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Speaker Build

Discussion in 'Amps and Cabs [BG]' started by sheepdip, Jul 5, 2004.


  1. sheepdip

    sheepdip

    Apr 14, 2004
    Some time ago I decided to build my own speakers. Today they are cut and put togeather but not glued and screwed yet. Two 15's and one 18, all JBL. I just need to install the handles on the sides, the crossover on the 18, cut and fit the ports, amp connections, etc. etc. I will post a finished pic when I'm done. 9 ply cab. grade Birch, no particle board :hyper: :hyper:
     
  2. ESP Eden

    ESP Eden

    Feb 9, 2004
    washington mo
    I'm assuming that you are putting a tweeter in the 18 ( since you said you had to put in the crossover ), but where is it going to go? Are you putting it in one of the ports?
     
  3. sheepdip

    sheepdip

    Apr 14, 2004
    No, No tweeter, I just assumed I would need a 500hz for the 18 because of the low freq. response of that speaker. Any highs that I will need will come from the 15's
     
  4. ESP Eden

    ESP Eden

    Feb 9, 2004
    washington mo
    Good thinking. Tweeters suck anyway. ;)
     
  5. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    sheepdip..when the time comes to stuff the cab you might want to check this company out www.basslinear.com I heard some great things about their product
     
  6. sheepdip

    sheepdip

    Apr 14, 2004
    I'll check out their product
     
  7. seanm

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

    Feb 19, 2004
    Ottawa, Canada
    Now there's a quote you don't hear every day! "Just slapped in a couple of 15s to add some highs." :D
     
  8. Am curious about the crossover. I have just built an 18 and didn't need a cross-over. I did electrical and electornic engineering at Uni and decided i didn't need it.....the 18 acts as a low pass filter, hence it rolls off any highs.

    You only really need a c-o if you have a tweeter installed or if you are pushing low frequencies through a high frequency speaker......ie lows through a 8"

    Hope this helps. I'll be posting some pictures of my effort when i get the grill!

    Chris
     
  9. sheepdip

    sheepdip

    Apr 14, 2004
    How does the JBL 2245 act as a low pass filter????????? I Was going to add the crossover because of JBL's recommendation of 800hz and lower. I am, however, willing to defer to others more learned than I.
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I'd be trying it both ways. True 18's tend to have a natural high end roll off, but sometimes they can create some nasty resonances in the mids. A crossover smoothes that out.

    An 800Hz crossover shouldn't be hard to make. Assuming the 18 is 8 ohms, you'll need a 2mH Inductor and a 15uF capacitor. Both are readily available and inexpensive.
     
  11. Can't you just buy a set low/high-pass (I forget which does which) filter and install it in series with the 18?
     
  12. sheepdip

    sheepdip

    Apr 14, 2004
    I'm looking for one now. I know JBL made one I think its a 3110 0r 3115. Seems like somebody should make a 800hz. :crying:
     
  13. Rich Piche

    Rich Piche

    Jun 29, 2004
    Why not go all the way with an electronic crossover and a pair of power amps. This would give you a choice for the crossover frequency, before settling on a passive (and fixed) one. Although I would use smaller drivers for mids and highs (the 15" are just a little too big for proper high end response). I use a single 15" cab powered by a 3B Bryston (bridged 400 watts) and a 4 X 10" cab for mids and highs powered by a second 3B. I use a Peavey Pro 1000 pre-amp with the crossover set at around 250 hz. This amp ROCKS!!!
    Good luck with your rig.
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I think you answered your own question. In this case, to use an active crossover would rob the 15's on anything under 800Hz ish, when they're capable of much more.

    You'll struggle to find an 800Hz premade crossover. But don't be affraid to knock one up yourself. Wire it up like this:-


    <------|---------< 2mH Inductor <----------< (+)
    .15uF Capacitor
    <------|----------<--------------<---------< (-)

    The arrows indicate the direction on the signal flow, so the amp would be on the far right and the speaker on the far left.

    Again, this assumes the speaker is 8 ohms. If it isn't, let me know because the inductor and capacitor values will change.

    We may even be jumping the gun. This 18 speaker may not even need it. Tryi it both ways.
     
  15. sheepdip

    sheepdip

    Apr 14, 2004
    What kind of voltage on the cap or does it make any diff???? I could use a 500HZ crossover and still be doing O.K. spkr is 8 ohm, which in itself presented another problem. I plan on using a
    SVT CL, they don't have a 8 ohm feed only 2 or 4. I can wire the two 15's for 4 ohm but don't know of any way to make the amp see 4 ohms on the 18 so I have decided to not worry about it. :eyebrow:
     
  16. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Don't give up yet, you still have options:-

    1) Wire the 2x15 as 4 ohms, run it parallell to the 8 ohm 18. Total load is 2.667 ohms, so use the 2 ohm tap on the amp. The 2x15 will get twice as much power as the 18. That may or may not be a drama depending on cabined efficiencies. And if you think about it, each of the 3 drivers gets one third of the wattage.

    2) We go back to looking at Rich Piche's idea of putting a crossover on BOTH cabs, except we'll use passive instead of active to keep the SVT in the equation. Impedance changes as frequency changes. A 4 ohm cab doesn't see 4 ohms all the time, only at frequences near the speakers resonant frequency (Fs). So if the 2x15 is crossed over at least one octave above it's resonant frequency, it will never see an impedance anywhere near it's rated minimum. In effect the total "nominal" impedance of the 2 cabs will be 8 ohms because the 2x15 is hiding behind the crossover.

    With option 2, I'm not sure if running an 8 ohm load to a 4 ohm tube amp is ideal. You may have to bounce this off someone who knows more about tube amps.
     
  17. sheepdip

    sheepdip

    Apr 14, 2004
    I talked to a tech at JBL and asked him about making the 8 ohm into a 4 ohm but he said it's not happening. then he asked me what kind of amp I was using when I told him he said don't worry about it.
     
  18. Have you already bought the drivers? If so, can you not just exchange the 18" for a 4ohm?
     
  19. sheepdip

    sheepdip

    Apr 14, 2004
    Nope, already have the driver and it is real tough to find a 18in speaker in 4 ohm.