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Polyfill for ported box-thoughts?


TheSpicySpider

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Building a new box to match an American Bass XFL 12 I am buying. The original plan was a 2.3 ft^3 net internal vol. tuned to 32 hz (slot ported). About 50% through building it (back, bottom, both sides assembled and all cuts made). However, it is my first build and I made the beginner mistake to not subtract the internal port wall's displacement from the overall internal volume (ironically, I remembered to subtract bracing and 45's). I redid my calculations and I am now facing a net volume of 2.1 ft^3 tuned to about 34 hz. I don't want those specs but don't really have the time to start over, so I am considering polyfill. I have heard that polyfill is a great choice for sealed enclosures, and have heard mixed reviews for ported enclosures. Overall, I have heard it both increases the effective box size and decreases port tuning. Is this correct? Does adding polyfill mess with the SQ of the enclosure? Thanks for any thoughts.

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I saw that 1 lb of polyfill caused a 1.4ft^3 enclosure that was originally tuned to 42hz to effectively become a 2.0 ft^3 box tuned to 34 hz. I want to get closer to an overall tuning of 30-32 hz and 2.25 ft^3 to 2.4ft^3. Doing some math from those results, it looks like I should use maybe 1/3 lb of polyfill. Does the fact that my enclosure is larger affect the amount needed? 

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I highly doubt your gonna notice any large difference in 2 tenths of a cube dude. Just me  ...

Invert the drivers if you can, gain that space and see. I doubt it's gonna make any magic. That's almost nothing. 

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Don't u think the polyfill will blow out the port, I've never seen it in a ported box.

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what are your box specs? poly fill in a ported box from what i have read lowers tuning typically but also lowers efficiency quite a bit too. not sure that id what you are after here.

 

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3 hours ago, Ron36 said:

Don't u think the polyfill will blow out the port, I've never seen it in a ported box.

The polyfill would be glued or stapled to the inside of the box. There are a few types of polyfill, and the really fluffy stuff isn't very usable. The kind I would be using is called batting, it resembles carpeting in a way. Still pretty cheap and fluffy, I can just work with it how I want to.

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2 hours ago, bcbrassard said:

What about using say 1 1/2-2" acoustic foam on a side of the box? You would think that would be better that poly-fill. Just a thought. 

I haven't heard of that being used before, but I think that poly-fill is actually the preferred option because(what I have heard from a post from SSA) is that the way the poly-fill works is actually through thermodynamics. The small fibers in the polyester "wiggle" as the air moves, creating friction and heat. The air temperature in the box rises, the air becomes less dense, subwoofer thinks it's in a bigger enclosure because sound travels easier through denser mediums(like how sound travels incredibly far underwater).

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