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WinISD and cab box size/tuning recommendations?

Discussion in 'Amps and Cabs [BG]' started by Magneto, Nov 25, 2005.

  1. I'll try to keep this short, but I probably won't be able to :D

    I have 2 Eminence Kappa Pro 15 LF-2s. I recently rebuilt an older 2x15 cabinet and have been using them in that. I now want to build 2 smaller, individual enclosures.

    For the SBB4 alignment, WinISD seems to call for 2.570 cu-ft, tuned to 35hz. Now that would be one seriously-small cabinet, even with a bunch of internal bracing, etc..
    I've seen a few cabinets that used these drivers, and none were anywhere near that small. I've seen recommendations for boxes in about the 4.0 cu-ft size, but no real information as to why.

    When I rebuilt my cabinet, my internal volume was about 4.2 cu-ft, and I tuned to 40hz. It was suggested (discussions in this forum) that this arrangement was not ideal for these drivers, but I was in a needful situation with less-than-optimum resources.. oh well..

    How many of you would follow WinISD's recommendation for volume/tuning, and why? Would I get a tighter bass response? A more effiicient cab?

    Thanks alot for your opinions.

  2. Do you mean that your current cab has 4.2 cu. ft. for both speakers? If so that wouldn't be much different than the suggested SBB4 tuning for these drivers. Before making your final decision change the tuning to 50hz to get more usable low end. If you like that I would suggest the small 2.5cu. ft. per driver tuned to 50hz. If you want more low end then I would suggest 4 cu.ft. per driver tuned to 45 hz. You will notice that the bigger box and lower tuning will increase low end response at the expense of power handling and group delay. You should also realise that when you add bass from your amp you are also incresing group delay and decreasing power handling. You can verify this by adding parametreic EQ under the EQ/filter tab. That means if you want more low end from the smaller cab you will nullify the advantages the small box has.

    For reference the Avatar B115 has an internal volume of about 3.6 cu. ft. and is tuned to 50hz. Doesn't sound boomy or slow to me!
  3. MuzikMan,

    I'm sorry.. No, I meant 4.2 cu-ft PER speaker. I have a separator partition built into the cab, and each speaker basically has its own compartment sealed off from the other. Each compartment has two 3" ports, the top one has a Foster horn too.

    I'll have to go over your suggestions. I still haven't really got a grip on WinISD's graphs and what everything means. It's hard to take that information and figure out how that applies to how a cabinet will sound. When I was rebuilding this cab, I finally gave up and just decided on a tuning of 40hz for the internal volumes I had to work with, and only because I play 4 string and 40 is pretty much the low E.
    With WinISD, any cab volume above the suggested 2.5 seems to have negative results on everything. But even a 18x18x16 inch internal box yields 3 cu-ft. This is what makes me wonder if WinISD is right or not. Sure, by the time all the internal bracing and driver displacement gets taken off, it would be closer to the 2.5 cu-ft.

    BTW, have you designed and built a cab according to WinISD's recommendations and had good results? Were your results anything like you thought they would be?


  4. seamonkey


    Aug 6, 2004
    Winisd usually gets it right but double check the parameters entered for the speaker.

    As a crosscheck try going to
    Search for the speaker and they will usually have Project Ideas with a suggested cabinet design.

    Hope this helps.
  5. WinISD isn't able to tell you what the best configuration is on it's own. It is only able to tell you what the response will be based on popular configurations. The fine tuning is up to you and you will find that the popular ones are right for some drivers and not for others.

    I did build a 4x8 box using WinISD but I didn't use the recommended volume and tuning. I fiddled with it until I saw what I liked. The results were as predicted so I can't complain.

    As far as the Kappa Pro 15LF2 is concerned I have read that a 3.8cu.ft. box is ideal. The tuning is up to you but anywhere between 40 and 50hz will work well. BTW don't worry about getting the tuning perfect right away. You can always change it later. The box size is as simple as the bigger the lower.

    As long as you build a good quality box and the size isn't way over or way under it will sound fine.
  6. seamonkey


    Aug 6, 2004
    For fun I went into winisd and pulled the kappa from the DB, picked a 3db shelf and it came up with:

    6.190 ft^2
    32.5 hz
    4" vent at 2.27"

    I usually find that winisd usually does give a ideal design at first to which you need to tweak. I've heard of people building prototypes of cardboard just to try things out especially with multiple drivers and they can interfere with each other.
  7. Mag, your numbers for the LF-2 in SBB4 are correct.

