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Polyfill doesn't itch and the amount of displacement is easier to adjust. I like to adhere it behind the speaker to avoid it blocking vents. If the speaker is closer to the back wall I'd staple grill cloth over it to keep it out of the speaker.

That said I used fiberglass insulation in my car because I got scraps for free.
 

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Vance Dickinson's LoudSpeaker Cookbook I think concluded that polyfill wasnt dense enough to have any affect on subwoofer performance and it's better to use some sort of insulation
 

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Vance Dickinson's LoudSpeaker Cookbook I think concluded that polyfill wasnt dense enough to have any affect on subwoofer performance and it's better to use some sort of insulation
That explains why I’ve never heard a difference in all my subs before and after polyfill. I still do it out of superstition, but now I won’t bother unless I’ve got some rock wool on hand.
 
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Ahem... :)

Make a small box act like a larger one with polyester fiberfill
By
TOM NOUSAINE

The word "FIBER" is turning up in a lot of hip conversations these days – you know, the ones that take place in art galleries, bistros, and install bays. In the galleries, they're talking about the fiber-optic conduits through which compressed digital audio and video will travel when the Intergalactic Superhighway concludes the long and winding road to our homes. In the bistros, they're talking about the colon-scrubbing glory of fiber-rich delicacies like oatmeal quesadillas and bran flan. But, to us – the few, the proud, the mighty Box Builders – fiber means dacron-polyester fiberfill, that magic and powerful ingredient that helps deliver maximum bass from a tiny space.


SEALED ENCLOSURE
1.4-ft³ Box
Stuffing Density
(lb/ft³ )
System Resonance
(Fsb)
Effective
Size
Percentage
Gain
0
56.6​
1.4​
--​
0.70
53.0​
1.6​
14%​
0.75
52.7​
1.7​
21%​
1.50
51.7​
1.8​
29%​
1.75
50.8​
1.9​
36%​
2.60
50.4​
1.6​
14%​
3.10
52.6​
1.2​
-14%​


It's no secret that you can use fiber- fill to make low-end magic; clever installers have been using it for years Take two boxes of the same size and type, insert the same woofer into each one, and stuff one with some fiber-fill – the one with the stuffing should kick out lower bass.

In simple terms, it works like this: The fiberfill fools the woofer into thinking that it's in a larger box (one with more air, or internal volume, in it). than it really is. And, in general, the larger the box, the lower the bass you can get out of it.

Fiberfill stuffing is a popular alternative for people who can't or don't want to allot a lot of space for a subwoofer box. A compound or Isobarik configuration, which pairs two woofers in one box, is another popular option, though it has some considerable downsides: For one thing, you have to buy two woofers. There is also a theoretical sensitivity loss (on the order of 6 dB) because you end up with twice the cone mass, though you can cut your losses – losing only a few dB SPL – by running a pair of the drivers in parallel.



SEALED ENCLOSURE
5.1-ft³ Box
Stuffing Density
(lb/ft³ )
System Resonance
(Fsb)
Effective
Size
Percentage
Gain
0
42.0​
5.1​
--​
0.25
42.0​
5.1​
0%​
0.50
41.2​
5.8​
14%​
0.75
40.3​
6.2​
22%​
1.00
39.4​
6.5​
27%​
1.25
38.6​
6.5​
27%​
1.50
40.2​
5.6​
9%​


The particulars of fiber stuffing are pretty interesting: The air inside your enclosure actually heats up as your woofer moves, making the air stiffer. (I'm absolutely serious.) When the enclosure is stuffed with fiber, the fibers wiggle, dissipating some of the heat and making the system work as though the box were larger. Theoretically, your woofer/box bass system can act like a system that's a maximum of 40 percent larger when you've latched onto the right stuffing recipe – in other words, if you have an enclosure that offers 1 cubic foot (1 ft³ ) of internal volume, in a perfect world a good stuffing job will make it perform like an enclosure that offers 1.4 cubic feet of internal volume.

