X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail-fx0-f216.google.com ([209.85.220.216] verified) by logan.com (CommuniGate Pro SMTP 5.3c2) with ESMTP id 3976838 for flyrotary@lancaironline.net; Sun, 15 Nov 2009 08:47:12 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.220.216; envelope-from=msteitle@gmail.com Received: by fxm8 with SMTP id 8so4941244fxm.27 for ; Sun, 15 Nov 2009 05:46:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=O86xxUQDD2HS+vIgrxzueb+BkdZh8ot9V9rTta61dg0=; b=e9rIoNZpR7Uj387n9qtXGu/oodLV44Zxf5snF8NqXJSiKqcUV3X7MXMtyYifSSs5mC z12rA2NVh+gzdJ2PfPCeaAQ8Hj/MUWTqzy4WB2d5QIxURDtecFDpA96G1wyP+zaNlLJn LO4GNMFYY/5mjUuB4q9qtGx6oKABgzvyLLTmE= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=QzF7tIF4FpjECF62Cy9zx6XnXdSogBX59kerm6rCyEIVKBoV9e6yPYHnRY/M3nzWxc 49K5LE/LfIjY9PnTpWMc6wi04El+Tsp6fu1gZBwXdrgE9VX+iYENyj5zMu/SReaj8MoR JnqV4fscmqao890TxP/7a983e4WINyaPUmjB8= MIME-Version: 1.0 Received: by 10.204.153.202 with SMTP id l10mr4549844bkw.92.1258292797178; Sun, 15 Nov 2009 05:46:37 -0800 (PST) In-Reply-To: References: Date: Sun, 15 Nov 2009 07:46:37 -0600 Message-ID: <5cf132c0911150546qa15c0dey8e5287ade9db5618@mail.gmail.com> Subject: Re: [FlyRotary] Phononic bandgap muffler From: Mark Steitle To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=0015175d07503304880478691f5c --0015175d07503304880478691f5c Content-Type: text/plain; charset=ISO-8859-1 Ernest, This is very interesting and applicable to every rotary installation. Sooner or later everyone must deal with the exhaust noise one way or another. For me, I'm waiting to hear more (no pun intended) about your experiments. Mark S. On Sat, Nov 14, 2009 at 11:37 PM, Ernest Christley wrote: > 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 > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html > > --0015175d07503304880478691f5c Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Ernest,
=A0
This is very interesting and applicable to every rotary installation.= =A0 Sooner or later everyone must deal with the exhaust noise one way or an= other.=A0 For me, I'm waiting to hear more (no pun intended) about your= experiments.
=A0
Mark S.

On Sat, Nov 14, 2009 at 11:37 PM, Ernest Christl= ey <echristley= @nc.rr.com> wrote:
Here's a question for you au= diophiles on the list. =A0How much effort is 10dB of muffling worth?
I've expanded on my experiments with phononic bandgap filters, and I th= ink I've fairly conclusively demonstrated up to 15dB of attenutation in= the frequency ranges between 8kHz and 12kHz. =A0I used the run-up video th= at Mike Wills provided for us a few weeks back (thanks Mike), and I was a l= ittle 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 filter= ing specific vibration frequencies. =A0It appears that 1/2" diameter t= ubes, arranged in a grid with 1" centers does a nice job of attenuatin= g frequencies in the 8kH to 12kHz range.
I set up my simulated muffler...a wooden shell with PVC filter elements. = =A0 I stuck a couple speakers in the inlet side, and a microphone on the ou= tlet side. =A0In this setup, there is going to be all sorts of losses from = the conversion from an electronic signal to sound in the speaker, then conv= ersion of sound to an electronics signal in the microphone. =A0Comparing th= e original to the recorded muffled sound, which I did in the first experime= nt, is not valid.

What I did this time instead, is to compare several recordings. =A0Each= with one less row of filter elements than the last, until I was measuring = an empty box. =A0The empty box measurement is the control that lets me know= if I'm doing anything with the array of tubes. =A0What I found was tha= t each row of tubes provide a significant attenuation in the frequencies be= tween 8kHz and 12kHz. =A0The ones that give us the weed-wacker sound. =A0I = 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)= . =A0The xcf format allows you to keep an image in layers. =A0Each of the p= lots is in a separate layer, and by playing with the opacity individual lay= ers, you can easily see where the attenuation occurs. =A0The file is 465kB = so I can't post it to the list, but if anyone is interested, I'll b= e happy to send it direct. =A0I'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 ru= n. =A0The 0 run is the lighter purple shade. =A0There are some some frequen= cies where the =A04 row would be louder....around =A04kHz and 7kHz, but I t= hink the attenuation of those frequencies around 10kHz would be most benefi= cial.

--
Ernest Christley, President
Ernest@TechnicalTakedown.com
<= br>TechnicalTakedown, LLC
www.TechnicalTakedown.com
101 Steep Bank Dr.
Ca= ry, NC =A027518
(919) 741-9397


--
Homepage: =A0http://www.flyrotary.com/
Archive and UnSu= b: =A0 http://mail.lancaironline.net:81/lists/flyrotary/List.= html


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