Ozzy,
The porcelain cable risers (nice looking- whitish base and brown top) are actually high voltage line insulators and as such they are brilliant. As a cable riser they are out of place due to the brown top- this is actually an iron ferrite glaze which in its intended role, acts as a conductive surface so that high voltage uninsulated wires do not spark when they come in contact with the insulator (in the old days when insulators were made out of either bear porcelain or glass they did spark). However when a speaker cable comes in contact with the iron ferrite glaze it creates an electromagnetic "bump in the road" that manifests itself as a thickening of the mid-range, loss of low frequency control, and a loss of air and slight compression of the sound stage when compared to either wood or Plexiglas cable risers.
Ideally you should look for a speaker cable riser that does not conduct electricity. If you live in an area that has a lot of static electricity, take a very thin wire and some electrical tape, give your speaker cables a few wraps with the thin copper wire (bare 28 gauge and not more then one or two wraps), and secure with electrical tape. Now place the bare wire in contact with ground- this will give your speaker cables a electrostatic drain without the detrimental effect of draping your cables over a conductive medium.
A good zero cost way for people to experiment with cable risers is to take 8 CD jewel cases (empty- CD's contain a metallic disk- usually aluminium) laying your CD cases in a "V" pattern on the floor 4 per 8ft speaker cable run. Now lay your speaker cables atop your CD case risers being careful to position the risers below each speaker cable in such a say as to allow the speaker cable to lay the way it wants to- not forcing it into a position if possible- this too will improve sound. Many people are surprised at the clarity and control this imparts to their speaker cables and best of all, its a free experiment.
Yours in music,
Ted Denney Lead Designer Synergistic Research Inc.