Re: more speakers - more sound

Chris Hornbeck wrote:

> On Thu, 17 Nov 2005 11:23:45 -0500, "Arny Krueger" <arnyk@xxxxxxxxxx>
> wrote:
>
> >"Ron Capik" <r.capik@xxxxxxxxxxxxxxxx> wrote in message
> >news:437C8F49.39060051@xxxxxxxxxxxxxxxx
>
> >> Push the gain up in a quiet room and many modes will be
> >> above the feedback threshold
> >
> >If the system is linear, there is no threshold.
>
> Y'all have raised a very cool point. Is oscillation
> truly a linear deal-e-o? Or is it a form of
> chaotic behavior?
>
> < ...snip.. >
>
> Chris Hornbeck

Well, you said systems are more interesting in the
transition from stable to unstable (or some such.)

As for "feedback threshold" a better descriptor
might have been instability threshold; as this is
a (quasi) closed system so there is always some
feedback. Sorry about that chief...

Anyway:
As I see it, the oscillation progression is linear but the
transition to oscillation is chaotic. Up to the transition
the chaotic input (noise) is driving the system. As the
gain goes up modes compete with each other for that
one leg up ...a gain margin greater than one. The
relative gain fluctuates because energy is stored
(via any delay; i.e. acoustic path, filters, room modes,
etc... ) in the system to be released later, thus adding
to (or subtracting from) the relative gain. At some point
a mode may synchronize and build oscillations. These
oscillations can cause another mode to synchronize
and suck gain away from the first mode. Thus the
feedback will swing about these competing modes. The
exchange of energy between these competing modes
may be chaotic or periodic depending on the influence
of all those other sub threshold modes, noise, vibration,
etc. ...or something like that.

It's a fun experiment but we never want to run our systems
that close to the edge, except maybe when ringing out the
room.

The system gets real nonlinear when we add in human interaction.
Movement on stage as well as the interaction of the sound tech
are very nonlinear. <G>

You may take all my rantings with a grain of some metallic halide.
[ I find that lithium chloride works well, ;-} ]

Later...

Ron Capik
--


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