GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.

Post Subject: Bite into itPosted by jessie.dazzle on: 9/1/2010

Paul S wrote:

"...I am not sure what you mean by "rigid" foam..."

By rigid I mean brittle; foam that does not bend, but breaks with a loud snapping "pop". Rigid foam urethane does not rebound at all after compression... In fact there is no compression unless you consider crushing to be compression; given sufficient force (a lot) it can be crushed, but the destroyed cells will not rebound at all.

This foam (see previous post) was developed for industrial pattern making where stability and consistency of density are the most critical properties. In lower densities, as would be the case if pouring it into a rear chamber with cover removed, it is very easy to cut or abrade.

Cut it with a serrated blade for best control; abrade it with a half-round Surform or "cheese grater" file (just the blade without the handle) about $3 at Home Depot etc.
http://cpc.farnell.com/productimages/farnell/standard/42352550.jpg
Avoid the flat-section blades.

Again, I'm not familiar with all spray can foams; some may be rigid. Before committing to any of them for use in back-filling a rear chamber, I'd do a rebound test by simply biting into a sample. If there were any evidence of rebound, I would not use it, as its presence would somewhat cancel out the investment made to ensure rigidity of the rear chamber walls.

jd*

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