Box stuffing materials

[jbruner]

Does cheap pillow stuffing or regular Poly-Fil increase effective air volume? Is Acousta-Stuf worth the extra cost?Fiberglass? I am building a sealed rs hf 15, and I want to stretch 4.7 ft as much as I can without too much expense. Thanks for your help. Josh

[damkor]

Fiberglass works very well. Acousta-stuf is safer. Poly-fill isn't quite as good.

[Jethro]

> Does cheap pillow stuffing or regular
> Poly-Fil increase effective air volume? Is
> Acousta-Stuf worth the extra
> cost?Fiberglass? I am building a sealed rs
> hf 15, and I want to stretch 4.7 ft as much
> as I can without too much expense. Thanks
> for your help. Josh

When it comes subs, there really is no replacement for displacement (real airspace = better). Adding fill can help if the box is undersized, but with that sub in 4.7 ft^3, you will be close to .707 anyway... so you will get very little benefit (if any) from using fill material. Still, it doesn't hurt to throw a little in there... I usually do 25-50% just for anyhow.

It really doesn't matter what you use. I bought a pkg. of Acousta-Stuf just to see what it did. I found no measurable or audible difference between it and plain old polyester fiber-fil (pillow stuffing).

[billfitzmaurice]

> When it comes subs, there really is no
> replacement for displacement (real airspace
> = better).
Yep. The added volume effect of stuffing is grossly over-exagerrated.

[marlboro]

You can go up.

I have a design that I'm implementing using a 15 inch diameter sonotube 86 inches high. It looks like a Grecian column. Floor space is is just 15 inches in diameter.

Its ported, and has a volume of 8.79 cu ft.

Here's real volume, real low, and hardly any floor space. make it match your wall and no one will know its even there.

Marlboro

[thenoid]

Provided Link: theNoid's DIY Raffle (http://www.angelfire.com/jazz/noidster/raffle.html)


Josh, I have been using plain old poly-fill for almost 20 yrs now. It has yet to let me down. I have used the Acousti-Stuff and such as well and like others, heard no real difference to justify the extra money.

There are some that say if you build a box the right size then no stuffing is needed period. But I know this, every time (and it's been many times) I have added poly to someones stuffing-less speakers or subwoofer, they have always agreed with me and left it in.

Maybe it's all in the our heads, maybe not...but as long as it was/has been/or will be perceived as being better, then it's all good in my book.

Noidster


________
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[Paul K.]

The primary advantage of Acousta Stuf is, that, once you fluff it and tease it to fill up the cabinet volume, it tends to stay in place and not settle to the bottom of the cabinet, unlike polyfil, which sinks pretty quickly. This may or may not be beneficial to a specific design, however.
Paul

> Does cheap pillow stuffing or regular
> Poly-Fil increase effective air volume? Is
> Acousta-Stuf worth the extra
> cost?Fiberglass? I am building a sealed rs
> hf 15, and I want to stretch 4.7 ft as much
> as I can without too much expense. Thanks
> for your help. Josh

[Paul K.]

It's been clearly proven that adding an appropriate amount and type(s) of stuffing increases the effective volume of the cabinet typically by 20%, lowering the Qtc appreciably. The stuffing has this effect because it changes the temperature/pressure characteristic from adiabatic towards isothermal. Adding stuffing will not, however, make much if any difference in F3, which is what most people expect or hope for.
Paul

> Yep. The added volume effect of stuffing is
> grossly over-exagerrated.

[billfitzmaurice]

> Adding stuffing will not,
> however, make much if any difference in F3,
> which is what most people expect or hope
> for.
And since that's more often than not why they do it therefore my point. 99% of the posts I see asking this question all relate to getting significantly lower response if they stuff the box, and it just isn't going to happen.

[billfitzmaurice]

> There are some that say if you build a box
> the right size then no stuffing is needed
> period. But I know this, every time (and
> it's been many times) I have added poly to
> someones stuffing-less speakers or
> subwoofer, they have always agreed with me
> and left it in.

Stuffing is beneficial in direct radiators, especially VBs, to absorb driver generated harmonics inside the box, keeping them from reflecting back to the cone and especially out the port. In folded horn subs that distortion is filtered out by the bends in the horn, so stuffing serves no useful purpose and can even result in lessened performance.

[bogie]

Okay...

Took the Small Boxes o' Whoopass...

(15" Quatros in 1.85 cube (0.9Q approx) sealed enclosures)

...and stuffed the bleep outta the things... Actually not that hard, but hey...

Noticed a definite change in output. They're smoother, but they also don't seem to "kick" as hard... Can't really decide which is best.

I _do_ think that the project, if you've got a kid goin' off to kollidge, and you want him to be popular in his dorm, is a Good Thing.

[thenoid]

Provided Link: theNoid's DIY Raffle (http://www.angelfire.com/jazz/noidster/raffle.html)


> ...and stuffed the bleep outta the things...
> Actually not that hard, but hey...

> Noticed a definite change in output. They're
> smoother, but they also don't seem to
> "kick" as hard... Can't really
> decide which is best.

Now shoot for about 50% fill and see what you like.

