Review and Measurements of Benchmark AHB2 Amp

[josh358]

Power can be calculated even without a clip light. Typical speakers give > 86db for 1 watt power. That's at 1m and we typically listen farther out, but there's room gain to compensate so it's about a wash. Then 100 watts is 106db. Listening levels can be checked with an spl meter. My normal listen level is around 70db, and as expected I've never seen the clip light turn on.

You have to be cautious with SPL meters. Despite what you'd think, the "fast" reading isn't a peak reading. The peak to average ratio of music is typically 10, even (in the case of piano) 20 dB. If you want to check peak levels, a digital peak reading meter is probably your best bet. Or you could set your volume level at the level at which you're listening and then send tone through at -20 FS: that will let you calculate what the amplifier is doing with a fully modulated signal.

 

[josh358]

No doubt you are comparing the AHB2 and the A21 reproducing piano attacks with an onsite, good sized, say 7-foot plus, grand piano? Such a comparison isn't double blind, but does seem to be a requirement for any sort of even semi-valid test.

Without an onsite piano you of course are just providing a subjective judgement. That's fine for you use, but do you feel it has much of any validity as a measurement?

Wondering into conjecture:

The added distortion of the A21, some of which will be at higher frequencies than the fundamentals and overtones of the piano, perhaps is adding a sharpness to the tone, the opposite of rounded off. Much of the output of a piano falls off after 4kHz, so added output at higher frequencies from distortion may not be subject to significant auditory masking, and thus affect how the piano is heard.

That's a valid question, which, unfortunately, applies to almost any comparison not made in a recording session, no matter how well controlled. And the answer is that I *don't* feel it has validity as a measurement. The test was level matched and blind, so I feel reasonably confident that the *difference* I heard was real, but I can't say *objectively* that one or the other amp was more or less accurate.

But while I don't have a 7-foot plus grand to compare it to, I did grow up in a home with a Steinway L, hearing and sometimes playing it almost every day of my life, so I'm pretty familiar with the sound of a good grand piano, and I based my personal subjective judgment on that. Not ironclad, no, but as good as I was able to do.

By the way, I made a level-matched, blind comparison not only between the A21 and the AHB2, but to three other amplifiers as well. The A21 seemed to me the best with piano transients. A Crown Class D PA amplifier was far and away the worst (in other respects as well) -- it made pianos sound like electric pianos! Yes, it was that bad.

I guess your conjecture is as good as any other. I just don't know. Can we hear distortion products at the level produced by a good Class AB amplifier? (No way can we hear them at the level produced by the AHB2, since they're below the threshold of hearing.) Harmonic distortion on a pure tone is *very* hard to hear -- the distortion levels have to be higher than they are in any good amp. Other forms of distortion, though, are more audible.

So it's something that I'm curious about.

 

[RichB]

I have a baby grand piano and

No doubt you are comparing the AHB2 and the A21 reproducing piano attacks with an onsite, good sized, say 7-foot plus, grand piano? Such a comparison isn't double blind, but does seem to be a requirement for any sort of even semi-valid test.

Without an onsite piano you of course are just providing a subjective judgement. That's fine for you use, but do you feel it has much of any validity as a measurement?

Wondering into conjecture:

The added distortion of the A21, some of which will be at higher frequencies than the fundamentals and overtones of the piano, perhaps is adding a sharpness to the tone, the opposite of rounded off. Much of the output of a piano falls off after 4kHz, so added output at higher frequencies from distortion may not be subject to significant auditory masking, and thus affect how the piano is heard.

I have a baby grand piano and the stereo piano recordings that I have pale in comparison.

The AHB2 has two important features it is nearly perfect voltage source and maintains low THD+N at all power levels.
An amplifier that does not perform as well alters the sound, perhaps audibly.

Sound alteration that occurs though distortion or linearity can be audible, is undoubtedly a deviation that may be desirable to some.

- Rich

 

[Vasr]

Did you view Amir's testing with square waves video? The video essentially says that testing with square waves a bad idea. Which it is.

Evidently you disagree with Amir. Have you explained to Amir the error of his ways?