There are three types of stuffing that are commonly used for this purpose: fiberglass insulation, long-fiber wool, and polyester fiberfill. Fiberfill is the best choice because it doesn't come loose and fly around and irritate your skin or lungs like fiberglass, it works as well as either of the others, it's a lot cheaper than wool, and moths hate it. I recently bought five 20-ounce bags of it at $1.99 a pop (a total of 6.26 pounds for $9.95) at Minnesota Fabrics; that turns out to be about $1.60 a pound. You should be able to find some at any fabric store or in the bedding section at friendly stores like K-Mart or Home Depot.

To evaluate the effectiveness of box stuffing, I used an MLSSA analyzer to measure the impedance of three enclosures – 5.l-cubic-foot sealed, 1.4-cubic-foot sealed, and 1.4-cubic-foot ported (the port measured 3 inches in diameter and 6 inches in length) – with various densities of stuffing. For the sealed boxes, I was able to determine the effective box size – as enhanced by the stuffing – using the system's resonant-frequency and Qes values. For the ported box, I compared the tuned frequency of the empty enclosure to the tuned frequency of the stuffed enclosure, using the Speak for Windows computer program; this enabled me to find the effective box size that fit the actual resonant frequency I'd measured.


PORTED ENCLOSURE
1.4-ft³ Box
Stuffing Density
(lb/ft³ )
System Resonance
(Fsb)
Effective
Size
Percentage
Gain
0
42.0​
1.4​
--​
0.40
39.1​
1.6​
14%​
0.85
37.2​
1.8​
29%​
1.25
35.2​
1.9​
36%​
1.40
34.2​
2.0​
43%​
1.75
35.2​
1.9​
36%​


In each case, the news was good – make that very good. With all three boxes, I enjoyed roughly 25 to 35 percent of "space gain" by using stuffing at a rate of 1 to 1.75 pounds per cubic foot of internal volume.

When making system performance predictions, be aware that the Qes figure – and, therefore, the Qts figure – of the sealed boxes dropped. And with the ported box, the peak of the impedance curve on the lower side of the tuned frequency became heavily damped below the box's point of resonance. I also found that there is such a thing as too much of a good thing: System resonance (Fsb) rises again, beginning with densities of around 1.5 pounds of stuffing per cubic foot of box volume; this happens because the fibers are jammed so tightly together that they stop wiggling and, consequently, stop dissipating heat.

I also found that stuffing gets less effective as box size increases. The morale: The bigger your box is, the harder it is to fool your woofer.

A few rules of thumb: Stuff small enclosures – those with up to about 3 cubic feet of internal volume or less – with 1.5 pounds of fiberfill for each cubic foot of internal volume and you should get about a 30-percent increase in box volume without seriously affecting other performance variables. For larger enclosures, add stuffing at a rate of approximately 1 pound per cubic foot and you should get a virtual-space boost of about 25 percent. One thing's certain: You'll impress the heck out of your friends at the art gallery and bistro.


Source:
 

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from vance Dickinson LoudSpeaker Design Cookbook

There is one last point that you will hear from time to time regarding polyfill: that polyfill stops standing waves in an enclosure. When referencing an enclosure for a subwoofer playing a fundamental frequency that falls in the typical range, this is simply false. A standing wave in this range of frequencies would be several feet long and, thus, unlikely to occur. However, higher order harmonic distortion is possible, and can potentially colour music. Being that these higher order harmonics will be progressively shorter (in terms of wavelength), polyfill can be effective for this purpose. However, audibility, particularly at high SPL, can be quite minimal. Using polyfill in an effort to absorb standing waves or various distortion is most effective in large enclosures for your midrange and is not particularly effective for a subwoofer.

In general, if the reccomended enclosure size for a driver is 1.0cu ft and want it to sound like it's on a 1cu ft enclosure....put it in a 1.0ct ft enclosure.
 

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Blackhole stuff is recycled denim. It's very dense. Too much can alter the enclosure size. I've used inside midbass and midrange enclosures before and had to move a substantial amount bc speakers were being choked .

