I haven't seen many isobaric subwoofer enclosures in recent years, and
while they were extremely popular for a while, looking back at it I
can't remember exactly what their appeal was in the first place.

If I remember correctly, the advantage was that you could put two
subwoofers in an enclosure volume that would normally only be enough
for one sub. Since you could use two subs, you could use double the
amplifier power without having to make room for a larger enclosure.
This made sense back in the days before we had subs that could handle
the huge amounts power that today's subs can take. If your sub could
only handle 500WRMS, you could put a second identical sub sharing the
same airspace and feed them with a total of 1,000 WRMS.

What confuses me is that I also recall that the isobaric enclosures
were less efficient than a traditional sealed box, by about 3 dB.
This 3 dB loss would seem to cancle the benefit of doubling the
amplifier power, so that your final SPL number from 500W into a single
sub in a sealed enclosure would end up being about the same as 1000W
into two identical subs in an isobaric enclosure.

So, what was the benefit of isobaric enclosures that made them so
popular (if only for a short time)?

Scott Gardner