X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail-bw0-f226.google.com ([209.85.218.226] verified) by logan.com (CommuniGate Pro SMTP 5.3c2) with ESMTP id 3976973 for flyrotary@lancaironline.net; Sun, 15 Nov 2009 12:24:42 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.218.226; envelope-from=msteitle@gmail.com Received: by bwz26 with SMTP id 26so5043067bwz.27 for ; Sun, 15 Nov 2009 09:24:07 -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=irJLKEcIPQPHeQJGIHSudzlOY5jlfzLGAIS7o07RTQI=; b=BjmS02kATHGsyr3daJckSZMBSVZMRF+/Xoprt7qRFb5Mke9Y//FUOlRNWmbnWceTZP /SGgeCbQoDKTJsgB1jFKa4hklX/WcwlKWqnh0waLvIK7vSfnYvNr2xOMjHa+3cnrTln9 l/LeuuqZMUWHUHejQUVlgR2fHv4/xvrfG7dEk= 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=kmPjm7t7tBj06fmzGD9SAj7oZWZYKS3yQXFHuIbP6rPOCBMnOfx8xhYRT01JKZ1XTg th+uDTmn+USrUbjNWsHdb9bbYy0GX3XKl6cIJ7r6p2HT/q0dqnJeeDiJSc/NJWu/qwpP 8OipTl7nWTfSStIxNVepXC/rS/96rQ7oSBvQ8= MIME-Version: 1.0 Received: by 10.204.148.78 with SMTP id o14mr1469604bkv.83.1258305846844; Sun, 15 Nov 2009 09:24:06 -0800 (PST) In-Reply-To: References: Date: Sun, 15 Nov 2009 11:24:06 -0600 Message-ID: <5cf132c0911150924qa93e85flf624bf0b9e316178@mail.gmail.com> Subject: Re: [FlyRotary] Re: Phononic bandgap muffler From: Mark Steitle To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=0015175cac2e051d2f04786c29c0 --0015175cac2e051d2f04786c29c0 Content-Type: text/plain; charset=ISO-8859-1 Al, It would be great if it would reduce both high and low frequencies, but I would be happy to be able to just silence the high frequency noise as my Lightspeed does a good job of cancelling out the lower frequencies. Mark S. On Sun, Nov 15, 2009 at 11:05 AM, 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? > > Best, > > Al > > -----Original Message----- > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On > Behalf Of Ernest Christley > Sent: Saturday, November 14, 2009 9:38 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] Phononic bandgap muffler > > 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 > --0015175cac2e051d2f04786c29c0 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Al,
=A0
It would be great if it would reduce both high and low frequencies, bu= t I would be happy to be able to just=A0silence the high frequency noise as= my Lightspeed does a good job of cancelling out the lower frequencies.=A0 =
=A0
Mark S.

On Sun, Nov 15, 2009 at 11:05 AM, Al Gietzen <ALVentures@cox.net= > wrote:
Ernest;

Interesting stuff= . =A0Just a guess; but it seems to me that, while 15 db is an
appreciabl= e reduction, having that reduction only over the 8K to 12K maybe
isn't all that productive. =A0It would reduce the 'harshness', = but isn't the
greatest amplitude at lower frequency? =A0Also, do you= envision that this can
be made into a compact, workable package for air= craft application?

Best,

Al

-----Original Message-----
From: Rotary motor= s in aircraft [mailto:flyrot= ary@lancaironline.net] On
Behalf Of Ernest Christley
Sent: Saturd= ay, November 14, 2009 9:38 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Phononic bandgap muff= ler

Here's a question for you audiophiles on the list. =A0How mu= ch effort is
10dB of muffling worth?

I've expanded on my expe= riments with phononic bandgap filters, and I
think I've fairly conclusively demonstrated up to 15dB of attenutation<= br>in the frequency ranges between 8kHz and 12kHz. =A0I used the run-up vid= eo
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 arrangemen= t of dissimillar materials, with the goal of
filtering specific vibratio= n frequencies. =A0It appears that 1/2" diameter
tubes, arranged in a grid with 1" centers does a nice job of attenuati= ng
frequencies in the 8kH to 12kHz range.

I set up my simulated m= uffler...a wooden shell with PVC filter
elements. =A0 I stuck a couple s= peakers in the inlet side, and a
microphone on the outlet side. =A0In this setup, there is going to be allsorts of losses from the conversion from an electronic signal to soundin the speaker, then conversion of sound to an electronics signal in the microphone. =A0Comparing the original to the recorded muffled sound, which<= br>I did in the first experiment, 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 thatlets me know if I'm doing anything with the array of tubes. =A0What I<= br>found was that each row of tubes provide a significant attenuation in the frequencies between 8kHz and 12kHz. =A0The ones that give us the
wee= d-wacker sound. =A0I determined this by taking a time sample across
each= of the 5 recordings and having Audacity plot the spectrum.

I have a= n 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 plots is in a separate layer, and by playing with the opacityindividual layers, 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
inter= ested, I'll be happy to send it direct. =A0I'll do a writeup withlinks to the audio files "real soon now".

I have attache= d a flatten image showing the 0 row run, against the 4 row
run. =A0The 0 run is the lighter purple shade. =A0There are some some
fr= equencies where the =A04 row would be louder....around =A04kHz 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.
Car= y, NC =A027518
(919) 741-9397



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

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