In general, while the modern bookshelf/subwoofer combo can deliver more
bass energy than classic designs, the classic drivers with large
cones-particularly the 15" coax drivers in suitable boxes- gave a more
natural sound presentation in many cases. There are two reasons for the
modern trend, SAF-or spousal acceptance factor-and build cost.

Unless one is an aficionado of pipe organ music, the lowest frequency
of substantial musical interest is probably 30.87 Hz. This is the low B
string on the five string electric bass. While most of the classic
designs had little output even at 55 Hz-the frequency of the A string
of the bass-any working bass player of the era will attest to the
"kick-ass sound" of their bass lines through the old Altec green boxes
in playback.

Objective measurements aside, the big high build cost drivers such as
the Altec 604 and others provide (present tense!) a listening
experience very difficult to emulate with small speakers and a sub.
Generally, small speakers have a pleasing midrange and lack drive in
the lower registers. A 12-inch woofer is probably the smallest that can
be taken seriously for good baritone and upper bass performance under
any circumstances. Were it not so, the single driver solutions such as
Lowthers would be taken more seriously than they are-and, outside such
cabinetry as Mr. Pass's "J-Low", they aren't.

Small box speakers that are not optimized for nearfield use (and used
accordingly) are a limited proposition and should be presented with
that in mind. If one is limited in space, one may do the best he can,
but even after sixty years of development, in speakers as in engines,
"There is No Replacement For Displacement". High end saloons selling
ridiculous speakers with small drivers and byzantine crossovers, such
as Thiel, know better, but if the customer base is that gullible,
figure they are giving the customer a benefit in allowing the client to
have "spousal acceptance" to the wife and "mine's bigger" to the
client's male 'friends' simultaneously.