One of the Zu Essence's unique selling points is its very high efficiency. While my estimate of its sensitivity, 92.5dB(B)/2.83V/m, is lower than the specified 97dB (due, I suspect, both to the 12 ohm impedance and to the lack of presence-region energy in the on-axis response—see later), it's still 10dB higher than the sensitivity of the BBC LS3/5A. Probably to oversimplify, the Zu speaker driven by 10W will play as loudly as the LS3/5A driven by 100W—assuming the little BBC monitor could actually handle 100W without melting!
Not only does the Essence not…