If sub box is the correct size based on manufacturer recommendation or based on specific install requirements there is no need for any sort of fill
 

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Vance Dickinson's LoudSpeaker Cookbook I think concluded that polyfill wasnt dense enough to have any affect on subwoofer performance and it's better to use some sort of insulation
agreed, and eric stevens told me that he only used pink fiberglass insulation. So thats all i use too LOL>
 

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Discussion Starter · #14 · (Edited)
Ahem... :)


Make a small box act like a larger one with polyester fiberfill
By
TOM NOUSAINE

The word "FIBER" is turning up in a lot of hip conversations these days – you know, the ones that take place in art galleries, bistros, and install bays. In the galleries, they're talking about the fiber-optic conduits through which compressed digital audio and video will travel when the Intergalactic Superhighway concludes the long and winding road to our homes. In the bistros, they're talking about the colon-scrubbing glory of fiber-rich delicacies like oatmeal quesadillas and bran flan. But, to us – the few, the proud, the mighty Box Builders – fiber means dacron-polyester fiberfill, that magic and powerful ingredient that helps deliver maximum bass from a tiny space.


SEALED ENCLOSURE
1.4-ft³ Box
Stuffing Density
(lb/ft³ )
System Resonance
(Fsb)
Effective
Size
Percentage
Gain
0
56.6​
1.4​
--​
0.70
53.0​
1.6​
14%​
0.75
52.7​
1.7​
21%​
1.50
51.7​
1.8​
29%​
1.75
50.8​
1.9​
36%​
2.60
50.4​
1.6​
14%​
3.10
52.6​
1.2​
-14%​


It's no secret that you can use fiber- fill to make low-end magic; clever installers have been using it for years Take two boxes of the same size and type, insert the same woofer into each one, and stuff one with some fiber-fill – the one with the stuffing should kick out lower bass.

In simple terms, it works like this: The fiberfill fools the woofer into thinking that it's in a larger box (one with more air, or internal volume, in it). than it really is. And, in general, the larger the box, the lower the bass you can get out of it.

Fiberfill stuffing is a popular alternative for people who can't or don't want to allot a lot of space for a subwoofer box. A compound or Isobarik configuration, which pairs two woofers in one box, is another popular option, though it has some considerable downsides: For one thing, you have to buy two woofers. There is also a theoretical sensitivity loss (on the order of 6 dB) because you end up with twice the cone mass, though you can cut your losses – losing only a few dB SPL – by running a pair of the drivers in parallel.



SEALED ENCLOSURE
5.1-ft³ Box
Stuffing Density
(lb/ft³ )
System Resonance
(Fsb)
Effective
Size
Percentage
Gain
0
42.0​
5.1​
--​
0.25
42.0​
5.1​
0%​
0.50
41.2​
5.8​
14%​
0.75
40.3​
6.2​
22%​
1.00
39.4​
6.5​
27%​
1.25
38.6​
6.5​
27%​
1.50
40.2​
5.6​
9%​


The particulars of fiber stuffing are pretty interesting: The air inside your enclosure actually heats up as your woofer moves, making the air stiffer. (I'm absolutely serious.) When the enclosure is stuffed with fiber, the fibers wiggle, dissipating some of the heat and making the system work as though the box were larger. Theoretically, your woofer/box bass system can act like a system that's a maximum of 40 percent larger when you've latched onto the right stuffing recipe – in other words, if you have an enclosure that offers 1 cubic foot (1 ft³ ) of internal volume, in a perfect world a good stuffing job will make it perform like an enclosure that offers 1.4 cubic feet of internal volume.

There are three types of stuffing that are commonly used for this purpose: fiberglass insulation, long-fiber wool, and polyester fiberfill. Fiberfill is the best choice because it doesn't come loose and fly around and irritate your skin or lungs like fiberglass, it works as well as either of the others, it's a lot cheaper than wool, and moths hate it. I recently bought five 20-ounce bags of it at $1.99 a pop (a total of 6.26 pounds for $9.95) at Minnesota Fabrics; that turns out to be about $1.60 a pound. You should be able to find some at any fabric store or in the bedding section at friendly stores like K-Mart or Home Depot.

To evaluate the effectiveness of box stuffing, I used an MLSSA analyzer to measure the impedance of three enclosures – 5.l-cubic-foot sealed, 1.4-cubic-foot sealed, and 1.4-cubic-foot ported (the port measured 3 inches in diameter and 6 inches in length) – with various densities of stuffing. For the sealed boxes, I was able to determine the effective box size – as enhanced by the stuffing – using the system's resonant-frequency and Qes values. For the ported box, I compared the tuned frequency of the empty enclosure to the tuned frequency of the stuffed enclosure, using the Speak for Windows computer program; this enabled me to find the effective box size that fit the actual resonant frequency I'd measured.



