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Tuning Cabs

Discussion in 'Amps and Cabs [BG]' started by davetsbass, May 7, 2001.


  1. davetsbass

    davetsbass Guest

    Mar 24, 2001
    burnt hills NY
    I'm not planning on build a cab soon or anything like that, but I was wondering how you 'tune' a cab. Does it depend on the cubic space you have in the box? Or the port size?
     
  2. Bass drivers have a published set of design data called Thiele-Small data. You can plug these data into a computer program and use the results to design your speaker cabinet.

    The relationship between a bass driver and its cabinet is an intimate one. Incorrectly matched, you will blow the driver up in short order if overdriven. Short of blowing it up, it will sound like crap if mismatched.

    You have to determine if you want Loud or Low. They don't go together. Most of the big name cabinets I've seen with high SPL ratings are down -3dB or more by 50 Hz. This can be bad news if you are a 5-string player and frequently play low B at 31 Hz.

    Maybe.

    You can boost the anemic bass in a high efficiency system with a parametric or shelving type EQ. There are caveats here as well. Ported enclosures unload the driver below the frequency where the box is tuned. If you have a box tuned at 45 Hz, and are playing at 31 Hz, you risk blowing the driver to pieces.

    It is possible to design a cabinet specifically for equalization using high efficiency driver such as the Eminence Kappa 15 and still get good results. This particular combination requires a 12db per octave equalization and allows tuning the cabinet at 31 Hz to protect against driver blowout. It is less than -3dB all the way down to 31 Hz.

    I have a musicians' reference spreadsheet on my site and a computer design program that runs in a DOS box. The XLS file has a lot of speaker and other stuff in it.

    http://www.ofgb.org
     
  3. Hey bgavin. We meet again!

    I think you're supplying way too much info, if I may say so ;)

    Anyway. Tuning a bass cabinet is like matching a speaker, an air volume, and a resonant port to obtain a desired frequency response. The bigger the cabinet, the more efficient lower frequencies are radiated. There are sharp limits to this. Generally speaking, a larger speaker will require a larger box.

    The port is a resonator. It resonates at the point where the speaker begins to roll off (output lessens when frequency drops), compensating for the speaker's roll-off and straightening out the lower part of the spectrum. But of course there are limits to this as well.

    Some speakers are easy to tune, i.e. they aren't very critical when the tuning is a bit off. Speakers within certain ranges (Qtc > 0.45) of Thiele/Small (bgavin mentioned them) parameters, are very hard to tune, as they will resonate very sharply. Measurements will be necessary after building the cab.
     
  4. Why too much information? When I ask a question, I really appreciate somebody taking the time to tell me what he knows. It saves me from a lot of unnecessary work trying to dig it out for myself.

    <<
    Does it depend on the cubic space you have in the box? Or the port size?
    <<

    Yes.
     
  5. Well, very funny. What I meant is: you skipped the basics. The man asking the question wasn't asking about active shelving EQ and misaligned cabs and blown speakers.

    He wanted to know how box volume and port size affect the performance of a speaker cab. Automatically, I assumed he wasn't very knowledgable about this subject (cause why else would he have popped the question?)

    But I can be to the point (too):

    Bigger cab: lower frequency
    Larger diameter port: higher frequency, higher power capability and port linearity
    Longer tube: lower frequency

    No disrespect intended and no hard feelings, m'kay?
     
  6. None at all. I got out to your band's site. Very nicely done, and I have great appreciation for the amount of projects you've accomplished.

    I tried your personal page link in your signature, and found it broken. That is when I went to the band site, which works fine.

    Those bass cabs you put together are very nice. I'm very impressed with the quality of your rack and bass case also. The Penn and Tek extrusions, etc, let a person build some very nice equipment.
     
  7. Hey thanks man! I finally got the link to your site to work, and took a look at the (quite extensive) XL sheet. Must've been a hell lotta work! Looks great! I have a similar sheet with all speakers within my range of purchase, including Monacor, and RCF, which is what I'm using lately. They're in Italy, pretty closeby (for US standards anyway).

    My personal link works from here. I'll put an alternate URL under it, see if it works then!
     
  8. I work on my XLS constantly. If you are so inclined, email me a copy and I will update mine. You already have mine, as it is always available on my site.

    Last night I put up a nice windows sweep signal generator for download. The nice part about this one is, it shows the frequency number as it sweeps. The rate and span can be set by the user.

    I need to write one, but haven't gotten around to figuring out how much is involved in talking to the sound card. If it is just calling an API, I should be able to whip one out without too much problem. There are a few things I would add to a generator to make it really useful for tuning bass cabs.

    It looks like you build your own electronics as well. You have any good recommendations for a quality bi-amp rig, active 4th order crossover in the preamp stage, and a couple of power amps? I want to bi-amp my Rockford setup.