Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Shakti Stones test data
Have any of the EE types here looked at the results of a test
of the Shakti Stone's ability to attenuate EMI, posted on the company's website? http://www.shakti-innovations.com/emitests.htm Googling doesn't seem to show any discussion of same in the audio newsgroups. Since I can't make heads or tails of the graphs as presented (to answer even simple stuff like, how big is the measured effect?), I'm curious to hear the opinions of those who can. These results, btw, are being used to bolster the claim that Shakti Stones might work, over on audioasylum, in the Randi threads. |
#2
|
|||
|
|||
Steven Sullivan wrote:
Have any of the EE types here looked at the results of a test of the Shakti Stone's ability to attenuate EMI, posted on the company's website? http://www.shakti-innovations.com/emitests.htm Googling doesn't seem to show any discussion of same in the audio newsgroups. Since I can't make heads or tails of the graphs as presented (to answer even simple stuff like, how big is the measured effect?), I'm curious to hear the opinions of those who can. These results, btw, are being used to bolster the claim that Shakti Stones might work, over on audioasylum, in the Randi threads. Well, if you place a piece of metal over a transmitting antenna, you will perturbate the field pattern of the emissions. Would you think that putting a piece of sheet metal somewhere around the stereo system would improve the sound? The test conducted is really meaningless. If you look carefully, the received strength is actually higher at the bottom of the band, around 312 MHz. If they want to prove that effectiveness of the stones, conduct audio measurements with and without the stones. Measure frequency response, signal-to-noise ratio, distortion, etc. You know, things that have something to do with audio. |
#3
|
|||
|
|||
In article ,
Steven Sullivan wrote: Have any of the EE types here looked at the results of a test of the Shakti Stone's ability to attenuate EMI, posted on the company's website? http://www.shakti-innovations.com/emitests.htm Googling doesn't seem to show any discussion of same in the audio newsgroups. Since I can't make heads or tails of the graphs as presented (to answer even simple stuff like, how big is the measured effect?), I'm curious to hear the opinions of those who can. These results, btw, are being used to bolster the claim that Shakti Stones might work, over on audioasylum, in the Randi threads. The elephant they're trying to hide in plain view is this: So a big slab of apparently solid material placed directly on the radiating antenna attenuates the signal. This is supposed to be a surprising and significant result why, exactly? It is not exactly an unknown phenomenon that solid matter blocks radio frequency EM radiation better than air. Where are the comparisons to other materials and especially other shapes? I'd like to see a comparison to, say, a simple Faraday cage made of ordinary sheet steel or aluminum. (More on that below.) A quick & easy attenuation demonstration you can perform with no expensive equipment: Take a cellphone with an external antenna, preferably the extendable type. With the antenna extended, note how many bars the signal strength meter is at. Now, without changing the position or orientation of the phone (either of which can change signal strength all by itself -- you only want to test one variable), close the fingers of one hand around the antenna so that it is surrounded on all sides. In most cases you'll lose at least one bar on the signal strength meter, if not more. (Be sure to give it some time to settle for both readings; I just did this with my phone and the meter has a multi-second lag time.) For a cruder demonstration, just walk inside a cave. I mentioned Faraday cages above. These are nothing more than conductive enclosures around an EMI source which cover it on all sides. A Faraday cage must have no openings larger than the minimum wavelength the cage is expected to contain. Holes smaller than that do not significantly affect how much radiation escapes. Faraday cages are by far the most common method for reducing EMI in consumer electronics, since you get one for free if you build your product's enclosure out of metal. For a great example of how much you can puncture a Faraday cage without reducing its effectiveness, take a look at Apple's PowerMac G5. This brings me to the next elephant Shakti doesn't want you to notice. The major issue in designing an enclosure to contain EMI (or prevent its entry) is simply avoidance of holes or slits larger than the critical length. Problems typically arise wherever the enclosure is punctured for connectors, user controls, and so forth, because many of these items are large enough to form exit/entry paths. The theme you should be getting here is that EMI problems require fully enclosing a device and paying attention to all possible paths in and out. But the Shakti Stone is just a slab or bar which cannot possibly fully enclose anything! For all I know it may do an excellent job blocking what heads in its direction, but it does absolutely nothing for any other path. It's like saying that if you put a 3x3 inch square of cardboard next to a naked 100 watt bulb, you've successfully blacked out that light. Well, no, you haven't. You've blocked some paths for light to leave the bulb, but plenty of light will radiate out all the other angles that are still open. Even objects in the cardboard's shadow will typically receive some light that originated at the bulb, due to diffuse reflections off other surfaces and so forth. And that analogy isn't actually an analogy! Light and RF EMI are both examples of electromagnetic radiation. The principles are the same in both cases; the main difference is that visible light is at much higher frequencies (shorter wavelengths) than RF EMI. Please feel free to repost this on audioasylum if you like. -- Tim |
#4
|
|||
|
|||
In article , Timothy A. Seufert
wrote: The elephant they're trying to hide in plain view is this: So a big slab of apparently solid material placed directly on the radiating antenna attenuates the signal. This is supposed to be a surprising and significant result why, exactly? It is not exactly an unknown phenomenon that solid matter blocks radio frequency EM radiation better than air. Where are the comparisons to other materials and especially other shapes? I'd like to see a comparison to, say, a simple Faraday cage made of ordinary sheet steel or aluminum. (More on that below.) In fact, the "stone" probably didn't attenuate the signal at all. The most likely thing to have happened is that it changed the impedance of the antenna. This would have increased the VSWR so that less energy got to the antenna to be radiated. To any engineer at all familiar with EM and especially with EMI the idea that placing a material in proximity to a piece of electronics will significantly and reliably change the EMI environment is laughable. You might as well chant "EMI go away" while dancing naked. Marc Foster (Designing and analyzing antennas since 1979) |
#6
|
|||
|
|||
On 29 Nov 2004 04:16:26 GMT, Steven Sullivan wrote:
Since I can't make heads or tails of the graphs as presented (to answer even simple stuff like, how big is the measured effect?), I'm curious to hear the opinions of those who can. I can. The graphs show clearly that with the shakti stones applied on or near the device under test, or in the same room as the device under test, the curves are lower than without. So we have, eh, lower MHz noise floors. And, if you have looked further on, your car will run faster, or better, as much as 6 mph. The next huge improvement will be reached when you place a shakti stone on your head. As you will know the brain produces a lot of electric noise, which causes all kinds of stray fields and uncontrollable electromagnetic eddies in and around your head. Wearing a shakti stone in a hat on your head, will concentrate and absorb those eddies into the stone, where this spurious energy will be transformed into heat (a nice side effect during the dark and cold winter days), leading to less distortions in the brain and hence to CLEARER THINKING. Also recurring bouts of winter depression will be alleviated. Ernesto. "You don't have to learn science if you don't feel like it. So you can forget the whole business if it is too much mental strain, which it usually is." Richard Feynman |
#7
|
|||
|
|||
|
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
What are they Teaching | Audio Opinions | |||
A comparative versus evaluative, double-blind vs. sighted control test | High End Audio | |||
Comments about Blind Testing | High End Audio | |||
Mechanic blames amplifier for alternator failing?? Help>>>>>>>>>>> | Car Audio | |||
Richman's ethical lapses | Audio Opinions |