Oh yes the AR 18S, now there is a subject dear to my heart. In fact these are my favorite small bookshelf speaker. Did you know there are are two different varieties of the 18S. The original version on top and the newer one on the bottom.
Here are the differences I can see. The newer version is 1/2 in wider. Has a terminal cup instead of a standard spring strip and the plastic woofer ring is outbound instead of recessed like the original. They all come with the 5uf NPE cap, fiber fill instead of fiberglass, and vinyl covered cabinets. Why not drag all my 18S examples out. Two of each variety.
The first thing I do is re-foam the woofers with surrounds supplied by Rick Cobb. I believe they are the correct foams. Replace the 5uf with 5.1uf Daytons. Replace the spring clips with binding post from Parts Express. I have the binding post terminal cups for the newer version, but haven't got around to it yet because it will require slightly larger holes and re-positioning the caps. Did I say I really like these speakers. I have a 18B and Rock Partner example. Have not run across the 18 model yet. Not interested in the the other versions. I like the way the 18S model has inline drivers.