Master Thread: Are measurements Everything or Nothing?

[acetogen]

You won't find two amplifiers that measure exactly the same from two different manufacturers, often not even the same model, from the same manufacturer...

Wait, what? Is that true of everything else in audio (speakers, preamps)? It would imply one should take measurements with quite a bit of skepticism since the engineer tested one one unit (Stereophile always includes the serial number) . Perhaps what you meant is if two identical amps (brand and model) might measure 93 and 95 dB on the SINAD scale, so they are not strictly identical, put for practical purposes they can be assumed to be.

 

[acetogen]

Seems like so many review threads get challenged with:

1. Measurements are not everything.

2. You all never listen.

3. I trust my ears, not graphs.

4. I don't listen to graphs. I listen to music.

5. You all must not listen to music at all.

6. Why don't you all buy the best SINAD gear?

7. I have heard your best SINAD gear and they sound terrible. I don't like any of this Chinese stuff.

8. You don't trust your ears. I/we do.

9. All these reviewers/youtubers/audophiles say these amps, DACs, etc. sound different and you say they don't. They can't all be wrong.

10. Surely designers have created certain house sound for each equipment which your measurements don't show.

11. Your measurements are only at one frequency. You need to also measure X, Y and Z like impulse response, slew rate, etc., etc.

12. You guys run a cult here where you only go by measurements and no one is allowed to disagree.

On and on...

I have had to answer these so many times that I thought it is time to stop having them go into every review as they are not product specific. From here on, any such questions should be posted here. Answers will be given in this thread and simply referenced in future challenges in other threads.

@AdamG247 and @BDWoody, please direct any future posts in review threads to here and not allow discussions there.

Thanks. You all are free to discuss this topic, provide answers, argue, whatever, in this thread.

Maybe you shouldn't answer these questions, I wouldn't. It takes time from testing and web development activities that are essential to ASR. With respect to the question asked my answer is measurements are necessary but not sufficient. Thank you for creating this site.

 

[symphara]

When you only meant it has specs for 2 ohm than this is a misunderstanding (but then you should have quoted the previous post).

Yes that is all I meant. I wrote "mine does X", mere statement of fact (assuming spec is true). It obviously doesn't have perfect linearity but it's ok and at least they list it. I'm curious to know about amps with better behaviour, and it's a shame this particular spec isn't often listed or measured.

 

[DanielT]

Wait, what? Is that true of everything else in audio (speakers, preamps)? It would imply one should take measurements with quite a bit of skepticism since the engineer tested one one unit (Stereophile always includes the serial number) . Perhaps what you meant is if two identical amps (brand and model) might measure 93 and 95 dB on the SINAD scale, so they are not strictly identical, put for practical purposes they can be assumed to be.

There is nothing, absolutely nothing, that throughout the physical world that measures exactly the same. The question is more when that difference is perceived by us humans.

These are the biggest questions, which are most written about here at ASR:
* When does the distortion become audible
* How much effect is needed ...
(for those who are thinking about how the boat performs in rough seas. How the amplifier copes with impedance waves and so on)

Completely reasonable and sensible questions.

 

[DanielT]

Yes that is all I meant. I wrote "mine does X", mere statement of fact (assuming spec is true). It obviously doesn't have perfect linearity but it's ok and at least they list it. I'm curious to know about amps with better behaviour, and it's a shame this particular spec isn't often listed or measured.

Tube amp?

 

[rcarlbe]

I think ASR does decently at coaching peeps through the tests and charts. Are you saying you believe this ^^^or you need this?

Hi, I'm not sure the purpose of the question, but I'll can explain more. I could benefit to a degree, but my post was mainly meant to lead to benefit everyone. There is one particularly great thread that provides example explanations about hearing mapped onto the measurement graphs, which is useful. Building on that approach in the equipment reviews or elsewhere in a concise relatable way could help data sceptics see the how the tests do and do not address attributes of human hearing. I think the data tends to float free from explanation about how and what we hear and that opens the door wider for golden ear arguments. I frequently read people asking people to read more, try harder (perhaps for decades), stop asking for handouts etc. The frequency to which this is done indicates it's not working. If the reviews are meant to be generally understood by those into consumer electronics, and not for the purpose of publishing in a engineering journal for example, then tying them to human hearing in a more comprehensive and relatable way could be worth pursuing.

