KEF KUBE 107 Universal Bass Equalizer for KEF 107 Reference Speakers

From the 1998 Stereophile review:

KUBE Stands for KEF Universal Bass Equalizer and takes the form of a separate solid-state component that connects in the tape monitor loop or between the preamp and power amp. The KUBE supplied with the 107 includes a speaker-specific equalization module that provides level equalization for the tweeter and mid driver, as well as an inverse of the 107's LF response. Furthermore, the KUBE allows the user to control several parameters not previously accessible. First, the LF cutoff is adjustable in four steps: 50, 35, 25, and 18Hz. Second, "Q" of the bass response is continuously variable from 0.3 (overdamped) to 0.7 (maximally flat). The Q parameter describes the sharpness of a speaker's bass resonance. As the Q increases, bass damping decreases until ultimately a response peak develops. The Q parameter also correlates well with bass transient behavior, high-Q designs resulting in underdamped, boomy bass with a lot of overhang.