# Polyfill, the magic ingredient??



## the_dealer

I've read so much about polyfill, and its contradictive. Some say add it to any box, ported or sealed and it fools the sub into an "increase" in cuft. Others say it doesn't do anything, or it makes the box actually smaller. I see people adding 1lb polyfill per 1cuft. Is this something everyone is doing? I've never used the stuff besides what came in prefab boxes, so I couldn't tell a difference either way. Most of what I've read pertains to the box being too small, either due to limited space, or measuring/building f**k ups. So what if the box is the correct size? Do you still want to add some? 

I've seen where people not concerned with space issues purposely build the box smaller, and add polyfill to make up for it. I know from personal experience that if you build a sealed box too big for a lower xmax sub, the sub will bottom out way too easy. Yea it plays deep, but it's still limited. So what happens of you build a box small and fill to simulate the box being bigger? Do you still get the "spring" the small sealed box has but with the ability to play deeper, or does the sub handle the same? I've been practicing my box fan skills, building boxes for friends, people from work, etc. I'd like to start charging for the labor as well lol, but I still have alot to learn. Polyfill seems to be an argumentive subject, and its just a matter of opinion. Is there any real proof to back it up?


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## therapture

My only proof is my ears. I run a sealed enclosure 1.44ft*³, which is larger by .44 than the "spec" size for my sub...and I add 1.5lbs of polyfil. The sub is slightly smoother, cleaner, and seems to have less "ring" when driven a bit too hard.

I have listened both ways, and my ears say "add polyfil" every time I heard it without it.


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## CrossFired

Fill is good, as it help to kill the back wave of the sub. Without some sort of fill, the back wave will reflect off the back of the box and fight the sub. I say the correct size and 35% fill will sound best.


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## Mic10is

polyfill will have little effect in a sub enclosure. "Fill" in general works based on thermodynamics. Speaker is basically a piston. When it moves, it creates heat. Adding fill helps to dissipate the heat as the small fibers wiggles and move through the air movement. 
Thus the theory is that if enough heat is being dissipated by the fill, the speaker is "tricked" into behaving as if it were in a larger enclosure bc more heat can be produced.

The issue with polyfill in general is that it is not dense enough to have any real effect, from a thermodynamic or an absorption stand point.
using a denser material like Fiberglass insulation (yellow or white), Rock Wool, Roxul etc...

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.*


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## Ray21

In my experience, using polyfil makes an audible difference that I like. I haven't measured before/after using polyfil but I know Tom Nousaine did and had an article about it that had some good solid info. 

Here's the article:
http://www.nousaine.com/pdfs/Box Stuffing.pdf


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## UNFORGIVEN

IM-SG Sealed Box Vid 3 in series - YouTube
Polyfill is added @5:00 mark with testing


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## RNBRAD

When I was younger I just took the heat dissipation or thermodynamic benefits of polyfill as gospel. I always wanted to try to control the air temps inside the box in other ways beyond polyfill but never did. 

The reason I question this theory is polyfill is a good insulator thus a poor conductor, so not much air cooling happening with conduction. Now these fibers move around from air movement and molecular vibration. Could they be dissipating the heat by convection? I'm not buying it!! 

Here's what I think is happening: Poly is great for trapping air and preventing it's movement just like pretty much any good insulator does. When the air molecules are excited, these thousand of minute fibers resonate and in doing so absorb this excitation and transfer sonic energy into mechanical energy. Remember that sound travels at almost 800mph, so think how fast the sound is moving inside a box. So it acts like a dampner doesn't it? You darn right it does, no question. Now these fibers are excited but granted they have a greater, however slight, property to return to rest than air, this is how it dampens the sound waves. Ok now think of air as a dampner, cause it is. The further sound travels through air the more decay created. Air can be a sound barrier in and of itself, just like it can be a good insulator. This happens once you control it's movement, then these properties become apparent. If sound travels through a box, the amount of excitable air has an effect on the sound characterisitics within the box. The less the volume of air, the less molecules to excite, so less dampening, however slight. It takes energy to move air molecules, the more of them the more energy, so more air has a dampening effect, that's a given. So if we look at 2 boxes with nothing in them, one is slighly bigger than the other and we introduce a frequency within the box, the larger box will provide a slightly greater sound decay than the smaller box just based on the number of molecules available to excite. 

