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Box Building Questions - Polyfill and cu.ft.


Transplanted Bostonian
November 4, 2002
Reaction score
City, State
East Brunswick, NJ
Year, Model & Trim Level
97 Mountaineer V8 4x4
I purchased a Kenwood eXcelon 1025dB 10" DVC subwoofer. I'm building a stealth box for it, to put it into the factory subwoofer location.

I'm using 5/8" MDF, with a thin fiberglass liner.

My problem is that I can't get the volume of the box greater than 0.62 cu ft. (I'm designing in Autocad). Kenwood recommends that the sub be in 0.8 cu ft for a sealed enclosure, however it does have a range of 0.6-1.25 cu ft. How will a smaller box effect the sound? Kenwood says the smaller the box, the "tighter" the bass - what exactly does that mean - more SQ, but less SPL?

The sub itself displaces 0.085 cu ft, so my 0.62 encolsure will be even smaller!

Will polyfill be my savior/magic cure? How much should I add to the box? I would love to make the box even small - can I say go down to 0.55 cu ft, and make up the rest in polyfill?

Also - my box design is quite abnormal, I'm form-fitting it to the rear quater around the steel box beam as well as the wheel well. Will this effect sound?


When I built my box I took the factory's reccomendation (ex. .75ft3) added the displacement of the sub (ex. 08ft3) and then added polyfill until halfo of the box was full. So your box technically shouldn't be getting samller w/ the sub displacement, it infact should be gettign larger if I'm not mistaken.

I think it's 1.5lb. of polyfill per cubic ft. of volume.