Probably a stupid question on my sub enclosure, but...

[Junkyard81]

I had a friend who knows a lot about car audio build a box (sealed enclosure) for my sub (JL 12W0) about 2 years ago. I opened the box just now (removed the speaker) b/c I am planning on using the same box for my new sub, but I noticed he put like big sheet of 1" thick cotton in there.

Is this normal? Does this not effect the overall volume? Why did he do that? Any response would help..

[the_flatlander]

it makes the sub think the box is bigger than it actually is

[bri487]

the myth is that fill within a box makes the sub think that it is in a bigger box, it is completely untrue. stuffing the box only hides the fact that you have the wrong box for that sub. if the box is wrong, then nothing is going to change that except for having the correct cabinet. you can make the box sound larger with small amounts of fill, but that is more of tuning, than making the sub think and act like it is in a larger box.

[Junkyard81]

Really, ok so he did know what he was doing.....but where exactly, or rather how, does the sub think the box is "bigger than it is"? Any explanations on this myth?

[audioholic]

the myth is that fill within a box makes the sub think that it is in a bigger box, it is completely untrue. having fill is normal for fine tuning a box for things like achieving a bit smoother bass response, but never will it make the sub act as though it is in a biger box.

Then can you explain exactly what it does to smooth out the bass response?

[bri487]

fill is not used to make the box seem larger to the sub, it is used for fine tuning a speaker cabinet. many times a smoother bass response will be achieved through usage of fill.

[Junkyard81]

How?

[bri487]

well, ok here is my best shot. polyfill is just a sound dampening material so when used within a box it slows down the bass resulting in smoother bass response rather than snappy, energetic bass.

[DFW40]

In a sealed box especially in home audio this is very common and will smooth out the bass response but probably nothing that you would really notice. It can make the very low end .5db louder etc but that was just one graph that I saw. I have always used a thin sheet of this on my walls in sealed enclosures, this is different than stuffing 1 pound of polifill per cubic ft. Kicker recommends 50% loose polifill in some of their enclosures. Look at page six on the top right column on this attachment.

http://www.kicker.com/images/manuals...r%20Manual.pdf

Here is a little segment from the JL site.

Any standing waves that might be generated by upper ordered harmonics (caused by distortion) in the enclosure can be readily absorbed with the addition of damping material such as polyfill (available at your local cloth store--it is used to stuff pillows and quilts) or Fiberglastm (the pink stuff) and/or they can be broken up with strategically placed bracing within the enclosure.

[audioholic]

well, ok here is my best shot. polyfill is just a sound dampening material so when used within a box it slows down the bass resulting in smoother bass response rather than snappy, energetic bass.

You are debunking the well accepted idea of what polyfill does as 'completely untrue' and a 'myth', based on this? Its vague, and really doesn't even make sense.

No offense, but its obvious you haven't done alot of research on the topic yet. It does make the enclosure appear slightly larger to the woofer by lowering the Fsb, which will increase the low end. You can call that 'smoother' if you want, but it clearly gives the same result as increasing the box size slightly. Some people claim it also help with the woofer's cooling capabilities.

[JimJ]

polyfill isn't a "myth"...it really does slow down the rear wave, making the sub think it's in a bigger box. There really isn't anything to argue about that

[Termlab]

fill is not used to make the box seem larger to the sub, it is used for fine tuning a speaker cabinet. many times a smoother bass response will be achieved through usage of fill.

the above statement is pretty much true.....


basically i think it only helps in a ported enclosure. fill can be used to "eliminate free standing air waves". or stagnant sound that isnt really there for anything other than the purpose of being "loud". so again, it will basically make it sound "smoother" or have a little better SQ.


as to weather it "makes the subwoofer -think- its in a bigger box"..... i have no idea about that. i just know it makes it sound a little better. but probably not enough to notice.

[Junkyard81]

It seems that everyone agree's that polyfill helps out, but does anyone know *how* ? The scientific reason behind it? maybe this in depth of a question isn't for this forum, but i figured i'd ask

[audioholic]

I dont think anyone is arguing subwoofers 'think'. The point was is does affect the Fs, and Qtc, in the same characteristis as a larger box would.

[audioholic]

It seems that everyone agree's that polyfill helps out, but does anyone know *how* ? The scientific reason behind it? maybe this in depth of a question isn't for this forum, but i figured i'd ask

That's been a pretty hotly debaed topic, exactly why and to what degree, for years now. Some people say it breaks up standing waves, while others says the wavelengths of freqs in a subwoofer enclosure are too long to be affected, etc. Pick a side.