Now compare this with what the poly is doing. It is mimicking the sound decay of a box with more molecules exposed to frequency vibration. What is happening is the same principal as sound deadening. Polyfill is decreasing reverberation time, decay time whatever you want to call it. Whether this is a stadium, large room, or a box, same principal applies. To deaden it, decay time is shortened. a box with poly matches or mimicks the decay time of a larger box. 

That's what I think, I just can't buy the thermodynamics of it. If dissipation of heat was that noticeable, I think we would notice a major sound change as the air inside the box heats up during a normal listening session, or maybe during peak transients and sound changes with lulls as the air cools. I've never heard this happening. Also sealed boxes would be more prone to a heating affect more so than ported due to the trapping of heated air versus the venting of it. When you place poly in a box, it is immediately noticeable from the 1st note whether internal air temp is 70 or 110. When someone talks about thermodynamics of poly, it's always obscure reasoning with no sustance. If it's true, I need some sound explanation of the scientific process, not that it dissipates heat thus fooling a woofer. Just a good explanation of how it dissipates heat would be a good start. Cause if anything, it's trapping air, not moving it. Also poly is not a conductor, but we could mimick poly inside a box with a different material that is a good conductor if that was the case. Anyway just my opinions and thoughts on the subject.


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## Gilroy

RNBRAD said:


> When someone talks about thermodynamics of poly, it's always obscure reasoning with no sustance. If it's true, I need some sound explanation of the scientific process, not that it dissipates heat thus fooling a woofer. Just a good explanation of how it dissipates heat would be a good start. Cause if anything, it's trapping air, not moving it. Also poly is not a conductor, but we could mimick poly inside a box with a different material that is a good conductor if that was the case. Anyway just my opinions and thoughts on the subject.


I agree, the thermo and heat transfer being put forth is not making much sense. 

If someone were worried about heat behind their woofer in a sealed box, they would build the box out of a good conductor and put an A/C vent blowing on it. The sealed box portion behind the woofer is basically an oven (heat being provided by that giant resister we call a subwoofer), putting an insulator inside of an insulator is not going to do much for you by way of cooling.


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## luisc202

Mic10is said:


> polyfill will have little effect in a sub enclosure. "Fill" in general works based on thermodynamics. Speaker is basically a piston. When it moves, it creates heat. Adding fill helps to dissipate the heat as the small fibers wiggles and move through the air movement.
> Thus the theory is that if enough heat is being dissipated by the fill, the speaker is "tricked" into behaving as if it were in a larger enclosure bc more heat can be produced.
> 
> The issue with polyfill in general is that it is not dense enough to have any real effect, from a thermodynamic or an absorption stand point.
> using a denser material like Fiberglass insulation (yellow or white), Rock Wool, Roxul etc...
> 
> 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.*


Thanks for the informative response as I was having doubts it would help in a sealed sub enclosure.


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## TOOSTUBBORN2FAIL

My measurements didn't find it effective for absorbing midrange or even treble frequencies in a large midrange enclosure either. Nor did acoustuff work, or black hole tiles.


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## spyders03

I have it on pretty good authority to stuff a box with as much as it would hold. Haven't tried it, this way yet, but I trust him.


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## moparman79

I would try some of this stuff. works good for me in sealed enclosures (one all four sides).Blackhole / High Efficiency Dampening Products

Then this on the back of the box were the magnet is. Blackhole / High Efficiency Dampening Products


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## RNBRAD

spyders03 said:


> I have it on pretty good authority to stuff a box with as much as it would hold. Haven't tried it, this way yet, but I trust him.


Polyfill is like salt, it takes a certain amount for optimum benefit. Adding too much will reverse the effect and it is definitely audible. Give it a try!!


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## TOOSTUBBORN2FAIL

I would highly suggest measuring the response before and after to make sure its not a placebo effect that your hearing. When I tested my home bookshelfs, neither polyfil, nor acoustuff, nor black hole tile made any measureable difference in response, nor could you hear a difference. Ill be testing black hole tile again, but I dont believe for a second it is effective at absorbing anything. Black hole 5 might be better at absorbing, but not in the sub bass frequencies.


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## RNBRAD

I use poly for large sealed subwoofers. I'm not sure there is anything to gain on a bookshelf speaker? The results of poly I think we're posted earlier in the thread of a change in frequency response on a 10" driver essentially performing as if it were in a larger box. Applying more than optimum just reversed the effect.


