The BBC LS5/5 is a large three way monitor designed in 1967.
A 12 inch drive unit handles the low frequencies up to 400Hz. At this point, an 8 inch midrange takes over before handing over to the 1 inch soft dome tweeter at 3.5kHz. Overall, the frequency response is flat to within ±2dB from 40Hz to 20kHz.
Straight away you’ll notice that the bass and midrange drivers are mounted behind slots on the front panel. This feature is highly unusual today, but it works to control the off-axis response of the drive units which results in a smoother response through the crossover regions in typical listening environments. Not surprisingly, we get a lot of questions about this, so we have written an in-depth article explaining how the slots work.
Naturally, this is a BBC “thinwall” cabinet, where the relatively thin panels are mass-loaded to ensure that resonances are moved away from the mid-range region, and Rockwool provides air damping. Hand-matched veneers are applied and finished to a very high standard. The grille is carefully designed to minimise diffraction effects and is held in place by concealed rare-earth magnets.