    You can also consider the QB3 alignment, Fb=44.6 and F3=52.7 Hz. This would give you an ever so slightly bigger bottom and no discernable difference in tightness. The box is also slightly smaller at 2.35 cubic feet net.

    The disadvantage to the higher QB3 tuning is more exposure to port chuffing at high power from too small a port. Getting a sufficiently large vent area in a small box requires a long vent. This requires increasing box volume to accomodate the much longer vent.

    The SBB4 (35 Hz) is tuned below your low E, so chuffing is much less a problem. You can skimp on the 5" optimal port diameter with SBB4 because you won't ever hit 35 Hz with a 4-string.
  8. Thanks to everyone for the replies and ideas.

    BGavin: I am sooo lost when it comes to the various alignments in WinISD. I really want to understand what these different setups give in terms of bass guitar cab sound, however I just don't have the resources to keep building cabs until I find one that I like. I know that I can do better by these drivers than what I have now.
    I'm trying to sort through the variables and prioritize. In terms of what I'm looking for, I would rather have a tight, punchy box than a deep/boomy one. Believe me, these 15s never seem to run out of low end, and deep bass never cuts through worth a hoot on stage anyway.
    So? What's more important? lower F3? Low group delay? Power handling? Tuning at or below the lowest notes to be played? All of the above?

    Is SBB4 more of bass guitar cab design? If you had one of these drivers and were going to build a single cab, would you go with these volumes and tunings? I'm not trying to pin anyone to anything, but I'd feel much better about beginning my design if I knew, especially since the box volume is really small. I have nothing against building a small, light box, but I'd like to get close the first time around.

    "MuzikMan: WinISD isn't able to tell you what the best configuration is on it's own. It is only able to tell you what the response will be based on popular configurations. The fine tuning is up to you and you will find that the popular ones are right for some drivers and not for others. "

    Yeah, I really wish it had a "bass guitar optimal cab" alignment!..

    Thanks for the ideas.. Keep em coming..

  9. WinISD is a graphing program, so it will let you visually compare different alignments. The intent is getting as "much area under the curve" like they used to say when designing hot cams for cars. Play with a few different alignments, and see which one gives you the flattest curve, down to your lowest expected note. The SBB4 will give you the most rolloff, everytime.

    If your basses don't put out much fundamental, the lowest effective note on your 4-string would be the 2nd harmonic at 82 Hz. You can measure this, or you can run your bass through a 31-band EQ and drop all sliders below 82 Hz and see if you like the sound. If the bottom falls out, then your bass produces useful content below 82 Hz, and so should your cab.

    Small vented boxes require design compromises. There is always less vent distortion with a larger vent area due to lower air velocity. As vent area decreases, its air velocity increases until it becomes audible. In any box, a larger vent areas requires a longer duct than a smaller vent in the same box.

    If you build to SBB4, QB3, or Optimal Flat you will not wind up with a flabby, boom box. The boom comes from stuffing an acoustically large driver into a small box which causes a hump in the mid-bass.

    IMO, the reason for the boominess is the vented box upper resonance. All vented boxes have a resonance (impedance peak) both above and below the tuning frequency Fb. Altering the size of the enclose while keeping Fb the same, changes the amplitude of the impedance peaks. Making the box too small increases the upper peak and diminishes the lower peak. I have noticed the audible boominess being most prominent at the upper impedance peak on boxes I measure. This includes the XLT-410.

    The EBS (extended bass shelf) alignment is the opposite: the box is overly large and the upper impedance peak is reduced, and the bass response is extended lower. Group delay is significantly increased, so the box will measure "flabby" compared to the SBB4 box. If the GD is less than 25msec, you will never hear it. The Avatar boxes are EBS designs. So are the JBL designs for their E-1xx drivers.

    All of this is nice to know, but does it work on stage? The Eden XLT is renowned for its ability to cut through a noisy mix. My daughter's bassist (www.aroarah.com) plays one, even in drop-D tuning. Her XLT has the classic mid-bass honk resulting from big drivers in a small box. The XLT is gutless in the lowest octave, but is a master at "cut through" on stage. Chelsea uses it as a stage monitor, because she is usually DI through a dozen Crowns and a dozen subwoofers.