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## TOOSTUBBORN2FAIL

I tested after seeing multiple posts about polyfil and like materials helping to smooth midbass and midrange frequencies, and the results I got were pretty much negligible, which means none of them actually are absorbing anything in the midbass frequencies, and not enough up high to make a difference. That said, i havent tested with subwoofers, I just think one should measure if possible when doing it to get the best results.


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## cubdenno

Data-Bass

A great article


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## thehatedguy

I wonder how many of those problems that were fixed would occur in a smaller auto sized sub enclosure?


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## TOOSTUBBORN2FAIL

While the measurements provided are very good, the explanations they give for the results are just plain wrong. For instance, they talk about polyfil absorbing the 170hz peak, well 170hz is a 79.4' wave. Your not absorbing that in a box, period. Something else is definitely happening, but your not absorbing the wave. There wouldn't even be any standing waves at 170hz.


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## cubdenno

TOOSTUBBORN2FAIL said:


> While the measurements provided are very good, the explanations they give for the results are just plain wrong. For instance, they talk about polyfil absorbing the 170hz peak, well 170hz is a 79.4' wave. Your not absorbing that in a box, period. Something else is definitely happening, but your not absorbing the wave. There wouldn't even be any standing waves at 170hz.


Contact Josh. He is always (at least in my experience) willing to talk and answer questions.

He goes by Ricci on AVS. Great guy with some awesome horn designs for home theater use.


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## TOOSTUBBORN2FAIL

I'll look into that when I'm ready to test it. Most of the information in the article (and obviously the measurements) are solid. Its just not because polyfil is absorbing anything. And like I said, it has almost no effect on 80hz and up in my .54cf enclosures for 6.5" speakers (which play full range and roll off on their own.)

Also, check out this link

http://www.diymobileaudio.com/forum/member-reviews-product-comparisons/157862-enclosure-stuffing.html


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## TOOSTUBBORN2FAIL

I'll look into that when I'm ready to test it. Most of the information in the article (and obviously the measurements) are solid. Its just not because polyfil is absorbing anything. And like I said, it has almost no effect on 80hz and up in my .54cf enclosures for 6.5" speakers (which play full range and roll off on their own.)

Also, check out this link

http://www.diymobileaudio.com/forum/member-reviews-product-comparisons/157862-enclosure-stuffing.html


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## RNBRAD

It doesn't matter how long a wave is, if the frequency can move or vibrate a poly fiber, then yes it is essentially absorbing it. Just because a person can't measure a change or hear a change doesn't mean we can assume that it's not absorbing it.


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## Jroo

I dont know the science behind it and cant speak on anything but sealed boxes. I have used polyfill several times on sealed boxes. Each time I used it, they low end sounded smoother to me. It does have effect on the sound when you use it and when you dont. Next I want to try the the Focal/Black Hole stuff, heard that it is the best polyfill out there.


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## TOOSTUBBORN2FAIL

You're not absorbing standing waves in a subwoofer box. The wavelengths a sub is playing and its first few harmonics are bigger than the box itself. So inside the box, you have pulsating air pressure. Like I said, the polyfil is obviously doing something, but it is not absorbing sound waves. It may be converting some of that pressure into heat through the vibration of the polyfil. And in my tests, above 80hz, its not doing anything audible in the frequency or time domain.


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## TOOSTUBBORN2FAIL

In fact, if you really think about it, that's exactly what it has to be doing for the sub to act like its in a larger enclosure, lowering pressure in the box by converting some of that energy to heat.


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## TOOSTUBBORN2FAIL

Jroo said:


> I dont know the science behind it and cant speak on anything but sealed boxes. I have used polyfill several times on sealed boxes. Each time I used it, they low end sounded smoother to me. It does have effect on the sound when you use it and when you dont. Next I want to try the the Focal/Black Hole stuff, heard that it is the best polyfill out there.


Black hole stuff isn't really polyfil, its recycled denim. In fact, I'd bet my L6SE'S that it wouldn't measure any different than if you used recycled denim insulation, like you can get at Lowe's in huge packs for $52.


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## RNBRAD

So now were saying that poly can absorb pulsating pressure but not a sound wave? What is a sound wave? And how do we come to a conclusion to say a sound wave is too long to be absorbed? That would mean it's too long to vibrate my eardrum. I don't care how long a frequency is, if it can move or resonate a poly fiber it can be absorbed. Realize sound waves are nothing more than displaced air particles. If air moves, it can be absorbed, period. Does not matter how long this wave of air movement is. Now some frequencies may be too high and lack the amplitude, displacement, or pressure to be absorbed or in other words lack the ability to move or vibrate the poly fibers. That's why we hear the effect on the lower frequencies more so than upper frequencies.


