub.
     
  8. soundhound

    soundhound Well-Known Member

    Here's a link to where you can get one.

    http://www.zzounds.com/item--BEHFBQ2496

    You use it essentially as a 20 band per channel fully parametric EQ, and turn off the feedback suppression fucntion.
     
  9. Aaron German

    Aaron German Active Member

    What setting are you using on the receiver? I think I have to choose a x-over freq on my receiver. Or are you running your mains through the sub?
     
  10. Botch

    Botch I.Y.A.A.Y.A.S! Superstar

    Darn it, I was gonna guess that right off the bat!

    Uh, what is "XO"?
     
  11. Zing

    Zing Retired Admin Famous

    Botch - XO = crossover.

    Aaron - I currently have my pre/pro crossing all my speakers to the sub at 80hz. I had been using 100Hz, which helped fix one problem but it still left others. So for the past couple of weeks I've been running things at 80hz. By enabling the crossover (or XO, Botch) on the sub, I'm effectively using a second crossover which is considered a no-no. It was sheer desperation that made me try it and, frankly, I was expecting to see more problems than I had before. I was floored when I saw what it corrected.
     
  12. Aaron German

    Aaron German Active Member

    What do you have the x-over on the sub set at?
     
  13. Zing

    Zing Retired Admin Famous

    80Hz.

    When I flicked the switch, I heard a distinct difference in sound. It was a reduction higher frequencies and a seemingly increase of lower frequencies. So I assumed the markings were inaccurate. When I clicked the Quick Sweep button, as mentioned, I was floored with what I saw. For shits and giggles, I ran the sweep 3 more times. Once with the knob set at 70Hz, and once at 90Hz. After seeing only the slightest change in response, I set it back to 80, ran another sweep and that's the yellow trace you see above.
     
  14. Zing

    Zing Retired Admin Famous

    You know, I've been seeing tons of people using this thing and I never really understood how some anti-feedback device could cure the ills of a problematic frequency response.

    Can you select multiple frequencies to adjust or are you limited to picking just one like most PEQs?
     
  15. soundhound

    soundhound Well-Known Member

    There's nothing necessarily wrong with using cascaded crossovers if it accomplishes the final goal. What you are doing when cascading crossovers at the same frequency is making the resulting slope sharper than with a single crossover alone.

    Still, problems with bass response are better solved through placement and EQ.
     
  16. soundhound

    soundhound Well-Known Member

    There are 20 available bands per channel, and these can be at any frequency, with any "Q" (width of the peak or notch), and with any boost or cut. The bands can be moved around freely to address each of the problem frequencies. At some frequencies I have two or three bands close together with a narrow notch; at other frequencies I have a single, wide notch - it depends on the nature of the problem frequencies. The two channels are independent, so you have 20 bands per channel if you are using stereo subwoofers.

    To address feedback, you tune the bands to the frequencies which are causing the feedback and insert a sharp notch; the unit can do this automatically also.
     
  17. Aaron German

    Aaron German Active Member

    When I get the chance, I'm going to play around with this double x-over deal.
     
  18. DIYer

    DIYer Well-Known Member Famous

  19. PaulyT

    PaulyT Behind the Curtain Staff Member Administrator Moderator Superstar

    Glad you got it working, but it's mysterious to me why setting a crossover at 80Hz had such an effect on the frequencies well below that. Yeah I mean I know the xo point is a shoulder, so there's some slight falloff below it, but still shouldn't it basically be a low pass filter? Why does it seem to be boosting the 30-70Hz range so much?

    Not arguing that your RTA result isn't real, just wondering how what you did accomplished that...
     
  20. yromj

    yromj Well-Known Member

    The first thing that comes to my mind is that the settings on those XOs are notoriously inaccurate. He could be selecting 80Hz and actually setting it to 60Hz.

    As to why it made an improvement at all, well if his mains were somehow creating sound that low (where the null is) and he removed the sub's output down there, that could explain why the null disappeared.

    Of course the switch could have been installed upside down also; thus, reversing the "ON" and "OFF" positions.

    John
     

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