From: Brian Marston <marstonb@x??x.xxx.xxx
Date: Mon Dec 27, 1999 9:20 am
Subject: Re: Fiberglass panel
Dan Nelson wrote:
> From: Dan Nelson <dprimary@e...>
> They could be of use in a studio, it would give you a more industrial look.
> The metal covers will decrease the the amount of high frequency absorption
> you have to track down the manufacturer for the absorption coefficients.
> Adding more thickness of fiber glass would increase the low end absorption
> Dan Nelson
> Lasse Andersson wrote:
> > (snip) .....
> > Here is my question: A friend of mine offered me several dozens of
> fiberglass panels to buy. They are made of dense fiberglass and they are 3 cm
> thick, 59 cm wide, 119 cm height. What is interesting about them is, that
> they are covered whith a metal plate full of holes. I think they are
> originally made for isolating machine rooms in a factory or something
> similar. The plate is 1/2 mm thick, it covers the front and long sides and
> bends to the back 1 cm. The holes are 3 mm wide, and they are 4,5 mm away
> from each other when measured from the edge of the holes. What is the effect
> of the plate? Does it make the low end absorption better, does it act as a
> diffusor or what is the meaning of it?
The facing would be acoustic perforated metal facing that protects the fibre
glass from being damaged. If the open area is about 11% the perforated metal
is enhancing the low frequency performance and slightly reducing the high
frequency performance. This will provide mid range and upper frequency
performance. The holes act as "helmholtz resonators".
To move down into the lower frequencies you should be looking toward 10 cm
thick minimum 20 kg per cubic metre fibreglass. Simply layering extra layers of
fibreglass will not achieve the results that you expect.
They do not act as diffusers.
> > Is it of any use in a studio I'm going to build? It is quite easy to take
> the plate away if it works better that way.
> >Any comments?