# Fiber Fill - use it or not?



## pat_smith1969 (Feb 17, 2010)

Hi all...
I have built a box that houses two 10 inch Morel subs. Per specs it says from .7 to 1.1 per sub.. I built the box to have .8 per sub (so 1.6 total). I see people use fiber fill to fudge the measurements a bit but since I am right on.. do I need fiber fill? The box looks kind of empty...Should I just get some of that egg crate looking stuff instead since I don't want to simulate more air space, or just leave it empty?


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## 1990tsi (Dec 9, 2011)

pretty easy to try it. If you like it, keep it, if not toss it.


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## pat_smith1969 (Feb 17, 2010)

I had thought of that.. but it is going in a friends car and once installed I won't hear it much so I would like to do it "right" or "best" the first time. 

Also two punds of fiber fill is not exactly cheap $20 for two pounds.. not tons of money but I would hate to drop a 20 for just to rip it out later and throw it on the floor/trash.


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## Pitmaster (Feb 16, 2010)

I heard somewhere that you lose a bit of output with fiberfill


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## Viggen (May 2, 2011)

Been thinkinig of trying that myself

I had a shop make a fiberglass box for my morel 12 sc.... I told them 1.25-1.5 cu ft

What did they do?? about 1.1 cu ft, whatever the manual stated

I am happy with the sound but I am thinking of snagging some fill just so I can see/hear what the difference is.


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## thomasluke (Jun 10, 2011)

polyfill can be usefull in taming peaks and making it act like the enclosrire is a little bigger than it real but it in taming the peaks it often seems like you lose a little output.
But it can help.


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## Catman (Mar 18, 2008)

Polyfill is a tuning aid. It is not something that you automatically stick in everything you build. Sometimes you need to put blocks in a cabinet to reduce the volume. Install the box in the car ....test with PNG and RTA. Adjust if needed.

>^..^<


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## VWTIm (Apr 10, 2010)

My last (2) sealed boxes have sounded better with fill. One was undersize due to install constraints, the other was built to spec. As others have said, it seemed to "tame" the sound. Want to be cheap? Unstuff and old pillow, if it helps, spend a few $ on real stuff.


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## jcollin76 (Oct 26, 2010)

I'd agree, you don't necessarily need it, but it's an option or tool for tweaking your response. 
It's very useful when dealing with small enclosures due to space limitations. It can gain you a "little" extra internal volume. 
What some people think of less output, I tend to like... The sound seems less hollow to me. But like mentioned, this could just be taming a peak in the response. If it is a true loss in output, it's very minimal. Testing would be the Only true way to tell how it will affect your setup.

And $20 sounds kinda high for 2lbs. I go cheap and grab a big bag at Walmart, just to have on hand. Think it's was under $10, and easily enough for 4-5 enclosures. I'd check around on prices...


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## Bayboy (Dec 29, 2010)

jcollin76 said:


> And $20 sounds kinda high for 2lbs. I go cheap and grab a big bag at Walmart, just to have on hand. Think it's was under $10, and easily enough for 4-5 enclosures. I'd check around on prices...



I hope it's Acousta-Stuf that goes for $10 per pound not the poly-fil you get at walmart or other stores. Acousta-Stuf is supposed to be quite denser & better suited for speakers.


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## sqshoestring (Jun 19, 2007)

The last bag of poly I got at walmart was $1.97 and nearly the size of a pillow.

It tends to cut back the upper bass so say around 50Hz up to your LP. Sure a sub always 'sounds' louder if it has more output at 50Hz that is the whole idea with SPL. You need to determine if it has too much output at ~50 and more or not, which often happens with too small a box, but depends on your install and taste in sound. My taste leads me to nearly always make a box larger than the minimum recommended, and my favorite subs are the ones I have now with no box at all. Because I like 30Hz and anything close to it. A lower tuned enclosure typically has less output in SPL because the Q is lower.


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## nick650 (Feb 7, 2011)

I generally put some in every box and make the box slightly smaller then spec so I can use it. Just clears up unwanted frequency's/ resonances and makes the sub sound better. Downfall is, it CAN lower output but the quality gain is 0_0


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## Q-Authority (Mar 31, 2008)

Poly-fill, etc. is not just a tuning aid. It is used to eliminate standing waves caused by the shape of the typical sealed speaker box. It is extremely difficult to design a sealed box without standing waves, which can cause cancellations at various frequencies depending upon the size and shape of the box. The typical sound of a sealed sub box without fill material is somewhat hollow, which has been mentioned previously. I am amazed that this is still an issue that people still have questions about. If you don't want to radically change the characteristics of the box size simply do not use that much fill. And, yes, poly fill is quite adequate, and quite inexpensive.


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## Bayboy (Dec 29, 2010)

It has already been noted that standing waves are of no problem in automotive sub enclosures. At this point it will only have a very small useful effect in lowering Qtc.


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## Mirage_Man (Jun 29, 2007)

Q-Authority said:


> Poly-fill, etc. is not just a tuning aid. It is used to eliminate standing waves caused by the shape of the typical sealed speaker box. It is extremely difficult to design a sealed box without standing waves, which can cause cancellations at various frequencies depending upon the size and shape of the box. The typical sound of a sealed sub box without fill material is somewhat hollow, which has been mentioned previously. I am amazed that this is still an issue that people still have questions about. If you don't want to radically change the characteristics of the box size simply do not use that much fill. And, yes, poly fill is quite adequate, and quite inexpensive.


Just out of curiosity what freq would those standing waves in a sub enclosure be?


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## ATOMICTECH62 (Jan 24, 2009)

Standing waves are a product of the wavelength to box size.Sub frequencies are to long to be affected much.It usually starts around 300hz and up.


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## rideit (Nov 20, 2011)

sqshoestring said:


> my favorite subs are the ones I have now with no box at all. Because I like 30Hz and anything close to it. A lower tuned enclosure typically has less output in SPL because the Q is lower.


what subs are running free air, just out of curiousity?


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## Q-Authority (Mar 31, 2008)

Sorry, I meant *reflections*, which can be a real problem in any speaker design, but I guess you all knew that. 

Overall, stuffing or damping the inside of a subwoofer’s enclosure is generally a good idea to prevent the internal reflections inside of the enclosure from bouncing around and coloring the response and sound. If you are looking for the utmost in uncolored and well-damped sound or if you intend to use the system extra high in frequency up into the lower midrange, it is recommended. If you are trying to be as absolutely loud and efficient as possible, then leave it out.


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