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Natural Science Forum / Physics / Acoustics / December 2004New thread- doppler
I pick up the discussion from Peter Larson's message of Last October,'04: "According to Art Ludwig's analysis of Doppler distortion produced by a piston in an infinite tube, there are fundamental differences between IM produced by Doppler and IM produced by a quadratic mechanical non linearity. According to Art's analysis, for fixed velocities of the high frequency and low frequency motion, Doppler IM is proportional to the frequency of the high frequency carrier, whereas there is no such dependence in the case of IM distortion produced by a quadratic mechanical non linearity. "Also, the level of Doppler IM relative to the level of the high frequency carrier, is independent of the level of the of the high frequency carrier, whereas there is a linear level dependence for quadratic IM distortion, Lastly, for the case in a tube where sound pressure at the low frequency is proportional to the cone velocity, quadratic IM distortion is independent of the frequency of the low frequency signal, whereas Doppler IM is inversely proportional to the frequency of the low frequency signal. "The difficulty is not that Doppler IM can not be distinguished from IM produced by a mechanical non linearity. The problem is that if IM produced by mechanical non linearity predominates, then the measurement of Doppler IM is impossible because the IM side bands produced by both are at the same frequencies. The only way to accurately measure Doppler IM is to reduce mechanically produced IM to a lower level. For a loudspeaker, this is difficult if not impossible because sound pressure is proportional to cone acceleration. As a result very large amplitudes of cone displacement are required at low frequencies. "The measurement situation is much better for a piston in a tube because in that case sound pressure is proportion to piston velocity. Additionally, by using an accelerometer attached to a high quality vibration exciter in a servo feedback loop, it is possible to reduce IM distortion in the measured motion of the accelerometer to levels that are 80dB below the level of the high frequency primary. One can then use the top face of the accelerometer as vibrating piston in a tube and therefore be be able to measure piston velocity and the resultant sound pressure simultaneously. In this situation, with IM distortion in piston motion 80dB down, Doppler IM distortion is very easily measured. Hope this gets us back on track. Angelo Campanella > I pick up the discussion from Peter Larson's message of Last October,'04: > [quoted text clipped - 40 lines] > > Angelo Campanella In the future, if you cut/paste any of my posts and repost them verbatim, please at least have the professional integrity and courtesty to give me credit/blame. I assure you that I can handle it. For those who care, the original post can be found at: http://groups- beta.google.com/group/alt.sci.physics.acoustics/msg/ea35a4afd44a6a86?dmode= source Ghost >From what I have seen of Angelo's dedication to this discussion group and willingness to give answers to all sort of questions, I would not doubt his professional integrity and courtesty. The group is second to none in terms of professional support for anyone interested or involved in acoustics. This is largley due to a tremendous effort by Angelo. Tom Harper > Ghost > [quoted text clipped - 7 lines] > > Tom Harper Generally true, but totally irrelevant. Ang reposted the text of one of my previous posts, verbatim, and deleted all references to the author. While that is something that may be ok with you, it's not something that's ok with me. And, I couldn't care less what the consensus of opinion is on the matter. > Generally true, but totally irrelevant. Ang reposted the text of one of my > previous posts, verbatim, and deleted all references to the author. While > that is something that may be ok with you, it's not something that's ok > with me. And, I couldn't care less what the consensus of opinion is on > the matter. OK. Sorry. That message was sufficiently complex, that I truncated too much. Correct. ghost did indeed publish that. I repeat it more completely as: //////quote//////////// Subject: Re: Doppleritis, the cure [Fwd: Re: Experimental Evidence for Dynamic Doppler Shift] From: The Ghost <theghost@sbcglobal.net> References: <4160E57C.16B95169@mail.tele.dk> <6NFed.1612$C_6.913@trnddc04> <417EA5B9.503AA113@mail.tele.dk> Organization: Your Company Message-ID: <Xns958E94B2F8A21theghosthotmailcom@64.164.98.7> User-Agent: Xnews/5.04.25 Lines: 50 NNTP-Posting-Host: 69.227.64.244 X-Complaints-To: abuse@prodigy.net X-Trace: newssvr14.news.prodigy.com 1098826410 ST000 69.227.64.244 (Tue, 26 Oct 2004 17:33:30 EDT) NNTP-Posting-Date: Tue, 26 Oct 2004 17:33:30 EDT X-UserInfo1: FKPO@SBDAZR[CR\YIBIZ__DBUSXB@DTMNHWB_EYLJZ]BGIELCNVOPCWZBL[\YUWHANGYZEFNHFZPNLOBUNSS^_LGEVWEY\PHO@YJSSWBBDT\PFD^ESBTXVCCMTD]JCJLE\_IJMFNRY]SWE[S[D_CNB__ZK^VGVCKHA[S@COB^[@ZQSDFQ\BPMS@DZVUKQTJL Date: Tue, 26 Oct 2004 21:33:30 GMT Xref: wnmaster12 alt.sci.physics.acoustics:26896 X-Received-Date: Tue, 26 Oct 2004 21:35:02 GMT (bgtnsc04-news.ops.worldnet.att.net) Peter Larsen <SPAMSHIELD_plarsen@mail.tele.dk> wrote in news:417EA5B9.503AA113@mail.tele.dk: > It may of course be that my reading cabability is somewhat challenged, > but if the assertion that IM and Doppler