This is one one of the few early 80s loudspeakers I remember listening to (back then) : very "muscular" rendition, tight and controlled, far from a "romanticised" sound. It's written on them : MONITOR.
What is not written on them (but is if one attempts to move them) is their weight : 85kg, each.
The honeycomb structure of the drivers were Technics' staple, just like Sony's earlier APM square drivers were ; the structure, however, is here very different and, yes, much cheaper.
The three controls set the level for the tweeter (+1/-6dB), high-mid (+2/-6dB) and low-mid (+1/-6dB) respectively, with an added but non-descript "min." setting for each pot.
A relay-activated protector sets in if the tweeter temperature goes too high ; a related LED is present on the front panel for indication.
The regular SB-M1 was available in a "civilized" dressing as well : it is the M version, made with a real wood enclosure and weighing even more than the regular SB-M1S (Studio) version.
The M version was not made available in Europe and I wonder if it even got produced at all, besides the one or two samples for the ads...