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My DIY cab plans

Discussion in 'Amps and Cabs [BG]' started by jock, Aug 19, 2004.

  1. jock


    Jun 7, 2000
    Stockholm, Sweden
    I´ve set my sight on the Beyma 115 Nd/W and an Eminence Alpha 6 or Beyma 6MI9 for mids/highs. I dont think I will need a tweeter as Im a 4-string/flatwound kind of guy.
    What do you think? Light weight and powerful right?
    How do I choose a crossover?
  2. Nice driver. Cross over at 800 Hz to the Alpha 6" or whatever. The Alpha will take you to 8000 Hz, which is all you need for full harmonic response from a bass.

    Box is 1.87 cubic feet net internal volume, tuned to 37 Hz. The driver displaces 0.18 cubic feet, so add this to your sizing to get a net 1.87 cubic feet volume.

    Enclosed below is a plan that will get you awfully close for the Beyma driver. It does not account for an internal mounted midrange, but it is tall enough to allow for an Alpha 6.

    SBB4 Design
  3. A9X


    Dec 27, 2003
    Sinny, Oztraya
    Good choice of driver for the bass, and I'd probably go for the 6MI9 myself. Either way it should be an excellent speaker.
    Not really neccessary.
    Very good, should be as light as possible for the sort of design it is.
    bgavin's design also looks good for the enclosure. Good piece of software you have there sir.

    I'd multiamp it myself and use an active xover.
  4. jock


    Jun 7, 2000
    Stockholm, Sweden
    Thanks for the feedback. How does one make the ultimately proportioned cab? I meen how should HxWxD be related? Does it have to have a certain minimum depth?

    BTW I will ad my homebrewed Eminence Omega Pro 12 sometimes if needed. Its quite heavy though. Just the driver weighs 11 kg.
  5. jock


    Jun 7, 2000
    Stockholm, Sweden
    Hmmm. I just compared the specs on Beymas site to the ones in Bgavins "musicians reference". And the values from beymas site into WinISD Pro Alpha version gives a voloume of 78 liters while bgavin suggests 53 liters. Why is that? Both are tuned to 37 Hz.
  6. Petebass


    Dec 22, 2002
    QLD Australia
    I'd say Beyma have changed some of the driver specs and didn't tell Bruce. How dare they? :) Neo's woofers are a newish invention so it wouldn't surprise me to see small changes as they fine tune the designs.

    I've punched the T/S paramaters into WinISD pro and I get 76 litres at 37Hz for SBB4. -3dB at 52 Hz and an honest 700W right down to 31Hz. Nice driver alright!
  7. Yes, they sure did change the specs. Quite a bit, actually. The Qts is substantially higher, and the Vb jumped up quite a bit. The Xmax also increased.

    I replaced the drawing that the link above points to. The link will now open the 2.71 cubic feet at 37 Hz SBB4 drawing, that reflects the current PDF.

    Dharma, thanks. I've rewritten it a number of times, but this versionc is pretty close. The weight estimates for MDF based cabs are within 4 percent, consistently. I don't factor in the screw weight, which appears to be the overage amount.

    [ edit ]

    I updated the spread sheet with the new specs.

    The Golden Dimension shown in the drawing is for the exterior of the cab, and not quite accurate on slot port designs. The actual ratios are certainly close enough for optimal standing wave cancellation in a parallel-wall configuration.

    It is approximately 1.6 x 1.0 x 0.6 in ratio.

    I calculate it by finding for X which is the cube root of the external volume of the cab. This is the 1.0 dimension.

    1.0X factor = cube root of interior volume
    1.6X factor = X * ((1+SQRT(5))/2)
    0.6X factor = X / ((1+SQRT(5))/2)
  8. jock


    Jun 7, 2000
    Stockholm, Sweden
    Thanks a lot!
    One more question: Is this driver loud or low driver? Will I need a really big amp to drive it or would say 400W be enough?
  9. Petebass


    Dec 22, 2002
    QLD Australia
    It's loud and a bit low. 97dB sensitivity for a single driver is pretty good. -3dB at 52Hz isn't thunderously low, but it's low enough for most players, certainly for a 4 string.

    At 400w you looking at max SPL of about 123dB. At the full 700w, is't only a couple of dB more at 125. You should be fine. I've been using 400w amps for 17 years and I'm always loud enough.