> >I don't get what the beat freq has to do with this. A beat shouldn't be
> >able to excite a resonance at the beat freq, unless there are significant
> >nonlinear mixing effects going on.
>
> I don't know either but windows usually don't close perfectly and have
> some play, especially large tall church windows. Maybe this was the
> 'diode'. Anyway they took a few seconds to start 'singing'. I'm pretty
> sure damage would have occured before too long (I did not intend to do any
> damage - I was quite scared in fact).

I'm not sure that the electrical analogue applies fully here. Unlike EM
waves we are certain that there IS an "ether" in this case - the air is the
medium that the waves are produced in. When two such waves interact they are
represented by real pressure phenomena in the gas and "mixing" occurs at all
points.

In the case of my locomotive beating experience (which occurred
intermittently but on numerous occasions over the years that I lived there)
the effect was extremely real and manifestly repeatable. While I am not
CERTAIN that the effect was in fact caused by the two engines running side
by side at nominally identical rpm I can not think of a more probable
explanation. This only occurred in the early morning before (winter) dawn
and only for a limited period in each case. The "sound" levels were high and
they came from the shunting yard. I can imagine that the workers may even
have worked hard to produce the effect by careful idle speed adjustment :-).


        Russell McMahon

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body