The LS5/1

The LS5/1 preceeded the classic LS5/1, and used commercially available
drive units from Plessey and GEC. Two tweeters were required to achieve
the required power handling. In the case of the LS5/1 – but not the OB
version (the LS3/1, which was smaller, used a sealed enclosure and placed
the tweeters in front of the woofer) – the upper tweeter rolls away at
higher frequencies to avoid the acoustic lobing effects associated with
two sources producing the same output when the spacing between them is
comparable to the wavelength.

The woofer is 15 inches, which is almost unheard of today in the domestic
market. Using modern materials and techniques, our unit has greatly
improved power handling and bandwidth over the Plessey original.

Of course, with such a large woofer, “beaming” is a serious problem
at the upper ranges of its operation. The BBC’s answer to that was to
use slot loading, as many have already seen in our LS5/5. This approach
really helps to improve the off-axis response, making it possible to
use larger drive units in typical domestic listening rooms. Much
more information about how this works can be found in this in-depth article.

The floor-standing cabinet uses the traditional BBC approach of
(relatively!) thin panels that are mass loaded to move the resonances
down away from the critical midrange region. High quality hand-selected
veneers are applied, and the grille is held in place with concealed
magnets so can be readily removed if desired.