(91) Square Wave Testing of Audio Products (Video Tutorial) | Audio Science Review (ASR) Forum

You need to tone down your attitude and putting up straw arguments without understanding what was said. I understand that this type of ad hominem flows below the radar of moderation but encourages rancor that escalates into both sides later.

Which part of "may provide some measurement differences but I don't know how much of those differences are audible and/or what they manifest as in hearing" suggest disagreeing with Amir to you?

You and whoever provided the noise explanation don't understand the issue, or evidently how power amplifiers are designed.

I didn't provide any noise explanation.

On to ignore list. Seems like you were chased out of the Anthem owner thread on avsforum as well for trolling them. Seems to be habit against all non D&M equipment. Ok. Bye.

 

[Vasr]

The same Stereophile measurements were included for both amps so the comparisons within each are evidence.
In general, the Damping Factor discussions are about bass control. There have been informative posts but the discussion of bass control is largely hand-waving.

I am not sure you understood the point of my post. The measurements provided are a narrow snapshot by controlling all parameters except one. It is not disputing those measurements or the narrow conclusions you can draw for that very specific context.

The problem is it is difficult to interpolate what happens when multiple parameters vary since we don't have a good model for that.

If a subjectivist says, an amp sounds much better in low-mid frequencies with better precision and control as part of a specific subjective evaluation, it is difficult to make the connection to which measurement proves or disproves it since none of the available measurements may model all parameters that might be at play for that particular observation.

Hence, we have two groups talking past each other.

 

[RichB]

I am not sure you understood the point of my post. The measurements provided are a narrow snapshot by controlling all parameters except one. It is not disputing those measurements or the narrow conclusions you can draw for that very specific context.

The problem is it is difficult to interpolate what happens when multiple parameters vary since we don't have a good model for that.

If a subjectivist says, an amp sounds much better in low-mid frequencies with better precision and control as part of a specific subjective evaluation, it is difficult to make the connection to which measurement proves or disproves it since none of the available measurements may model all parameters that might be at play for that particular observation.

Hence, we have two groups talking past each other.

This is true.
However, subjective observations on this have been attributed to damping factor or power limitations.
Some of us try to match that up with objective measurements. That is appropriate for this forum.

- Rich

 

[Vasr]

This is true.
However, subjective observations on this have been attributed to damping factor or power limitations.
Some of us try to match that up with objective measurements. That s appropriate for this forum.

- Rich

Agreed. Although I think that "attributed to damping factor or power limitations" is a bit too simplistic of an explanation.

I do wonder if there would be some benefit to measuring an amp by measuring the audio output of a speaker connected to it in addition to the electrical output. Not to determine the performance of the amp (which would be masked by the speaker) but to determine differences in driving specific speakers. I would at least be curious to see what the results would look like.

Because there is no standardization of speakers, it wouldn't mean much in an absolute sense. But if for the same exact speaker and measurement procedure, two amps showed a difference in such a measurement (even as simple as FR) then that would point to some characteristic that would need to be explored even if the electrical output measurements as currently done were the same for both.

This would be much more closer to proving or disproving subjective claims as all the various parameters that may affect the sound would already be factored into it.

 

[RichB]

Agreed. Although I think that "attributed to damping factor or power limitations" is a bit too simplistic of an explanation.

I do wonder if there would be some benefit to measuring an amp by measuring the audio output of a speaker connected to it in addition to the electrical output. Not to determine the performance of the amp (which would be masked by the speaker) but to determine differences in driving specific speakers. I would at least be curious to see what the results would look like.

Because there is no standardization of speakers, it wouldn't mean much in an absolute sense. But if for the same exact speaker and measurement procedure, two amps showed a difference in such a measurement (even as simple as FR) then that would point to some characteristic that would need to be explored even if the electrical output measurements as currently done were the same for both.

This would be much more closer to proving or disproving subjective claims as all the various parameters that may affect the sound would already be factored into it.

At one point, HomeTheaterHiFi used to measure large monoblocks driving Carver ribbon speakers. I often wondered what those measurements would look like with lesser amps or even AVRs.

- Rich

 

[pogo]

I have not seen evidence nor measurements of benefit of damping Factor over 50.