 

[Ingenieur]

Measurement are a starting point and correlate to SQ. But they vary in weighting depending on the item:
Amps, good correlation
Speakers, less so

It's like buying a car:
You look at for example, 0-60 time, if a few tests have put it at 3 sec, you KNOW it will be fast. If skid pad is 1 g, you know it corners. One may feel faster /better, but it is not, it is the same.

But until you drive it you won't know how it feels to YOU. But whether you like it or not does not change the 3 sec (fast) and 1 g (corners).

Taking it further:
Same drivetrain layout
Same power, torque, engine type.
Same weight and weight distribution.
Steering type, ratio
Tires, brakes, etc.
Identical times, brake distance, cornering g

Only the name badge changes, at that point imo any preference is purely subjective, not real world performance based.

One may feel better/faster, but it is not, it is the same.

 

[DanielT]

Measurement are a starting point and correlate to SQ. But they vary in weighting depending on the item:
Amps, good correlation
Speakers, less so

It's like buying a car:
You look at for example, 0-60 time, if a few tests have put it at 3 sec, you KNOW it will be fast. If skid pad is 1 g, you know it corners. One may feel faster /better, but it is not, it is the same.

But until you drive it you won't know how it feels to YOU. But whether you like it or not does not change the 3 sec (fast) and 1 g (corners).

Taking it further:
Same drivetrain layout
Same power, torque, engine type.
Same weight and weight distribution.
Steering type, ratio
Tires, brakes, etc.
Identical times, brake distance, cornering g

Only the name badge changes, at that point imo any preference is purely subjective, not real world performance based.

One may feel better/faster, but it is not, it is the same.

Class D Caterham vs Class AB Porsche. Ehh,. Just an introduction to pasting a fun video. There are no parallels, as far as I know. ...or...

 

[symphara]

Tube amp?

What, my amp? No way, I hate tube amps. It's an Electrocompaniet. Is there a tube amp that powerful even??

 

[DanielT]

What, my amp? No way, I hate tube amps. It's an Electrocompaniet. Is there a tube amp that powerful even??

Just a question . I really like carbonated water, my ex-wife did not like it at all. Colored or neutral?

Of course there are powerful tube amps. The solution is spelled $.

Edit:
When a transistor-based amplifier is driven into clipping, how does it sound vs a tube amp that happens to (when that happens, the wall that is)?

 

[ahofer]

What, my amp? No way, I hate tube amps. It's an Electrocompaniet. Is there a tube amp that powerful even??

VTL made some pretty powerful tubes. I have a pair of 225 (watt) Monoblocks.

 

[shal]

You have a much different view of musicians than I do.

In my musical world, I advocate for a science-based understanding of how our instruments work. Yet even world-class performers are subject to a range of biased perceptions, and also show great difficulty in connecting effect to cause. Thus, they change to overweight mouthpieces (or skeletonized mouthpieces to lighten them) based on the fad of the moment. They attribute special qualities to the specific formulation of the brass. They argue about whether a lacquer finish or a silver finish (on an instrument that makes precisely zero sibilant transients) affects the sound. Their eyes glaze over if I talk about the bell as an impedance matching device--impedance not being a common topic in music school. They argue about whether brass, bronze, or stainless steel is the better mouthpiece material--again for instruments that do not produce any useful/measurable sounds above a couple thousand Hz. They can do things that make me cry--at the beauty they produce and at my own incompetence as a performer. But science ain't their thang.

I do know some extremely qualified physicists with expertise in acoustical science who also play tuba. Let's just say they have a different view of causes and effects than the above examples. This forum is populated with people like that, even those who are musicians.

Rick "doubting that Jeff Beck has subjected his listening to controls, but confident that he gets the effects he wants" Denney

Hi,
As trumpeter I am agree.

When I am (more)young , I have personally overweighted my mouthpiece with lead so I understand what you said

Science is more and more present in instrument making.

Yamaha is one of the big maker , based more and more on computer modelisation.

But little maker too, For e.g Harreslon was a trumpet maker .
Watch the test to understand who a instrument sound :

PS: look the t-shirt , the word science is there !

