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Discussion Starter #1
Here's a 100$ question...

If you're building a box in which you put around 1lb polyfill per cuft of volume.

Does the polyfill "reduce" the box capacity.. IE do I have to account for the polyfill value when simming the drivers ?

Filling with polyfill artificially makes the driver think the enclosure is bigger. That in turns increases the spl at lower frequencies, right ?

In artificially increasing the box "volume" does it also increase the driver's excursion ?

1- Is excursion increased by using polyfill ?
2- Do we have to account for the polyfill "volume" inside the box and reduce the box volume accordingly like we'd do with a port, braces, amplifier and driver volume ?
3- Can I "sim" using polyfill in Winisd to attain a certain QTC, SPL and freq response ?
 

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Polyfill will not make a big difference. You don't need to account for it when modeling drivers. It does not increase excursion.

I don't believe that WinISD has an option for fill %, I believe that LspCAD does, but that is a commercial product.

For all intensive purposes, you should really just worry about getting a relatively accurate volume of the enclosure - and not about the minor impact that polyfill will have on it.

I'm assuming that you're talking about a sealed box?
 

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Here's a read on the effects of polyfill.

http://www.nousaine.com/pdfs/Box Stuffing.pdf
I highly recommend that URL as well. I've read through it a few times before.

I've read that some people have questioned the accuracy of that (being a little dated now), but I think that it still stands as the most authoritative testing that's been one on stuffing subs.
 

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Discussion Starter #6
Yep, I read it as soon as he sent it. I really liked it ;)

Now I'm moving onto finding the best box size.
 

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Discussion Starter #7
So, thinking that stuffing increases displacement by up to 30%.

Does that mean that if I want a box size of 7.5cuf I need to stuff a 6ft size box with 6lb and then it would net me what I want for final size ??
 

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Polyfill will not make a big difference. You don't need to account for it when modeling drivers. It does not increase excursion.

I don't believe that WinISD has an option for fill %, I believe that LspCAD does, but that is a commercial product.

For all intensive purposes, you should really just worry about getting a relatively accurate volume of the enclosure - and not about the minor impact that polyfill will have on it.

I'm assuming that you're talking about a sealed box?
It actually does in the advanced settings. I don't remember the exact method for doing this since I no longer use inisd, but it is actually in there. That said polyfill may not increase box size but any kind of stuffing will improve overall SQ based on my experience. This is because it will reduce internal reflected distortion on the driver. I suggest at least 4 inches of mineralwool behind the driver with enough gap for the pole vent of the voice coil to breath. You can use a couple pillows as an alternative, but given the cost of the wool there is no reason not to use the best stuff for the job.
 

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Discussion Starter #9
Its going to be tight in there then...

I will have around 5 inches inside behind the driver as it is...

So with stuffing it might leave what, 1 inch ?

Is that going to be an issue ?
 

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It actually does in the advanced settings. I don't remember the exact method for doing this since I no longer use inisd, but it is actually in there. That said polyfill may not increase box size but any kind of stuffing will improve overall SQ based on my experience. This is because it will reduce internal reflected distortion on the driver. I suggest at least 4 inches of mineralwool behind the driver with enough gap for the pole vent of the voice coil to breath. You can use a couple pillows as an alternative, but given the cost of the wool there is no reason not to use the best stuff for the job.
Wow, I never knew that. Glad to learn something new.

What do you use instead?

I've thought about investing some money in LspCAD, but I think that's beyond my level of interest.

I highly recommend Bonded Logic / recycled cotton insulation for stuffing/lining. Good stuff.
 

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So, thinking that stuffing increases displacement by up to 30%.

Does that mean that if I want a box size of 7.5cuf I need to stuff a 6ft size box with 6lb and then it would net me what I want for final size ??
Generally my train of thought is model it, build it the largest you can (within reason) and if you get some gains from stuffing......great........ But I wouldn't build something - and count on the improvement that stuffing gives you. Stuffing is never going to be quite the same as building a properly sized enclosure.
 

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Discussion Starter #12
Hmm that sounds great but just from an availability and cost perspective its most likely going to be some polyfill. 6 pounds is like 18$ here.

Also, since im going to have about 1 inch between the back of the sub and the poly fill. And that its going to be downfiring. Can I use some chicken wire to hold it in place ??
 

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I've never worried too much about clearance between stuffing and the driver. Some have used a fabric mesh to keep the clearance. I'd be a little reluctant to use metal near the driver, although it should work.

The Bonded Logic is more work to find (I found it it Menards), but it ends up being waaaaay cheaper than Polyfil.. Just figured I'd throw it out there since it's a fascinating fill material.
 

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Discussion Starter #14
Well, just telling me that maynards might have that, i can look around and find it.

Why do you say its cheaper ?

I mean, I'd probably use MAX 6 pounds of polyfill that I can get for around 20$. 16x2x48 looks to be around 50$ for the bonded logic at home depot ?

If I'm going to line all the walls, I would probably use hmm 3 of these panels ?
 

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Discussion Starter #16
Isnt that number 48" ??

hold on, I might've misread... lol

48' deal of the century
48" expensive !


hehe
 
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