This is much
more easily quantifiable than a sort of forced air convection mechanism,
which I'd argue is much less prevalent than you think.

Yes external methods of forced air are not prevalent, concept died in late
90's with the advent of smaller motor structures that don't hold as much
heat and advanced VC binding. But venting the GAP and forcing air around
the VC via excursion is very prevalent, almost standard in professional
loudspeakers.

Perhaps I wasn't clear. I didn't mean that it wasn't prevalent. Many
speaker designs rely on this mechanism for standard operation. What I meant
was that it is less prevalent for this to be the dominant cooling mechanism.
In other words, it's not always vital, and loudspeakers can get along
without it. Disclaimer: of course a certain degree of air flow is necessary
in all designs, but it's passive (well, as passive as you can get in a
moving structure at least). Conversely, there are some designs which seem
to revolve around such a mechanism.

BTW we are shrinking magnets as car audio seems to grow them,
which is something I have never understood. Nothing like slowing your car
down with ferrite and chrome. We choose neo to reduce chiropractor bills,
Neo has advanced to the point where it is not as temp dependent.

It's quite simple. 99 out of 100 car audio buyers are under the impression
that bigger magnets = better speakers. Give the customer what they want.
They're just getting out of hand these days. Personally, I tend not to buy
that crap.


And I'd suspect then
that the variation of power handling with coil motion in most drivers
could
be almost entirely accounted for by the theoretical gain due to
increased
surface area (although this is entirely hand waving on my part).

I agree! If air were more dense (like water) our LF transducers would be
able to shrink, now if fish made music not Phish keep in mind that
the conducting medium has a response also, look what happens to the speed
of
sound at different freq's as humidity rises.

Good example.

For
instance, look at tweeters. Also, based on your argument, low
efficiency
drivers should then have *dramatically* lower power handling
capabilities,
but this of course is not true.

One of the reasons that they arent as efficient is because they have HUGE
motors on them. Copper weighs an awful lot and a big thick cone is heavy
also. If a speaker has to handle the power it has to have weight, weight
causes moving mass and we all know what that leads to. Also see above.

Right. After rereading what I wrote, I see that I could have expanded it to
"low efficiency system" rather than "low efficiency drivers". Basically,
what I was getting at is the ratio between excursion and electrical energy
dissipated in the form of heat. If speakers truly relied on air flow as
heavily as you've implied, there would appear to be a major departure from
the theoretical effects of increased surface area associated with excursion
as a function of input power, and this would be apparent by looking at two
speakers with similar VCs and geometries, but different efficiencies
(perhaps due to suspension or enclosure differences). In other words, take
the same speaker and put it in two very different sized boxes and you'll see
that in one case the cone moves a lot and in the other case it moves a
little, even with the same input power (of course, accounting for the
differences in back emf, etc). My argument is that any differences in VC
power handling that arise as a result could more closely be accounted for by
a decrease in effective VC surface area, rather than what you would predict
if the dominant mechanism was air flow. If the dominant mechanism was flow,
then the difference in power handling would probably be huge.

By the way, I have no data to back any of this up. It's just hand waving on
my part.



One point I've tried to make in the past but have only alluded to in
this
thread is that there really is no such thing as "RMS power handling."
This
is a variable, dependent on too many factors - for example, ambient
temperature, playing time, enclosure effects (because of its effect on
motion), and so forth. Another influence should in theory be the
waveform
itself. But my own experiments have failed to bear this out.

I couldn't agree more! Add to that power compression As for waveform
I
have seen more mechanical damage than heating and electrical.

I'm sure that's true. I don't know that power compression belongs on the
list though, because you're decreasing the power delivered to the coil due
to the increased DCR, even though the amplifier's output voltage remains
unchanged. So it's not really a power handling difference.

But I'm
still not quite grasping your point here - if you get too high, the
impedance will just be too much for high freqs to be a contributing
factor.


Still blows 'em up, and remember I'm kinda OT here because I'm using
different drivers. I use 12's and 15's as mids in my paying job. And they
easily go up to 1.5K +

Single layer aluminum ribbon wound edgewise will have a different
inductive
properties than multiple layers of round copper.

Got it.