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Cabinet Design Question

Discussion in 'Amps and Cabs [BG]' started by nick98338, Aug 3, 2012.


  1. I'm planning my first DIY speaker cabinet project. I chose an Eminence Legend CB15 driver, since it's suitable for bass guitar, the driver gets some respect around this forum, and I'm getting a pretty good deal on the purchase. I go to the Eminence web site, and I print their specs on a small, sealed cabinet. About 1.7 cu. ft. box. I plug the driver and cabinet specs into WinISD. WinISD gives me the "optimum" dimensions for the box. Those numbers are a bit funny. The optimum width is 15.52in. Well, allowing for the thickness of the plywood boards, an overall width of 15.5 would give me a baffle of 14.5. No way to mount a 15in speaker on a 14.5in baffle. So, I'm asking for advise on how to adjust the overall dimensions so the baffle will be wide enough. Is there a minimum amount of baffle space that I should plan around the outer edge of the driver?
     
  2. mulchor

    mulchor

    Apr 21, 2010
    St Pete, FL
    There's definitely room for common sense. And aesthetics. Note you need 1.9 ft^3 internal volume. Internal dimensions, not external. Eminence doesn't specify the dimensions of the box with the understanding that if you choose a shape that's not crazy, it's gonna work as expected. It can't be so shallow your speaker hits the back of the box, it can't be narrower than the speaker is wide...
     
  3. will33

    will33

    May 22, 2006
    austin,tx
    You using WinISD Pro Alpha? It's a more detailed program, bit doesn't have the physical box dimension thing, that's the older "beta" version.

    Anyway, make the box how you want it to sound. Ignore that default, "optimum" stuff.
     
  4. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    As mulchor stated, any dimensions you see are going to be interior dimensions.
     
  5. dhomer

    dhomer Commercial User

    Apr 9, 2009
    Hickory Corners, MI
    Owner, Gigmaster Soundworks, Auth. greenboy designs builder, MI
    The CB15 isn't optimized for a sealed box.. As you found out the box would have to be too small to mount the driver. you'll have to design a ported box for it..
     
  6. Thanks for the advise folks. I have re-worked the dimensions of the plan some. Made it wider and a bit deeper. About 2.0 cu ft internal. The baffle will have enough room to add ports, if needed. The driver may not work to max efficiency in a sealed box, but Eminence does say it will be OK. The graphs don't show 100db all the way down to 40hz, but the graphs look acceptable to me. No big bumps or sharp drops.
     
  7. Phendyr_Loon

    Phendyr_Loon

    Sep 4, 2010
    I don't believe 2 cubic feet is going to suit if you plan to add ports later. Your best bet is to build a vented box from the start. In the end its less time and money spent dicking around with trying to port an undersized cab.
    You're one step ahead with the use of WINisd.
    I've been down this road before, it was an aggravating learning process with lots of clipping, chuffing, and a huge db drop on a low B.
     
    PawleeP likes this.
  8. will33

    will33

    May 22, 2006
    austin,tx
    If you're going to make it ported, you'll do better up around 3.5 cu.ft. net.

    CB15 does OK in a sealed box but one that small isn't going to have much lows. If you make it big enough to get some lows, then you pay a pretty big penalty in power handling. You'll get a lot more out of that driver in a ported box, even as small as 3 cu.ft. Do both a sealed and ported model and lay them both on the chart and you'll see the difference.
     
  9. I got the WinISD Pro (beta). Wow, what a difference! You guys were right. In a 2.0 sealed box, the chart cliffs at about 100hz. Down about -12db at 50hz. My new HipShot tuner would be worthless unless I eq'ed the heck out of the amp. A 2.0 *vented* box is better. A bigger box, is better still. I'm starting to think that I should be looking for a different driver, all together. I don't want to have to go to Kappalite 15, but I guees I might have to.
     
  10. will33

    will33

    May 22, 2006
    austin,tx
    Try it in 3.5 cu.ft. tuned ~47hz or so, then switch to the max power graph and look at that dip just above the tuning frequency. Then do the same thing with a 3015.

    Legend is a gooe driver. The Kappalite can take more power down there but not all that much more. It does have a little more xmax though.

    If I was switching to a Kappalite, it would be for more uppermids and topend. Has a more "aggresive" sound or more "bite" to it. Legend is on the warmer side of the tone spectrum. Not dark, but warmer, more mellow by comparison.
     
  11. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Think of some cabs you do like, and model them in winISD (if you can figure the driver) then manipulate your plot to look like that.
     
  12. will33

    will33

    May 22, 2006
    austin,tx
    For a size comparison, 3.75 cu.ft. tuned anywhere between 40 and 50hz would be a fairly typical size off-the-shelf commercial 115 cab no matter who makes it. Smallish ones maybe 3.5. Folks who just stick them in the same box they use for their 410's (which is a lot of them), maybe 3.9-4.0.
     
  13. Syco_bass

    Syco_bass Supporting Member

    Aug 13, 2008
    Tucson, Arizona
    Custom builder - Arizona Bass Company/Curcio Custom Basses
    Getting ready to the exact same thing. I'm using a Faital Pr400 in a 3.2 cubic ft. box (similar to TL-606 box only with 1/2" ply and lighter/stronger bracing) I'm also going with round tube ports vs. square ports. I'll try a few different port lengths as well as plugs just to see what I like better.