    For maximum punch and least boom, I would do the Omega 12 and Alpha 6" in SBB4 with a PXB2:800 crossover.

    Do not forget that a single 12" direct radiator isn't very loud. So if you play outdoor gigs, need to brutalize people or eat Ampegs for breakfast, then build a Tuba 30 and a DR2xx top. Caveat: a 30" cube weighing 135+ pounds is a pain in the butt to haul around. And the FOH engineer will hate you if you bring this on stage.
  10. The correct Omega Pro 12 SBB4 is:

    Vb = 1.23 cubic feet
    Fb = 39 Hz (not 35)
    F3 = 70 Hz
    Optimal vent diameter = 4" for 0.045 mach
  11. bgavin: Thanks for your in-depth explanations. I've been reading over it, and I'll surely add this to my notes.
    I do have a 31-band EQ hooked up to my rig, so I can do some experimenting as you've suggested.

    I wonder how the Kappa Pro LF-2 and an Alpha 6 would pair up with the x-over you described? Right now I'm running both of the Kappas with a Foster horn and Avatar 4 ohm x-over panel. This was a BIG help over running the 15s alone, but I'm missing some sweet frequencies.
    I guess I'd probably do better with some 10s, which is something I'm gonna look into in the future. A good 2x10 box on top of one of these 15 cabs would probably be a better combination.

    I'll keep on researching..

  12. The Alpha 6 drivers would match up well with the Kappa pro 15-LF. As you suggested it would bring out the upper mid frequencies you can't get with a tweeter. The only way I would choose a 2x10 cab over them is if your rig isn't loud enough.
  13. It's most definately an idea. Since I'd be building separate cabs anyway, I could experiment with the first and see how it goes before building the second. I do wonder if that Alpha6 would have enough high end. I don't usually go for a super-bright sound, and the Alpha6 seems to have a higher usuable frequency range than most 10"ers..

  14. Plenty of high end comming out of the Alpha-6. I actually prefer the slightly reduced high end response of the Alpha-8 better but that's just my opinion. I should comment that I own 4 of each so I have experience with them.
  15. In sensitivity, the Alpha 6 is 1.7dB less sensitive than the LF-2. These are all small signal numbers, and will change under full power. I would expect the LF-2 to suffer some power compression, reducing its output up to 3 dB, or more.

    You can feed the LF-2 300W before it exceeds Xmax in SBB4. The Alpha 6 is good for 100W, power compression is unknown.

    The amount of energy in the upper frequencies will be quite a bit less than the low frequency band. Experimentation would be required to see if more than 1 Alpha 6 is required.
  16. I have successfully run 1 Alpha-6 with a 2 way 4th order linkowitz riley (spelling?) crossover @800hz in a 2x12 deltaLF cab. They just seem to be louder than the numbers suggest. If I were you I would install 1 with an attenuator in each 1x15 cab. When you use them together you could lower the level on one (bottom cab?) until you get the tone you like. This method would reduce comb filtering because one Alpha-6 would be louder than the other.
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    What I'd do is mount the 6 above the 15, when using two boxes place the upper box upside-down over the other for a W-M-M-W. End of combing problem.
  18. Great suggestion! I hadn't though of that. That helps me with my single 12 boxes I plan on building. Thank you!

  19. Reduced output? Is this because it would be used with the Alpha6? I guess I need to buy a book and start studying.. This is sooo far over my head..

    Thanks for the replies..

  20. Nope.

    Power compression happens when the voice coil heats up as a consequence of running the driver at power. The T/S characteristics change significantly under power, which is why T/S is always "small signal" and taken at 1W or 2.83V.

    Some drivers resist power compression better than others, but they all suffer it to some degree. Selenium and Beyma, and some JBL data sheets publish power compression specs. Eminence does not, to my knowledge. Education can be had by reading a few of the data sheets with power compression charts. Many of these are well under way by 100W or so. Think about holding a bare 100W bulb in your hands, and you will see how much heat they generate.

    You can get around this somewhat by using a cooling device for the driver. Check out Wayne Parham's work on his forum at AudioRoundTable.

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