Noidster

________
YummyBunnys (http://camslivesexy.com/cam/YummyBunnys)

[Paul K.]

Still, being able to lower the Qtc from around 0.9-1.0 down close to or at 0.7, which is not at all atypical, is a significant difference.
Paul

> And since that's more often than not why
> they do it therefore my point. 99% of the
> posts I see asking this question all relate
> to getting significantly lower response if
> they stuff the box, and it just isn't going
> to happen.

[billfitzmaurice]

they also don't seem to
> "kick" as hard... Can't really
> decide which is best.
What's often defined as 'kick' from direct radiator subs is actually driver generated midbass harmonics outside of the nominal passband. Their wavelengths are short enough to be reinforced by reflections inside the cabinet back to the cone, but long enough so that an inch or two of damping isn't enough to tame them. Fully stuffing the box will.

[Jethro]

> Still, being able to lower the Qtc from
> around 0.9-1.0 down close to or at 0.7,
> which is not at all atypical, is a
> significant difference.
> Paul

A jump like that may be possible with Fiberglass, but from my own testing, neither Acousta-Stuf or plain ol' poly-fil will give you that much change in Qtc.

Using either type of poly-fil, you will see the most significant gain with higher unstuffed Qtc's. In my own testing (using 100% fill), a starting Qtc of ~.95 can be brought down to ~.87 with stuffing -- and make an audible difference -- there is reduced upper bass boominess, but the difference is still subtle.

The closer you get to .707, the less impact it has. As your unstuffed Qtc gets down below .8, the difference becomes less and less audible. Again, from my own testing, I was able to go from .78 down to .74 with 100% fill -- and I really could not hear any difference.

So, in the OP's situation, he has an unstuffed Qtc of ~.707 -- trying to calculate a precise amount of stuffing is really an effort in futility. All he has to do is throw some stuffing (25-50%) in there and call it a day.

Even after the testing I did, I still throw some in -- even if my Qtc is already close to .707 -- because it surely doesn't hurt anything.

[Paul K.]

While you're quite correct that fiberglass will have a bigger impact on reducing Qtc than Acousta Stuf (or Polyfil), Vance Dickason's tests clearly show a 17% reduction in Qtc from unstuffed to "100%" stuffed with Acousta Stuf, with Qtc going from 1.22 to 1.02. Whether or not the same percentage reduction would occur starting with an unstuffed Qtc of 0.9 or 0.8, I have no documented test data, but I see no logical reason why it wouldn't or couldn't happen.
Paul

> A jump like that may be possible with
> Fiberglass, but from my own testing, neither
> Acousta-Stuf or plain ol' poly-fil will give
> you that much change in Qtc.

> Using either type of poly-fil, you will see
> the most significant gain with higher
> unstuffed Qtc's. In my own testing (using
> 100% fill), a starting Qtc of ~.95 can be
> brought down to ~.87 with stuffing -- and
> make an audible difference -- there is
> reduced upper bass boominess, but the
> difference is still subtle.

> The closer you get to .707, the less impact
> it has. As your unstuffed Qtc gets down
> below .8, the difference becomes less and
> less audible. Again, from my own testing, I
> was able to go from .78 down to .74 with
> 100% fill -- and I really could not hear any
> difference.

> So, in the OP's situation, he has an
> unstuffed Qtc of ~.707 -- trying to
> calculate a precise amount of stuffing is
> really an effort in futility. All he has to
> do is throw some stuffing (25-50%) in there
> and call it a day.

> Even after the testing I did, I still throw
> some in -- even if my Qtc is already close
> to .707 -- because it surely doesn't hurt
> anything.

[Jeff B.]

> While you're quite correct that fiberglass
> will have a bigger impact on reducing Qtc
> than Acousta Stuf (or Polyfil), Vance
> Dickason's tests clearly show a 17%
> reduction in Qtc from unstuffed to
> "100%" stuffed with Acousta Stuf,
> with Qtc going from 1.22 to 1.02. Whether or
> not the same percentage reduction would
> occur starting with an unstuffed Qtc of 0.9
> or 0.8, I have no documented test data, but
> I see no logical reason why it wouldn't or
> couldn't happen.
> Paul

There would be an improvement, but remember Vb's increase is not linear as Qtc decreases. In other words as you approach lower Qtc's (relative to Qts) the necessary increase in Vb gets bigger and bigger....So don't expect the same improvement below Qtc .8 and you get at Qtc 1.2

Jeff

[Paul K.]

You're likely correct but just to make sure we're talking apples and apples, I'm not saying that the numerical decrease will be the same, like Qtc going from 1.2 to 1.0 and expecting it would also go from 1.0 to 0.8. Rather, as in this example, Qtc would go from 1.0 to 0.83, or decrease 16.7%, the same percentage decrease as from 1.2 to 1.0. But, I won't argue with you regardless because I have no documented data to which to refer nor do I have any personal experience one way or the other.
Paul

> There would be an improvement, but remember
> Vb's increase is not linear as Qtc
> decreases. In other words as you approach
> lower Qtc's (relative to Qts) the necessary
> increase in Vb gets bigger and bigger....So
> don't expect the same improvement below Qtc
> .8 and you get at Qtc 1.2

> Jeff