 

[rdenney]

Yes, but some amplifiers are not capable of driving low impedance loads. This is my point. The fact that it can drive Scintillas, which are rated at 1 Ohm, I presume is a good indication of a very stable linear power supply. Not all amplifiers will have this.

Sufficient power supply, yes. Linear, not necessarily—and those can sag, too. Check out DonH56’s thread on the topic (I think it’s a sticky)—he shows how output impedance with respect to load affects frequency response.

Rick “it’s about design, not topology” Denney

 

[rdenney]

Hi, I'm not sure the purpose of the question, but I'll can explain more. I could benefit to a degree, but my post was mainly meant to lead to benefit everyone. There is one particularly great thread that provides example explanations about hearing mapped onto the measurement graphs, which is useful. Building on that approach in the equipment reviews or elsewhere in a concise relatable way could help data sceptics see the how the tests do and do not address attributes of human hearing. I think the data tends to float free from explanation about how and what we hear and that opens the door wider for golden ear arguments. I frequently read people asking people to read more, try harder (perhaps for decades), stop asking for handouts etc. The frequency to which this is done indicates it's not working. If the reviews are meant to be generally understood by those into consumer electronics, and not for the purpose of publishing in a engineering journal for example, then tying them to human hearing in a more comprehensive and relatable way could be worth pursuing.

But at some point the issues refuse simplistic models and understanding. At that point, who can a person only willing or able to go that far trust?

For me, it would be the experts—those who have demonstrated that they have that technical understanding. Let me see what they use and recommend. Those who merely repeat that knowledge, or eschew it altogether, are secondary sources at best.

If careful subjective reviewers agree, so much the better. But only after receiving the blessing from the real experts.

Being able to discern real expertise is the perpetual human challenge, isn’t it?

Rick “not all credentials are valid, but here they are mutually validated” Denney

 

[rcarlbe]

You picked up on my mention of providing a music enthusiast level of communication as preferable in this type of forum. I find this site does strike a good balance there. I didn't mean that to be read as a strong critique. My main point is the suggestion that information about how human hearing overlays with testing in a comprehensive and rigorous way can give measurements more credence in light of the ubiquitous misunderstanding that seem to consume a disproportionate amount of air time on ASR. Speaking of time(!) I appreciate the conversation and I'm stepping back now to create airtime for others. Cheers.

 

[Holmz]

Some brands specify a lower power rating at higher impedances so they can make it look the amp is capable of doubling power at lower impedance. They know audiophiles see the power doubling trick as a sign of quality. The only thing that matters is that it's capable of providing the power you need for your speakers and your preferred listening level.

I guess that depends on the definition of quality?
In the past some amps were rated for peak power of kW and RMS power down in the hundreds.
And their claim was that was a sign of quality.

It is only a sign that the power supply can hold the rail voltage independent of output load draining the energy off.
It does seem like quality, but it is more a metric of power supply stiffness.

Mines does, according to the spec:

125W@8Ω
250W@4Ω
375W@2Ω

I wish more amp specs would show 2Ω delivery since lots of speakers seem to dip under 4.

I, and maybe others?, wish a lot of speakers did not dip that low.

There are tolerance variations and so they build them a bit better than spec. So they don't sell one that's under-spec. It only requires small decreases in the rail voltage(s) to change a power rating enough to be under spec with regards to the power output.

Some other amps are just on the spot correct? Better parts used in the build? Better design?

How does one not keep the rails at their voltage?
A voltage regulator is about the easiest thing to do, and one of the most common and heavily used ICs.

I would like to know if there are examples where rail voltage is off?

…
Can't somebody just test a variety of speakers looking at impedance/phase and see how cheap amps perform in those circumstances? Then pick the speakers that cause the most problems in cheap amps in terms of FR. I don't think we need to have data to compare to on day 1. If the test is done over and over again on new amps being tested over time there will be data to compare to.
…..

I would assume that most of the wild impedance is solely in the passive XO?
(I looked at a Mundorf AMT,. Accuton MR and ScanSpeak Wu18 at Madisound.)

