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QTC, Displacement and Excursion question

3K views 16 replies 4 participants last post by  Scyan 
#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 ?
 
#2 ·
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?
 
#8 ·
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.
 
#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 ??
 
#13 ·
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.
 
#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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