X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost03.isp.att.net ([207.115.11.53] verified) by logan.com (CommuniGate Pro SMTP 5.3c2) with ESMTP id 3976847 for flyrotary@lancaironline.net; Sun, 15 Nov 2009 09:33:58 -0500 Received-SPF: none receiver=logan.com; client-ip=207.115.11.53; envelope-from=keltro@att.net DKIM-Signature: v=1; q=dns/txt; d=att.net; s=dkim01; i=keltro@att.net; a=rsa-sha256; c=relaxed/relaxed; t=1258295639; h=Content-Type: MIME-Version:In-Reply-To:Message-Id:Date:Subject:To:From; bh=fh5gQO L8QeXnMrBwYFZrc5W8OC8VVyVFGu0GGbqAENc=; b=ItNXn6mbRLn6i1lg8FGvhX6Qc fC/+tUYFd9w06rKjcfrXl9jM0/K0NzMltK53qxrTenHLVTIskzC439s4RKcAQ== Received: from fwebmail33.isp.att.net ([204.127.221.133]) by isp.att.net (frfwmhc03) with SMTP id <20091115143324H0300rsjcee>; Sun, 15 Nov 2009 14:33:25 +0000 X-Originating-IP: [204.127.221.133] Received: from [208.114.35.168] by fwebmail33.isp.att.net; Sun, 15 Nov 2009 14:33:24 +0000 From: "Kelly Troyer" To: "Rotary motors in aircraft" Subject: Phononic bandgap muffler Date: Sun, 15 Nov 2009 14:33:24 +0000 Message-Id: <111520091433.11557.4B00113400071A2000002D2522243323629B0A02D29B9B0EBF019D9B040A05@att.net> In-Reply-To: X-Mailer: AT&T Message Center Version 1 (Mar 2 2009) X-Authenticated-Sender: a2VsdHJvQGF0dC5uZXQ= MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_11557_1258295604_0" --NextPart_Webmail_9m3u9jl4l_11557_1258295604_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit Ernest, Please send the xcf file to me................. -- Kelly Troyer "Dyke Delta"_13B ROTARY Engine "RWS"_RD1C/EC2/EM2 "Mistral"_Backplate/Oil Manifold -------------- Original message from Ernest Christley : -------------- > Here's a question for you audiophiles on the list. How much effort is > 10dB of muffling worth? > > I've expanded on my experiments with phononic bandgap filters, and I > think I've fairly conclusively demonstrated up to 15dB of attenutation > in the frequency ranges between 8kHz and 12kHz. I used the run-up video > that Mike Wills provided for us a few weeks back (thanks Mike), and I > was a little more methodical than last time. > > For those that don't remember, a phononic bandgap filter is created by > geometric arrangement of dissimillar materials, with the goal of > filtering specific vibration frequencies. It appears that 1/2" diameter > tubes, arranged in a grid with 1" centers does a nice job of attenuating > frequencies in the 8kH to 12kHz range. > > I set up my simulated muffler...a wooden shell with PVC filter > elements. I stuck a couple speakers in the inlet side, and a > microphone on the outlet side. In this setup, there is going to be all > sorts of losses from the conversion from an electronic signal to sound > in the speaker, then conversion of sound to an electronics signal in the > microphone. Comparing the original to the recorded muffled sound, which > I did in the first experiment, is not valid. > > What I did this time instead, is to compare several recordings. Each > with one less row of filter elements than the last, until I was > measuring an empty box. The empty box measurement is the control that > lets me know if I'm doing anything with the array of tubes. What I > found was that each row of tubes provide a significant attenuation in > the frequencies between 8kHz and 12kHz. The ones that give us the > weed-wacker sound. I determined this by taking a time sample across > each of the 5 recordings and having Audacity plot the spectrum. > > I have an xcf file created by The Gimp ( a free image editing > software). The xcf format allows you to keep an image in layers. Each > of the plots is in a separate layer, and by playing with the opacity > individual layers, you can easily see where the attenuation occurs. The > file is 465kB so I can't post it to the list, but if anyone is > interested, I'll be happy to send it direct. I'll do a writeup with > links to the audio files "real soon now". > > I have attached a flatten image showing the 0 row run, against the 4 row > run. The 0 run is the lighter purple shade. There are some some > frequencies where the 4 row would be louder....around 4kHz and 7kHz, > but I think the attenuation of those frequencies around 10kHz would be > most beneficial. > > -- > Ernest Christley, President > Ernest@TechnicalTakedown.com > > TechnicalTakedown, LLC > www.TechnicalTakedown.com > 101 Steep Bank Dr. > Cary, NC 27518 > (919) 741-9397 > --NextPart_Webmail_9m3u9jl4l_11557_1258295604_0 Content-Type: multipart/related; boundary="NextPart_Webmail_9m3u9jl4l_11557_1258295604_1" --NextPart_Webmail_9m3u9jl4l_11557_1258295604_1 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable
Ernest,
   Please send the xcf file to me.................