products are by definition [quoted text clipped - 4 lines] > Is there *any* difference of *any* kind between "IM distortion" and > "Doppler distortion? According to Art Ludwig's analysis of Doppler distortion produced by a piston in an infinite tube, there are fundamental differences between IM produced by Doppler and IM produced by a quadratic mechanical nonlinearity. According to Art's analysis, for fixed velocities of the high frequency and low frequency motion, Doppler IM is proportional to the freqeuncy of the high frequency carrier, whereas there is no such dependence in the case of IM distortion produced by a quadratic mechanical nonlinearity. Also, the level of Doppler IM relative to the level of the high freqeuncy carrier, is independent of the level of the of the high frequency carrier, wherease there is a linear level dependence for quadratic IM distortion, Lastly, for the case in a tube where sound pressure at the low frequency is proportional to the cone velocity, quadratic IM distortion is independent of the frequency of the low frequency signal, whereas Doppler IM is inversely proportional to the frequency of the low frequency signal. The difficulty is not that Doppler IM can not be distinguished from IM produced by a mechanical nonlinearity. The problem is that if IM produced by mechanical nonlinearity predominates, then the measurement of Doppler IM is impossible because the IM sidebands produced by both are at the same frequencies. The only way to accurately measure Doppler IM is to reduce mechanically produced IM to a lower level. For a loudspeaker, this is difficult if not impossible because sound pressure is proportional to cone acceleration. As a result very large amplitudes of cone displacement are required at low frequencies. The measurement situation is much better for a piston in a tube because in that case sound pressure is proportion to piston velocity. Additionally, by using an accelerometer attached to a high quality vibration exciter in a servo feedback loop, it is possible to reduce IM disortion in the measured motion of the accelerometer to levels that are 80dB below the level of the high frequency primary. One can then use the top face of the accelerometer as vibrating piston in a tube and therefore be be able to measure pistion velocity and the resultant sound pressure simultaneously. In this situation, with IM distortion in piston motion 80dB down, Doppler IM distortion is very easily measured. ////end quote///////////// > While that is something that may be ok with you, it's not something that's > ok with me. there seems to me a lot of things that ain't okay with you. have you tried prozak? > And, I couldn't care less what the consensus of opinion is on the matter. that ain't gonna make you popular with the girls.  Signaturer b-j rbj@audioimagination.com "Imagination is more important than knowledge." >> While that is something that may be ok with you, it's not something >> that's ok with me. > > there seems to me a lot of things that ain't okay with you. have you > tried prozak? I think I'll pass because Prozak obviously hasn't helped either you or your buddy Bob Cain. It has, however, negatively impacted your ability to discern right from wrong. Perhaps you should join Bob Cain in some electro shock therapy. If you decide to go that route, let me know because I'd like to come over and set the voltage. :-) >> And, I couldn't care less what the consensus of opinion is on the >> matter. > > that ain't gonna make you popular with the girls. Certainly not with any that are on your wish list. :-) > Perhaps you should join Bob Cain in some electro shock therapy. > If you decide to go that route, let me know because I'd > like to come over and set the voltage. :-) hmmm. where do you live? Starke Florida? the electro shock machine there is maybe a little overly therapeutic. Signaturer b-j rbj@audioimagination.com "Imagination is more important than knowledge." >> Perhaps you should join Bob Cain in some electro shock therapy. >> If you decide to go that route, let me know because I'd >> like to come over and set the voltage. :-) > > hmmm. where do you live? Starke Florida? the electro shock machine > there is maybe a little overly therapeutic. You're supposed to be a smart guy. Surely you can come back with something better than that!! :-) >>>While that is something that may be ok with you, it's not something >>>that's ok with me. [quoted text clipped - 4 lines] > I think I'll pass because Prozak obviously hasn't helped either you or your > buddy Bob Cain. No sane reason for my name to come into this conversation. You are obsessed, boy. Get some help. Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >>>>While that is something that may be ok with you, it's not something >>>>that's ok with me. [quoted text clipped - 8 lines] > You are obsessed, boy. Get some help. > Bob Quite the contrary, and on ALL counts. For whatever reason, your technical incompetence hasn't yet been spotted by people in the dsp group. As a result, you still have RB-J fooled, but that will eventually come to an end. Your recent flip/flop comedy act regarding the Doppler distortion issue clearly demonstrates that you are technically inep when it comes to college level math, physics and engineering. Lastly, YOU are the one who is obsessed, BOY, and YOU are the one who is in serious need of some help. |
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