Sophisticated analog processor necessary to control and protect the MSL-2/USM-1 speakers. Meyer is the epitome of high end sound. Disclaimer: not recommended by Meyer as the above are 15" woofers, but I used this for Meyer UPA speakers and it sounded fine. The main technical difference is the crossover point is 1400Hz whereas the UPAs are 1600Hz. Only 200Hz difference. Most other functions are compatible. Minor cosmetic scratches (gaff tape residue) but electronically functions as designed. Has a barely perceptible electrical hum which does not affect the sound at standard gain and PA levels. Sold As Described.