Build a 80Hz LP x-over?

Discussion in 'Archived Threads 2001-2004' started by Anthony Sa, Apr 15, 2002.

  1. Anthony Sa

    Anthony Sa Agent

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    As some of you may have read from my last thread with my speaker troubles, my sub-out does not have a crossover. I can up with a plan to get around this.
    I will build (in the spirit of DIY) a simple LP 80HZ crossover. This way I will have a static crossover for now and later on when I get my new Pre/Pro I will most likely be able to adjust the crossover seeing in the processor.
    So here is how it would look:
    Reciever -> RCA to XLRM cable -> amp -> terminal cup -> crossover (inside of the box) -> speakers.
    Does that look right?
    Now All I need to do is find out how to build this simple crossover and I should be good (I have some soldering experience so that shouldnt be a problem). I have tried www.passivecrossovers.com and that didn't tell me how to build them, just told me what they were and how they worked. Can anyone suggest a website on how to build a LP crossover?
     
  2. Saurav

    Saurav Cinematographer

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    There was a thread on this a week or so ago, I think in the Speaker forum. I posted a link to a kit for an active line level crossover. Run a search on all forums for "John Pomann", and you should be able to find that thread. You might find that discussion useful.

    Edit: If you build a line level XO, it would go between your sub-out and the amp, but I'm sure you realize that.
     
  3. jeff lam

    jeff lam Screenwriter

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  4. Anthony Sa

    Anthony Sa Agent

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    I did realize that a line-level crossover would go inbetween the sub-out and the amp but I figured it might be easier to build a passive crossover, maybe I was wrong? It has happened before!

    And those line-level crossovers from parts express. will those work alright? If those do, I might actually consider those instead of building. But they seem to be for car stereos?
     
  5. Anthony Sa

    Anthony Sa Agent

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    Well I might as well post this here. I was reading about the ATTENUATORs and i was wondering. Could i something like this to boost the subwoofer signal from my reciever? It is a very weak signal it seems and i have the sub boost up 12Db. So could I use some sort of line-level converter to boost the signal to the amp?
     
  6. Richard Greene

    Richard Greene Stunt Coordinator

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    FMODS claim to be 12dB/octave filters.

    I have five pairs at home and every one has been measured at 6dB/octave.

    In addition, each FMOD reduces output by 2-3dB.,

    so you will have to turn up the volume control by 2-3dB.

    FMODS are not quite the bargain they appear to be if you believe the 12dB/octave specifications.

    If you plug two FMODS together you do get 12dB/octave

    filtering but then overall output will be down 4-6dB (both above and below the turnover frequency). I use two 50Hz. FMOD low-pass filters plugged together as a 50Hz. 12dB/octave low-pass filter on an inexpensive stereo.
     
  7. Alexis

    Alexis Stunt Coordinator

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    If you plug two fmods together in series, does that change the crossover frequency? The graph on their website suggests that it does? It looks like putting two 100hz crossovers in series gets you a 50hz.
    http://www.hlabs.com/technical/crossovers/
     
  8. Anthony Sa

    Anthony Sa Agent

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    Well is there anything that will actually BOOST the signal? My signal seems very week, meaning I have to have the amp almost all the way up and the reciever more than half way up to get any sound out of the sub. Anyway to change this? As I said, I already have the SUBOUT set to +12db in the reciever.
     
  9. Alexis

    Alexis Stunt Coordinator

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    The SVS black box or a Radio shack line level amp will boost your signal
     
  10. Marc Bodin

    Marc Bodin Extra

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    If you build a passive crossover, the simplest being a coil in series with the speaker, you will lose output, as the crossover itself will steal power from the speaker, and create more heat. An active crossover is a better way to go, though designing one is much more complicated than a passive crossover. I would suggest buying an active crossover, you could even use a 12 V one.
    http://www.eatel.net/~amptech/elecdisc/passxovr.htm
    This site will tell you all you need to know about designing a passive crossover.
     
  11. jeff lam

    jeff lam Screenwriter

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    I would also recommend not using coils (passive x-over). BTW, what amp are you using?
     
  12. Jeff Rosz

    Jeff Rosz Second Unit

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    heya Anthony,
    just to get an idea for a line level active you might wanna look at this site
    ThomasW,
    good link, got anymore like that?
     
  13. Anthony Sa

    Anthony Sa Agent

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    I am using a QSC RMX 2450 (big amp... ton of power. If i could get a strong low passed signal!)
     
  14. ThomasW

    ThomasW Cinematographer

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    Jeff

    What specifically are you looking for? I have hundreds of audio related links

    Marc B

    Anthony is dealing with a line level output. One doesn't use standard passive crossover components with that type of signal.

    Anthony

    BTW, attenuate = decrease, not boost
     
  15. Marc Bodin

    Marc Bodin Extra

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    Thomas, if you read the original post you will see that he intends to place the crossover between the amp and the crossover, which would mean a passive crossover.

    Again, an active crossover is the better choice as it creates no signal loss, is generally more flexible than a passive, and you are able to incorporate features such as bass boost into the design. I would suggest buying one though, as you will find that designing your own active crossover is much more complicated.
     
  16. Jeff Rosz

    Jeff Rosz Second Unit

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    thanks thomas,

    as of late my interests have been in LT, active xo, biamping, DIY amps.
     
  17. jeff lam

    jeff lam Screenwriter

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    Anthony,

    I would suggest a Paradigm X-30 crossover. I am told it also doubles as a line driver so that will help boost the signal to your pro amp.

    I too am using a pro amp but I use the Ebtech Line level shifter to get added voltage gain. Some features I would like to have in one unit is:

    Sub x-over

    variable phase

    line driver

    subsonic filter

    The SVS black box would be perfect if it included a sub crossover.

    Don't know how much gain the paradigm will give but I'm sure you could try it out and return it if it doesn't work out right.
     

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