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  • Overstuffing?

    So I want to see if my mind is playing tricks on me. I recently built a pair of three ways with the peerless sls 10in. in a sealed enclosure (taken me so long that I forot air vol :o). I stuffed the hell out of them not thinking about QTS. They sounded a little lacking in the upper bass and slightly boomy down low. While tweaking I removed some stuffing and it seems like my upper bass is back and the boom is gone.

    So I guess my question is what are the symtoms of an overstuffed box and do you think what I am hearing has anything to do with this?

  • #2
    Re: Overstuffing?

    i guess the only way to be sure is to measure the sound until the fill starts to take away from the desired sound. it's tough for me to decide on fill because where i listen is not ideal. sorry i don't have more, but i'm still wondering about this myself.

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    • #3
      Re: Overstuffing?

      Originally posted by killa View Post
      So I guess my question is what are the symtoms of an overstuffed box
      Model the box in WinISD Alpha pro. In the Box parameters page click on 'Advanced'.
      Click on Qa, which is set to 100 as the default for an empty box. Change it to 50 to see a well lined box. Change it to 5 to see a heavily stuffed box, change it to 1 for a seriously overstuffed box. You'll see it kills the low end.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #4
        Re: Overstuffing?

        My impression is that, on average, DIYers add far too much lining and/or fill. Perhaps this happens because of a vague feeling that fill "removes resonances" and "increases effective volume" and so must always be a good thing. Of course, the proper thing to do is start with no fill or lining and measure the effect of adding it. In a ported system (which must account for 90% of designs) adding lining/fill will rapidly reduce the port output exactly as Bill notes above.
        Action speaks louder than words but not nearly as often. -- Mark Twain

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        • #5
          Re: Overstuffing?

          Great thread! Now I understand the lack of low bass in my builds.

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          • #6
            Re: Overstuffing?

            I test the actual Qtc, system Q in sealed enclosures with damping, with one of the woofer tester programs. Excluding computer, the programs cost about $100, which includes hardware and software. You can then tune the Qtc by adding or removing damping material then retest.

            30 to 50% fill is what I typically use for sealed enclosures. That's a combination of semi-rigid fiberglass and polyester fiber fill.

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            • #7
              Re: Overstuffing?

              If you don't have Qtc measuring capability, you can't go wrong stuffing a closed box at 1 lb/cu. ft. of internal volume Owens Corning Pink FG. I buy rolls of R-13, strip the paper backing and stuff as already recommended. If you would rather use polyester (not as effective as FG), use at a rate of 0.8 to 0.9 lb/cu. ft. due to the differences in specific density of the FG vs PET.

              Dickason's LSDCB has a very good in depth investigation into closed box stuffing with different materials and stuffing rates, repleat with response curves.
              Live in Southern N.E.? check out the CT Audio Society web site.

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              • #8
                Re: Overstuffing?

                Originally posted by jcandy View Post
                In a ported system (which must account for 90% of designs) adding lining/fill will rapidly reduce the port output exactly as Bill notes above.
                The effect is the same in both ported and sealed. The difference is that with ported one generally uses the port tuning to arrive at the desired response. With sealed that's not an option, so varying the density of the stuffing is the only tool to change Qtc. If you have to tame a midbass hump with a VB you can do so with stuffing just as with a sealed box, but just designing the box without a midbass hump to begin with is a better option, as you don't lose overall sensitivity along with the hump.
                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

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                • #9
                  Re: Overstuffing?

                  Originally posted by carlspeak View Post
                  ...you can't go wrong stuffing a closed box at 1 lb/cu. ft. of internal volume...
                  Agree, as that's the maximum amount to use, imo.

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                  • #10
                    Re: Overstuffing?

                    Years ago one of my ex-wife's nephews stuffed a box so tightly that it decreased the volume of the box by about 90 percent. Yeah, he jammed it in there so tight it was like solid rock rather than fluffy stuffing.
                    "We are just statistics, born to consume resources."
                    ~Horace~, 65-8 BC

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                    • #11
                      Re: Overstuffing?

                      This explains why I so dislike the DynAudio Contour 1.1 speakers I bought some years ago. It is ported and I took one apart and it had tons of stuffing in it!

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                      • #12
                        Re: Overstuffing?

                        so lining all the walls of the cabinet with foam first, and then adding polyfil behind the woofers is a bad idea? It would be a pain to remove on most towers I've built. Should I just be lining the back of the cabinets and adding/subtracting poyfil to taste?
                        thanks,
                        nikkoluvr

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                        • #13
                          Re: Overstuffing?

                          Originally posted by nikkoluvr View Post
                          so lining all the walls of the cabinet with foam first, and then adding polyfil behind the woofers is a bad idea? It would be a pain to remove on most towers I've built. Should I just be lining the back of the cabinets and adding/subtracting poyfil to taste?
                          thanks,
                          nikkoluvr
                          Unless you have midbass hump issues that can't be cured with the port tuning you should only line a ported cab. For that matter you could say the same about a sealed cab, that you should only stuff it if it's necessary to get rid of a midbass hump, otherwise just line it. Before I bothered removing anything from a cab I'd measure the response first to make sure of the need for it.
                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

                          Comment


                          • #14
                            Re: Overstuffing?

                            Originally posted by jcandy View Post
                            My impression is that, on average, DIYers add far too much lining and/or fill. Perhaps this happens because of a vague feeling that fill "removes resonances" and "increases effective volume" and so must always be a good thing. Of course, the proper thing to do is start with no fill or lining and measure the effect of adding it. In a ported system (which must account for 90% of designs) adding lining/fill will rapidly reduce the port output exactly as Bill notes above.
                            Bingo! I agree completely. I believe most builders way over-use stuffing. First, we really need to move past the concept that it increases effective volume. That's not really true. When used in moderation is reduces effective enclosure Q, which is similar in terms of reducing a slight midbass hump. However, anytime we reduce the Q we have by definition added losses to the system.

                            In vented systems I may use some directly behind the driver to reduce rear-wave midrange output, but beyond that I try to keep the main cavity free of stuffing. And if you want the most efficient port output don't put anything near the port. Any damping material near the port will reduce port output, sometimes significantly.

                            Finally, as has already been stated by others, too much stuffing will greatly reduce the bass response and significantly reduce the effective internal volume of the enclosure. If someone has DATS or a Woofer Tester then it is very simple to measure the enclosure Qtc,which is a good idea when using stuffing. I use the stuff very lightly.
                            Last edited by Jeff B.; 03-07-2014, 09:44 PM.
                            Click here for Jeff Bagby's Loudspeaker Design Software

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                            • #15
                              Re: Overstuffing?

                              Originally posted by johngalt47 View Post
                              Great thread! Now I understand the lack of low bass in my builds.
                              This reminds me of your comment on the "Docere". I did not "stuff" the original enclosure. Damping material was used very lightly.
                              Click here for Jeff Bagby's Loudspeaker Design Software

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