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From: "George Lendich" <lendich@aanet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-3977559@logan.com>
Subject: Re: [FlyRotary] Re: Phononic bandgap muffler
Date: Mon, 16 Nov 2009 12:43:25 +1000
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 Ernst,
Thinking out loud, I'm wondering if the tubes can be on an angle and still 
do the same job - perhaps even better?. The reason I ask is that air can 
travel through the tubes if their welded to the outer skin and can act as 
cooling tubes through the muffler.
Often sound is converted into heat when traveling through an exhaust, so 
cooling could be an advantage.
George ( down under)

> Al Gietzen wrote:
>> Ernest;
>>
>> Interesting stuff.  Just a guess; but it seems to me that, while 15 db is 
>> an
>> appreciable reduction, having that reduction only over the 8K to 12K 
>> maybe
>> isn't all that productive.  It would reduce the 'harshness', but isn't 
>> the
>> greatest amplitude at lower frequency?  Also, do you envision that this 
>> can
>> be made into a compact, workable package for aircraft application?
>>
>>
> Al, you prompted me to run the same analysis on a different sample.  I
> picked a section of the sound where Mike was revving the engine.  The
> first analysis was from a section where he was idling.
>
> This time, I kept an outline of the original sound in the background.
> You can see that my experimental setup has a lot to be desired.
> However, the loss from the original to the light purple peaks is the
> same loss in all the later samples.  The light purple is the straight
> through, no interference sample.  The sample with 4 lines is in light
> green.  Where the green overlaps the purple, we get a dark grey.  The
> purple above the dark grey is the attenuation from adding the 4 lines of
> baffles.  Any green above the grey is energy added.  I would be tempted
> to say that the green peaks at 16.5kHz and 20kHz are artifacts of the
> experimental setup, except that the artifacts move predictably with the
> addition of more rows, ie, the arrangement is moving sound energy out of
> the lower frequencies and out beyond what we find audible.
>
> Now, I'm tempted to find out what will happen if I add more rows.
>
> -- 
> Ernest Christley, President
> Ernest@TechnicalTakedown.com
>
> TechnicalTakedown, LLC
> www.TechnicalTakedown.com
> 101 Steep Bank Dr.
> Cary, NC  27518
> (919) 741-9397
>
>


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