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Need help building a crossover

Discussion in 'Pro Audio Equipment' started by Paanther00, Jun 20, 2004.

  1. Paanther00

    Paanther00 Guest

    I need to make a crossover.. nothing fancy or anything... I remember in college we went over how to make a crossover and I think it had something to do with a resistor and a capacitor... Anyway, here's what I'm trying to accomplish...

    I have a bass rig and the cab only goes up to 5kHz... I want to insert the crossover between the pre and the power so the power amp isn't wasting its time with frequencies that the cab doesn't even support... I need it to crossover at 5kHz and slope at 18dB/oct... Any help is good help... thanks again
     
  2. JeffreyMajeau

    JeffreyMajeau Active Member

    Your amp is spending the bulk of it's energy powering those low-frequency excursions. 5K takes very little power to make loud, compared to 30Hz.

    It's not really necessary, unless you're looking to shape your tone. If that's the case, just use an EQ pedal.
     
  3. Paanther00

    Paanther00 Guest

    I have a QSC amp... The back has a filter and Ive got it set to 50Hz so im not worried about the lows... I just wanna filter out the nasty high stuff so I dont blow the amp or the speakers with a slap or pop
     
  4. bgavin

    bgavin Guest

    Don't build a crossover, buy one.

    The design is VERY intricate, and the passive crossover components have to be very closely matched to the true electrical parameters of the two drivers, at the crossover frequency.

    Since you are asking these questions, I know you don't understand this, nor how it is done. I'm not being a dick here, just advising you not to do your own dental work.

    If you have need of a crossover, Eminence makes very nice ones for reasonable prices. See http:// for details. I own (3) QSC amps and you are not going to blow one up slapping.

    The way I read your post, are you planning on a crossover into nothing? I didn't see mention of the drivers you plan to use for the highs. A passive crossover will not operate correctly if the Highs do not have a load attached. This is a bad idea.

    The highest harmonics of your bass quit about 7500 Hz, unless something artificial is involved, such as a fuzz box.

    My advice: leave the 50 Hz filter in place and play the rig as it is.
     
  5. Randyman...

    Randyman... Well-Known Member

    I'd even say open up that 50Hz filter to the lower 30Hz setting if you cab will handle it. A low "E" is what, 42Hz? You are already loosing part of your bass's fundamental before it is heard.

    Loosing the highs will not give you any benefit (unless bi-amping which you are NOT), and will make your bass sound "dull".

    Just because your bass cab is rated to "roll off" at 5KHz, it IS still producing 10KHz, just in a lower amplitude relative to full volume output.

    No need to complicate the simple... But if you insist, a simple 6dB/Octave inductor would do the trick. You must know the impedance of the cabinet AT THE DESIRED FREQUENCY as the "4 Ohm" rating is "Nominal" across the whole bandwidth, and likely very far off in the high end and low tuning frequency of the box (impedance varies with frequency).

    Then you can find the "First Order Passive Crossover Guide", and find what value inductor you need for the desired frequency at your cabinet's impedance (referenced to the crossover frequency). I'd use no smaller than 14Ga air core inductors for this. Parts Express has a good selection and has an online crossover chart, too...

    OOPS - Just realized you are talking "Active" here... Filtering out the highs BEFORE the amp will not provide any benefits either (unless bi-amping), and an active X-Over is even more hairy and un-needed in your application.

    Later :cool:
     
  6. Paanther00

    Paanther00 Guest

    UPDATE ---

    Well I played my first show with my new Ampeg 810 and it sounded like the thunder of the gods... I think I just get ancy for new gear sometimes... Thanks for the help..

    BTW -- We play in drop C tuning
     
  7. sdevino

    sdevino Active Member

    What you wanted was a Low Pass Filter but what you needed was to just let the amp run broadband. Beleive it or not there is a lot of important stuff in the bass sound up above 2k. And it takes almost no energy to supply that (as Dan pointed out earlier).

    Use you tone controls if you are really worried.

    Steve
     
  8. Randyman...

    Randyman... Well-Known Member

    Even MORE of a reason to set that HP filter to 30HZ instead of 50HZ! You are missing almost 1 octave of lows (maybe more @ low C)! That 8 x 10" can handle that, no problem!

    That is a nice cab, push it to its full potential!

    Later :cool:
     

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