--
Kelly Troyer
"Dyke Delta"_1= 3B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifol= d



 
-------------- Original message from Ernest Christley <ec= hristley@nc.rr.com>: --------------


> Here's a question f= or you audiophiles on the list. How much effort is
> 10dB of mufflin= g worth?
>
> I've expanded on my experiments with phononic ba= ndgap filters, and I
> think I've fairly conclusively demonstrated u= p to 15dB of attenutation
> in the frequency ranges between 8kHz and= 12kHz. I used the run-up video
> that Mike Wills provided for us a = few weeks back (thanks Mike), and I
> was a little more methodical t= han last time.
>
> For those that don't remember, a phononic = bandgap filter is created by
> geometric arrangement of dissimillar = materials, with the goal of
> filtering specific vibration frequenci= es. It appears that 1/2" diameter
> tubes, arranged in a grid with 1= " centers does a nice job of attenuating
> frequencies in the 8kH to= 12kHz range.
>
> I set up my simulated muffler...a wooden sh= ell with PVC filter
> elements. I stuck a couple speakers in the inl= et side, and a
> microphone on the outlet side. In this setup, there= is going to be all
> sorts of losses from the conversion from an el= ectronic signal to sound
> in the speaker, then conversion of sound = to an electronics signal in the
> microphone. Comparing the original= to the recorded muffled sound, which
> I did in the first experimen= t, is not valid.
>
> What I did this time instead, is to comp= are several recordings. Each
> with one less row of filter elements = than the last, until I was
> measuring an empty box. The empty box m= easurement is the control that
> lets me know if I'm doing anything = with the array of tubes. What I
> found was that each row of tubes p= rovide a significant attenuation in
> the frequencies between 8kHz a= nd 12kHz. The ones that give us the
> weed-wacker sound. I determine= d this by taking a time sample across
> each of the 5 recordings and= having Audacity plot the spectrum.
>
> I have an xcf file cr= eated by The Gimp ( a free image editing
> software). The xcf format= allows you to keep an image in layers. Each
> of the plots is in a = separate layer, and by playing with the opacity
> individual layers,= you can easily see where the attenuation occurs. The
> file is 465k= B so I can't post it to the list, but if anyone is
> interested, I'l= l be happy to send it direct. I'll do a writeup with
> links to the = audio files "real soon now".
>
> I have attached a flatten im= age showing the 0 row run, against the 4 row
> run. The 0 run is the= lighter purple shade. There are some some
> frequencies where the 4= row would be louder....around 4kHz and 7kHz,
> but I think the atte= nuation of those frequencies around 10kHz would be
> most beneficial= .
>
> --
> Ernest Christley, President
> Ernest= @TechnicalTakedown.com
>
> TechnicalTakedown, LLC
> ww= w.TechnicalTakedown.com
> 101 Steep Bank Dr.
> Cary, NC 27518=
> (919) 741-9397
> 
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