On 1 June 2011 11:24, Ralph Hall <[email protected]> wrote: > > Ralph R. Hall > [email protected] > Ralph R. Hall > http://www.brasshausmusic.com > > I'm no scientist but does the Doppler effect only become operative > when sound source is moving? I'm confused because some of my reading > on the subject lays great emphasis on the distance between sound > source and receptor and others lay greater store on the movement. >
It is definitely the movement. Come on folks, the doppler effect is well enough documented, it even has an article in Wikipedia for goodness sake. http://en.wikipedia.org/wiki/Doppler_effect If you want to find out, then look it up. But when this thread had been going for some time, don't say words to the effect of "I don't know, but I think it might be the distance". We live in an age when it is unprecedentedly easy to find out. Please take advantage of this. > If distance is a factor then this is what we are talking about with > offstage playing. It certainly isn't psychological - it's a fact that > instruments flatten when they are played away from the stage. > It is an audiitory illusion. > > In the Philharmonic Hall in Liverpool, at the end of The Planets where > the ladies chorus has a morendo, they were shuffling backwards > (offstage) to achieve the effect. Their pitch flattened (although not > in actuality) but what didn't recede was the voice of the choir > conductor (also offstage) shouting out the beats of the bar as they > moved away from him: "One, two, three, four, five; one, two ....." etc. > I'm afraid it is still an auditory illusion. The wikipedia article has a paragraph on this titled "A Common Misconception", worth repeating. "Craig Bohren pointed out in 1991 that some physics textbooks erroneously state that the observed frequency *increases* as the object approaches an observer and then decreases only as the object passes the observer.<http://en.wikipedia.org/wiki/Doppler_effect#cite_note-3>In most cases, the observed frequency of an approaching object declines monotonically from a value above the emitted frequency, through a value equal to the emitted frequency when the object is closest to the observer, and to values increasingly below the emitted frequency as the object recedes from the observer. Bohren proposed that this common misconception might occur because the *intensity* of the sound increases as an object approaches an observer and decreases once it passes and recedes from the observer and that this change in intensity is misperceived as a change in frequency. Higher sound pressure levels make for a small decrease in perceived pitch in low frequency sounds, and for a small increase in perceived pitch for high frequency sounds." Regards Jonathan West _______________________________________________ post: [email protected] unsubscribe or set options at https://pegasus.memphis.edu/cgi-bin/mailman/options/horn/archive%40jab.org
