X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta06-srv.alltel.net ([166.102.165.167] verified) by logan.com (CommuniGate Pro SMTP 5.0) with ESMTP id 814169 for flyrotary@lancaironline.net; Thu, 03 Nov 2005 20:13:33 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.167; envelope-from=montyr2157@alltel.net Received: from Thorstwin ([4.226.237.68]) by ispmxmta06-srv.alltel.net with SMTP id <20051104011248.ZKZM12191.ispmxmta06-srv.alltel.net@Thorstwin> for ; Thu, 3 Nov 2005 19:12:48 -0600 Message-ID: <000001c5e0dc$e05f8330$44ede204@Thorstwin> From: "Monty Roberts" To: Subject: muffler new info. Date: Thu, 3 Nov 2005 19:12:08 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C5E0AA.7C7742E0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0002_01C5E0AA.7C7742E0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I finally got the recordings from our experiments loaded up onto my = computer from my PDA. I actually got some good data before the mic = saturated.=20 Turns out, to my great surprise, the muffler did just what it was = supposed to do. It eliminated the harmonics above about 750 hz. The wave = form was clipped and the output much closer to a sine wave. The problem = was the amplitude of the sound it let through. The fundamental 200hz = amplitude was very high. Most people (including me) who were standing = close to the test stand probably had saturated eardrums and were not = able to detect the change in the sound quality. There was just too much = of it (first row at a Stones concert sounds pretty crappy, back off a = bit and things get better). Those standing farther away could hear the = difference and thought it sounded good. I didn't think this was the case = until I could listen to the sound files on a good sound system where I = could turn the volume down.=20 So the next plan is to keep doing what I did before, but put a resonator = to attenuate the fundamental frequency down to something bearable. The = bad news is this frequency is between 100 and 200 hz depending on what = RPM the engine is at. That means a longer heavier muffler. Initial = numbers show it being about the same diameter and 15 in long. I also had a chance to ring the muffler and see what the resonant = frequency of the structure is. As fate would have it, the fundamental is = 2400 hz. This is a multiple of the 1200 hz resonant frequency of the = cavity of the muffler. So it will self excite when the muffler is really = working hard. This explains the horrible screech at 6000-6500 rpm. This = is also bad for fatigue life. I should be able to weld a couple of = strips of metal to it and fix that problem. Monty ------=_NextPart_000_0002_01C5E0AA.7C7742E0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

I finally got the recordings from our = experiments=20 loaded up onto my computer from my PDA. I actually got some good data = before the=20 mic saturated.

Turns out, to my great surprise, the = muffler did=20 just what it was supposed to do. It eliminated the harmonics above about = 750 hz.=20 The wave form was clipped and the output much closer to a sine wave. The = problem=20 was the amplitude of the sound it let through. The fundamental=20 200hz amplitude was very high. Most people (including me) who were = standing=20 close to the test stand probably had saturated eardrums and were not = able to=20 detect the change in the sound quality. There was just too much of it = (first row=20 at a Stones concert sounds pretty crappy, back off a bit and things get = better).=20 Those standing farther away could hear the difference and thought it = sounded=20 good. I didn't think this was the case until I could listen to the sound = files=20 on a good sound system where I could turn the volume down.

So the next plan is to keep doing what = I did=20 before, but put a resonator to attenuate the fundamental frequency down = to=20 something bearable. The bad news is this frequency is between 100 and = 200 hz=20 depending on what RPM the engine is at. That means a longer heavier = muffler.=20 Initial numbers show it being about the same diameter and 15 in=20 long.

I also had a chance to ring the muffler = and see=20 what the resonant frequency of the structure is. As fate would have = it, the=20 fundamental is 2400 hz. This is a multiple of the 1200 hz resonant=20 frequency of the cavity of the muffler. So it will self excite when the = muffler=20 is really working hard. This explains the horrible screech at 6000-6500 = rpm.=20 This is also bad for fatigue life. I should be able to weld a = couple of=20 strips of metal to it and fix that problem.

Monty

------=_NextPart_000_0002_01C5E0AA.7C7742E0--