Phil Allison wrote:
"Peter Larsen"
A sane way to design the 4 Ohm box would btw. be to stick with the same
midrange and top components as in the 8 Ohm box.
** Long as similar woofers and compression drivers are available in 4 and 8
ohms, that is the easiest way to do it.
( Note that the 8 ohm version uses a 16 ohm compression driver. )
But there sees to be no valid technical reason to make a 4 Ohm box for
those that can't afford large amplifiers if it ends up in toy class
efficiency so that they get more sound from the same amp by getting the 8
Ohm version.
** Obviously true.
Another way to convert any box from 8 to 4 ohms is to simply install a
matching transformer at the input, ie an auto-transformer that gives a 41%
step up in voltage.
A toroidal cored type would make it quite small and inexpensive too.
That seems like a free lunch. It isn't, but it seems like one
1.41 is dangerously close to sqrt(2).
BTW
The size of the magnet does not change with rated impedance - 4, 8 and 16
ohms versions have identical magnet structures.
I think that's probably true, based on what I've seen.
Speakers have been made with impedances from 0.5 ohms ( eg Bose) up to
hundreds of ohms and the only thing that changes in the gauge of the wire
wound on the voice coil.
FWIW, I have found trolling through the Eminence online catalog to be
a source of a great deal of data on loudspeakers.
.... Phil
--
Les Cargill