Polyfill! does it realy work?

[Xprime4 10+ year member]

maybe I should had some more

 

[bladebarrier 10+ year member]

http://www.bcae1.com/spboxad1.htm

If you scroll to the very last graph in the above link, you'll find a visual respresentation of the difference fill makes for a particular example. As you can see, the result is often so slight that only a side by side test could reveal any difference to the human ear, and even then it will generally be slight.

For $2 worth of stuffing, it would be silly not to have an improvement, no matter how slight, but don't expect any major changes to be heard after adding the fill. Only a db meter or a well trained ear, listening to very familiar tracks, will prove there's a difference.

However, in certain types of enclosures the difference will be much more substantial. It's best to consider these needs when drafting the design for an enclosure, in order to ensure you get what you expect.

"Better damping and better transients is achieved by shooting for a lower system Q which can be accomplished by either making the enclosure larger or by adding stuffing/damping material such as polyfill, Dacron, fiberglass, acoustic foam, or any other suitable type of fill material. Box stuffing will also affect f3 by either raising it or lowering it depending upon the type and amount of stuffing used." (In reference to sealed enclosures)

"The length of the transmission line corresponds to the 1/4 wavelength of the resonant frequency of the driver. The t-line is almost always filled with various types of stuffing material which help reduce the speed of sound through the t-line allowing shorter line lengths while still achieving the proper tuning. For example, a transmission line for a given driver with an Fs of 25 Hz without any fill would need to be nearly three times longer than the same driver in a transmission line that was damped with 8kg/m^3 of wool." (In reference to transmission line enclosures)

Source: http://www.danmarx.org/audioinnovation/theories.html

 

[GlocksRock 10+ year member]

http://www.bcae1.com/spboxad1.htm
If you scroll to the very last graph in the above link, you'll find a visual respresentation of the difference fill makes for a particular example. As you can see, the result is often so slight that only a side by side test could reveal any difference to the human ear, and even then it will generally be slight.

For $2 worth of stuffing, it would be silly not to have an improvement, no matter how slight, but don't expect any major changes to be heard after adding the fill. Only a db meter or a well trained ear, listening to very familiar tracks, will prove there's a difference.

However, in certain types of enclosures the difference will be much more substantial. It's best to consider these needs when drafting the design for an enclosure, in order to ensure you get what you expect.

"Better damping and better transients is achieved by shooting for a lower system Q which can be accomplished by either making the enclosure larger or by adding stuffing/damping material such as polyfill, Dacron, fiberglass, acoustic foam, or any other suitable type of fill material. Box stuffing will also affect f3 by either raising it or lowering it depending upon the type and amount of stuffing used." (In reference to sealed enclosures)

"The length of the transmission line corresponds to the 1/4 wavelength of the resonant frequency of the driver. The t-line is almost always filled with various types of stuffing material which help reduce the speed of sound through the t-line allowing shorter line lengths while still achieving the proper tuning. For example, a transmission line for a given driver with an Fs of 25 Hz without any fill would need to be nearly three times longer than the same driver in a transmission line that was damped with 8kg/m^3 of wool." (In reference to transmission line enclosures)

Source: http://www.danmarx.org/audioinnovation/theories.html

Use of poly-fill in a transmission line enclosure can be seen here...

http://forums.audioholics.com/forums/showthread.php?t=48686

 

[Xprime4 10+ year member]

got some more listening time. It sound a little different, like if it was tuned 2-3 hz higher. The low seem more subtile while it seems to peak higher

 

[Xprime4 10+ year member]

Sound well tough.. sharper

 

[bladebarrier 10+ year member]

got some more listening time. It sound a little different, like if it was tuned 2-3 hz higher. The low seem more subtile while it seems to peak higher

The increase in perceived box size has actually changed the tuning point of your port slightly.

There are three things you should now consider doing.

1. You like the new sound; so keep it as it is.

2. You like the slight gain in bass, but would like to push the tuning point back to where it was; so you need to re-design the port length to compensate.

3. You don't like it, and don't feel like re-tuning the port, and should remove the fill.

For the incredibly low cost of what you invested in the fill, you have opened up a choice of tweaking your subs that last little bit. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Xprime4 10+ year member]

that give me an idea...

