A listening test of two power amps

BTW, I don't believe in static tests very much.

That is, as a builder I use static tests such as frequency sweeps, voltage, etc. to guide my work, but I also know that these types of static tests may not cover all possible dynamic situations.  By this I mean frequency response, output, distortion.

We use these static tests and basic models because they are damn convenient and accurate for what they are, but the testing I'd want to see done, which I never see done, is to compare the output at the speaker or across the speaker cable with actual music.  With demanding speakers or loads we may very well see and measure dynamic behavior which is more complicated and unexpected based on the traditional static measurements say taken by Stereophile. 

@erik_squires "1. Match level by multimeter instead of SPL. Get a 60 Hz signal and check the output on either speaker. You can get really accurate this way."

I am a little ambivalent about using 60Hz sine and voltage to verify output level balance. It can tell you something about what an amplifier is doing, and something about speaker efficiency, but I am not sure it can translate into anything about sound quality. There is also the problem of ensuring the meter you are using is measuring true RMS versus average AC voltage. If you are trying to use that method to balance output level, I think you would be better to use pink noise which has a full frequency range. Measurement becomes more of a problem, but it more closely resembles what you may hear when converted to sound using real music. In other words, since speakers are a reactive load, frequency and duration affect response and the amplifier’s drive of voltage across a frequency and time response will vary and may affect actual perceived sound volume.

I don’t really understand why SPL would be frowned upon. It is specifically an agreed measurement of perceptual sound volume reference. It is tailored for a specific frequency range and can be A or C balanced for perceptual preference favoring broad frequency response (A) or lower frequency weighted (C). The only caution for use in this testing is that the ambient noise level is maintained the same, and the SPL is taken from the same location in the same environment. If you are within 0.1 or 0.2 db that is considered well matched.

The anti-testing and anti-measurement crowd certainly makes an impression. It's a good thing those folks aren't doctors or pharmacologists, or we wouldn't have gotten any further than "which medicine do I think makes me feel better..." [which, back in the day, is how people chose which, literally, snake oil product they'd consume]

I think it's a great post and even if not scientifically perfect, this is the type of thing that can actually validate all these claims of magnificent differences in amps, cables, whatever. So I have to assume they don't want to know what the emperor is wearing, or not. 

OP:

It’s your experiment, but as someone who worked quite a bit with microphones and speakers and electronics, the advice I gave you is solid.

Measuring the SPL of quasi random white or pink noise is hard to get precisely accurate, it’s even hard with a multi-meter, which is why level matching should be done with a multimeter and single signal.  60 Hz is a frequency which is convenient as any $10 multimeter will read it, and all are more relatively accurate IMHO than an audio meter, given they are not subject to random room noise or the periodic variability of white/pink noise sources. Level matched experiments comparing DAC’s for instance should be level matched this way and with a decent meter will give an accuracy well better than 0.1 dB.

Now, once we agree to use a multi-meter, and a standard sine wave, whether they measure RMS voltage accurately, peak or peak to peak is irrelevant so long as they are absolutely RELATIVELY accurate. That is, you can trust that 3V now will be 3V in an hour after you switch amps.

Also, with a 60 Hz sine wave signal, again, any $10 meter will measure the voltage pretty accurately and almost perfectly relatively accurately. A nice meter will give you more zeroes.

@surdo 

Finally got to due a little more compare of the e & t files. My first try was at a lower volume than I think should be used for comparison. First pass at that low volume, file e was much better than t, but on replay, t was closer to e than first pass of either. Maybe my electronics were not fully warmed up.

Today played at more reasonable listening level, and also played through headphones. Both files very close overall. Occasional portions sound a little better on one or the other. In general, I like the piano sound (tibre, resonance, attack) better on e than on t, but that is mostly from middle C and above. Lower octaves may be slightly better on t. Bass very close on both. Drums and Drum kit too low in volume and too far in behind piano and bass to judge.

In general, I think most of the differences may be more environmental and microphone, rather than effects of either amplifier and connection. Note especially squeaky wheel/bird song audible on file e from about 4’43’’ to 4’51”, but missing on file t.

So in all, I think you tried an interesting experiment, but I can only tell you about what I can hear differently on the 2 files, and I think there may be more environmental artifacts in the two files than you were hoping for. Some may even be from the microphone and tascam reaching a thermal equilibrium, as well as the electronics and the room. Not sure I would hear the same things if I were in the room listening without the microphone and Tascam involved, so I think any of my comments about the files should be discarded.

@erik_squires "It’s your experiment, but as someone who worked quite a bit with microphones and speakers and electronics, the advice I gave you is solid."

As I said, I am ambivalent regarding matching amplifier out at speaker via 60HZ for amplifier compare. 60Hz sine voltage matching thru the rest of the audio chain is a really good way to compare different pieces of the chain. It is also a good reference for speaker efficiency. For all that is going on between and amplifier and speakers I am not sure it takes everything into account. 

I would love to see a graphing/charting of 60Hz voltage matched amps to the same speakers done in an anechoic chamber with dbA and dbC with some wide frequency music to see the active perceptual effects. Know anyone that can perform this kind of testing? Will see if I can find anything regarding similar testing.