Midwoofer-tweeter-midwoofer

The midwoofer-tweeter-midwoofer loudspeaker configuration (called MTM, for short) was a design arrangement from the late 1960s that suffered from serious lobing issues that prevented its popularity until it was perfected by Joseph D'Appolito as a way of correcting the inherent lobe tilting of a typical mid-tweeter (MT) configuration, at the crossover frequency, unless time-aligned. In the MTM arrangement the loudspeaker uses three drivers: Two mid-range (or mid-woofer/woofer) for the low frequencies and a tweeter for the higher frequencies, with the tweeter being placed between the mid-range drivers (as shown in the second image below).

Source: Wikipedia — Midwoofer-tweeter-midwoofer (CC BY-SA 4.0)