BEAR wrote in message ...
Two corrections:

1. The "EBS alignment" is not popular *here*, it's popular on another forum
that I frequent. What it refers to is putting a long excursion/high power
woofer in a box that is actually a bit small, and then EQ'ing the thing to
get flat response down to some F3 (like 20Hz.) and then dropping the
response off below that with a HP filter to keep from really wasting more
power and heating the driver too much. It works nicely with the modern
drivers now available.

Actually, the excursion requirements for such an alignment are
no more stringent than for any other woofer for the bandwith and
SPL requirements. Driver excursion is determined by the frequency,
the radiating area and the total acoustic power, not by the aligment
of the system. In other words, to get, say, 100 dB SPL out of a 12"
woofer at 20 Hz requires an excursion of 1.35 cm, it makes NO difference
whether the system resonance is 15 Hz or 150 Hz.

However, here's the advantage of a very small box alignment. As you
approach resonance and, expecially, below, the driver is more and
more stiffness-controlled. That is, the mechanical and acoustical
stiffness control motion (above resonance, the system is mass-
controlled, the moving mass controls the movement). That means, at
low frequencies, where you are at or below resonance AND your
excursion requirements are increased, the linearity of motion is
more and more determined by the linearity, or more importantly,
lack thereof, of the driver suspension.

If you take a driver with a high compliance and a very low free-
air Qts, and place it in a VERY small enclosure, small enough that
it's system Qts is now raised to 0.707 (Butterworth 2nd order
rolloff), it is now no longer the driver suspension that dominates
the total system stiffness, it is the compression of the air in the
box, which is a WHOLE lot more linear than the driver suspension.
Further, since the volume of air is fixed and very accurately
determined by simple cabinet dimensions, it is the acoustical
stiffness that dominates over the mechnical stiffness, the latter
having very poor manufacturing tolerance.

These are precisely the arguments originally advanced by Villchur
for the AR-1 and subsequent speakers, the so-called "acoustic
suspension" principle. The technical arguments advanced are sound.

The twist here is that the original acoustic suspension systems
suffered from very poor efficiency. That problem is solved with the
use of active equalization. It's perfectly sound, technically, to
have a system that by itself has a system resonance of, oh, 150
Hz and a Qtc of 0.707, then be augmented with a +12 dB/octave boost
down to 20 Hz, with a rolloff below that. The result is a 4th order
system that's flat down to the system cutoff. The resulting system
has a 6 dB orn better advantage over an acoustic suspension system
of the same cutoff and bax volume.

But, again, the excursion requirements for a 12" acoustic suspension
and a 12" small-box, EQ'd design such as mentioned here are exactly
the same.