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Oversized/Detuned Cabinets

Discussion in 'Amps and Cabs [BG]' started by thumbtrap, Jul 1, 2003.


  1. thumbtrap

    thumbtrap

    Jun 26, 2003
    or "I think I'm going to need a bigger box"
    Let me preface this with saying: I've read the Cabinet Building 101 thread. I've built speaker cabinets before - a 6.5" 1ft^3 soft spoken bedroom B-box (84db 1w/1m, 50w), and a sealed 15 with better efficiency, but rolled off around 66 Hz. But I want more. I want what everybody else wants and can't have either - the mythical 1.5 ft^3 paint peeling low B box. But I'm prepared to deal with reality in small doses. I don't care if it's "Flat", as long as it's solid and won't be destroyed by a 5 string at volume. It doesn't need to be ridiculously loud, or terribly small. It doesn't really need gobs of power handling - I want a somewhat portable B box with reasonable efficiency - so my parameters are: Tuning at or slightly below 31 hz, adequate bass response for the low B, as high an efficiency as I can get through the rear door of a Honda Accord. Shooting for deep, but tight and solid. I slap some on my fretless, but not much on my fretted bass (the 5) - articulate but not really the modern super bright sound.

    I was playing around with WinISD and it seems that an Eminence Kappa 15LF in a 9ft^3 box tuned to 30 Hz is pretty flat down to 30 Hz. It has a shallow shelf beginning at 200 Hz, is down 1db at 100 Hz, 2db at 60 Hz, and 3db at 30 Hz, where it falls off. Group delay is a little higher, but I don't know enough to interpret those numbers yet.

    Has anyone experimented with sticking a driver in a cabinet intentionally oversized and tuned low in order to extend bass response? What are the tradeoffs of doing this? (Besides the obvious size increase.) Does anything really wierd happen that makes it unusable, unpalatible, or likely to destroy drivers?
     
  2. cjgallen

    cjgallen

    Oct 19, 2001
    I remember watching a video of some guy who made some enclosures for 6.5" woofer (six and a half inches!!).

    He was powering them with a 200W amp and was hitting 30Hz like nothing. Setting off car alarms too. The boxes weren't that big either.

    I'm searching for it now.
     
  3. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Andy Lewis has already done all the hard work for you. Why not just buy one of his cabinets?

    Disclaimer: I'm a happy customer, with no other ties to Acme.
     
  4. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    Group delays (mud) go up, plus you really dont want a 9ft box.
     
  5. thumbtrap

    thumbtrap

    Jun 26, 2003
    96 db 1w/1m is why. I'm not exactly rolling in surplus power. I hadn't really considered 410's, though 9 ft^3 is larger. 21.5"d x 30"H x 29"w would still fit through the door. The wood is a significant chunk of weight in a cabinet that size, but not compared to multiple speakers.
    The B4 is also out of my price range (and none too light.)
     
  6. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    Well if you dont want to add power then you will be forced to add size. Unless you dont want loud. SMall,Low or loud pick 2, but you cant get all 3.
     
  7. thumbtrap

    thumbtrap

    Jun 26, 2003
    What part of 9 ft^3 do you define as small?
     
  8. ThunderStik

    ThunderStik Guest

    Jun 25, 2001
    Claremore OK.
    Man that is just a big assed box. I would suggest you mock one up out of cardboard and see if it will fit into your car. After that hope that you will always have a buddy around if not 2.


    edit fat fingers
     
  9. cjgallen

    cjgallen

    Oct 19, 2001
  10. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    As mentioned, your group delay goes up with the size of the box.

    But also, the excursion of the cone goes up.

    High group delay = bad sound.

    Excessive excursion = (eventually) silence.........

    It's best to keep a speaker in a box size that will keep it's excursion fairly close to it's x-max up to it's power rating.
     
  11. I remember building 2 enclosures for an 18 inches woofer (eighteen inches!).

    We were powering them with a 1200W amp and we deliberately rolled off below 30 Hz in order to not crack the 10" concrete floor.

    Here's a picture:

    [​IMG]


    :) Sorry I couldn't resist :p
     
  12. thumbtrap

    thumbtrap

    Jun 26, 2003
    Ahh. Discussion.. Thank you.