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## TOOSTUBBORN2FAIL

I never said it can't absorb a sound wave, but, and this is the big but, it does not have a noticeable effect on standing waves, and standing waves don't occur in a subwoofer box. I've been harping on this because this is the most common reason I see people want to put things behind their speakers that are supposed to absorb sound. If it had an effect on standing waves, my boxes would have been the perfect chance to show it. I have HUGE dips in response at the frequencies corresponding to the dimensions of my box, which is 8"x8"x16.5", internal. The polyfil had no real effect on this. 

I also never said that a sound wave could be too long to be absorbed. I did say that you can't absorb standing waves in a box (which is irrelevant to subwoofers anyways because there are no standing waves in the box).

Now, are there sound waves inside a subwoofer box? Sure, partial ones. I've avoided calling them that, because I'm trying to avoid people thinking they can put polyfil behind any speaker and it will help improve sound because it will help absorb sound inside the box in anything but a subwoofer box. In my tests, its pretty clear the the speaker diaphragm and box are doing a good enough job at keeping the sound _inside_ the box from affecting what we hear _outside_ the box that it makes the effect of polyfil (or any other material used to absorb the sound inside the box) negligible, from 80hz up in the case of my tests.

Now, on a really technical note, I still assert that absorb is the wrong word for whats happening. To absorb is to take in energy, generally through porosity. In this case, what we are doing is converting energy to another form. Damping is a more accurate term, in the form of viscous drag.

Absorption would be more suitable in terms of an acoustic foam, where sound waves enter the pores of the material, and are damped to the point of significant or complete attenuation. In this case absorb is a better term, since the material has prevented a large amount or the whole amount of energy in the form of sound from escaping it. Of course in this case, what I've been stating comes into play, where it only truly starts to become effective when it is 1/4 as thick as the wavelength your targeting.


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## TOOSTUBBORN2FAIL

I also harp on measuring, because the optimum amount is going to be determined not by box volume, but by total qts of the sub in the box.


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## RNBRAD

I guess we may differ on what a "standing wave" is. By definition it can be a literal wave not moving or it can be a reflected wave propagating and moving against the initial wave. Does this happen in a box? You bet it does!!! Now can this wave of sound effect cone control as it bounces and propagates back and contacts the cone? You bet it does!! Can we eliminate or dampen or deaden or absorb these waves effectively decreasing the negative effects on the cone. You bet we can!! 

If you didn't hear or measure any benefits in your test, I would say you were either effectively operating above the poly resonant freq or they were packed too tight to resonate or your test equipment wasn't sensitive enough or perhaps even measured incorrectly. Like I say, if a sound wave can resonate the fiber of poly, visibly or not, it is effectively converting the sound wave to heat. Now whether this is audible or measurable is questionable and a lot of variables come into play. Most important would obviously be resonant freq range of the poly. This is probably only where poly will audibly and measurably benefit.


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## TOOSTUBBORN2FAIL

My definition of a standing wave is wavelengths that are the same length as an internal dimension of the box. For instance, like I previously stated, I have huge dips at the frequencies that correspond with 8", 16.5", and smaller but equally sharp dips at the frequencies that correspond with 16" and 33". Now, its likely that those are the frequencies that the wave is coming back into contact with the cone, as evidenced by the significant dips.  Now, I will assume the measurement equipment is fine, dayton omnimic and few, I havent had any reason to believe either has issues. Measurement technique was also fine. Now, I tried 3 different materials, at the commonly recommended amounts, and none of them made a significant difference at the problem frequencies.


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## oabeieo

I would get two night time pillows for every 10 or 12 ich box. thats enough


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## kmarei

Considering you can get it from Walmart for less than $5
I'd recommend at least trying to use it for your enclosure

I've personaly noiced an improvement in sound when I use poly fill
Sounds tighter, and more controlled
Do I know the scientific reasons why?
No
But I do know it sounded better with it

In any case
Unless you over stuff your box
There is no negative to using it no?


