I have never owned a pair of Sound Dynamics speakers but being a teenager in the 70's and 80's quite a few of my friends have owned them and are as far as I am concerned a quality great sounding speaker.
The local audio store where I grew up would almost always include Sound Dynamics speakers when someone would buy a Marantz powered setup from them and they always sounded great.
About a year ago at a thrift store I came across two pairs of Sound Dynamics one large pair and one pair of real nifty and heavy bookshelf size speakers (don't remember any model numbers). I had/have no room for the larger pair but I really wanted the smaller pair, they needed refoaming for sure and I wanted them to be my very first refoam job. But the tag on the speakers said both pair had to be sold together, I asked the guy if I could just buy the small pair but he wouldn't separate them no matter what. So I walked out with no speakers, but I still think about them now and then and if I see another pair I will grab them for sure.