On Sat, 07 May 2005 08:38:40 GMT, "Mark & Mary Ann Weiss"
wrote:
Adire Audio used to have some discussions on high excursion subs before
they trashed their web site. They said that a major problem with high
excursions was that an oversized speaker surround would collapse or
invert itself from the air pressure. It would sound very bad and soon
tear.
Another problem is the area of the voice coil that is not in a magnetic
field. It does nothing but make heat. There's also terrible distortion
if the amount of the coil that is in the field doesn't remain constant
as the coil moves.
Adire can custom build a +/- 80mm excursion subwoofer motor called the
Parthenon for $3000. The cone/diaphragm is up to you.
I found a partial mirror of their old page:
http://www.acousticconcepts.com.au/Parthenon.html
Facinating discussions from all so far... and pretty much what I expected in
terms of answers. And yielding one radical product which seems to be THE
design concept I was after. I LIKE the idea of moving 16 cu ft of air with
one driver. Cute!
You might think it's 'cute', but it will be much less cost-efficient
than using a bunch of 15" Tempests to do the same job. Note that the
Parthenon is not a driver, it's just a motor assembly. That 16cu ft
*theoretical* figure is for a non-existent extended motor with a
non-existant cone and suspension assembly, at an unmentioned total
cost - but figure say $15-20k ballpark, with a good risk that there'll
be something wrong with the first try. You can easily match that 16 cu
ft displacement with 160 Tempest drivers, which I'll bet you can buy
from Adire for less money, and they are known products which can be
driven as an array by a bunch of off-the-shelf amplifiers.
Getting back to some of the other replies in this thread, yes, I do observe
a correlation between optimal voice coil size and efficiency. I've noted
that the EVM 18B woofers with their smallish 2.5" coils seem to be
significantly more sensitive than offerings from JBL, Altec and others,
despite the 4" coils of the latter bunch. However, I don't think the
distortion levels are a match to the larger coils.
You don't 'think' the distortion levels are a match? If you don't
*know*, then don't speculate.
The greater the piston
area is backed by motor power, the more faithful the piston can move. Small
coil, big piston, lots of breakup, modal resonances and other nasties.
I think that one of the reasons why my little Dynaudio woofers which I use
in some nearfield monitors move so much air and have amazing transient
response is due to the fact that a large area of the cone, not just a dot in
the center, is driven by the coil. I think there is a benefit there.
Well, you're wrong. Transient response has *nothing* to do with coil
size, and neither does suspension travel. They do however handle large
power transients with little compression, and that does relate to
those oversized coils. Besides, those Dynaudio units are known to have
significant breakup in the 3-4kHz range, not true of several other
units with stiffer cones but smaller coils, as made by Focal,
Wilson-Benesch, and Wharfedale, among others. There's a reason why the
vast majority of top-class 4-6 inch drivers use 2-2.5 inch coils.
I've been thinking about a variety of loudspeaker designs, one of which was
similar to the Parthenon. I made some sketches 5-6 years ago, but never
persued it. I turned the skiver/surround 90º with respect to conventional
surrounds, and made it like an accordian hose, at the cone diameter. That
allows for lots of movement. The challenge was controlling lateral movement.
Note also the very first paragraph of this post............
Years earlier, I was brainstorming a more radical design, where the air
molecules are excited directly by electrical energy. This Ion Loudspeaker
would have no diaphragm at all. Frequency response would extend literally
from DC to in the megahertz range. Drawbacks were high voltages and ozone
emissions. :-)
No need for brainstorming, the IonoFane tweeter was a commercial
reality in the '60s and '70s.
--
Stewart Pinkerton | Music is Art - Audio is Engineering