# Should I add poly-fil to a sealed box of recommended volume?



## Dominyon (Nov 27, 2010)

I have a 10" JL sub that calls for a 0.625 cu. ft sealed box and has a driver displacement of 0.025 cu. ft. My sealed box is 0.66 cu. ft.

0.66 - 0.025 = 0.635 cu. ft. An almost perfect size box for said speaker.

I have heard many poly-fil pros and their debunks.

1) It tricks the speaker into thinking it's in a bigger box, while others say it does no such thing it just conducts heat for pulling the speaker back in better (if in an inadequately sized box) and it takes up volume.

2) It eliminates standing waves. Others say a standing wave for frequencies that low would be too long to be trapped inside the box.

3) It makes my subwoofer hit harder and lower. While others say you're are fooling yourself into thinking that because the speaker can only do what it is manufactured to do.

I've also read it can decrease "boominess", make the frequency response more linear and make the box not sound hollow (not that I might know the hollow sound if I heard it). I listen to mostly rock/metal so no boominess for me is fine. I am looking for tonal range and sound reproduction. As well as not advertising that my car has a sub in it (ie. lots of boominess) 

Anywho, back to the original question. If my box is practically perfect volume for the sub as recommended by the manufacturer, who I read is notorious for giving underrated box sizes, should I bother adding any poly-fil for potential benefits (what are they for real in this scenario?) or should I not be decreasing the volume of my box as it may degrade performance?

I have no real place to work on my vehicle other than the parking lot in my condo complex so "experimenting" with different amounts of poly-fil is pretty much out of the question. I don't want to tear down the interior of my car in the parking lot, adjust the amount of fill, put my car back together, go for a long drive on the highway where I can actually turn up the volume a little bit and then rinse and repeat every time I want to try more or less stuffing.

Thanks all for your time!


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## Catman (Mar 18, 2008)

Why do you 'think' you need polyfill other than you read about it on the internet. Polyfill is a tuning aid and is not automatically thrown at a problem you do not know you have. Car audio is all about tuning ...in MANY ways. An 'ideal' enclosure is somewhat of a misnomer since cabin gain is not taken into account when this 'ideal' is determined. In some cases you need to remove volume in a box with blocks of wood. Other times you need nothing ...other times you need different amounts of polyfill.

If you are wanting to 'do it right' you need to use a PNG / RTA and see what you have then adjust / listen / retest. If you just want a sub ...put some polyfill in it and be happy.

>^..^<


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## Dominyon (Nov 27, 2010)

Catman said:


> Why do you 'think' you need polyfill other than you read about it on the internet.





Catman said:


> If you just want a sub ...put some polyfill in it and be happy.


Basically I am a guy who (yes) just wants a sub for frequency range in my setup. I 'think' I want poly-fil because it may make my subwoofer perform better than if it were not present.

Other than setting high/low pass filters and gains on the amp I don't really plan on doing any adjusting. As you mentioned I will then just "be happy" with my louder, fuller range sound. However if there is a magical way (poly-fil) to make my sub sound better that is quick, easy and inexpensive why not do it. That i why I am seeking advice as to whether or not it is really beneficial with my given box stats.

And btw, thanks for the reply! I really liked the second comment I quoted, described me to a T


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## Bayboy (Dec 29, 2010)

I always use it even though box size accuracy is key. My main goal to absorb internal reflections from going back into the cone. Like Catman stated, this can very well also involve adding more fill or reducing the internal volume to keep Q constant. Unless your anal and/or your sub is in a trunk divided by the rear seat you're not going to notice it much. I always drive trucks, hatchbacks, or a small suv so it matters to me.


Just build the box according to specs and add a little so you won't wonder.


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## ZAKOH (Nov 26, 2010)

I have been told that most "recommended" box size specs are the specs at which the amp will handle fine the rated power. Less air == more spring power, less likely the amp will tear itself apart. Because of this, the "recommended" box sizes are unnecessarily small. They're meant for SPL, not SQ. A lot of people just double that size, and then add polyfill. I personally put a 300watt 12 inch sub, which has 0.7 ft recommended enclosure size, into 1.15 cu ft sealed box and added almost 1.5 pounds of polyfill extracted from a $5 wallmart pillow. I honestly can't vouch whether my sub sounds better or worse than before adding polyfill. I have been doing too much tweaking in other parts of system as well. It does sound awesome right now.


