Resilience and energy transfer, was Acetone

[Richard Brekne]

Sarah Fox wrote:

> Hi all,
>  
> Interesting question:  What happens to hammer felt when it is doped?
>  
> The same question can be asked about open-cell foam rubber.  Normally 
> it's nice and squishy (resilient), and although it can impede sound 
> reflection somewhat, it isn't that effective an acoustic material.  
> However, the stuff is commercially treated (doped with something, I 
> believe) to make it a bit stiffer and very slightly "crunchy," and 
> that stuff, when cut into wedges or egg crate, has great 
> antireflective properties and can be seen lining the walls of the 
> world's finest recording studios.  That's because it absorbs sound 
> energy, rather than reflecting it.
>  

Its not quite as straightforward as that when it comes to felt.  The 
felting process has a lot to do with why hammers develope there own 
distinct kind of resiliency.  You are not just filling up the empty 
space between the fibres by adding hardener, you are also coating the 
fibres, making them more stiff and less willing to give under stress.

Again... David Stanwood has a lot of stuff on this... if he's watching 
the list right now it would be nice of him to share a bit of what he's 
found out on the subject.

Cheers
RicB