when should you use polyfill?

i have a non ported box i made for my f150.im just using a kenwood sub and  the box is a little undersized for the sub.should i use polyfill or not?

Whenever you need something to rest your head on.

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Seriously though, yeah you should use polyfill.

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stupid question,but what does the polyfill do exactly,and how much should i be using in a box with about .75 ft

Definitely not a stupid question.  What it does is effectively slow down the air inside the enclosure, giving the illusion of a larger enclosure.  It also reduces standing waves within the enclosure.  The important thing is to try and get the fill in the center of the enclosure.  Some people line the walls of the enclosure, but that reduces the effectiveness of the fill as the air speed is already reduced from wall friction.

Steven Kephart

Adire Audio

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It's one of the few things in car audio where experimentation won't cause a possibility of harm.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

sorry to jump in your post but i have been wondering about the polyfill too.  i needed to know can you use this on a ported box.  and how do you know how much you need.  like is there a formula.  (this much poly equals this much imaginary  air space)?

Tim, if you are pressed for space and need to increase volume with fill, then use the high quality Acousta Stuf from PartsExpress.  It will give you more perceived volume per pound than polyfil.  And there is no steadfast rule with this or any other fiber fill.  Typically, the use is from 1/2 to 1 pound per cubic foot and volume growth can be as little as 10% to as much as 40%.  Ported boxes can use it just as well as sealed, but care must be taken to keep it out of the port opening, and at a distance from the port opening of at least the port diameter.  You can use wire screen to protect the port opening from intrusion.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Steven Kephart:

"It also reduces standing waves inside the enclosure"   <--  I really wanna bounce this off ya.. I read a *really* convincing argument (that is to say, what I understand about this stuff lead me to believe this guy knew what he was talking about) that there isn't such a thing as standing waves inside enclosures because to generate a standing wave you have to have half the space of the wavelength of the tone generated between the walls of the enclosures and... at such low frequencies, there simply isn't enough space.. like... at 60hz its supposed to be like 4ft or something.  I dunno to many boxes that big.

No, I can't source that at all.  But what do you think?

stevdart:

"It's one of the few things in car audio where experimentation won't cause a possibility of harm."   <-- that is what I've always been told as well... still I've found output takes a pretty big hit using polyfil and I've always preferred the sound of unstuffed boxes....   Indeed, in a recently constructed ported box for my 13W6 I used about a 1lb of the stuff and it made it *really* muffled and killed the low end.  I removed the stuff and it got louder and deeper.. much closer to the curve WinISD orginally modeled...   even when WinISD models a flatter and flatter curve as I add volume..  the finished volume was about 1.75 cft before the polyfill..  just a wee-bit smallish for that woofer.

Anywho, all that is to ask, what precisely is the other side of polyfill? I mean there has to be some specific downshots of the stuff other than simply forcing a flatter curve via larger box volume...  personal experience tells me efficiency can take a serious hit.... is that it or what?

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"I'm finished!" - Daniel Plainview

sedate wrote:

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Steven Kephart:

"It also reduces standing waves inside the enclosure"   <--  I really wanna bounce this off ya.. I read a *really* convincing argument (that is to say, what I understand about this stuff lead me to believe this guy knew what he was talking about) that there isn't such a thing as standing waves inside enclosures because to generate a standing wave you have to have half the space of the wavelength of the tone generated between the walls of the enclosures and... at such low frequencies, there simply isn't enough space.. like... at 60hz its supposed to be like 4ft or something.  I dunno to many boxes that big.

No, I can't source that at all.  But what do you think?

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Your source is correct in that it is much less of an issue at sub frequencies.  It really depends on the size of the enclosure though.  The larger the enclosure, the lower the frequencies that will ge effected by this.  It becomes an issue when half the wavelength of a given frequency is shorter than the distance between two parallel walls.  But either way, it is best to stuff an enclosure anyway just to be sure. 

Steven Kephart

Adire Audio

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