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## tornaido_3927 (Nov 23, 2009)

ZAKOH said:


> Less air == more spring power, less likely the amp will tear *the speaker* apart.


Fixed 

Dominyon, which JL sub do you have? And do you have any specs for it?

Generally polyfill will simulate a slightly larger box, so if the box is too small this can help, but not eliminate the problems associated with smaller than optimal enclosures. So I say that if your box is too small (which will affect the response and prevent it from going as low, "frequency range" as you put it would be restricted) then adding some polyfill may help your sub along a bit..

Have you listened to your sub in that box yet or are you waiting to make a decision on polyfill before you do anything to save having to mess around?


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## Bayboy (Dec 29, 2010)

Have to clarify my earlier statement about subs in the trunk. Meant to say that if it's in the trunk, filling to offset internal cone reflections won't matter much. 

Anyways, manufacturers tend to target Qtc or vented alignment for frequency response. Not all take into account the car's individual cabin gain because it's impossible to match all with one design. So yes you can adjust from there with no problem, yet the question is exactly where did they give the power rating at? Is the rms power rating given for the recommended size or in the smallest enclosure (sealed) with a Qtc of 1.1? I think that will differ per manufacturer, but as a consumer you have to use common sense as well.

If you increase the enclosure size then the sub's power handling will be reduced.


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## tornaido_3927 (Nov 23, 2009)

^^ That's not necessarily a bad thing though  It'll also go lower and have better transient response..


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## storm (Jul 21, 2006)

I believe you are looking for this article:

Sub Box Polyester Fiberfill


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## resko1 (Jul 29, 2010)

*I've also read it can decrease "boominess", make the frequency response more linear and make the box not sound hollow (not that I might know the hollow sound if I heard it). I listen to mostly rock/metal so no boominess for me is fine. I am looking for tonal range and sound reproduction. As well as not advertising that my car has a sub in it (ie. lots of boominess) *

This...
It can eliminate the box peak or at least reduce it. When testing, there will be 2 peaks in frequency. First will be the driver peak somewhere around the fs of the sub. Second will be box peak and usually larger. With sealed enclosures, there usually is no double peak. Only one "hill" sort to say. The fiber fill reduces that "hill" and extends the lower end out slightly. 

And not to bash a company, but i always have t/s parameters pulled on a sub i have. Ones for that specific driver. Company specs are random, usually pre-break in, and dont account for changes or build deviations. 
I suggest having tsp"s pulled on the actually driver, re-chart an enclosure for it using the tsp's you got. Then you will see exactly what the box transfer is. 
In car transfer is a whole different ball game!


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## Dominyon (Nov 27, 2010)

tornaido_3927 said:


> Fixed
> 
> Dominyon, which JL sub do you have? And do you have any specs for it?


I have the 10w1v2. Here are some specs pulled from the web.

Free Air Resonance (Fs): 25.24 Hz
Electrical “Q” (Qes): 0.432
Mechanical “Q” (Qms): 6.336
Total Speaker “Q” (Qts): 0.405
Equivalent Compliance (Vas): 1.783 cu. ft. / 50.46 liters
One-Way, Linear Excursion (Xmax)*: 0.375 in. / 9.5 mm
Reference Efficiency (no): 0.180%
Efficiency (1W/1m)**: 84.53 dB SPL
Effective Piston Area (Sd): 53.522 sq. in. / 0.0345 sq. m.
DC Resistance (Re): 4.086 ohm
Nominal Impedance (Znom): 4 ohm
Thermal Power Handling (Pt): 300W
Driver Displacement: 0.025 cu. ft. / 0.71 liters
Net Weight: 7.81 lbs. / 3.54 kg

I'll be quite honest when you guys start talking about this stuff I'm pretty much in the dark as I don't know what most of it means 



tornaido_3927 said:


> Have you listened to your sub in that box yet or are you waiting to make a decision on polyfill before you do anything to save having to mess around?