You can find it in my post #2277

 

[direstraitsfan98]

No doubt you are comparing the AHB2 and the A21 reproducing piano attacks with an onsite, good sized, say 7-foot plus, grand piano? Such a comparison isn't double blind, but does seem to be a requirement for any sort of even semi-valid test.

Without an onsite piano you of course are just providing a subjective judgement. That's fine for you use, but do you feel it has much of any validity as a measurement?

I’ve played in an orchestra for years I know what a piano sounds like... you don’t need double blind test to recognize how an instrument should sound when you’ve been next to one for 50 hours a week for 5 years straight. Granted I know not everyone is blessed with the privledge of being classically trained. Give me a break. Needing a grand piano at hand to DBT? It’s the people like you who give ASR a bad rep.

 

[pogo]

I do wonder if there would be some benefit to measuring an amp by measuring the audio output of a speaker connected to it in addition to the electrical output. Not to determine the performance of the amp (which would be masked by the speaker) but to determine differences in driving specific speakers. I would at least be curious to see what the results would look like.

Here is a possible measurement method:

3D Step Response Measurement - The sound quality of the reproduction made visible

The 3D Step Response measurement shows the behaviours of the sound reproduction in the non swung-in state. This measurement is very important to judge the reproduction of impulses. As testsignale preferably half sinus oscillations of different frequencies at the same time are used, since acoustic events are essentially based on these modes of motion.

View attachment 83902



The frequency response is totally inadequate for the judgement of sound quality. The frequency response is measured with non-changing (Static) signals such as sinus waves or calculated noise signals. Against that, a music signal consists of changing (Dynamic) signals. The study of music signals shows that the sound quality of a musical instrument is determined by impulses. Especially the first impulse, the stroke of a guitar string, the impact of a piano cord, the hit on a drum and the blow of an organ pipe or brass instrument is important for the sound. In the Step-Response, all acoustic parameter information of the sound reproduction is contained. This consists of the frequency response, phase response and swing-in behaviour. There for the display is so complex, that the sound quality judgement based on the measurement is not possible. That is why the 3D Step-Response measurement was developed. By the measurement, the Step-Response is analysed and displayed in a 3D graph. The 3D measurement shows the impulse reproduction for each single frequency with use of an additional frequency axis. The measurement makes it for the first time possible to analyse the sound quality through measurement technology.

(Source: Kirchner elektronik)



Testing is not incorrect in what it measures, but in what it does not measure. You have to swim against the stream to reach its source

 

[josh358]

signals such as sinus waves or calculated noise signals

Doesn't he mean "nose signals"?

 

[restorer-john]

Give me a break. Needing a grand piano at hand to DBT? It’s the people like you who give ASR a bad rep.

Doesn't everyone have a concert grand piano in their listening room in case some gecko asks for a quick DBT with a reference recording?

I sure don't. Pole home, timber floor. 30ft down to the forest floor it would be.

 

[josh358]

Here is a possible measurement method:

3D Step Response Measurement - The sound quality of the reproduction made visible

Seriously, this is a very interesting visualization. Sort of a waterfall from the rear? I'm not sure what the bottom represents. In any event, this is much like what I'd expect the ear to do -- rectify the impulse and transform it to the frequency domain.

 

[josh358]

Doesn't everyone have a concert grand piano in their listening room in case some gecko asks for a quick DBT with a reference recording?

I sure don't. Pole home, timber floor. 30ft down to the forest floor it would be.

I knew someone with two concert grand pianos in her living room. Of course, she was a pianist.

 

[pma]

The frequency response is measured with non-changing (Static) signals such as sinus waves or calculated noise signals.

Junk. Only DC or zero has a “non-changing” level. Sine goes from -Vpeak to +Vpeak through all levels with resolution limited only by the system used.

 

[RichB]

Doesn't everyone have a concert grand piano in their listening room in case some gecko asks for a quick DBT with a reference recording?

I sure don't. Pole home, timber floor. 30ft down to the forest floor it would be.

