Roger Sanders who designs and sold electrostatics once explained to me that a speaker that is 4ohm say with a rating of 94db (Decwares I used to have) are not really 94db efficient because of the 4 ohm rating. I Don't recall what his current company is now. What had got my attention though is he was pretty determined in explaining how that works and unfortunately I can't recall how to explain that. It did have me feeling a bit though that speaker manufacturers are mis representing . I do remember that he said for the db rating to be as stated it has to be for example -- 96db @ 8ohm 1 watt/1 meter.