Here is the Stereophile rpt on #9- The BBC's.
BBC LS3/5a loudspeaker
J. Gordon Holt & Various, March, 1977
These diminutive little sleepers have been available in the US for
quite some time but have attracted little attention because (1) they
have never really been promoted and (2) they are just too small to look
as if they could be worth $430 a pair.
Originally
designed by the BBC for monitoring of on-location broadcast and
recording pickups (footnote 1), they hide most of their cost—a complex
equalizer and phase-corrected crossover network—inside a cabinet only
slightly larger than a shoe box. They were intended for "close-in"
listening in a small control room rather than to fill a large room, and
they will definitely not put the kind of levels beloved of rock nuts without woofer-bottoming or ultimately permanent damage.
Despite what must be a rather large amount of built-in bass boost (to
compensate for the small size of the woofer), they are fairly
efficient: We would estimate around 1¾%, which is comparable to an
average acoustic-suspension system. Maximum safe output level is around
95dB SPL (sound pressure level) at a listening distance of up to 15',
which is about as loud as a symphonic crescendo from 10' behind the
conductor. This is with full-range program material; the limiting
factor on power input is the "woofer" (because of its bass boost), so
when the speakers are used with a subwoofer (crossing at 60 to 80Hz),
they are capable of a clean 100 to 105dB, which is enough to give any
masochist a most gratifying case of permanent ear damage.
Judging by their size, one's first thought is likely to be that these
will work just dandy up on the wall, right below the ceiling and toward
the room corners, where standing-wave resonances in the room will help
augment the speakers' thin bass. But their size is very deceptive.
These are not thin-sounding. In fact, they produce an overall
balance similar to that of a pair of large systems when they (the
Rogers) are located on 30"-high stands, right out near the center of
the floor. (This bass-balance design is consistent with the BBC's
recent research findings which showed that the smoothest bass response
is obtained when a speaker is as far as possible from room boundaries.)
It is because these speakers are so well-balanced when they are out in the room that they may well produce too much
bass when placed against a wall, particularly when located near the
junction between three room surfaces. In corners, they are (in most
rooms) intolerably boomy because they are designed for out-of-corner
placement, and because that location excites the maximum number and
amplitude of standing-wave resonances (footnote 2) in the room.
The close proximity of room surfaces (or, worse yet, of a box or shelf
under the speakers) also causes diffraction interference—the chopping
of deep holes in the frequency response due to selective cancellation
of certain frequencies. The smaller the speaker enclosure, the less
audible are these diffraction effects and the smoother the system
sounds. But nearby corners and surfaces can spoil the advantage of the
small enclosure.
Another advantage of a small sound source is
that it tends to radiate sound waves as expanding spheres rather than
as a planar wave (as from large screens). Human ears react in a
seemingly paradoxical manner to a spherical sound field: The reproduced
sound seems, much bigger than its source, yet the angular localization
of sounds across the "stage" between the speakers (ie, the
imaging) is dramatically improved. In fact, the apparent audible size
of these tiny speakers is almost laughable; we had the feeling that it
just could not possibly be.
Adding to the illusion of a
large speaker system, is the remarkable low-end performance, which is
not really all that deep (subjectively flat to a bit below 57Hz in our
rooms) but sounds deeper than it is because the response is
actually pretty flat down to there (rather than drooping), and the bass
detail is astonishing from 5" woofers. The speakers gave such a
startling account of themselves at the low end that we were not acutely
aware of the lack of deep bottom until deeper notes (as from bass drum
or the bottom range of the string bass) that we knew were on the recording failed to come through.
High-end performance is quite remark able. The speakers have a very
slightly rising response above about 5kHz (fig.1), but because there is
no audible peak at the top, the rise does not cause any sizzling or
spitting, but tends rather to exaggerate slightly the extreme high-end
energy in the program, adding a bit more sibilance to voices, a bit
more shimmer to cymbals, and a bit more overall airiness to the sound
than is actually in the program material (footnote 3).
Footnote
1: American visitors to England consistently report that the BBC
transmits superb-quality sound and that unlike the US (where
practically everything aired is canned), Britons are privileged to hear
frequent live broadcasts of orchestra concerts. It is thus reasonable
to assume that the BBC engineers know good sound when they hear it.