I have no method of listening to the sub prior to installation and it's installation requires tearing apart my interior which I only want to do once to put it all in. I don't want to mess around 



storm said:


> I believe you are looking for this article:
> 
> Sub Box Polyester Fiberfill


I have read that article numerous times and he makes it seem you should add fill no matter what as it WILL increase performance. However he makes no mention if the volume of his test boxes were too small, too large or spot on to the manufacturers specs. Pretty much everything you read on forums will reference a box that is too small and say you should add some.



Bayboy said:


> Have to clarify my earlier statement about subs in the trunk. Meant to say that if it's in the trunk, filling to offset internal cone reflections won't matter much.


I have a 350z and will be mounting it in the stock speaker cubby behind the driver's seat as I am doing a complete stealth install. The box is custom made for that space and the woofer is down firing. The box takes up pretty much the whole cubby and I am told it is a far from optimal spot for a sub which is why I am looking to get the best performance from it possible.



resko1 said:


> *This...
> It can eliminate the box peak or at least reduce it. When testing, there will be 2 peaks in frequency. First will be the driver peak somewhere around the fs of the sub. Second will be box peak and usually larger. With sealed enclosures, there usually is no double peak. Only one "hill" sort to say. The fiber fill reduces that "hill" and extends the lower end out slightly.
> 
> And not to bash a company, but i always have t/s parameters pulled on a sub i have. Ones for that specific driver. Company specs are random, usually pre-break in, and dont account for changes or build deviations.
> ...


*

As stated previously when you guys go into all your abbreviations and things that start with a Q I have no idea what any of it means *


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## Chaos (Oct 27, 2005)

You guys are thinking way too hard about this.

Put a handful of fill in the box. Listen. Adjust accordingly. That's it.


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## tornaido_3927 (Nov 23, 2009)

Chaos said:


> You guys are thinking way too hard about this.
> 
> Put a handful of fill in the box. Listen. Adjust accordingly. That's it.


If you read the thread you would know why this is not an option.



Dominyon said:


> I'll be quite honest when you guys start talking about this stuff I'm pretty much in the dark as I don't know what most of it means
> 
> 
> 
> ...


Right well I modelled that sub up in bassboxpro and it seems to do well in the size box you have for it. I am all for going for a bit bigger box than optimum purely so they can just dig a little deeper, but that's just me.

Regardless of whether the box is too large or too small, the polyfill will have the same effect, it just depends on your goals. Some people like to add polyfill to most of their boxes so that they can build a slightly smaller box and use it, or build an optimum box but simulate that box to be a little bigger.

Ideally you would just listen to the sub and add polyfill to test the difference, but seeing as that is impractical, if I were worried about the box size I would just line the inside of the box with a bit of fill, not cramming a whole bunch in there, but just lining the box..

Hope that helps


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## hottcakes (Jul 14, 2010)

"Q" values are somewhat rather important when you get into serious details aboot a sub and its' enclosure. do some research. you must learn to walk before you can run, Grasshopper.


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## Catman (Mar 18, 2008)

If you are worried about standing waves you will be better off building the enclosure so that the rear panel is not parallel to the baffle. 

>^..^<


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## Sarthos (Oct 29, 2010)

If you're worried about standing waves, put some freaking Dynapad material at the back..

Hate to say it, but honestly experimentation IS the only way to know if it'll help or not. You can pull all the TS parameters to make a good box, then find out cabin gain makes your box too big...or too small... what kind of vehicle is it? That might give some of us some idea of the cabin gain


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## Dominyon (Nov 27, 2010)

Sarthos said:


> If you're worried about standing waves, put some freaking Dynapad material at the back..
> 
> Hate to say it, but honestly experimentation IS the only way to know if it'll help or not. You can pull all the TS parameters to make a good box, then find out cabin gain makes your box too big...or too small... what kind of vehicle is it? That might give some of us some idea of the cabin gain


350z, sub will be down firing in the stock cubby behind the driver's seat.

This really is going way beyond what I had anticipated  I'm just tossing the sub into my car and thought I would ask in a general sense if it was a good idea to add some fill. I'm not an audiophile or expert on any level I just wanted to add some lower end to my stereo


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## Sarthos (Oct 29, 2010)

Not Dynapad, Dynaxorb, something similar to that is what I meant. Kill those standing waves. Just plain kill them.

