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Date: Sun, 12 Dec 2004 11:10:52 -0500
From: Finn Lassen <finn.lassen@verizon.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: exhaust design question
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Those triangular pieces are foam - some sound absorbing material. Hard 
materials like metal is not likely to absorb sound, rather they're 
likely to reflect it.

Look at arcustic (sp?) ceiling pates, carpet, curtains. Then compare to 
a naked room with hardwood floors.

Having the muffler, expecially a thin walled one, inside the cowling, 
and the cowling cowered with some fireproof sound dampening material, 
would undoubtedly help.

Finn

rijakits wrote:

>A wild idea/question: How is the sound emitted from something like a
>silencer?
>Remember any pics of sound proof chambers - like the car manufacturers have
>to check source and dynamics of sound coming of their cars. These chambers
>are all full of triangular foam (or so it seems) to eat up the sound, as not
>to reflect anything and falsify the data.
>
>Would it work to weld triangular shaped pieces on the OUTSIDE of a muffler?
>.... or better has anyone any idea or tried that already?
>I have no reason to believe that this works, but I think is worth a thought!
>Any sound engineers on the list?
>
>I remember in the old LP (music) times the very highend turntables would
>come with an accessory: a heavy glassplate that was to be supported by
>inverse ceramic cones or glasscones that in turn where supposed to be placed
>on ceramic or glass again (point down). Supposedly to not absorb any
>frequency from the floor/suroundings and to not loose any sound to the floor
>either....
>
>I am not enough of a music conoseur to ever have found a difference, but
>that doesn't mean it didn't work:))
>
>Any ideas?
>
>Thomas J.
>
>  
>