I tuned my home subwoofer to around 25hz and it's way too low for me. My brother in law living in the room next to me hear it more than My girlfriend only notice the bass coz the picture on the wall shake it's almost inaudible since it's tuned too low (2x reccomanded ported box since @25hz= low //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif)

So puting some polyfill in it could raise my tuning freq but at the same time boosting the low end with some more int. space

 

[GlocksRock 10+ year member]

25 hz. for a home theater sub is just right, if you can't hear it that well, you need to experiment with different placement, not different tuning.

 

[FoxPro5 5,000+ posts]

it also helps with sound dampening

And how does it do that?

 

[loud-n-low 10+ year member]

my ear tells me that polyfill in a sealed box makes my sub play a little lower so i disagree with that article

 

[JayRich 10+ year member]

my ear tells me that polyfill in a sealed box makes my sub play a little lower so i disagree with that article

you and me both. I just installed a system in my g/f SUV and have an OZ Audio 12 Matrix Elite in, and the box had no polyfil and didn't get low enough for my taste and also was way too punchy. I put roughly a lb of polyfil in the 1cu box and it says worlds better. The south smoothed out and was alot less puchy while maintaining accuracy and it gets the lower freqquencies with more authority.

 

[JayRich 10+ year member]

And how does it do that?

It helps with absorbing some of the noise that comes from standing waves as well as mimimizes noise coming from the box.

 

[JayRich 10+ year member]

25 hz. for a home theater sub is just right, if you can't hear it that well, you need to experiment with different placement, not different tuning.

I agree, I know my Velodyne DPS 10 is tuned to 27hz

 

[JayRich 10+ year member]

I must say I have never put polyfil in a vented enclosure, only sealed so im not sure if that makes a difference or not

 

[bladebarrier 10+ year member]

Here are some calculated examples of the effect. Calculations were made in Bass Box Pro 6, which allows for fill to be put into the equation.

ALL GRAPHS ARE MODIFIED FOR A "TYPICAL" CAR'S TRANSFER FUNCTION, AND THE RESPONSE IS NOT WHAT YOU WOULD GET IF YOU PUT THE SPEAKER IN THE MIDDLE OF A FIELD BY ITSELF.

I don't have a lot of time today to get into more extreme box types, and really grind out a whole lot of options, so I set up 2 scenarios using ported enclosures designed for spl, and one sealed design for SQ.

Having personally owned these drivers and having used them in multiple box types made it a familiar choice for me.

Here's the JL Audio 12W6 under various conditions:

First, a small sealed box. This design is for a reasonably flat response, a small size, and a nice emphasis on the lowest frequencies. The curve that is slightly louder almost all the way through, uses a heavy amount of fill. The curve that is about 1-2 db lower at peak points, has no fill.

Now the first of two SPL designs. In this design, the box is tuned for bass range to emphasize rap and hip hop, while producing maximum spl. The box size is increased to 2.75ft3 and the box has been ported to 42hz. The curve that hits higher at about 48hz is the box with NO fill. The curve that hits softer at 48, but harder at mostly unusable frequencies deep into the subsonic range, is heavily filled. In this case, for spl, the unfilled box is a sure win.

Now the second of the two SPL setups. It's the same amount of air space as the first ported box, but it's now tuned to the 22-23hz area. This is the hardest hitting of all the designs I tossed together (I spent about 15 minutes in all, so I'm sure it's not perfect). The curves here are almost identical, and while it's hard to see in the picture, the box that's filled is about 1db higher from 25 hz to 10hz, and then about 3db higher in the extreme subsonic range. The filled box was tuned just a tad lower in order to compensate for the fill. This box is designed for absolute spl geared towards bass cds, techno, and sin wave response. Using fill in this example shows that even in a ported box, the highest spl I could pull out of my butt in 15 minutes required fill, even if it was only a 1db increase, and this box hits harder than the higher tuned no-fill box in the example above.

Anyways, just food for thought. Some woofers get more out of fill than others, and some box types get more from it than others. The best bet is to experiment and find what works for you, and then decide for yourself.

P.S. I recommend using a staple gun to attach your fill to the sides of high spl ported boxes. It doesn't have to be flat to the wall, but a couple staples here and there will ensure it doesn't get moved around too much, or obstruct your port (which would really change your tuning a lot).