It's really impossible to answer whether adding some fill will make it sound better or not. It's possible the poly fill will be bad or good. It's possible that you should actually put a block of wood in the box to make the box smaller. I'd just fill it halfway, see if that makes the sound better or worse. If better good, be happy, if worse then take it out, it's not that big of a job. In all honesty though, you probably won't notice any huge difference.


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## Wheres The Butta (Jun 6, 2009)

well, rather than make a new thread I'll resurrect this one

I'm going to build a sealed box and was wondering whether I should use polyfill. I also had thought about using egg crate foam attached to the inner walls to manage standing waves. 

Anyone have experience using egg crate foam to line the walls of an enclosure? 

Are polyfill and egg crate synergistic, or would one make the other redundant?


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## Wheres The Butta (Jun 6, 2009)

anyone?


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## gnesterenko (Mar 17, 2011)

I've done a good amount of research on this, and while the folowing may be off in parts, I (personal opinion) would say that yes, it helps more then it hurts. If you can get it cheap, do it.

Now on to why.

First, as mentioned above, and possibly the biggest benefit, is reducing the frequency peak (hill), flattening it out a little.

Regarding it "tricking the speaker into thinking it's in a bigger box, while others say it does no such thing it just conducts heat for pulling the speaker back in better (if in an inadequately sized box) and it takes up volume." The later is correct, former is not. There is no 'tricking' a woofer into the fact that it has less air volume to use as a "spring". What happens when the woofer hits is that the air in the box is compressed, and its expansion assists the woofer in its outward return motion. In other words, there is energy transfer going on. Now, if a box is too small for the sub, then the sub has to work harder to hit at the same level, as it has more pressure to overcome - hence, a reduction in SPL potential, but increase in tightness/fastness. When polyfill is present, its little fibers vibrate when the air is compressed - absorbing some of that energy as heat, thus reducing the potential energy of the compressed air, and allowing the sub to not have to work as hard. Hence it mimics the effect of more air space by essentially creating an energy sink. That said, as mentioned above, there is actually an optimal box range, rather then fixed figure. Hence if your box is of the recommended size, you still have room to add polyfill. It will actually take up some of the volume if you pack it down more (this will also prevent the fibers from vibrating as freely), and extend your lower frequency a bit.

Regarind it eliminates standing waves. The other's are correct. The wavelength of subwoofer frequencies are far too long for polyfill to do anything about them. Midsize and smaller woofers, sure, but not subs. Think of it this way. If sub frequencies were blocked by essentially loosely packed cotton, how would they ever get from the trunk to your ears? Standing waves are almost never a consideration in subwoofer construction.

Regarding it making your subwoofer hit harder and lower. The above reasons should explain why this is the case. Those that say that a sub can only do what its manufactured to do are wrong wrong wrong. I think of woofer design as its 'genes'. While the genes may define limits of a subs potential on the low and high end, they are not deterministic. Based on environment, the genes can achieve optimal expression, or they can be supressed and stunted. Hence, the final sound is about 75% enclosure geometrical design, if not more. System tuning is another another 15%.

Final point - eggcrate foam/other lining vs Polyfill. These two are used for completely different purposes. Internal wall liners are meant to mitigate the actual enclosure from vibrating - they are dampeners. Ideally, your enclosure remains rock solid, creating a perfectly fixed point for the woofer coil to vibrate off. If the box is vibrating, its like trying to pogo-stick on a speeding boat. You can do it, but you'll waste a LOT of energy just compensating for the boats movement. Liners are meant to be glued to the actual inside walls of the enclosure. Polyfill on the other hand is a empty space filler. It should be loosely and evenly distributed throughout the empty space (perhaps retained a bit with a net of some type to ensure the actual subwoofer doesn't come into contact with it). The two achieve completely different goals.


Hope that was informative/helpful. If I'm incorrect on any point, someone please call me out on it.

Posting from work, so need this disclaimer:
"The views expressed here are mine and do not reflect the official opinion of my employer or the organization through which the Internet was accessed."


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