    Good luck on your adventure. I'd highly recommend the Kappalite 3015 or Faital Pr400. There are some good cab designs out there that will work with those speakers. (1X15 or 2X15)
     
  14. BogeyBass

    BogeyBass

    Sep 14, 2010
    efficiency bandwidth product or (EBP)
    is a good way to determine if a speaker is better for sealed or ported.

    Simply take the resonant frequency (Fs) and divide it by the Electrical Quality (Qes) so if we are talking about a legend CB158?

    then Fs 34 and Qes .36 so 34/.36 = 94.4 EBP so you would defiantly be looking at ported box.

    General rule of thumb is below 50 is better for sealed and above 50 is better for ported.
    Many more things come into play, it is just a basic rule of thumb, but with Pro audio applications you can put a speaker with a EBP around 70 into a sealed box. Usually if the speaker has a higher mechanical quality (Qms) it is a ok choice if the EBP is a little high.

    Anyhoo, sticking a 15" in a 3cubic box is a waste of time.
    Trying to scrub a extra 20 or so 30 watts by sticking it into a smaller box isnt going to change its max SPL much higher.

    Same thing with tuning it to some obnoxious high tuning to try and cut down on cone excursion to drag a few watts out of it. Port frequency affects cone movement, and at port frequency their is very little cone movement. So reproduction of notes is lowered above and below tune frequency, one of the downsides to ported boxes. Because the speaker and box are slowly starting to resonate . Which can be observed in WinISD in the cone excursion window.
    place a CB15 in 4 cubic at 34 and 50 hz and you can observe how cone movement is restricted in the audible portion of a bass guitar.

    So in order to obtain more bass or more accurate bass you would want a speaker with a low resonate frequency, and then try to tune the system below the lowest fundamental you are trying to produce. So a system tuned below the fundamental of low E 44hz could possibly achieve more detail, since port frequency reduces cone movement.

    Wonderful news CB158 has a Fs of 34 hz so we can tune below lowest fundamental. a BB4 alignment will tune to the Fs of a driver and volume will be for the closest match to the lowpass response the model is trying to achieve.

    (all TS alignments are based on their relation to a low pass response)

    so a BB4 for a CB158 is about 6cubic feet tuned at 34hz.

    6cubic is great for bass but yes lowers power handling,
    so you simply just hold onto the BB4 tune frequency
    and put it in a smaller box around 4cubic feet.

    4 cubic 34hz. 24 wide x 19.5 tall x 16.5 deep.

    external dimensions will give you around 4.5 cubic
    actual internal after you add ports and braces and stuffing will be around 3.8 to 4.2

    using 4 round 3" symmetrical ports mounted closely to the woofer will produce a more accurate port, reduce smearing and help reduce cone distortion.

    also dont use the CB15 included in winisd it is a older model and is much different. enter the data as a new model according to the latest data sheet.
     

    Attached Files:

  15. Yes. Exactly.

    Thanks for the great info. The dimensions you suggested are doable, for me. I'm thinking that I would prefer the height to by 24 and the width to be 19.5. My guess is that would be OK.

    Yea. I noticed the difference between the driver parameters in WinISD and the parameters on the Eminence web site. I used the data from the web site as a new driver... once I read the tutorial about how to enter the data correctly. Thanks again. Your post is a sticky in my cabinet design documents.
     
  16. BogeyBass

    BogeyBass

    Sep 14, 2010
    well yes of course same box just set the other way, I guess sometimes your eye has to see it.

    But yes without going on forever, 19.5" width would be more ideal
    in a "hi fi" sense because you want to reduce baffle diffraction as much as possible and the only way to do it is make the width as small as possible.

    only problem with a 19.5 wide cabinet is some heads are 24" wide. so it would look goofy hanging off the sides.
    With this design you have both options 24wide or 19.5 wide.

    19.5 is just enough room to add a border/cloth grill if you liked it and even a false edge to make it look beefy like a Sunn ,boogie or marshall. just makes it look better like a frame, actually similar to the ampeg portaflex where there is a nice border of blue around the grill, not some thin looking walls, looks cheap to me.
     

    Attached Files:

  17. A questions about ports. I plug in 4 round 3in ports and WinISD gives me a port length of several inches. I'm guessing that is the total combined length of all 4 ports, not the suggested length of each ports. Yes? I would divide that total length by 4 and make each individual port the resulting length? Each port tube of equal length? Thanks.
     
  18. Growly Lytes

    Growly Lytes

    Dec 4, 2009
    Downunder Oz
    Bass player
    Yep people alot of first time makers do this thinking its the outside when its internal volume.
     
  19. No.
    Doing this will result in vents that are too short.
     
  20. Ah! OK. I see now. If I use smaller diameter ports, or use fewer ports, the port length becomes more realistic. I think that I now have all my questions answered and I can now start building. BTW, this is also my first project where I need to create boards which are squared with trued edges. I've built other things from wood before, but this is my first 6-sided box where the boards need to match closely. So, it's not only speaker design stuff I'm learning, it's also some precision wood working skills. Thanks to all.
     

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