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All other things equal, how does cabinet volume effect bass performance?

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  • All other things equal, how does cabinet volume effect bass performance?

    Everyone knows that a larger woofer is capable of playing deeper, generally speaking. But what about cabinet volume?

    So for instance, let's say I have two different simple, 2-way, vented TM designs. They both use a 7" woofer, but one is ideal for a cabinet volume of .75 cu ft, and the other is ideal for a cabinet volume of 1.5 cu ft.

    Generally speaking, how would you expect them to differ in bass performance? The obvious answer is that the larger one plays deeper, and sounds bigger, but I'm not sure if this is actually true, or if there are so many exceptions that it doesn't quite achieve "rule of thumb" status.

    And are there any inherent disadvantages to the larger cabinet? (besides WAF and floor space concerns)


  • #2
    Cabinet Qtc is a function of volume against driver Q. This equates to the damping in a sealed box. Volume also affects the air-spring, and the mechanical motion of the driver being used.
    Vented boxes also have Qtc, but a higher value. A boosted sealed box has the same group delay as a vented box with the same rolloff.

    That help?
    Wolf
    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

    *InDIYana event website*

    Photobucket pages:
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    My blog/writeups/thoughts here at PE:
    http://techtalk.parts-express.com/blog.php?u=4102

    Comment


    • #3
      More information:
      A sealed box has it's lowest F3 at Qtc = 0.707. To either side of that the F3 will rise. Q = 0.5 is considered critically damped, and closer to 0.707 is considered better for transient response. 0.8 - 0.9 Q yields a bump before rolloff, where the 0.5 - 0.7 is drooping before rolloff.

      A vented box tuned to driver Fs will have the best power handling of vented boxes as it keeps the Xmax to a minimum above tuning. It also likely has better Pe than a sealed alignment above tuning as the port handles the xmax near tuning and the driver in a sealed box has to reproduce all of the bass itself.

      Wolf
      "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
      "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
      "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
      "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

      *InDIYana event website*

      Photobucket pages:
      https://app.photobucket.com/u/wolf_teeth_speaker

      My blog/writeups/thoughts here at PE:
      http://techtalk.parts-express.com/blog.php?u=4102

      Comment


      • #4
        Originally posted by lunchmoney View Post
        Everyone knows that a larger woofer is capable of playing deeper
        Not everyone here knows that. A fair percentage even know that the only factor that can be solely attributed to driver size is dispersion.

        So for instance, let's say I have two different simple, 2-way, vented TM designs. They both use a 7" woofer, but one is ideal for a cabinet volume of .75 cu ft, and the other is ideal for a cabinet volume of 1.5 cu ft.
        Generally speaking, how would you expect them to differ in bass performance?
        Insufficient data. Just as driver size alone doesn't indicate how low it will play neither do just driver and box size. The larger box may go lower, but not if you apply Hoffman's Iron Law and trade off sensitivity to realize lower response from a smaller box.
        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

        Comment


        • lunchmoney
          lunchmoney commented
          Editing a comment
          What I should have said was "The common assumption is....", and I'm questioning said assumption. Poorly worded on my part.

      • #5
        Like asking how high can up be. Toss them in a SIM.
        Francis

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        • #6
          A 7" woofer that works well in a 1.5cu box will typically EITHER play louder (higher efficiency watt-per-watt) or deeper or a little of both compared to a 7" woofer that works well in a 0.7cu box.
          Speaking in rough generalizations.

          Often, a woofer's maximum output will be limited by XMAX (how far it can move forward/backward before distorting badly) before it runs into wattage limits, so efficiency tends not to be super important unless you're trying to eek out the most volume per watt for live sound or portable sound...and both of those applications may still prefer to benefit from smaller box sizes instead.
          My first 2way build

          Comment


          • #7
            (Broken record here - sgc)

            F3 (how low it'll go) is determined solely by Fs and Qts. Lower Fs and higher Qts will lower the F3.
            Vb (how big a box a driver "likes") is solely determined by Qts and Vas. A smaller box is the result of smaller Vas and/or lower Qts.
            Sd (piston area), Pe (thermal power handling), and Xmax are NOT included in the list of factors (or in the equations) that predict box size or "bottom end".

            If you had a 15" sub and a 4" sub, that both had (those 3) identical T/S parms, then they'd both end up w/the same F3 and the same (happy) Vb (box size).
            The big driver could kill the little guy when the power gets cranked though (probably). But it wouldn't play any deeper.

            Comment


            • #8
              Ok so it would seem that I was seeking a generalization where there wasn't one to be had. That's a good answer.

              So allow me to be more specific: I'm considering replacing my Zaph SR71's (mains in my home theater) with something a bit bigger. They are crossed at 80hz to a sealed 12" Dayton Ref sub. They are closer to the wall than I would like (about 8" away), but I've compensated by putting a 4" thick absorption panel behind them. Room is medium-sized, listening distance about 9 feet from the mains.

              Overall the SR71's + 12" sub sound great, and certainly plays deep enough, but I've always been haunted by the big, chesty mid-bass I've heard from some larger tower speakers, that really isn't there with this setup.

              I'm considering the Amiga's, which have the same size woofer but a much larger cabinet. Am I barking up the right tree here? Or would it be a disappointingly small upgrade for the mid-bass presence I'm looking for? I don't want to take up too much more floor space than the SR71's (they're on stands), so the Amiga's were appealing.

              Any other suggestions instead of the Amiga's?

              I've always wanted to build the Mini-Statements, but I'm concerned that an open-back mid is all wrong for my close-to-the-wall setup, and when all is said and done they're expensive. The CSS TMM towers would be amazing I'm sure, and also have a small footprint, but also quite expensive.

              Thanks

              Comment


              • #9
                FWIW, chesty is not something i want from my system. It makes things thick and muffled.
                Wolf
                "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                *InDIYana event website*

                Photobucket pages:
                https://app.photobucket.com/u/wolf_teeth_speaker

                My blog/writeups/thoughts here at PE:
                http://techtalk.parts-express.com/blog.php?u=4102

                Comment


                • #10
                  Hi Lunchmoney,

                  I’ve had a few 6.5” 2 ways. 1/2 cu ft, 0.70 cu ft, 1.35cu ft,
                  But never with the same driver. So I’m not sure how generalisable it is to say what a different woofer does in a bigger cabinet. The total system design is what matters.

                  if you use the same driver in a bigger cabinet, the low end would be extended with the bigger cabinet, which might match your room better. And most of us like more or deeper bass, even if it is incorrect. A obvious ported misalignment for one-note bass is the obvious exception.

                  There’s something about big speakers that makes it sound like a big speaker. I haven’t figured out what that metric it is. But I suspect it has to do with higher dynamic range, which seems to be related to higher max SPL at a set distortion level eg. 1% THD. Or lower distortion (they are different sides of the same coin IMHO)

                  I think you should simultaneously move to a smaller midrange for improved dispersion and a bigger woofer for higher SPL in the bass/more extension. In short, a 3 way.

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