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## 14642

cubdenno said:


> Data-Bass
> 
> A great article


Yup. This is correct. Up to some amount of fill, the Qtc of the system is reduced. Smoothing out the wiggle at 170Hz is also validated by the elimination of the secondary resonance in the impedance curve on the left. Whether that wiggle is the result of a standing wave isn't proven by the measurements. Considering that the wiggle is pretty far outside the passband for a sub once a low pass filter is engaged, getting rid of it may not be audible.


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## 14642

Now that I've read the rest of the responses here, there's no use in speculating about what's causing the resonance at 170Hz. It's entirely possible that a standing wave exists at 170Hz. 1/4 of a wavelength at that frequency is 1.66 feet. There are plenty of ways to test this, but none of them are included in the paper.


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## Victor_inox

Saying that polyfill dissipate the heat is to confuse people even more.

everything is very simple, it acts kinda like this








it converts sound wave into thermal energy by friction between polyfill fibers. actively destroying that back wave.


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## stochastic

The physics involved heavily depend on what type of box we're talking about. Ported in different manners will see many different airflow patterns, including harmonic resonances. If that port is into another small enclosure like a car's interior, then there's multiple non-linear interactions that will take place.

Many subwoofer box designs are large enough to contain a 1/4 wave of very long waves. Frequency - Wavelength - Period Chart



TOOSTUBBORN2FAIL said:


> While the measurements provided are very good, the explanations they give for the results are just plain wrong. For instance, they talk about polyfil absorbing the 170hz peak, well 170hz is a 79.4' wave. Your not absorbing that in a box, period. Something else is definitely happening, but your not absorbing the wave. There wouldn't even be any standing waves at 170hz.


The 170Hz wave dampening that occurred in the Data-Bass article is about a 6.75foot wave for a full cycle. A quarter wavelength of that would be just under 1.7 feet. The article claims they were measuring


> an 18” driver in a large sealed cabinet.


 Something I would fully expect to have a 1.7 foot resonance at.

From what I understand, the speed of the wavefront slows down as it travels through polyfil and air. The same would be true if you filled your sub-box with certain gasses (it's been patented). I don't know if this is also true of pressurization and depressurization speeds. In the very least this will dampen some harmonic resonances of enclosures. 

To actually absorb a 'back-wave' however, is nowhere near what it should be doing in my opinion. This is primarily based off my knowledge of bass-trap design.


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## audiosor

This thread is kind of old, however it still shows up as one of the top results regarding subs and poly fill.

I don't buy the thermodynamic 'wiggle' argument. The very minor levels of thermal energy that might be involved would be dwarfed by every day temperature swings.

Here's what I think is going on. 

First, sound travels differently in different mediums. All of the information people are posting about wavelengths and frequencies assume the behavior of sound in air at a specific temperature and pressure. A 60Hz wave can be ~19ft long in air, ~81ft in water, 280ft in iron.

Second, to understand what's going on, you have to do some research on what a speaker's "Q" values mean and how they're important to enclosures. It has to do with the speaker's suspension and how much push back it needs in order to move properly and not be too "loose" and bottom out. There's also an element of resonance. Adding poly simply changes the contents of the box, thus adjusting the boxes ability to provide proper suspension. Just like filling the box with lead, or foam, or vacuum would change the level of suspension the speaker gets out of the box. Also keep in mind there's an element of responsiveness, think of the difference between a metal spring and memory foam, one gives instant pushback, another conforms and is very slow to return the energy.

The actual effect it has probably varies based on the speaker, the power levels involved, the size differences. A box that is too big may not sound bad, but the speaker will be loose and moving more than it should at a certain power/volume and bottom out early, not reaching the full power it could. A box too small may also sound fine but not allow the speaker to move as much as it should, perhaps requiring more power. Thus to tell if a change has made a difference, you'd have to do a lot of testing, test the full range of frequencies, at various volumes, and look at the quality of the sound in addition to just the SPL to really tell if there's a difference (maybe it is just as loud but it is noisy because it is bottoming out). It's possible there may be a positive benefit in one aspect but a detriment in another.

So the real question is, does adding poly make the internals more compressible and result in a looser suspension (make the box seem bigger), or does it simply act as a non-compressible solid and reduce the available compressible air (make the box seem smaller), or does it not have enough volume to have any effect? It's possible one could measure the travel of the speaker with a laser at various running volumes/frequencies to characterize the variance in suspension with different fill.

