Bill, W4ZV wrote: "Guy, K2AV wrote: > > If one wants to dig up the research... >
http://www.audioholics.com/education/acoustics-principles/human-hearing-amplitude-sensitivity-part-1 "Speaking now in terms of dB SPL, the minimum discernable changes by the human ear/brain mechanism I've seen in the research that I've reviewed ranged from about 0.5 dB to 3 dB, depending on a number of factors." Table 1 (see the referenced link above or below) ...SNIP..." That someone can, with certain individuals and certain conditions detect less than 3 dB, I would not dispute, any more than I would dispute a Beethoven or John Williams. This is taken into account in the same article you referenced above. ***EMPHASIS ADDED***: ----begin reference quote ----- "For example, Reisz in his 1928 study used two tones, close in frequency that beat slowly. The beating caused amplitude fluctuations and the minimum audible fluctuation was ~ 1dB. Toole and Olive, on the other hand, in their 1988 study used pink noise for their acoustic signal source and determined that a 5 kHz resonance, with Q = 1 was just detectible at .25 dB. They found pink noise to be the most revealing signal. ***THEY DID EMPLOY OTHER TYPES OF ACOUSTIC SIGNALS IN THEIR STUDY*** and discovered that ***WHEN USING THE LEAST REVEALING*** of these that ***JUST DETECTIBLE THRESHOLD INCREASED BY A FACTOR OF 5***. >From the third column of Table 1, we see the ***MINIMUM** detectable value, for the most part, hovers around 1 dB, +/- a fraction of a dB, and and that attainable ***ONLY*** with ideal (or at least as ideal as technology allowed for at the time the study was done) ***[IDEAL] LABORATORY TEST CONDITIONS AND [IDEAL] TEST SUBJECTS.*** I tend to use .75 dB to 1 dB when considering minimums." ----end reference quote---- When using the least revealing of these acoustic signals Reisz detectible threshold increased by a factor of 5. 5 dB or 5 times the voltage? Either way that's a huge handicap for not having ideal conditions. Show me something less ideal than QRN based noise varying 20 db on 80 or 160, a pile up half composed of hams that used ctrl-arrow/F4 and a spot to drop on exactly the same frequency as the DX. And then remember it's THEIR ears we're talking about, not ours. We are not talking about ideal laboratory test conditions, or ideal most talented test subjects or about the best possible result. Reisz' work was available to Bell Labs when the 3 dB maintenance standard was decided upon. The "lab" the phone company was going to have to spend money on (lots of it) was the real world. The Bell System decided that if it got to be 3 dB they would hire employees, buy test equipment, pay salaries and lay away for retirements to fix it. If it's 3 dB or leads to three dB it has to be fixed. In my experience in the phone company, they WOULD fix the 0.2 in a bad (wrapped but not soldered) connection, the 0.4 in a coil gone bad, the 0.9 in a soft tube, but they would find it looking for 3 dB or maintaining components to a 3 dB overall performance. Overall connections less than 3 dB off were in the "ain't broke don't fix it", let maintenance snug it up whenever it happens category. Maintenance was the least expensive way to stay inside 3 dB. And they had gain controls to suck up a fair amount of routine variation. This is no different than picking appropriate feedlines for antennas, soldering coax shields in PL259 connectors (be surprised how many don't), etc, etc. We COULD see 0.1 dB in our AT&T themocouples and line meters but we wouldn't patch a circuit out of service and ticket it for 1 dB. Wasn't that where we started this discussion, at what dB do we spend money on it? At the time, with Reisz' work in hand, the phone company that the rest of the world envied, that had the labs that gave us the transistor, picked 3 dB. And still, no one talks about the 27 dB between the ears. What was it they called a lid with an amp? A loud lid? How smart is it to ctrl-arrow/F4 and call DX on exactly the same frequency as ten other stations that did the same thing. What's that worth? Minus ten dB? Minus twenty? I've heard a QRO east coast multi, with 4 over 4 on forty at 100' and 200' braying zero beat to the F4 mob and getting beat six or seven times, including by one guy I know was running a wire antenna. There is some ancient wisdom still around that hasn't lost its lustre. YMMV and everyone entitled to spend their money however they want, but I'm saying it takes a smart op (one of those "ideals" that Reisz was talking about) to make 1.5 dB pay for itself 73 all, and may you always work the DX. Guy. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
