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Can an EQ be a crossover?

Discussion in 'Amps and Cabs [BG]' started by MuzikMan, Mar 12, 2005.


  1. I want to start bi-amping lows to my 2x12 cab and highs to a 2x6 cab I have yet to build. I already own a stereo graphic equalizer and I was wondering if my speakers would be protected well enough with it or will I fry the little guys? :crying:
     
  2. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I think you will be OK. If the EQ has 10 dB boost and cut, that's 20 dB dynamic range -- enough to reduce the lows going into your tweeters by a factor of 10. You can probably let the highs continue going into the woofers, since they are a small fraction of your power and probably not being reproduced anyway.

    You can also do this passively by simply putting the tweeters in series with the appropriate capacitor. What impedance will that cabinet be, and what cutoff frequency do you want? The rule for the capacitor would be:

    C = 1/2/pi/R/f

    pi = 3.14
    R = impedance of the tweeters
    f = cutoff frequency

    Use a non-polar electrolytic. This is the simplest form of crossover, where you simply let the response curve of the woofer take care of itself.

    Out of curiosity, what 6's are you using?
     
  3. Thanks. I'm probably going to use Eminence Alpha 6 because they match up well with the Delta 12lf that I already have.
     
  4. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    like 'e said, it'll work to protect the sixes if you ahve sufficient cut, but it wont 'zactly be a crossover either. ;)
     
  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Don't. A graphic EQ cuts only by 12 to 15 dB. That's not enough to do the job. Even a 1st order crossover cuts at 6dB per octave, which gets you to 18dB rolloff at 3 octaves down, 24dB at four, 30dB at five, and so on. Most any electronic crossover is at least 3rd order, which gets you rolled off 18dB at one octave down, 36dB two octaves down, and so forth.

    If you go passive you can get away with a passive 1st order crossover if you place the crossover frequency at least two octave above the driver fs, which for the Alpha 6 is 118Hz, so a minimum 500 Hz crossover would be required. Going lower would require a steeper slope. Do not rely on the acoustic rolloff alone on the woofers, as they run to at least 2kHz and the interactions between the two sources would result in response anomalies.

    Whatever you do don't have the sixes mounted side by side or the comb filtering will make the horizontal dispersion and response quite horrible.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    What Bill said. A graphic only gives you 10-12dB of cut right through the range. So you're only 12dB down at those frequencies which really should be as close to zero as possible.

    You'd be better off building a passive High pass filter for the 6's of at least 12db/octave. Or go the whole hog, get an active crossover and bi-amp.
     
  7. Thank you for the replies. If I do this and it is evident that my EQ will not suffice I will go the active crossover route. I would like to have flexibility and I am under the impression that better sound quality is achieved when splitting the signal before the power amp.

    I will definately be building a vertical alignment for the sixes to reduce comb filtering.

    It seems to me i can get -24db if I use the entire dynamic range of the EQ. Start with full boost (+12db) and cut down to -12db somewhat after my chosen cutoff frequency. Since my EQ is stereo I could do the same (opposite direction) with the 12's.

    Am I missing something?
     
  8.  
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    No, I screwed up. Cutting the signal by 20 dB reduces your output voltage by 1/10, but your output power by 1/100. You would be putting 2 W into those 6's. But beware... that may still be enough to push the drivers to the excursion limit. Work this out in WinISD. Putting the drivers in the smallest possible cab would help here.
     
  10. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    A dbx 223 crossover is $150 new. Used, probably half that. I'd save up and get the piece of equipment you need.
     
  11. Lockout

    Lockout

    Dec 24, 2002
    Illinois
    Or you could try one of these, maybe.
     
  12. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Yep even that cheap Rolls crossover will work better than the eq.

    I see where you're comming from with the 24dB of cut with the EQ, but to get there, you've first boosted everything else. By doing this, you've increased the input gain of the signal, and you'd have to account for this in the next step in the signal chain to prevent the signal from clipping. SO you would have to turn down the gain at the preamp and that just puts you right back where you started.

