I have a pair of bookshelf speakers that have an “ESS” emblem on the front (see picture below). Has anyone ever heard of these before? They are in great condition except on the back there is a big hole on both cabinets… almost like there used to be a passive radiator there before. Inside there is sound dampening material with little chunks of what looks like old pieces of speaker surround foam (which supports my passive radiator theory). Not sure what the deal with the missing passive radiator or whatever on the back is, but if I could find out a little about this brand maybe that would be a start? Thanks.