Audio Science Review = "The better the measurement, the better the sound" philosophy

By crymeanaudioriver:

@fair  -- All that typing, and all that work, but not even a minute of research to understand why a resistive load is used for amplifier testing.

"Cute", isn't it? A typical example of a "gentlemanly" statement considered normal at ASR these days.

It took me a bit longer to understand this item. I think I spent almost 30 minutes, but now I am comfortable with the answer.

At this point a replying person usually goes into explaining what relevant educational, professional, and life experiences he had over prior 30 years to come to his understanding of the issue at hand. I know better now. I won't.

I also know now that everyone uses resistors for testing including Stereophile. Stereophile has a simulated speaker load, but this measurement provides no additional information that cannot be ascertained in other measurements.

This is emotionally a very strong, and technically a very wrong statement. For details, please see:

https://www.biline.ca/audio_critic/mags/The_Audio_Critic_20_r.pdf (page 16 on)

and

Measuring Power Amplifiers with Reactive Loads

I quickly found at least 6 and probably there are many more discussions on using complex loads for amplifier testing on ASR. I had to Google to understand some of the terms, but I muddled through. Even the stronger proponents of complex load testing, after the discussion progressed, agreed it was of limited and would only be valuable with an extreme speaker and a marginal amplifier.

I did such search too, yet got quite different results. There are a number of threads where the issue comes up, yet remains unresolved. For instance:

hypex power ratings

What is it about McIntosh?

KJF Audio MA-01 Review (Multi-channel Amplifier)

Review and Measurements of Accuphase E-270 Amplifier

 

One thread, dedicated to the subject, appears to be expressing virtually all conceivable points of view, yet it is inconclusive as well. Also, quite a few replies there were redacted: one can see quotations from them and references to them, but not the original replies in their entirety.

Complex Load for Power Amplifier torture testing

 

I thank you for encouraging me to look into this as I sort of understood it, but had not delved deep enough. It was a less complex topic than I was expecting.

Here we differ too. As technical as the dedicated ASR discussion thread was, it didn't touch on stochastic behavior of non-linear time-dependent systems, of which a practical multi-transducer loudspeaker is a prime example.

Attaching such a system to an approximately linear, approximately time-independent power amplifier leaves the combined system still non-linear and time-dependent.

The math describing non-linear time-dependent systems is far more sophisticated than the one underlying the simple measurements that Amir uses.

Providing strings of measurements that all demonstrate factors beyond anything that can be heard by anyone or have any effect whatsoever on the sound that can be heard is totally futile, making decisions on such data is totally ridiculous.

@fair 

https://www.biline.ca/audio_critic/mags/The_Audio_Critic_20_r.pdf (page 16 on)

A lot of trash in this collection of articles unfortunately. Interesting that you linked to the specific article on the power cube. They say in that article,

We do not perform such separ-
ate IM distortion tests here because they characterize the
same nonlinearities identified by the THD tests. A non-
linearity that gives rise to a high 20 kHz THD will also
cause inband distortion products in a multitone test. A
full-scale 20 kHz test has the advantage that it has the
maximum rate of change of any inband test signal and it
characterizes both even- and odd-order nonlinearities
[Borbely 1989], [Jung 1979]. Transient intermodulation
effects [Otala 1970] are also covered in this test.

I assume you agree with all that written above as well, or only what suits you? 

The article you link talks, often, about the performance of the current limiter inside the amplifier. If the amplifier is running into a current limit, it is clipping. If you are running your amplifier into clipping, then you are beyond the limits of the amplifier.

Note the only example they show of oscillation, the issue yielded by non-resistive tests, shows oscillation occurring at 2 ohms, 60 degrees, and 1 ohm 30 and 60 degrees. This is important as it relates back to this article on ASR you linked:

Complex Load for Power Amplifier torture testing

This specific issue is discussed, as they talk about how many speakers have both very low impedance and very large phase shift. The conclusion is very few. Hence why the consensus that resistive testing into low enough impedance is sufficient. Elsewhere there is a call to include 2 ohm testing which I think I have seen on some more recent tests.  It is probably important to identify from the articles linked that the worst issues are with tube amplifiers, lauded by audiophiles and rarely tested by ASR. When they are, the result is not positive.

The other threads you posted from ASR are primarily not technical discussions about testing, but more banter from what appears to be the less technical members. Not everyone on ASR is technical.

Also, quite a few replies there were redacted: one can see quotations from them and references to them, but not the original replies in their entirety.

If you are going to participate in a thread putting down a web site you should probably learn how that site works, or at least the "Click to expand" button. There is nothing redacted. The forum has a very good quote and reply system unlike another one I am thinking of.

 

Here we differ too. As technical as the dedicated ASR discussion thread was, it didn't touch on stochastic behavior of non-linear time-dependent systems, of which a practical multi-transducer loudspeaker is a prime example.

Attaching such a system to an approximately linear, approximately time-independent power amplifier leaves the combined system still non-linear and time-dependent.

The math describing non-linear time-dependent systems is far more sophisticated than the one underlying the simple measurements that Amir uses.

At first, that appears to be a lot to unpack. However, it can quickly be taken as a deflection. The topic at hand is the test of amplifiers. Specifically in this case resistive testing.

Attaching such a system to an approximately linear, approximately time-independent power amplifier

This negates all the other words used in the last paragraph. By your admission, the amplifier is time independent, approximately at least. That a speaker is not, is not relevant to the discussion. The only relevance would be if speakers drifted from a maximum of 30 degrees phase shift to 60 degree when they got hot and this is not identified in the ASR discussion linked. Is that what you are claiming? 

Providing strings of measurements that all demonstrate factors beyond anything that can be heard by anyone or have any effect whatsoever on the sound that can be heard is totally futile, making decisions on such data is totally ridiculous.

 

@henry53 the only way to interpret your statement above is that ASR is measuring to sufficient accuracy to far exceed human hearing. In a PM, you also stated -80db IMD is also inaudible, so that further supports a claim that ASR is measuring well beyond audibility.  Can we assume the same is true of their noise measurements?

 

The concept of preference has been raised many times in this topic and even Amir has said he is not here to tell you your preference. He did state that it was in your best interests to take into consideration the results when he tests, and his tests show no change. I think USB cables, and power conditioners were in that statement and likely others.  @henry53 , are you saying you agree with ASR, at least in this instance?   Or are you staying there are as yet undiscovered tests, which Amir is not doing. If so, can you allude to what those tests may be?