ATS Wrote:

Not really "twice as much money spent", because you'd never compare
single sub, to that same sub in a pair, mounted isobaric.  They'd b
two completely different animals.

A more appropriate comparison would be to one of today's mor
expensive, "small box subs", to an isobaric pair of less expensive
lower powerhandling, larger enclosure (and therefore inherently highe
efficiency) subwoofers.

As per Hoffman's Iron Law, the following three items are mutuall
exclusive in a subwoofer/enclosure alignment:
1) small enclosure size
2) low frequency extension
3) high efficiency

The "small box sub" must inherently trade off either low frequenc
extension, or efficiency (or both) to accomplish 'small enclosure size
performance.
Usually, low frequency extension is also desired... so efficiency i
traded off.
Now, because you've got a less efficient sub, it's appropriate to mak
it handle more power, so it can actually get loud in that smal
enclosure... because you'll need to stuff lots of wattage into it t
get it that loud.

Traditional "cheap subs" aren't "small box subs".  They are usually
simple happy medium, with decent low frequency extension, goo
efficiency, and needing a medium-large enclosure.  The fact that the
don't handle as much power even makes them more efficient... th
smaller gauge wire means more turns in the magnetic gap at any give
moment, resulting in higher efficiency.  The "lighter duty
construction often makes for a lower moving mass, resulting in mor
efficiency.

When looked at this way, it's not hard to find opportunities fo
isobaric alignments...
..even though so, so many subs today are "small box subs".

The flaw in the thought process of those stating "twice the cost", i
that they are thinking of taking two "small box subs", and using the
in an isobaric pair.  
That's not your most eligable candidates... I'd almost say you'd neve
do that. ;)

Another benefit of Isobaric alignments is that they iron ou
nonlinearities in the driver... at least when mounted clamshell (fac
to face).
If you picture the movement of a half-roll surround, and picture
cutaway of a sub moving in slow motion, you'd see that the half rol
deforms differently on an in-stroke compared to an out-stroke.
Also, some subs might not necessarily be electrically assemble
on-center.

When two subs are mounted mounted this way (clamshell isobaric), n
matter what phase of the signal, one sub is always moving in relativ
to it's basket, while the other sub is moving out relative to it'
basket... the cones move together.  ;)

Of course, this isn't specific to isobaric... you could do the sam
thing with two subs in a standard enclosure... mount one magnet out
one magnet in.
But... that's not really apples to apples, in the scope of "what sub
would suit THIS specific install?"... just like the consideration of
single small-box sub with the consideration of two small box subs i
isobaric... you are talking about a different animal, suited to
different install. ;)

I consider it simply something to open up your options, given a
install that can yield a certain size enclosure.
Sometimes, isobaric can even save you money, and gain you efficiency..
because you'd really never consider using the same subs isobaric vs
non-isobaric, in the scope of prospecting for a specific singl
install. ;
--
geolemo

think in 96 the best amp was the RF punch 500 and most subs would only
handle 500 watts or less, so this makes sense.