My own guess, I think that the speaker pushes on the air in the box, compressing it, but the air then compresses the poly fill. The poly fill is much slower to bounce back than compressed air (think again like memory foam), slowing down the spring action of the air by a small amount, thus softening the suspension somewhat to help mimic a larger box. I have no guess as to what degree this effect might occur, only that it seems plausible that it could happen, as the level of compressibility you get out of air is going to depend on the material enclosing the air and how it presses against it.


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## Holmz

audiosor said:


> This thread is kind of old, however it still shows up as one of the top results regarding subs and poly fill.
> 
> I don't buy the thermodynamic 'wiggle' argument. The very minor levels of thermal energy that might be involved would be dwarfed by every day temperature swings.
> 
> Here's what I think is going on.
> 
> First, sound travels differently in different mediums. All of the information people are posting about wavelengths and frequencies assume the behavior of sound in air at a specific temperature and pressure. A 60Hz wave can be ~19ft long in air, ~81ft in water, 280ft in iron.


The inside of my vehicles have always been air filled.




audiosor said:


> Second, to understand what's going on, you have to do some research on what a speaker's "Q" values mean and how they're important to enclosures. It has to do with the speaker's suspension and how much push back it needs in order to move properly and not be too "loose" and bottom out. There's also an element of resonance. Adding poly simply changes the contents of the box, thus adjusting the boxes ability to provide proper suspension. Just like filling the box with lead, or foam, or vacuum would change the level of suspension the speaker gets out of the box. Also keep in mind there's an element of responsiveness, think of the difference between a metal spring and memory foam, one gives instant pushback, another conforms and is very slow to return the energy.
> 
> The actual effect it has probably varies based on the speaker, the power levels involved, the size differences. A box that is too big may not sound bad, but the speaker will be loose and moving more than it should at a certain power/volume and bottom out early, not reaching the full power it could. A box too small may also sound fine but not allow the speaker to move as much as it should, perhaps requiring more power. Thus to tell if a change has made a difference, you'd have to do a lot of testing, test the full range of frequencies, at various volumes, and look at the quality of the sound in addition to just the SPL to really tell if there's a difference (maybe it is just as loud but it is noisy because it is bottoming out). It's possible there may be a positive benefit in one aspect but a detriment in another.
> 
> So the real question is, does adding poly make the internals more compressible and result in a looser suspension (make the box seem bigger), or does it simply act as a non-compressible solid and reduce the available compressible air (make the box seem smaller), or does it not have enough volume to have any effect? It's possible one could measure the travel of the speaker with a laser at various running volumes/frequencies to characterize the variance in suspension with different fill.
> 
> My own guess, I think that the speaker pushes on the air in the box, compressing it, but the air then compresses the poly fill. The poly fill is much slower to bounce back than compressed air (think again like memory foam), slowing down the spring action of the air by a small amount, thus softening the suspension somewhat to help mimic a larger box. I have no guess as to what degree this effect might occur, only that it seems plausible that it could happen, as the level of compressibility you get out of air is going to depend on the material enclosing the air and how it presses against it.


How would you test your theory?

What is the volume of the polyfill?
What is the mass of the polyfill
Is polyfill compressable?

You can make up a theory, but it needs to conform to reality. The polyfill is not magic, and it has been described in a few places.

the conversion to heat is not like an el nino.


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## Hillbilly SQ

So let's switch gears here. What about polyfil in ported boxes? I've seen it used and seen it suggested by ID in the smaller ported designs.


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## JI808

Hillbilly SQ said:


> So let's switch gears here. What about polyfil in ported boxes? I've seen it used and seen it suggested by ID in the smaller ported designs.


Tom's article from back in the day still applies today. I've built enclosures smaller than what I wanted due to physical available space and tuned slightly higher. Then it's a matter of adding polyfill to get desired Fb.


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## Jeffdachefz

I'd rather have a properly sized/designed ported/sealed box rather than relying on polyfill anyday. It comes into play when you are very tight on space other than that, there is no replacement for displacement.


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## 04quadcab

Jeffdachefz said:


> I'd rather have a properly sized/designed ported/sealed box rather than relying on polyfill anyday. It comes into play when you are very tight on space other than that, there is no replacement for displacement.


I did a lot of research about 3 years ago when I installed my subs (only had .65 cuft per sub). This is the conclusion that I reached as well. Adding polyfill will lower the Fb in a sealed enclosure.


