So-called (actually, mis-named) 'isobarik' systems are a way of
obtaining a given response in half the volume, since the arrangement
results in half the total equivalent compliance volume and thus
requires half the enclosure volume for the same response function.

My Isobric has been constructed to improve LF ouput (it seems) not reduces
size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic
secondary, I guess that they have decided that the cone mass of an 8 inch
drive in isobaric has advantages over that of an 12 inch driver (at the size
of the brute it could easily use a 12 inch drive, one thing did occur to me
is that perhaps due to its age that duel VC speakers were not avalible and
the only method of getting a phase and anti phase driver easily was to use
two drivers.

As to "true hifi response," such a term needs definition to be
anything but meaningless jargon, in precisely the same way that
a "specification" like "20Hz-20kHz" is meaningless without
qualification.

I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with
gradual roll off above and below. If that is 'hi fi' or not is questionable.
I spent some time years ago analysing CD's to find usual and lowest
frequency's (plus HF, lots of CD's have significant output above 15Khz
(components up to 25Khz+ can be present) but at my age thats starting to get
above what I can easily here!) LF it seems stops round the ~30 Hz, few
instraments produce much less than this (yes I know that alot can) a lot of
the very LF on disk is artificial (1/2 frequency echo and its that it is
possibly added to give 'space' to the recordings) unless you are a pipe
organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or
such as the LF in these type video recordings is huge it seems (and
unnatural in my books) )

THe fundamental efficiency/enclosure volume/cutoff frequency equation
will ALWAYS rule. But, interestingly enough, driver diameter simply
does not enter into that relation. Specifically, the relation:

n0 = kn Vb F3^3

where n0 is reference efficiency, Vb is enclosure volume, F3 is is
low frequency cutoff and kn is the efficiency constant has NO term
in it in any way depedent upon driver diameter. This directly refutes
your assertion that it's not possible to get your "unqualified" 'hifi
response from an 8 inch driver. One needs to simply balance the three
terms of efficiency, enclosure volume and cutoff frequency and you're
there. You seem to intimate that low efficiency is incompatible with
'hifi response," for example, an unjustifiable viewpoint in light
of the lack of qualification of 'hifi response.'

kn = efficiency constant derived from driver (this figure will improve with
driver diameter, thus a large driver will allow a a small enclosue to
produce the same output at the same frequency with less power - correct me
if wrong)

However in order to get usable (at say 32Hz) levels the enclosure volume
(8 inch) will become so large as to be impactical in a lot of cases. This
equates to the 'You can put an airplane engine in a submarine' but who wants
too?

An enclose that is over 32 cubic feet will meet significant resistance when
placed in the home! (Test this by asking you wife if you can shift 2 small
fridges into the lounge!)

I tend to deal with and try and work in what can be achieved reasonably
easily in real world situations, absolutes and what is theoretically
possible don't fit! (But are well worth knowing and considering (Hey I own a
leak stereo 30 once discribed as all the power a home stereo would ever need
and enough th have your neighbours complaining! This we all know not to be
true!))

As a side issue I see that companies are producing very large (24 inch
diametre) woofers now. how well do these work and are they worth the
premiums being asked for them?