Stereophile Burmester BA71 and BA31

The larger BA-71 uses four 160mm woofers while the BA-31 employs two woofers. The B71 employs two 160mm midrange drivers in a D'Appolito array around a single front-firing air-motion-transformer tweeter, the B31 a single midrange unit. These speakers differ from the rest of the Burmester loudspeakers because they incorporate a user-adjustable air-motion-transformer tweeter on the upper rear panel of the cabinet.

i-fidelity Burmester BA 71 Review (pdf)

With the impressive BA 71 acoustic transducers, Burmester aims to set a new record in the realm of audio. To accomplish this, even the backsides of these stylish made-in Berlin loudspeakers emit sound.