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.
