Moving the Helmholtz frequency down a little bit shifts the alignment towards an overdamped condition. This has a benefit of being forgiving of certain conditions. Adding series resistance from long wire runs or heated voice coils won't make the box sound boomy. On the other hand, it isn't an alignment that works well in wide open spaces without a sub. A flat or even slightly underdamped alignment sounds better if used in open areas, particularly if no subs are used.

When the box is tuned to 40Hz, all box sizes from 2.0ft3 to 5.0ft3 work well, having flat response and cutoff somewhere between about 40Hz and 60Hz. They are slightly overdamped, so they are forgiving of high power levels and long wire runs. Larger boxes, up to 5.0ft3, yield an EBS alignment that rolls off about 40Hz.

There are lots of prosound 15" drivers that have been made to work well in 2.0ft3 to 5.0ft3 boxes tuned to 40Hz. That's a standard target, so many manufacturers have made speakers that have suitable electro-mechanical specs for this application.

So the difference is largely a matter of bass extension. You have about a half octave span to play with, and about 2x box volume to work with too.

Second is that there ain't a lot of 1.5" throat horns around, very few actually and P.Audio has most of them

Third reason is that the baby cheek thing seems to work well up close, as opposed to the PA CD types, although the 1.5" P.Audio at 12" X 12" looks more like Jessica Alba's ass than a baby's.

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