Cross over question

Discussion in 'AV Receivers' started by Victor Ferguson, Oct 13, 2005.

  1. Victor Ferguson

    Victor Ferguson Stunt Coordinator

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    Is there any harm in using a predefined crossover on your AVR and setting the crossover on the sub to the same value to get a steeper crossover? What I have found is that when using a 80hz crossover the sub still gets way to much info.
    For example - I have set my crossover to 80hz and unplugged my mains, I can hear low voices and other sounds coming from the sub. My thinking tells me this is a bad thing as it makes the sub easier to localize. Where as if I run both cross-overs and get lets say a 24db slope as opposed to a 12db slope it gets rid of those sounds.
    Any input would be appreciated.
     
  2. John Garcia

    John Garcia Executive Producer

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    Your sub should be getting those frequencies, and that's why you hear the sounds coming from it. If you remove them with a steeper x-over, you will create a dip around the x-over point. If you aren't actually able to localize the sub, I wouldn't consider it a problem. I believe most receivers already have a steeper x-over on the sub pre-out, 18dB or higher. You CAN use them both though, if you happen to have a noticable peak above the x-over point, I have seen at least two people tame them by adjusting the sub's x-over point down until the peak is tamed.
     
  3. Victor Ferguson

    Victor Ferguson Stunt Coordinator

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  4. mackie

    mackie Supporting Actor

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    A couple of other things that may help is to use a SPL meter to make sure your sub's output matches your main speakers, and you can use an equalizer like a BFD to remove any peaks. This won't affect the crossover points but will help if you sub is easy to localize.
     
  5. Victor Ferguson

    Victor Ferguson Stunt Coordinator

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    Update and Information:
    I am using a H/K 335. I am using the dedicated sub out. The sub I am using is a JBL S120PII, it's -3db at 24hz in my room, BFD'ed and +/- 3db through 100hz with the exception of a 6db dip at 70hz. It's not that the bass above 80hz is very loud, it is not even really noticable with the mains on. It just seemed to me that hearing the dialouge (even very faint) through the sub could potentially cause localization and color the dialouge. Last night I changed to a 60hz crossover and it pretty much eliminated the faint dialouge coming through the sub. My mains and surronds can do 60hz fine and I guess for me in my room this is the best compromise. My only problem with the 60hz crossover is I'm afraid I'm not doing justice to the LFE signal by crossing over that low.
     
  6. John Garcia

    John Garcia Executive Producer

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    LFE is a separate, dedicated channel that isn't affected by the x-over, only the bass redirected from your other speakers. What is the highest -3dB of your other speakers? That should determine if 60Hz is too low, as the rest of your speakers should be able to handle at least 40Hz well, because they will still be receiving stuff lower than that (at a much reduced level). Based on what you said though, it sounds like a 60Hz x-over may have combined with the natural rolloff of your mains better than 80Hz, effectively filtering them a lot steeper and giving you a better in room response and blend with your sub and/or the lower x-over basically killed off a room response issue with your sub.
     
  7. Victor Ferguson

    Victor Ferguson Stunt Coordinator

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    Mains are -3db at 35hz (RTi8)
    Center is -3db at 42hz (CSi5)
    I havent measured surrounds (Rti4), Polk has them rated at 50hz. With my other Polks I seemed to benefit from a little room gain and they faired better than speced by Polk. I'm probably pushing it with the surrounds using a 60hz crossover. I can independently set them higher but have avoided it as from what I have read about using independant crossovers a FR gap could be created.
     

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