All aftermarket speakers are four ohms and coaxial (two way,with a tweeter for highs). Almost all coaxial speakers are made "off shore". We do not make these in the U.S. Most are made in South Korea because of the low cost. Although huge advertising would lead us to think that a particular coaxial is much better, the truth is the major difference is the efficiency, which is why some seem to play louder in the stereo store. Most of us buy speakers based on what they look like....imagine! There are several very fine quality coxial speakers that always cost more. Some of these are MB Quart, Focal, Dyneaudio, Morel, and the new JL speakers. These speakers are not Asian made. The front car speakers are 4" and the backs are 5", but aftermarket speakers come in 5 1/4" and fit fine. The metal clips must be removed from the cylindrical mount before laying a bead of silicone adhesive around the edge. Simply press the 5 1/4" speaker onto the silicone and replace the grille. Ancient Becker Grand Prix radios do not have a four ohm output but all aftermarket CD head units are four ohms...a perfect match! P.

 

http://www.mercedesshop.com/w124_stereo_removal.htm
Try this.
Gman