PORTED ENCLOSURE
1.4-ft³ Box
Stuffing Density
(lb/ft³ )
System Resonance
(Fsb)
Effective
Size
Percentage
Gain
0
42.0​
1.4​
--​
0.40
39.1​
1.6​
14%​
0.85
37.2​
1.8​
29%​
1.25
35.2​
1.9​
36%​
1.40
34.2​
2.0​
43%​
1.75
35.2​
1.9​
36%​


In each case, the news was good – make that very good. With all three boxes, I enjoyed roughly 25 to 35 percent of "space gain" by using stuffing at a rate of 1 to 1.75 pounds per cubic foot of internal volume.

When making system performance predictions, be aware that the Qes figure – and, therefore, the Qts figure – of the sealed boxes dropped. And with the ported box, the peak of the impedance curve on the lower side of the tuned frequency became heavily damped below the box's point of resonance. I also found that there is such a thing as too much of a good thing: System resonance (Fsb) rises again, beginning with densities of around 1.5 pounds of stuffing per cubic foot of box volume; this happens because the fibers are jammed so tightly together that they stop wiggling and, consequently, stop dissipating heat.

I also found that stuffing gets less effective as box size increases. The morale: The bigger your box is, the harder it is to fool your woofer.

A few rules of thumb: Stuff small enclosures – those with up to about 3 cubic feet of internal volume or less – with 1.5 pounds of fiberfill for each cubic foot of internal volume and you should get about a 30-percent increase in box volume without seriously affecting other performance variables. For larger enclosures, add stuffing at a rate of approximately 1 pound per cubic foot and you should get a virtual-space boost of about 25 percent. One thing's certain: You'll impress the heck out of your friends at the art gallery and bistro.


Source:
I’m well aware of Tom Nousaine’s (RIP) article. It was ripped from the 1995’s Sound & Vision column found here: https://www.ranger5g.com/forum/attachments/box-builder-fill-er-up-pdf.35156/
 

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Discussion Starter · #15 ·
Polyfill doesn't itch and the amount of displacement is easier to adjust. I like to adhere it behind the speaker to avoid it blocking vents. If the speaker is closer to the back wall I'd staple grill cloth over it to keep it out of the speaker.

That said I used fiberglass insulation in my car because I got scraps for free.
Title is a sealed enclosure, not ported
 

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Discussion Starter · #16 ·
That explains why I’ve never heard a difference in all my subs before and after polyfill. I still do it out of superstition, but now I won’t bother unless I’ve got some rock wool on hand.
You would only do it if you have a legitimate reason to use it, like having a sealed enclosure on the small side, and having a WinISD model showing the driver performs better with a slightly larger enclosure. Otherwise just putting insulation in an enclosure hoping for the best won’t work.

I only have enough room for a 23L sealed enclosure which is a little small for my 12” sub. According to above, if I use 1.75lb/ft3 insulation, volume can be increased by around 35%, which brings volume to 31L. I’ve done the modelling that shows my driver plays a lot better in 31L gross versus 23L gross
 

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Here’s what you do.
you try the stuff you have in the pictures.
step 2. Decide if you like it
step 3. If you didn’t like it, try something else
 

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Discussion Starter · #19 ·
Blackhole stuff is recycled denim. It's very dense. Too much can alter the enclosure size. I've used inside midbass and midrange enclosures before and had to move a substantial amount bc speakers were being choked .

If sub box is the correct size based on manufacturer recommendation or based on specific install requirements there is no need for any sort of fill
I only have enough room for a 23L sealed enclosure which is a little small for my 12” sub. According to above, if I use 1.75lb/ft3 insulation, volume can be increased by around 35%, which brings volume to 31L. I’ve done the modelling that shows my driver plays a lot better in 31L gross versus 23L gross
 

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I understand it's sealed but polyfill will be more effective if its compressed. That's why you need a large volume to make a difference. I don't like threw idea of it being able to blow around into the woofer.
2-3" thick wool pads are an alternative also. Plus overall material but with much greater density
 
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