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## ckirocz28

Here's an idea, if you want to know what polyfill does to sound, wrap your head in it while listening to music; or stick some cotton in your ears. It does something to cancel out some sound. Stops resonance (ringing?) inside subwoofer boxes. It affects the sound of your subwoofer, plain and simple. It's dirt cheap, and if you don't like it, remove it.

Sent from my SM-G935U using Tapatalk


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## SkizeR

ckirocz28 said:


> Here's an idea, if you want to know what polyfill does to sound, wrap your head in it while listening to music; or stick some cotton in your ears. It does something to cancel out some sound. Stops resonance (ringing?) inside subwoofer boxes. It affects the sound of your subwoofer, plain and simple. It's dirt cheap, and if you don't like it, remove it.
> 
> Sent from my SM-G935U using Tapatalk


Pretty poor way to put it. It does not cancel out anything. It just makes the enclosure seem larger to the driver. 

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## Locomotive Tech

I always thought of it this way, the rear wave in an enlcosure will have a reflection of the surfaces in the enclosure. Poly, will dampen the reflection and "assist" the rear waves collision when they return to the back of the cone.

I could be wrong here, but the poly should act as a dispersion material that will spread out the wave rather than have the wave bounce out in a cone shape and reflect directly back to the rear of the cone?

I suspect that this effect causes the soud wave to act on the entire ( or more of ) the interior surface of the enclosure. Thus utilizing more of the enclosure geometry????


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## ckirocz28

SkizeR said:


> Pretty poor way to put it. It does not cancel out anything. It just makes the enclosure seem larger to the driver.
> 
> Sent from my SM-G950U1 using Tapatalk


That was meant to be a SIMPLE explanation. Sometimes people on forums get too involved in scientific explanations and lose their perspective. The bottom line is polyfill is dirt cheap, so it doesn't hurt anything to try it, just a few minutes. of labor.
By the way, HOW does it make the enclosure seem larger to the driver? Does it convince it, or is there hypnosis or something else involved?

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## SkizeR

ckirocz28 said:


> That was meant to be a SIMPLE explanation. Sometimes people on forums get too involved in scientific explanations and lose their perspective. The bottom line is polyfill is dirt cheap, so it doesn't hurt anything to try it, just a few minutes. of labor.
> By the way, HOW does it make the enclosure seem larger to the driver? Does it convince it, or is there hypnosis or something else involved?
> 
> Sent from my SM-G935U using Tapatalk


simple and wrong arent the same. also, the answer is in this very thread... you didnt bother reading it, did you?


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## ckirocz28

SkizeR said:


> simple and wrong arent the same. also, the answer is in this very thread... you didnt bother reading it, did you?


You must be a liberal, you can't identify sarcasm when it smacks you in the face.
The scientific explanation for why polyfill works is long and unnecessary, involving multiple pathways and lengths of pathways causing soundwaves to cancel each other out thereby reducing internal resonances.
See, totally unnecessary.
Polyfill works, try it, if you don't like it, remove it.

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## ckirocz28

SkizeR said:


> simple and wrong arent the same. also, the answer is in this very thread... you didnt bother reading it, did you?


And please, wrap your head in polyfill and tell me I'm wrong. I'd like to see a pic of that, too.

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## ckirocz28

SkizeR said:


> simple and wrong arent the same. also, the answer is in this very thread... you didnt bother reading it, did you?


Oh, and I did read the erroneous explanations involving thermodynamics and stating that polyfill doesn't work in subwoofer boxes. The effect of polyfill has nothing to do with thermodynamics, that was the whole reason for my original comment.

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## Holmz

ckirocz28 said:


> That was meant to be a SIMPLE explanation. Sometimes people on forums get too involved in scientific explanations and lose their perspective.
> ...


Not usually.

It is usually more common to have magic and hand waving, and accusations of over thinking things.


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## Locomotive Tech

Ok so I might be the only fool who wrapped a pillow around my head, it was then, while listening to the home theatre I realized why this is not a very accurate representation of what polyfill does.


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## Holmz

Locomotive Tech said:


> Ok so I might be the only fool who wrapped a pillow around my head, it was then, while listening to the home theatre I realized why this is not a very accurate representation of what polyfill does.


I am doing the Winnie the poo with a head full of cotton, and a T shirt.


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## Locomotive Tech

Holmz said:


> I am doing the Winnie the poo with a head full of cotton, and a T shirt.


Yeah, I realized that this could only work if the sound came from inside my ear.


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## Holmz

Locomotive Tech said:


> Yeah, I realized that this could only work if the sound came from inside my ear.


