Hello Kitty Debunks Flawed EMC Theories from Exotic A/V Manufacturer
I often get bombarded with snake oil from some esoteric audio manufacturers (usually cable vendors). You gotta love this for two reasons: 1. debunking this nonsense is at the very core of why I started Audioholics nearly a decade ago. 2. It keeps your skills sharp making you think of how many different ways a misguided manufacturer can rape and pillage sound engineering principles in efforts to gain a selling point advantage.
This time around, I was not solicited by an exotic cable vendor, but instead a â€œhigh endâ€ furniture A/V rack company who will remain nameless in this editorial but will serve as an example of lunacy. I will show you how I disproved this vendors claim using my daughters Hello Kitty Radio and a cell phone.
Our shielded passive shelving system will redirect EMI/RFI noise of near field electronics providing up to 100dB of noise suppression from 100MHz to 18 GHz.
I thought it would be appropriate to give our readers some history of my background related to EMI/RFI as aside from my love of audio, I am well versed in RFI/EMI mitigation and countermeasures. I spent 3 years as a board designer for a major telecommunications company not only designing circuits but also testing products in EMI chambers to meet regulatory emissions of FCC/CISPR, etc. I also spent 4 years working for a defense contractor â€“ Raytheon, developing secure audio devices that not only had to pass FCC regulations but had ultra stringent requirements for isolation, HEMP hardening, TEMPTEST, etc. So as you can imagine, Iâ€™ve logged quite a few hours in EMI chambers and devising solutions to quite board designs and integrated systems down.
That being said, most competently designed A/V gear already does a good job at EMI/RFI noise suppression via proper board layout, filtered inputs/outputs, no right angle traces, plenty of ground plane, etc. This especially applies to the stuff that is certified and goes thru regulatory testing so it can be sold throughout the global marketplace. Thus, the extent of shielding needed in a rack in minimal if at all existent. I certainly never run across a situation that required it. As example I have a 7ft Middle Atlantic rack loaded with gear and I have never experienced noise or operational issues at all.
While I donâ€™t doubt their shelving system exhibits lossy parameters conducive of a good shield, unfortunately, their methodology of implementation into a rack is all wrong. A passive plate shield scheme found on their shelving system can at best serve as a partial shield for low frequencies such as radiated emissions from a transformer. But then again, most amplifiers use toroids whose far field radiated emissions are negligible since they are mostly self contained. There is NO possible way a passive shield such as this can even be marginally effective in the 100MHz â€“ 18 GHz range like the manufacturer reports in their white paper.
As a side note, the manufacturer would not allow me to redistribute or even discuss their white paper among my colleagues or readers as he fears some â€œevilâ€ competitor might copy his idea. Hmmâ€¦. He went on to further his case stating that this is an unconventional shielding methodology that few know about but is highly used by NASA and government contractors such as Raytheon.
Some Real Theory on Shielding
Ok back to this shielding stuffâ€¦ If their shield truly encases the noise source then yes it doesnâ€™t need to be grounded. However, if the shield is broken via gaps and/or wires connecting to the outside world, than if must be grounded to prevent it from radiating induced emissions from the cables which are coupling energy around the shield to the outside world. This is basic EMC 101. Remember this basic law that shield effectiveness is determined by the leakage at seams and joints, not by shield effectiveness of the material itself. Further, shield effectiveness decreases with the square root of the # of apertures and directly with the maximum linear dimension of the aperture.
EMI/RFI fields donâ€™t simply radiate vertically so sticking a lossy metal plate in free space wonâ€™t do anything beneficial. This isnâ€™t opinion, but well known fact based on sound engineering principles. As a reference, I suggest picking up a copy of â€œNoise Reduction Techniques in Electronic Systemsâ€ by Henry Ott and read Chapter 6.
To give the manufacturer a benefit of a doubt, I ran two experiments that he asked me to conduct from his colleagues, one being a professor at MIT and the other his physics guys in Germany or so he says.
Experiment #1: RF controller for my XBOX 360
Experiment #2: Portable Radio and Cell phone that you mentioned in a later email
1. I placed my XBOX 360 on the shelf below the shielded one. I then put my controller on top of the shielded shelf and had NO problems controlling my XBOX 360. I even reversed the game console and control on the two shelves, including varying distances and locations for the controller relative to the surface of the shelf. As suspected, the controller worked fine despite the manufacturers claims in their white paper that it would only work line of sight.
2. I took my daughter Hello Kitty AM/FM clock radio and placed my cell phone next to it while making a call. At certain positions of the phone antenna located in close proximity to the radio, I could hear distortion while the phone was receiving or transmitting. All I had to do was move the phone antenna about 3 inches away from the radio and the problem went away. Thus the only benefit of the shielded shelf in this case was it physically moved the phone away from the radio. I noted the same results between an air gap with no shelf vs the shelf thickness.
So as you can see, Hello Kitty once again saved the day by discrediting junk science. If you ever doubted the power of Hello Kitty, I hope this editorial serves as an example of her might. I certainly gained new respect for her and will keep this radio in my proverbial EMC toolbox for future installations and EMI mitigation troubleshooting.
The bottom line is this manufacturer makes a quality A/V rack. No doubts there. But their efforts to stand apart from their competitors has clouded their common sense and in my opinion credibility â€“ a similar pitfall of many exotic cable vendors. Build us a better rack/cable for a reasonable cost, drop the BS and let the consumer decide if the product is worth its coin. Conjure up marketing BS to justify an overpriced product and feel the wrath of Hello Kitty. Manufacturers be warned!