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Crossover questions

Discussion in 'Amps and Cabs [BG]' started by seanm, Sep 3, 2005.


  1. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    I have an LDS 1x12 1x6 cab. The crossover is at 1.6kHz, which is the lowest high pass filter Eminence makes.

    I actually thought the speaker was broken because I could not hear anything from it. It just turns out that you don't get much from it until you are way up the neck.

    Since the Eminence crossovers are cheap (< $50), I thought I might try changing the crossover. Could I take a 2-way crossover, say the Eminence pxb2-500, and just use the high pass filter? Or will I get noise if the low pass filter is unused?

    Or, does anybody know of another source of good crossovers < $50? I would like a 500Hz high pass but up to 800Hz would be ok.

    The speaker in question is the LA6-CBMR.
     
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I doubt that the problem is with the crossover point per se, at 1.6kHz you should have no trouble at all hearing output from the six even with an open E. I suspect the problem is either a blown crossover component or the six just has insufficient sensitivity to match the twelve. What 6" driver is in there now?

    You don't want to just use a high pass, that allows half the amp output to go into the woofer where it doesn't do anything instead of into the mid where it does. Using it with a twelve I wouldn't go with less than an 800 Hz crossover.

    If it turns out the present crossover is OK and the six just isn't up to snuff just going to the LA6MR might do it. But you might want to consider the Alpha 8 MR also for even higher sensitivity.
     
  3. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Thanks for the reply. The cab has a 12" Eminence Kappa Pro and the 6" LA6-CBMR.

    Maybe I am just thinking about it too much. This was not ment to be a full range cab. I bought it to add a more "classic rock" tone when paired with my CLX-112. And it does that beautifully.

    I don't think the crossover is blown. When I run a CD through it, the two speakers balance nicely.

    I would still be interested in your comments about the two speakers though.
     
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    My mistake, I thought you had a different mid in there that you were considering replacing with the LA6. The Kappa Pro 12 has a very strong midrange response. The LA6 is a bit hotter than the Kappa, but only by 3dB. I think the main reason you don't hear much from the LA6 is that it's only working from 1.6kHz to perhaps 6.4 kHz or so, a mere two octaves, while the Kappa is covering over five octaves. The Kappa's dispersion angle starts shrinking at about 1 kHz, so taking the crossover down to 800 Hz would balance things out a bit better, but I wouldn't go lower than that. You could experiment with running the low pass filter out of the circuit but only if the drivers are vertically aligned, otherwise having overlapping responses will lead to serious comb filtering.
     
  5. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Thanks, that helps a lot. I may just look into an 800Hz crossover.

    I know think I probably would have been just as well off with the 12" all by itself. For this application, anyway. Would have been lighter and cheaper.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    If you can't find a crossover at the frequency you want, make your own. It's not hard or expensive, and there's lots of help available here.
     
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Not really, even though the Kappa has adequate on-axis response off-axis it isn't worth anything above 2kHz. No twelve is. That's why you can't hear any highs from your guitar players rig even though it's only eight feet to your side, while people in front of him three tables back from the dance floor are stuffing napkins in their ears.
     
  8. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Ok, dredging up an old thread. I was going to sell the cab, but now I plan on using it at a rehersal space. So I am interested in the crossover again :)

    I am thinking of a 3rd order 800Hz crossover for the 8ohm speaker with the following components:
    • 18 uF cap
    • 1.2mH coil
    • 50uF cap

    My question is, have I done the math right?

    I was also thinking of a second order, but I calculated that I needed a 2.2mH coil and the price goes way up. But not enough that I would rule it out if there was an advantage.
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Yep you math is correct for a 3rd order Butterworth. Nice job. I'd go for the 3rd order filter over the 2nd order. It gives additional protection for the driver, and eliminates the phase issues typically associated with 2ns order crossovers.

    Let us know how you go.
     
  10. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Thanks! I will.
     
  11. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    With the Christmas break, I had a chance to actually put the parts into the cab. The caps are HUGE. I reused the PCB from the original crossover and it was not easy getting the caps to fit. So I cut them in half. Just kidding :p

    The 800Hz crossover makes a huge difference. I am actually getting output from the 6" speaker at bass frequencies. It really perks the cab up. I would not consider this a full range cab by any means, and I think that slappers would hate it, but it will meet my requirements as a rehersal cab.

    And to reiterate, the cab as I got it from LDS did exactly what I asked Don to make it do. I asked for a cab to pair with my EA CXL-112 to give a more vintage sound and that's what it did. My needs have changed to a more full range sound.
     
  12. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Really? A 50uf Cap shouldn't be too big. The one I have in front of me is only 1.5 inches long and 1/2 an inch in diameter. The 18uf Cap should be smaller again.
     
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    True of an electrolytic, but if it's a poly it could easily be twice that size or more. A cap in the signal path should either be a poly or a large value electrolytic paralleled with a small value poly. Electrolytics alone are fine when they're used as shunts to ground, as in LP filters.
     
  14. Doug Parent

    Doug Parent Supporting Member

    May 31, 2004
    San Diego, Ca.
    Dealer Nordstrand Pickups.
    sorry for the hi-jack but I'm interested in this little Eminence 6"'er myself. If I get the sealed back version, do I still have to use a cross-over with it-say around 800 hz? Or can I let the natural roll off of the driver "do the job"?

    Also, is the spl of the sealed 6" too much to be combined with a Delta 12LF, ie:do I need a two way cross-over with attenuator for the mid?
     
  15. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You still need a high-pass filter on the closed back driver; the closed back doesn't change the power handling of the voice coil. You don't need attenuation of the mid-driver, but without a true crossover half your HF power is going into the woofer where it will be wasted as heat, not sound.
     
  16. Doug Parent

    Doug Parent Supporting Member

    May 31, 2004
    San Diego, Ca.
    Dealer Nordstrand Pickups.
    Thanks Bill, makes sense about needing a cross-over. Having looked the website at Eminence over, I see there are actually 3 line array drivers availiable. I'm eyeing the mid bass la6mb for its broad range response, and considering I'd be using a tweeter, I'm not concerned about this particular 6 topping out at 4.5 khz. However it's sensitivity is only 92 db, which might not be a good match for my Delta 12LF or Kappa Pro 15LF.

    Do you think the MR might be a better choice?
     
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    There's no advantage to the LA driver when used singly, I'd stick with the Alpha 8MR, unless it won't fit your cab, then I'd go with the LA6-CBMR. Using the D12LF as a direct radiator I'd cross to the mid at 800 Hz.
     
  18. Doug Parent

    Doug Parent Supporting Member

    May 31, 2004
    San Diego, Ca.
    Dealer Nordstrand Pickups.
    thanks Bill.
     
  19. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    Both the caps are poly. The dimensions of the 50uF are 77mm x 37mm, that's roughly 3" x 1 1/2"!

    Dayton DMPC-50