Re: 2 source interference - setup

["Bernard G. Cleyet & Nancy Ann Seese" <georgeann@REDSHIFT.COM>]

I don't have much time so bear w/ errors ---  High end spk. mfgs. take care to make as
little as possible phase shifts between the spks in a system by e.g. placing them @ diff.
distances from the listener  to compensate from the phase shift caused by the
cross-overs.  If not,  phase distortion occurs which changes the timbre of the
instrument.  In the case of your xpts.  this probably won't cause a problem except when
the freq. is intermediate between the cut off of the crossovers), i.e.  sig. power is
going to both spks.  This I would expect would cause a broadening of the nodes/anti's As
some-one else suggested, use single unported speakers.

more later, maybe.

bc

I don't think Denker was using the democratic method to find truth, but to get various
ideas to think about and xptly verify.    One may make a crude anechoic chamber by
covering the objects with blankets, etc.

overdriving the speakers and, or amp. will produce distortion that you should hear, so can
easily be avoided.  However, it's easy to overdrive at low freqs (<200 Hz.)  as the first
harmonic may be mistaken for the fundamental.  You did this on a grassy field?  Much more
absorbent than concrete.  the berkeley Pays Lab. does this xpt. using peizo transmitter
and rcvrs at ~40kHz. -- spaced two sources, single with slits, etc.  thereby one may do it
in a lab. room.

John Denker wrote:

> At 01:31 PM 4/10/00 -0400, GARY HEMMINGER wrote:
>
> > Using a wavelength somewhere around a meter we set up our
> > speakers about five lambdas apart and facing across the field.
>
> Did you check the directionality of the speakers?
> Did you check the directionality of the microphone?
> Did you measure |A| and |B| and |A+B| separately, or just |A+B|?
> Did you account for the wind?
> Did you measure the variation of |A| with height?
> Did you measure the THD (total harmonic distortion) of your generator / amp
> / speakers / mike / analyzer?
> Did you clap your hands to get an estimate of the echo intensity from
> obstructions in all directions (including behind the speakers)?
>
> > > I doubt that crossovers are a factor.
> >
> > There seem to be differing opinions here - I'd be interested to hear
> > more.
>
> The laws of physics are not usually considered matters of
> opinion.  Collecting more opinions is unlikely to settle the issue.
>
> Can you pose a more specific question?
>
> Do you think crossovers are a factor?  If so, can you state a hypothesis as
> to why Floquet's theorem (as previously discussed) does not apply?
>
> Have you considered the competing explanations for the lack of an
> easily-observable interference pattern?  Can you rule them out?