    Unless of course the eq IS the pre-amp, which raises signal/noise ratio concerns. All for 24dB of cut right through the range........

    Doing the math, lets say you cross it at 800Hz, and lets say the -24dB EQ idea actually works. I used 800Hz because that's what Bgavin recommends as a crossover point for the Alpha 6's as a midrange driver. It's a cheap driver so you're better to limit it's use where it's limited X-max wont be a factor.

    At 200w, your method has you -24dB at right across the range, so the 6's are recieving a bit less than 10W at every frequency below 800Hz. 10w doesn't sound like much but the kicker is that the speakers still recieve 10w right down at 40, 30,20,10, 1 Hz, all low enough to give many speakers trouble, especially little 6's.

    Using a 24dB/octave crossover like the Rolls one, you're -24dB at 400Hz (10w), -48dB at 200Hz (5w), -72dB at 100Hz(2w), -96dB 50Hz, which is cose enough to zero watts to say the speaker recieves nothing below 50Hz. This is much better for the speaker overall.
     
  13. Ok I get what you're saying. For the record my EQ is my preamp so boosting would actually be OK in my case but I see your point with the noise issue. I also understand that at very low frequencies I may not be cutting enough. I could use the 50hz filter on my QSC power amp. That should help.

    So I have concluded that my EQ may work but not as well as an active crossover. I guess I just can't get away with being a cheap bastard! :D

    Today I went to practice with a jam band I just joined up with and the guitarist's dad (bass player :cool: ) has a Yamaha PB1 sitting upside down unplugged on top of his Hartke rig. HHmmmmmmm I said to myself. I've heard of these here! I asked him about it and he said he doesn't use it anymore. I told him I may be interested in buying it. He said I could borrow it for a while but he wasn't sure if he would sell it or not.

    So I got it home now and tried it full range into my Avatar b212. At low volume (it's late so I can't turn up) it seems to have all the clarity and high end I could ever want for my fingerstyle playing, and that's with the tweeter turned off! I'm pretty sure if I use it in my rig I wouldn't need anything more than my 212 cab but the PB1 does have the active crossover I would need if I decide to continue the bi-amp route.

    I'm pretty sure I want this Yamaha PB1!............Yep. pretty sure...................Time to go test it out again! :bassist:
     
  14. I can't get a max power reading on WinISD for the Alha6 because I can't find an Xmax on it amywhere on the internet. Even Eminence has it listed at 0mm. Xmech, however, is a little over 10mm. FaR FROM WIMPY. It seems like it could handle the 24db cut at 800hz down to 41hz easily if I ran the full 450 watts available from my QSC USA900. I believe this is a workable option but I got my fingers crossed on the Yamaha preamp.

    Once again the talkbass pool has been extraordinarially helpful. I thank each and every one of you for contributing to such an awesome site! :)
     
  15. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Depends of your definition of "Handle". X-max when the speaker starts to distort. X-mech is when the speaker is physically damaged.

    X-max is listed as Nil. Fs is 118Hz. Which means if this sucker recieves anything close to 120Hz, it'll move and therefore distort. It'll "handle" it, but it not cleanly.
     
  16. I think my mind is changing about the whole thing thanks to this Yamaha preamp. I can see it is possible to get the clarity I am searching for out of my 212 cab which is great news. I'd rather switch to a real preamp than get more speakers.
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Cool. Let us know how it goes.
     
  18. iriegnome

    iriegnome Bassstar style Supporting Member

    Nov 23, 2001
    Kenosha, WI 53140
    I am sorry. An EQ Will not work even remotely like a crossover. An eq shapes signal. A Crossover routes frequencies to different locations. To run Bi-Amp, you do not really need a CrossOver, unless you want just certain frequencies to run through the 12's.
     
  19. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago