Although we are talking about an entirely different field of “filters” I must comment that many of my commercial clients for hvac filters have begun discussing the “harmonic filter” issue frequently. Out of curiosity, I did some research and find that this article is likely the most comprehensive one on the net regarding this subject. Admittedly, I do not have the brain power to intelligently discuss this issue. But I must say that anyone who does have that capacity has a Texas “hats off to you” salute for your level of intelligence and comprehension. Now I know what blog to recommend to my clients I will surely send some traffic your way! Best regards! John Mauldin, Dallas, Texas