“I’m redesigning and installing my studios patch bay and it’s time to do the S/PDIF lines. I went out and bought some Belden coax and thought that it was 75 ohm, but found out just as I was about to start making my cables that the cable is 50 ohm. My question is, will this be a big problem considering the cable runs are about ten feet from equipment to bay?”
It depends on what constitutes a big problem for you. First, your 10-foot lines to and from the patch bay dictate that your actual cable runs will be at least 20 feet long in practice. A 20-foot S/PDIF cable is not trivial, though it’s not a huge problem either. The spec does call for 75 ohm cables, but considering many users get by with standard phono style audio cables one can clearly see there is some tolerance. So if your definition of a “big problem” is no signal passing at all you probably don’t have to worry about that. The connection points are more critical to this than whether the wire is 75 or 50 ohms.
However, if you are a nut about sound quality and mad about reducing jitter and other problems caused by poor cabling (among other things) then you probably will want to get the proper cable for the job. Will you hear a difference? Obviously there is no way for us to answer this question for you. Some people claim to be able to hear differences in the types of batteries used in guitar effects pedals. Some people use cheap molded cables of unknown impedance for S/PDIF connections and say it works fine. Your call.