On Thursday 06 September 2007 13:30, Schiffel, Jeffrey A wrote:
> ...
>
> It is an example of inadequate design, and is quite easy to achieve.
> Consider that the hall consists of an audience chamber and a stage
> house. The chamber is quite high with reflective walls. Sound,
> especially from high-pitched instruments, ascends into the upper
> stage house and into the hall. In a hall 120 feet deep, sounds would
> only need to be deflected a couple of feet (at 440Hz) when bouncing
> off the walls to hear a doppler shift of a quarter tone. (01)
Something has to be in (relative) motion for the doppler effect to take
place. Either the source, the receiver, an intermediate reflecting
surface or the medium. (02)
Perhaps there's a coherent air-flow through the hall that causes a
frequency shift? But that would be a linear (additive) shift and the
concept of a "quarter tone" is multiplicative (we're all quite
conditioned nowadays to hear in an equal-tempered scale where each
halftone is a factor of the 12th root of two change in frequency). (03)
> > For example, suppose the incoming frequency f was X Hertz and
> > the outgoing frequency was X-y Hertz. That would imply that
> > y vibrations per second were somehow "lost"
> > or, even worse, "stored" for future transmission.
> >
> > That is an extremely complicated nonlinear transformation.
> > You could accomplish it by recording the sound and later
> > playing it back with a slower turntable or the equivalent in
> > electronics. But I don't believe a typical music hall could do
> > that.
>
> In fact, they do. So does "echo point" in the mountains, where the
> sender often hears the reflected sound a bit lower. (04)
Perhaps in an open environment there are further dynamics (and certainly
net, though non-uniform motion of the air would be the rule rather than
the exception). Also, the atmosphere outdoors could be dispersive, for
example. (05)
There's also the possibility of purely psycho-acoustic effects causing
the impression of a pitch change. (06)
In any event, I am inclined to agree with John that a static structure
such as a concert hall could not produce a frequency multiplying effect
such as rendering all pitches a quarter tone flat. (07)
Another perspective on this (putative) phenomenon is that such a hall
would have no resonances, since any sound would have a continually
declining frequency. Sort of like the Bohr atom, now that I think of
it. (08)
> Regards,
>
> -- Jeff Schiffel (09)
Randall Schulz (010)
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