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 Post subject: Polyfill
PostPosted: April 7th, 2019, 1:58 am 
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Joined: June 22nd, 2013, 11:00 am
Posts: 473
https://www.walmart.com/ip/Poly-Fil-Pre ... z/26678911

https://www.parts-express.com/acousta-s ... l--260-317

Any difference in the polyfill?


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 Post subject: Re: Polyfill
PostPosted: April 7th, 2019, 7:28 am 
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Joined: January 15th, 2015, 7:19 am
Posts: 813
Location: Baltimore MD
You will soon get a post from Walt that one can do better than poly fill. Fiberglass (pink stuff) will work better, or better yet real raw wool if you can find it. I am not advocating anything. Your speaker will make sound no matter what you use if anything at all. Just depends to what lengths you go to for the best that can make the speaker perform to you liking


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 Post subject: Re: Polyfill
PostPosted: April 7th, 2019, 8:04 am 
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Joined: February 28th, 2013, 3:31 pm
Posts: 1091
Whatever you use for stuffing, the goal is to make the internal box volume look bigger than it is. Mind you I am not talking about vibration damping put on the walls. Up to a point, more stuffing make the box volume seem to go up to around 30% larger than it really is. This results in lower Fb and Qb. If you put in too much, the apparent volume begins to go back down. Another benefit of stuffing is the reduction in amplitude of internal acoustic reflections.


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 Post subject: Re: Polyfill
PostPosted: April 7th, 2019, 9:04 am 
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Joined: July 8th, 2016, 4:34 pm
Posts: 261
See link for details -

http://bgavinsound.com/Reference/Speake ... hermal.txt

It makes the box look bigger at low frequencies and damps reflections at high frequencies.


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 Post subject: Re: Polyfill
PostPosted: April 7th, 2019, 10:59 am 
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Joined: July 24th, 2015, 4:17 pm
Posts: 864
Location: Parkville, Maryland
Paul was right on when he said I would comment. As it turns out -- the only reason the industry uses polyester pillow stuffing is because it is cheap and gets the job done up to a point. That's the good news. The bad news is that poly-fill is reactive and can create issues especially with the delicate mid-range. The industry pretty much used fiberglass in speakers in the distant past -- but cost and O.S.H.A. kind of ended the practice. The Brits and some U.S. manufacturers used washed wool to great effect since wool is not reactive. Washed wool is difficult to find but raw wool is plentiful. I bought a batch from a farmer on the Eastern Shore through eBay. Foam fill is the absolute worst as it is very reactive.

That said -- fiberglass fill or wool fill or an amalgam of both will serve you well. Follow Tom's advice and you then nailed it. The rule-of-thumb is to not overfill to a point where it is seemingly dense. You should be able to stick your hand in the box easily with the fill in place. For those small speakers I would try 80-grams of fill by weight evenly distributed within the enclosure as a first trial. You look for a neutral but open mid-range and tight bass. Bass extension will be a moving target of course, but more fill is not necessarily better. BTW -- weighing the fill enables exact matching the speakers. Always know how much you are using by wight whether you are adding or subtracting. That way your efforts can be tracked and trial tests better controlled.

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 Post subject: Re: Polyfill
PostPosted: April 7th, 2019, 1:29 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 584
tomp wrote:
Whatever you use for stuffing, the goal is to make the internal box volume look bigger than it is. Mind you I am not talking about vibration damping put on the walls. Up to a point, more stuffing make the box volume seem to go up to around 30% larger than it really is. This results in lower Fb and Qb. If you put in too much, the apparent volume begins to go back down. Another benefit of stuffing is the reduction in amplitude of internal acoustic reflections.


I think Steve is using TL speaker in which case damping is not the primary concern. The filling in TL speakers should absorb high frequencies and let tuned frequencies passthru. It takes several iterations of trial and error to get it right.

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 Post subject: Re: Polyfill
PostPosted: April 7th, 2019, 6:52 pm 
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Joined: January 15th, 2015, 7:19 am
Posts: 813
Location: Baltimore MD
If he is using a TL speaker then the best think he could put inside is a couple of bricks. A s on top


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