Source: Tom's Guide US | Keywords: decibels, noise, canceling | Themes: Audio/Video Players
11. Enter the Chamber
In years past there has been considerable and better-founded debate surrounding CRT monitors. However, the electromagnetic emissions from CRTs have been found to be nominal and totally non-harmful by every reputable study I could find. Government controls on CRTs refer back to the Code of Federal Regulations, title 21, section 1020.10, which governs televisions and states that “radiation exposure rates produced by a television receiver shall not exceed 0.5 milliroentgens per hour at a distance of five (5) centimeters from any point on the external surface of the receiver.” This regulation became effective in 1970 and has governed not only TVs but computer CRT monitors ever since. And in terms of radiation, TFT LCD screens are far safer than even CRTs, and so the issue of computers displays being hazardous due to electromagnetic radiation is effectively dead.
So much for monitors, but what about the rest of the system? I had my doubts, but to really put matters to the test, I needed two things: 1) a testing facility and 2) an acrylic case. Not just a windowed case with only one side that lacked the benefit of shielding metal, but a real wall-to-wall clear case often used by gamers that would offer no more radiation protection than a case-less config lying open on my test bench. Intel was kind enough to offer the use of one of the EMI test chambers in its Hawthorn Farm 3 building in Hillsboro, OR and its resident testing expert, Mike Haines, to go with it. Logisys Computer generously contributed its CS888UVBL UV-reactive clear case. Some will find it relevant that this chassis features four case fans, and I made sure we had all four spinning during testing with the side panel screwed into place, just as you’d have during normal operation.
That massive antenna you see shown here scans for electromagnetic radiation in the roughly 30 MHz to 2 GHz range, which is what regulatory bodies such as the FCC want to examine. The system table is mounted on a turntable. During testing, the table rotates so that the antenna can have a 360-degree view of the system. This way, if you have emissions escaping from the back or side, these will be captured, as well.
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One word: Google.
Gosh, we're not the general public... we're nerds
correction, physical pain doesn't set in at 130db, feeling sets in at about 130 db, so that bass that you feel thumping is above 130db, but since volume is a function of decibels and frequency it is very quiet. but children wailing is very high pitched so them at 80 db is significantly louder than the bass in your car. if you want to learn more than just do some more googling around. try searching "volume"
A clarification on ANC theory. There is no "anti-noise" generated. Ambient sounds strike the speaker cone moving it. Essentially the ANC signal applied to the diaphragm resists this motion of the cone, holding it still. Without movement the sound energy is dissipated as heat on the back surface of the cone. It is not canceled out in the classic sense, the compression and rarefaction of sound waves are mechanically destroyed.
One more really simple thing to add here. Put some really high-quality foam earplugs in your ear canal AND use your ANC headphones. This is what I do when I fly (Bose QC2's and custom-fit plugs). You've got to have enough sound without distortion in your headphones to overcome the attenuation of the plugs but for the most part their response curve is flat (if not a bit high on the low end). So your tinny-sounding earphones are actually going to have a bit more bass overall.
I've also been known to wear my Shure earbuds under my QC2's but they stick out far enough that I have to be careful not to touch them against the inside of the headphones. The nice bit is that even sitting in the back of an MD-80 I've only got to put my iPod at about 25% volume to hear every detail.
Shures with QC2 sounds like Heaven...assuming Heaven is a very quiet place. :-)
Regarding joeman42's comment, first, I'm going to say that I am definitely not a sound engineer nor any kind of other acoustic specialist, so the depth of my understanding may need improvement. However, the description I gave of ANC fits every description of the technology I've been exposed to over the years. For example, check this paper: http://doctord.dyndns.org:8000/Pubs/POTENT.htm, which describes the ANC process like so: "the noise is modeled to produce an anti-noise waveform at the output speaker." Given this guy's title as Vice President of R&D for Noise Cancellation Technologies, Inc. and the fact that this paper appeared in an IEEE publication, I'm pretty confident of the source.
Another very entertaining article from you.
“(Once again, you can tell something about the quality of a site’s content by the frequency of typos and errors in its text.)”
You might want to change that line before someone of bestofmedia knocks on your door and gives you a kick in the nuts when you open.
Another very entertaining article from you.“(Once again, you can tell something about the quality of a site’s content by the frequency of typos and errors in its text.)”You might want to change that line before someone of bestofmedia knocks on your door and gives you a kick in the nuts when you open.
Yeah, I can add that to the list of reasons I've given them. ;-) But really, you can tell the difference between a rushed schedule and borderline illiteracy or outright disregard for quality. If I've got to take one in the giggleberries for saying that Web sites in general need better quality control, so be it, but I think Bestof has a good crew that does good work. I'd rather have a few typos and solid reporting from people who care about the readers' best interests than a lot of the over-polished, under-thought dreck common in the field.
Thanks for the kind words.
Interesting article
I have hearing loss. I was born since birth, and therefore, I can't use headphones or go to rock concerts, lest I risk damage to my ears. I have never used an i Pod for more than a few minutes, and I'm glad.
I'm 15 years old, and I estimate that by the time I'm 40, my generation will have worse hearing than me. I'll be laughing "I HAD hearing loss BEFORE it was POPULAR!"
I should hope so.