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Micke Y
100.000-klubben
7709 Posts |
 Posted - 2004/09/20 : 10:06:17
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Jag såg den här frågan på Audioasylum.com och tyckte svret var så kul att jag undrar om någon har testat den här mätmetoden??
Fråga
Are there any standard measurements that measure the deviation of the output from its input in the time domain across the entire 20Hz-20kHz spectrum for amplifiers and source components and are these measurements in use in any publicly available magazines?
Svar
I you measure the phase from input to output over the range, you will effectively have a time delay reading. Might take a little conversion from phase angle to time, but it's an easy calculation.
OR, you can use one of the really old tricks from the 30's. Use an oscilloscope as an X-Y plotter with the input on the vertical axis and the output on the horizontal. For a perfect amplifier, what you get is a straight line at 45 degrees that gets longer and shorted as the level changes. At clipping you get little vertical "wings" on the ned of the trace. Any time shift or phase shift shows up as the line changing to an oval. Non-linearities show up as curvature or kinks in the line. Reportedly, this method correlates extremely well to audible changes. (if it makes a sonic difference, you can see it) And that has been my experience with the method. I have used this a number of times over the last 35 years or so, and it is very effective. All you need is an oscilloscope with X-Y capability. That was hard to get in 1967, but easy to find today. It works best if the amplifier is loaded with the speaker you plan to use. The input signal is music. There is no need to use test signals. So with your speakers connected, and real program material going through, you get to see what's happening under actual conditions.
This method is described in the old Radiotron Engineer's Handbook, 1953 copyright.
Jerry
Micke
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