ScanSpeak Illuminator 18WU/8741T 7" Woofer, 8 ohm

Scan-Speak Illuminator 7" Paper Cone Woofer 18WU/8741T-00. 8 ohms. The Illuminator woofers are based on compact under-hung motor systems with large neodymium ring magnets. The patent pending motor offers a very long linear excursion together with a very high force factor. The top plate is shaped...

www.madisoundspeakerstore.com

They all show an impedance rise around FSport (or below)… nothing I saw shows the impedance going low, only going higher.

So in my mind the most obvious solution is to use active XO, and multiple smaller amps.

I suppose the other solution is to use better passive XOs, however the magic with fancy inductors and expensive caps sort of precludes ease of tuning… and one is still left with the FR in the room.
And the amplifier manufactures, and much of the speaker industry, have a vested interest in passive XOs… it is where a lot of the magic lives in a speaker box.

 

[Doodski]

How does one not keep the rails at their voltage?
A voltage regulator is about the easiest thing to do, and one of the most common and heavily used ICs.

I would like to know if there are examples where rail voltage is off?

I am not referring to a voltage regulator circuit.
I am referring to the rail voltages used in the voltage amp stage and current amplification stage/the unity gain stage of a discreet amplifier.
Examples of the rail voltage being off are amps that test higher or lower than their rated power output spec.

 

[restorer-john]

Do you believe there are manufacturers (or their marketing divisions) that under-rate amplifier power to appear more conservative, or more robust, in the eyes of consumers? IOW, to cultivate a "reputation" in their customer base. The previous example of power at 8, 4 and 2 Ohms illustrates this. It's difficult to manufacture an amplifier that accurately doubles wattage into half the impedance. So some advertising divisions might shave the 8 Ohm and 4 Ohm power to make it appear that the amp numerically doubles its power right down to the 2 Ohm output.

I wonder how often that happens. Jim

All the time Jim. It has been going on since the 1980s. Hardly any of it in the 1970s.

Ever since the early 80s when the whole so-called HCC (high current capability) designs hit the market. Harman was one of the biggest proponents of the under-rating of 8R outputs, so their 4R numbers looked good. Also, the peak current numbers being thrown around to get the point across even more.

Bear in mind, many of the peak current numbers (that are used to calculate peak powers over a load) are obtained with single cycles into very small resistances (<0.5R-1R) and extrapolated to the 2/4/8R numbers you see on spec sheets. A single cycle (or low cycle count) can be employed so as to not destroy the OPTs and/trip the OC protection.

They are mostly mathematics exercises and don't exist for any appreciable time, as most people expect power or current to exist for in relation to an amplifier's output.

 

[BDWoody]

Ever since the early 80s when the whole so-called HCC (high current capability) designs hit the market. Harman was one of the biggest proponents of the under-rating of 8R outputs, so their 4R numbers looked good. Also, the peak current numbers being thrown around to get the point across even more.

I believe my Kav250a is rated at 250w@8r, and 500w@4r, but tests closer to 300@8r for likely that very reason.

 

[acetogen]

There is nothing, absolutely nothing, that throughout the physical world that measures exactly the same. The question is more when that difference is perceived by us humans.

These are the biggest questions, which are most written about here at ASR:
* When does the distortion become audible
* How much effect is needed ...
(for those who are thinking about how the boat performs in rough seas. How the amplifier copes with impedance waves and so on)

Completely reasonable and sensible questions.

I do measurements for a living, of things that cannot be assessed by subjective evaluations. For example, Lead in the water does kind of taste sweet to most people, but they can't tell how much is present in a glass of water. Instrumentation measures trace metal concentrations to answer that question. Now heavy metals in water is not a product of engineering, but of nature altered by human activity, unlike electronics. But I would have assumed as a non engineer that capacitors, transformers, transistors, circuits, etc. were built to some specifications and some tolerance (+/-) of those specifications, and thus one would expect the same of any integrated component. Moreover an engineered component would be expected to be far less variable than a sample from nature for obvious reasons. Your assertion that the physical world does not measure the same is not correct. The length of an Earth's orbit is 365.24 days, the age of this planet is 4.5 billion years, and they have been confirmed many times. There are uncertainties associated with those numbers, maybe this is what you mean by "exactly the same".

So my question again is if two DACs of the same model CANNOT "measure the same", then what's the use of measurements?

The 3 answers that you provided are not relevant because they relate to subjective evaluations (audible, distortion, sensitivity).