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Is there any downside to box stuffing to "increase" volume?

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  • Is there any downside to box stuffing to "increase" volume?

    I pulled this info from the March/April 1995 issue of Car Stereo Review. Is there any downside to stuffing an enclosure? Some of the densities mentioned are pretty well beyond some of the general recommendations that you'll find in various other sources.

    Unconfirmed negatives I think I've heard in the past:
    1) stuffing can impede the airflow through the port.
    - This seems intuitive but there is no mention of it in the linked article and the listed changes are measured, not theoretical
    - if this is an issue is it mitigated with the use of a passive radiator?
    2) intentionally building a box undersize and then stuffing to desired spec hurts efficiency
    - I think I heard this once, possibly years on this board. I'd need something beyond a Woofer Tester to verify this though.

    https://www.ranger5g.com/forum/attac...-up-pdf.35156/

    Aaron
    Attached Files
    Thanks,
    Aaron

  • #2
    Some additional tests by Troels here as well - http://www.troelsgravesen.dk/ports.htm. I generally factor in about a 10-15% "virtual" volume increase when working with ported enclosures and a reasonable amount of stuffing (the amount needed for killing standing waves, back waves etc).

    However, I would never undersize the box deliberately. It is much easier to take up a little extra volume in the final cabinets than it is to add some.

    Its not so much "flow" through a port as much as it is constantly changing air pressure (+/-). So long as the port isn't blocked it should be ok. Actually blocking the port with stuffing sort of has the effect of reducing air velocity which would make it act as if it was longer (or is that shorter? someone correct me) - the point being it would change the tuning from what you expect. There doesn't need to be any sort of free "flowing" connection from woofer back to port.

    People sometimes talk about an over-stuffed sound as being a little flat or dead - but this is mostly subjectivity. Under stuffed/damped would be objectively worse.

    Ultimately, in my experience, the final stuffing, volume, port size and tune have to be measured and tweaked before buttoning up a box.

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    • #3
      Over stuffing a vented or PR enclosure will decrease port output. As long as you are willing to live with that, maybe you'll like it. Seems pointless to add a port or PR though, and handicap it with too much stuffing. I agree with DeZZar, I'd also never deliberately undersize a ported box.
      Francis

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      • #4
        Stuffing doesn't make the box 'bigger', it lowers Q. The above charts are not accurate, being compiled with incomplete data. No disrespect to Tom Nousaine, RIP, but he missed the mark on this one.
        You can model the effect of lining and stuffing in a box program that allows adjustment of Qa. In WinISD 0.7 you do it in the Box tab, opening the 'Advanced' to reveal Ql, Qa and Qp. The default Qa value of 100 is a bare box. 50 is a lined box, 10 is a stuffed box, 5 is a stuffed and compressed box. The result of changing Qa can be seen on all of the graph options. Why it does what it does is most easily seen on the impedance chart.
        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

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        • #5
          The only time I'd stuff a reflex box is when I was stuck with a very non-optimum design in a small box. Then it can help tame a midbass hump. On the other hand, I like to fully stuff sealed boxes.
          Francis

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          • #6
            Back in the day (Vance's LDC Ed. 7) NO ONE suggested stuffing to help increase the "apparent volume" (to the woofer) of a VENTED box, only a closed (sealed) one. It was thought that you could get a volume increase (really change in "Q", as Bill has said) of about +20% when well stuffed.

            Comment


            • billfitzmaurice
              billfitzmaurice commented
              Editing a comment
              As I recall Vance initially accepted Nousaine's work at face value and even included his conclusions in one or more of his editions, removing it later on. He should have followed Reagan's admonition to trust, but verify. Nousaine can be forgiven to a point, as he didn't have the ability to fire up WinISD to check his work in 1995. But a better test protocol would have revealed his error. I think he was so excited to see the effect on Q that he got sloppy, and as a result drew some inaccurate conclusions.

            • aarond
              aarond commented
              Editing a comment
              Chris, your comments hint at what I recall as conventionally accepted guidance, there wasn't much readily available/digestible data to support it though.

          • #7
            Originally posted by Chris Roemer View Post
            Back in the day (Vance's LDC Ed. 7) NO ONE suggested stuffing to help increase the "apparent volume" (to the woofer) of a VENTED box, only a closed (sealed) one. It was thought that you could get a volume increase (really change in "Q", as Bill has said) of about +20% when well stuffed.
            Yeah, stuffing a vented cab is kind of a new thing. Probably featured on some YouTube video.
            Francis

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            • billfitzmaurice
              billfitzmaurice commented
              Editing a comment
              Probably. I would imagine someone who thought stuffing actually works the same as making the box larger decided that what's good for sealed must be good for vented, not realizing that what they really were doing was making the vented box act like a sealed box.

          • #8
            Originally posted by billfitzmaurice View Post
            Stuffing doesn't make the box 'bigger', it lowers Q. The above charts are not accurate, being compiled with incomplete data. No disrespect to Tom Nousaine, RIP, but he missed the mark on this one.
            You can model the effect of lining and stuffing in a box program that allows adjustment of Qa. In WinISD 0.7 you do it in the Box tab, opening the 'Advanced' to reveal Ql, Qa and Qp. The default Qa value of 100 is a bare box. 50 is a lined box, 10 is a stuffed box, 5 is a stuffed and compressed box. The result of changing Qa can be seen on all of the graph options. Why it does what it does is most easily seen on the impedance chart.
            Do you think an educated analysis of the impedance plot would tell you everything you need to know?

            In the case of the table I posted, if we compared the plots of the unstuffed 1.4cf to that of when it's the most densely stuffed, what do you think the difference would be?
            Thanks,
            Aaron

            Comment


            • billfitzmaurice
              billfitzmaurice commented
              Editing a comment
              Impossible to say for sure without having the driver specs to model it, but the usual effect is that any midbass hump is reduced.That also happens when the box is made larger, which led to Nousaine's conclusion. However, along with the lowering of a midbass hump when the box is made larger there's also an increase in overall sensitivity. When you tame a hump with stuffing it's accompanied by a decrease in overall sensitivity.

          • #9
            The difference is a change in Q of the enclosure, or the amount of damping. That is the change.
            Wolf
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            • #10
              I have found that stuffing usually improves the midrange but often reduces the amount of bass.

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