Variable Frequency Absorbers link?

[cordura21]

hi guys. I read on the eggs boxes thread that there is something like a variable frequency absorber.
Can you give me the link to that? I searched, but couldn't find anything?
Cheers, Andrés

 

[John Sayers]

Try this Andres:

http://home.locall.aunz.com/~johnsay/HR/index1.htm

cheers
john