    The Optimal K15LF hits Xmech at 600W, rated power limit. The overstuffed k15LF hits the limit with 330W of power. Group delay for Optimal shows worst case of 15.6 ms, and it shoots way up to 28.5 ms in my example. For comparison, the K18 is 23.8ms, in an optimal box, and we can do better than that (21.6 ms) if we limit the K15LF box size to a more manageable 6.7 ft^3 (while getting a more traditional rolloff and still getting a respectable -5db at 31 Hz).

    I'm not sold yet, but it's still interesting at this point.
     
  13. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    At what power level at 31hz does it pass Xmax?

    Is there a secondary peak between 50-90hz where it also exceeds Xmax? If so, what does that do to your available power level?

    IMO, Xmax is a better target than Xmech unless you really like distortion.
     
  14. thumbtrap

    thumbtrap

    Jun 26, 2003
    Do you mean at tuning frequency, or do you mean the secondary peak? The 400w driver in an optimal 5.022ft^3/40.37hz cabinet only takes 300w before Xmax at Fb, 37w at before the secondary peak around 60 hz exceeds xmax. The 9ft/31hz cabinet exceeds xmax at 110w @ 31hz - which isn't all that great a use of this somewhat expensive driver.
     
  15. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    OK. I found Bryan Steele's Excel spreadsheet to be very handy, if you haven't tried it, ported.xls at: http://www.diysubwoofers.org/prt/ported1.htm
     
  16. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    It's the high Fs that makes it a pain; the Omega Pro 15 is a little easier on that (for even more money).

    From what I have seen the highest excusion will be at your lowest note below Fs (call it 32hz) and that secondary peak. The secondary is probably more audible, but the lower one I bet is where speakers get destroyed since that lower one gets almost linear; more power-more excursion.

    Personally, I like the specs on the Omega and am only lukewarm on the Kappa Pro LF series. On the low/loud spectrum I lean towards low but you may have other priorities for this project.
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I'm at work so I don't have any of my "tools" with me. But can I please point out the obvious.

    Why does it have to be a 15? For what you're asking, you will be better off looking at 18's.
    Those group delay figures are dreadful. You won't be happy with it......
     
  18. The current version of my spread sheet has a column that shows which drivers stay within Xmax at their full rated power. The JBL (of course), as well as Fane, EV, and Selenium. The Eminence drivers exceed Xmax at rated power.

    The alignment will also have an impact on where the driver exceeds Xmax. The Optimal Flat is usually tuned higher, and has tendency to exceed Xmax than the SBB4 alignment does.

    Look into the Selenium 15SW1P 15" driver...
     
  19. thumbtrap

    thumbtrap

    Jun 26, 2003
    I been crunching drivers all evening, and I think I'm leaning towards the ACME approach.
    A pair of Pioneer A30IR50-51F's in 7.5 ft^3 @ 28.6 Hz gives -3db @ 31 Hz, 94 db 1w/1m, good for 300w RMS, I may not need no steenkin tweeters, midranges, or crossovers and the pair should only run $130. Group delay looks respectable. I don't have Le, Re, or Mms but since they're being operated more or less as intended - I'd expect excursions to be close to nominal.

    Overall I'd say it compares very favorably with the ACME B-2 except in size, and it's not too obese when all is said and done.
     
  20. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I haven't done a lot of research on this driver, but I'd say that 3mm of excursion is not going to make you happy. I use a pair of JBL GT-120's which are about the same price but have 12mm of excursion; they stop working at 400hz (and personally I find 200hz is a better crossover point).

    Although the idea of a single full range speaker is mighty attractive, it just isn't possible for a single driver to go down below 40hz and up to 3,000 as well.

    If your goal is building subs to go under a "full range" cab, join the club (and get a big power amp) but I didn't get the impression that was your goal in this project. It wasn't exactly my intention when I started my subs, but it's where I ended up based on wanting good specs.

    I'd say you are on the right track for going low (low Fs) but you also need high excursion. The bad part is once you make something go low, it's not loud and it doesn't go high (but highs are easy).