these look like LSI industrial speakers , the right round k77 is Alnico ,1970's , the bottom left K77 is 79-80, the other 4 silver ones are 80's k77 , they are not tagged as K77M --------but all square magnets are ferrite magnets - all aftermarket k77 diaphragms fit -5$ each , for all these tweeters -and it takes a 15 minutes to solder -screw-test per unit