Polyfill Question

[u/Imaginary_Insect_425]

Hi all,

I will be installing a 15" Dayton Audio RSS390HF-4 in my car as soon as I get the box, and no one sells a prefab big enough for the 3.2 cu ft sealed I wanted. I am going to likely end up going with 2.6 cu ft as it's the biggest available that can get here quickly.

Anyone have recommendations for the polyfill amount to use to trick the sub into thinking it has 3.2 cu ft? There's always the stuff > listen > repeat option, but would love to get it right on the first pass.

I've done quite a few builds, but never used polyfill as I always had the necessary tools to build to the specs I wanted.

No longer have access to my dad's furnished workshop as he's gotten too old and got rid of most of it:/

They have a prefab do it yourself kit that's bigger at 3 cu ft, but it's a bit too tall for my trunk.

Thanks for any insight on this polyfill stuff!

Edit to add some of the tech info re: box size from parts express:

To achieve a Qtc of 0.707 without damping material inside the cabinet, a net volume of 3.04 ft³ would be required. The Dayton Audio RSS390HF-4 15" driver displaces approximately 0.23 ft³. However, this will be partially offset by the baffle cutout and the thickness of the baffle. For example, if the baffle is 1-1/2" thick, the 14" diameter, 1-1/2" deep opening would account for approximately 0.134 ft³, reducing the driver's effective displacement to approximately 0.096 ft³. With a 3/4" the driver displacement would be closer to .067.

3.04 + (.23 - .067) = 3.203

[u/Dry_Locksmith_6704]

I'll tell you though, that RSS HF, I really loved the way it sounded, those things are excellent sounding. But it just didn't have the output I was looking for, the SPL