Well, it's clear that Lrsky and Balekan don't understand the test. Once again, a reference test was devised using the same software (CD of 1/3 octave warble tones), CDP, cables, speaker/positioning/room, microphone/meter/battery/tripod/positioning/decade-selection, and operator eyes, with the ONLY VARIABLE being the choice of amplifier. Three ss amps and one VAC AVATAR were tested. The three ss amps agreed with each other so closely in ALL results that it is easily said that they grouped as a "standard" curve. The VAC AVATAR's responses were extraordinarily different. I posted the results of two of the test runs in a previous post above, noting only the DIFFERENCE DATA from the ss amp to the AVATAR in each of the two test runs.
LRSKY, Everyone CANNOT "draw there own conclusions as to actually what was measured here"! What were measured were in-room responses of total systems, identical except for the substitutions of amplifiers. The difference-data was then plotted as a curve. It should appear as a straight line of zero slope, as it does between any two of the ss amps. When any of the ss amps is compared with the AVATAR the difference surve is as provided above. What the original data curves are doesn't matter, and of course WOULD differ dramatically would a change in ANY item in the reference system chain...especially a transducer (speaker or the test microphone) and/or its positioning. That's why I took GREAT pains to assure matched tested conditions for each pair of sessions. (Even test meter battery strength was assured). So now you understand that NO claims of linearity can be made for ANY amp in this test, as there is no absolute reference for linearity. Granted. Of course. I don't care. Nobody does. My only attemt was to validate what I heard empirically: the VAC significantly changed the sound of the Verity Audio speakers, and much for the worse (IMO), compared to other amps I had on hand. I wanted to see if I could bear this out spectrally, and indeed the results are all too obvious.
So Larry, I trust you understand that I wasn't attempting to measure amplifier output on an absolute basis. It's unnecessary in this case. Differential testing is much easier and at least equally valid, as common biases are eliminated. My background is in test methodology, so give me a nod here....
Balekan, you too misunderstand. The ss amps agree with EACH OTHER within a dB across the band, not with any other reference axis. Again, the actual curves plotted are pretty wild messes that combine the speakers in-room with the pretty serious errors of the SPL meter. But I've gotten good enough at REPLICATING test runs with this setup to be able to tweak crossover designs in 1/3dB increments in the past, so it's been a pretty subtle differential tool.
As others who use similar setups know head-movements account for the greatest amount of the imprecision of the noise-floor. The ss amps all agreed well within +/- 1dB of EACH OTHER as a group, which allows a conclusion ofan "ss standard" for this test, if you will. The two VAC curves agreed quite well with each other, also (I didn't test p level, as it's only two sets of data), and the differences between this data and the ss "standard" is so large as to be very significant, and remarkably audible.
Again, if you plot out this "difference" curve as provided above (either one...they look the same), you can get a sense of the acoustic analogue (no pun).
L&B, I'm trying to think of a good example to explain to you the differential testing method I used. If you and your buddy are having a race it's unnecessary to know far or how fast both of you have run to know who's ahead; you just have to measure the distance between you.
This setup has been used innumerable times by speakerbuilders, especially, to tweak their designs. Again, there's almost no interest in the ACTUAL reference level against 0dB, but only in what happens when you tweak a cap or resistor on that tweeter, for example. You rerun the curve, and look for a subtle shift in the results, and plot the difference data. Same thing applies for testing amps...especially those with high enough output impedences that could actually change speaker output spectrally. Again, the amplitude of the distortion here is what is so shocking, and I imagine said non-linearity was probably one of the reasons for the redesign of this amp. I didn't mean for this chapter to ambush the thread, but it's clear that
L & B didn't understand the test methodology nor the validity of the results. Thanks.
LRSKY, Everyone CANNOT "draw there own conclusions as to actually what was measured here"! What were measured were in-room responses of total systems, identical except for the substitutions of amplifiers. The difference-data was then plotted as a curve. It should appear as a straight line of zero slope, as it does between any two of the ss amps. When any of the ss amps is compared with the AVATAR the difference surve is as provided above. What the original data curves are doesn't matter, and of course WOULD differ dramatically would a change in ANY item in the reference system chain...especially a transducer (speaker or the test microphone) and/or its positioning. That's why I took GREAT pains to assure matched tested conditions for each pair of sessions. (Even test meter battery strength was assured). So now you understand that NO claims of linearity can be made for ANY amp in this test, as there is no absolute reference for linearity. Granted. Of course. I don't care. Nobody does. My only attemt was to validate what I heard empirically: the VAC significantly changed the sound of the Verity Audio speakers, and much for the worse (IMO), compared to other amps I had on hand. I wanted to see if I could bear this out spectrally, and indeed the results are all too obvious.
So Larry, I trust you understand that I wasn't attempting to measure amplifier output on an absolute basis. It's unnecessary in this case. Differential testing is much easier and at least equally valid, as common biases are eliminated. My background is in test methodology, so give me a nod here....
Balekan, you too misunderstand. The ss amps agree with EACH OTHER within a dB across the band, not with any other reference axis. Again, the actual curves plotted are pretty wild messes that combine the speakers in-room with the pretty serious errors of the SPL meter. But I've gotten good enough at REPLICATING test runs with this setup to be able to tweak crossover designs in 1/3dB increments in the past, so it's been a pretty subtle differential tool.
As others who use similar setups know head-movements account for the greatest amount of the imprecision of the noise-floor. The ss amps all agreed well within +/- 1dB of EACH OTHER as a group, which allows a conclusion ofan "ss standard" for this test, if you will. The two VAC curves agreed quite well with each other, also (I didn't test p level, as it's only two sets of data), and the differences between this data and the ss "standard" is so large as to be very significant, and remarkably audible.
Again, if you plot out this "difference" curve as provided above (either one...they look the same), you can get a sense of the acoustic analogue (no pun).
L&B, I'm trying to think of a good example to explain to you the differential testing method I used. If you and your buddy are having a race it's unnecessary to know far or how fast both of you have run to know who's ahead; you just have to measure the distance between you.
This setup has been used innumerable times by speakerbuilders, especially, to tweak their designs. Again, there's almost no interest in the ACTUAL reference level against 0dB, but only in what happens when you tweak a cap or resistor on that tweeter, for example. You rerun the curve, and look for a subtle shift in the results, and plot the difference data. Same thing applies for testing amps...especially those with high enough output impedences that could actually change speaker output spectrally. Again, the amplitude of the distortion here is what is so shocking, and I imagine said non-linearity was probably one of the reasons for the redesign of this amp. I didn't mean for this chapter to ambush the thread, but it's clear that
L & B didn't understand the test methodology nor the validity of the results. Thanks.