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Using Polyfill in a Subwoofer Box

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Polyfill is used in many subwoofer enclosures, yet not many people know why they are using it. They may see it done somewhere and think it would be a good idea to use in their own box. There are times when polyfill is needed and times where it is not, and knowing when to use it will allow you to get the best sound from your sbuwoofer box.

In general, a subwoofer box that would require polyfill would be a subwoofer box that is close to, or smaller than the manufacturer's minimum recommendations for internal volume. Polyfill will make a subwoofer perform as if it were in a larger enclosure by slowing sound waves as they pass through the polyfill. The physical internal volume of the subwoofer box remains the same, yet the effective internal volume changes when polyfill is added.

Sealed subwoofer boxes are the best candidates for polyfill. It is possible to use polyfill in a ported enclosure, but this is not recommended, as it would then change the tuning of the box. Sealed subwoofer boxes generally yield a better, flatter frequency response curve when the enclosure is larger (to a certain point). If you need a subwoofer box of a given size, and your available trunk dimensions do not allow you to customize a subwoofer box with enough internal volume, it is possible to get the subwoofer enclosure built a little smaller than desired and have polyfill added. This will make the subwoofer box "appear" larger to the subwoofer.

If your sealed subwoofer box has sufficient internal volume for your subwoofer, or towards the maximum recommended internal volume for your subwoofer, you do not need to add polyfill to your subwoofer enclosure. If you have too small of a sealed subwoofer box for your subwoofer, adding polyfill is a great way to make your box perform as if it were a larger enclosure. If you have your doubts, it is always possible to compare the performance of your subwoofer box with and without polyfill. You only need to do this by ear, as it is satisfaction from what you hear out of your system that really matters.

If you decide to use polyfill in your custom subwoofer box, you have a couple of options. One option would be to buy car audio specific polyfill from an audio shop, which can be very expensive. A cheaper alternative that yields almost the exact same results is to buy polyfill from the craft section of your local Walmart. There is virtually no distinguishable difference between the effects of the two types of polyfill, and the craft polyfill is very inexpensive when compared to the car audio polyfill.

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