moving system of the mid-range speaker 20gds-3 of soviet production. diffuser and magnetic coil speaker

audio equipment mobile system midrange speaker 20gds3 soviet production diffuser magnetic coil suspension repair 20gds 15gd11 basket cap magnet ferrite vintage frequency revision upgrade professional tweeter studio sound technology loudspeaker metal decoration bass reflex texture back rectangular record object monitor old radiotehnica box radio engineering small party subwoofer 1985 wooden factory