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How much polyfill is too much?


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luckydevil 
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Posted: August 28, 2006 at 3:02 PM / IP Logged  
I'm working with a .7ft^3 fiberglass enclosure for a single 12, and I am using polyfill to try and make up for the small amount of volume. A larger enclosure is just not feasible, and .7ft^3 is the largest it can be physically.
I am using 1.2 lbs of polyfill, and the polyfill is so dense in the enclosure that I am wondering if it is not doing more harm than good.
I've read that up to 1.5lbs of polyfill per cubic foot can be used successfully on larger enclosures, but I'm not sure about the small volume I am working with.
Any thoughts?
haemphyst 
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Posted: August 28, 2006 at 4:21 PM / IP Logged  
When you add polyfill, you are actually INCREASING the size of the box, acoustically. If you box is too large, you must fill in the space with solid objects, NOT polyfill.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
kfr01 
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Posted: August 28, 2006 at 4:23 PM / IP Logged  
Polyfill really doesn't "do" that much. (see comparison graphs in The Loudspeaker Cookbook). Don't get me wrong, it helps, but an extra 0.3 lbs isn't going to affect much of anything. So, work on the safe side and use whatever fits comfortably.
If 0.7ft^3 is still far too small for your subwoofer, time to pick a different sub.
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haemphyst 
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Posted: August 28, 2006 at 4:28 PM / IP Logged  
haemphyst wrote:
When you add polyfill, you are actually INCREASING the size of the box, acoustically. If you box is too large, you must fill in the space with solid objects, NOT polyfill.
Sorry... misread your post. You ARE trying to make it larger. Yeah, as kfr01 sez, if .7 is still far too small, time for a different woofer.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
DYohn 
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Joined: April 22, 2003
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Posted: August 28, 2006 at 6:00 PM / IP Logged  
If you smell burning polyester and see white stuffing blowing out of your port, you've used too much.  How much polyfill is too much? -- posted image.
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luckydevil 
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Posted: August 28, 2006 at 7:51 PM / IP Logged  
Thanks guys. The amount of polyfill I am using actually ended up being fine and from my calculations makes the enclosure respond similar to a .9ft^3 enclosure (which is what I need).
Turns out the phase was wrong and once that was corrected everything sounds great. The low output initially made me think it was the polyfill because I have never used that much before.
austincustoms 
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Posted: August 29, 2006 at 9:45 AM / IP Logged  
In my experience, any is too much.  You can't really compensate for a poorly built box.
Flakman 
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Posted: August 29, 2006 at 11:52 AM / IP Logged  

austincustoms wrote:
In my experience, any is too much.  You can't really compensate for a poorly built box.

I have to disagree...subwoofers are imperfect. Even a well built (to manufacturers specs) box cannot necessarily compensate for what a subwoofer doesn't recreate correctly. A little polyfill can sometimes be just what is needed. This may be getting into picking nits regarding sound quality from the sub. I WILL agree that for most, a well built box will satisfy most without the polyfill.

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5150azn 
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Posted: August 29, 2006 at 12:46 PM / IP Logged  
When your mom is asking where the pillows are... You know you are using too much insulation.
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kfr01 
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Posted: August 29, 2006 at 1:23 PM / IP Logged  
austincustoms wrote:
In my experience, any is too much. You can't really compensate for a poorly built box.
I also disagree.
Just because a user wants to dampen the box a bit more, doesn't mean the box is poorly built.
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