I wonder if this would work with pants... add polyfill to make them seem bigger, and they would fit again.

I can see a cartoon with "do these make my b... lol big?", and the answer of, "you need a pound and a half of polyfill."


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## Locomotive Tech

Holmz said:


> I wonder if this would work with pants... add polyfill to make them seem bigger, and they would fit again.
> 
> I can see a cartoon with "do these make my b... lol big?", and the answer of, "you need a pound and a half of polyfill."


Not sure if they woulf "fit" again but my fat Arse could use some dampening! My rear wave creates a resonance at about 1.7 Hz, 3.7 if I am late for dinner!


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## openglcg

Really nobody figured it out??? Its on the internet do a search or better yet here:

compression increases temperature and decomperssion lowers it.

As the air in the enclosre compresses and decompersses it temporarily rises and falls in temperature.

Increasing temperature increases pressure.

Polyfill has a super high surface area and being a fiber can also retain some amount of kenetic energy within itself.

The polyfill helps to regulate the temperature as it changes, absorbing heat in the higher pressure air and emitting heat in the lower pressure air.

Since this means the higher pressure air will be a slightly lower temperature, this also lowers the peak pressure that the air reaches.

Lower pressures against the sides of the box and the air within make the system react like a slightly bigger box with no polyfill.


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## Aculous1

this thread has me so confused...when the hell did polyfill become a conversation about heat dissipation? 

Everytime I hear people talk about polyfill its seems like BS for a lot of reasons. But in the more sane conclusions its to breakup the soundwave coming from the back of the cone from echoing or reverberating off the cone causing efficiency loss and cone breakup/intelligibility issues. 

food for thought...anechoic chambers, least the ones I have seen are not stuffed floor to ceiling with polyfill. In fact I've never seen polyfill used in a anechoic chamber. But then again material science has come a long way...what we used in the past for speakers may not be needed anymore because we surpased it with stiffer enclosure design, better foams and other things that solve the issues polyfill was once used for.


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## openglcg

Heres a simple article showing a slight difference in fc as well as it smoothing out some distortion.
https://data-bass.com/data?page=content&id=79

But really system design comes first. It's not insanely good at shaping frequency response. It wont turn a poorly designed setup into a good one.

It doesn't significantly slow down or reflect waves in any way that affects the properties of the enclosure. It mediates pressure effects by mediating temperature changes that come along with them. But even in this respect the effect can only be used as an aid to enclosure design rather than a dictating it.


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## Holmz

Aculous1 said:


> this thread has me so confused...when the hell did polyfill become a conversation about heat dissipation?
> 
> Everytime I hear people talk about polyfill its seems like BS for a lot of reasons. But in the more sane conclusions its to breakup the soundwave coming from the back of the cone from echoing or reverberating off the cone causing efficiency loss and cone breakup/intelligibility issues.
> 
> food for thought...anechoic chambers, least the ones I have seen are not stuffed floor to ceiling with polyfill. In fact I've never seen polyfill used in a anechoic chamber. But then again material science has come a long way...what we used in the past for speakers may not be needed anymore because we surpased it with stiffer enclosure design, better foams and other things that solve the issues polyfill was once used for.


Just because people may not understand does not mean that it may do some good.
Sort of like how the sun comes up every morning, whether one has a flat earth or a chariot to drag the sun around the earth daily. Whether we understand it or not has no impact on reality.

But polyfill does seem to have a magical element associated to it.


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## Hein_

Informative thread. I've always stuffed sub enclosures with 3M Thinsulate acoustic insulation. 3M says it contains micro fibers that absorb acoustic energy.

all the best,
Hein
DIYvan
541 490 5098


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## MaddMatt

I watched a video of actual testing with polyfil and the results were that they’re almost identical. But as stated above, wasn’t dense enough. The results changes when they used sheep’s wool in the form of a thick pad.


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## Gary S

All polyfill does is get into voice coils. There is no reason to have something destructive like that in a subwoofer box.


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## Dano

I am just going to fill my box up with water and do some molly. I can't notice a difference between polly or not but I know the bigger the better when sealed. I am going to try one 12 ported rockford fosgate putting 700 watts 4 ohm to it and 13 RF putting 1300watts 2ohm sealed with no insulation. My ported box I bought online and I am not impressed. I am making my sealed box as big as I can without looking too crazy. I should get some midrange.....


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