Hardie concrete backerboard as a liner?

[mfishmike]

Hi all,

I've built a dual driver 12" Titanic MKIII sub and am going to remove the 4" port and add 4 15" passive radiators to it. I've got them on order from Acoustic Elegance. While I've got the unit dis-assembled, I thought about lining the inside walls with a layer of 30 # roofing felt, and a layer of 1/4 or 3/8 " James Hardie concrete backer board to further help reduce cabinet resonance. The concrete siding material is on my new home, and drastically reduces the sound to the outside. Has anyone in the group used this material in your projects? The walls are 1 1/8" particle board already, but there is a certain amount of radiating resonance, even with heavy internal bracing, which I'll lose some of when I install the pr's. I'm open to any thoughts, and thanks in advance.

Mike Cason

[ThomasW]

As long as the Fs of the cabinet is out of the woofer's passband and the walls don't flex, the construction of the box doesn't much matter.

I doubt that you'd gain much using the backer board. There won't be much surface area left after you cut the holes for the PRs. It takes a ton of added mass to get the Fs lower than the passband.

I'd recommend adding a layer of 3/4" ply (BB if possible) to stiffen the box. Then add the max amount of bracing possible, the goal being to raise the cab Fs.

[mfishmike]

Hi again Thomas,

Looks like I've got to get into the books to figure out those F's.

I was reading Vance Dickason's cookbook and read about the double-walled design of a couple of other builders, and the concrete board would seem to be a much better damper than the multiple felt layers, or double sheetrock layers. That's what this stuff is all about.....trying and playing.....glad it's hobby! It's sure fun when you're done and it sounds good....kinda like a well executed 9 iron shot to the pin..... :lol:

Thanks again....