Some assembly required

- Rich

 

[RichB]

You can find it in my post #2277

To link to a post, click on the post # in the top right and then paste.
Her is a link to your post (1) Review and Measurements of Benchmark AHB2 Amp | Page 114 | Audio Science Review (ASR) Forum.

It is a bit odd to paste a chart from Dr. Floyde Tool's article titled: "DAMPING DAMPING FACTOR AND DAMN NONSENSE" and claim it proves the importance of damping factor

If you think a wiggly chart with no axes, the discussion should just end here. If you don't care about linearity into load or distortion buy a Parasound. If you care about those and want to buy on Damping Factor (output impedance), but a Purify amp. I have not heard them but they are intriguing.

There have been many informative posts concerning Damping Factor including this one by t@DonH56 that examines the effect at different DF and frequencies:
(1) Review and Measurements of Benchmark AHB2 Amp | Page 111 | Audio Science Review (ASR) Forum

If you are seriously interested in learning about this topic the Benchmark article is excellent:
Audio Myth - "Damping Factor Isn't Much of a Factor" - Benchmark Media Systems

This must be read carefully. The Focal speaker used in the analysis is specified at 8 Ohms but has a minimum impedance of 2.6 Ohms. Benchmark uses 2.6 Ohms during the article not 8 Ohms. 0.1 dB is used as the target response range that could be identified in a ABX test. There are reasonable values.

The effectiveness of higher damping factor is limited by cables:

SPEAKER CABLES SET A PRACTICAL LIMIT ON THE DAMPING FACTOR
A typical set of 10-foot 12-AWG speaker cables will have a round-trip series resistance of 0.0318 Ohms. If these were driven by a zero-ohm amplifier (if such an amplifier existed), the damping factor would be 200. Benchmark offers 11-AWG cables that have a round-trip series resistance of 0.0252 Ohms. These would limit the damping factor to 317 if driven from a zero-ohm amplifier.

In other words, damping factors greater than 200-300 can rarely be achieved at the speaker terminals. If damping factors near 1000 were important, we would need to place the amplifier very close to the drivers and/or use some very large conductors. However, don't go out and buy welding cables; large conductors have inductance problems. Skip the welding cables, as this paper will show that we don't need a damping factor of 1000.

If you think DF of 2000 is going to make any difference, DF of infinity is not more than 317 with 12 foot 11 gauge wire.

Stereophile's simulate speaker has a minimum impedance of 6 Ohms which is not stressful.
Real-Life Measurements | Stereophile.com
However, they describe their cables as well since they know cables limit DF.

Here is a summary of the discussed measurements and specifications:

AHB2 DF and measurements:

• 0.09 ohm at 20Hz and 1kHz
• 0.22 ohm at 20kHz
• Simulated speaker deviation: ±0.1dB
• Damping Factor 130 at 20Hz with published curve
• DB loss into 4 Ohms up to 2 kHz: 0.2 dB
• DB loss into 2 Ohms up to 2 kHz: 0.25 dB

A21 DF and measurements:

• 0.077 ohm at 20Hz and 1kHz
• 0.1 ohm at 20kHz
• Simulated speaker deviation: ±0.1dB
• -3dB point close to 100kHz
• Damping Factor 1100 at 20Hz, other frequencies not specified
• DB loss into 4 Ohms up to 2 kHz: 0.5 dB
• DB loss into 2 Ohms up to 2 kHz: 0.75 dB

The Stereophile simulated speaker has a minimum impedance of 6 Ohms.
So what would be the likely impact comparing these amplifiers with a speaker that has a minimum impedance of 2 Ohms?
That can be inferred from the above measurements because we can see the effect of lower impedance and simply multiply simulated speaker (and cable) deviation by 3.

For argument's sake, lets only apply the simulated speaker deviation to the AHB2 and not to the A21. In reality, the A21 will probably incur increased deviation.

So here are the estimated effects in the bass frequencies for each amplifier using the Stereophile measurements:

Estimated deviation of the AHB2 into 2 Ohms DF + Load: -0.3 (DF) + -0.25 (Load) = -0.55 dB
Estimated deviation of the A21 into 2 Ohms DF + Load: -0.1 (DF) + -0.75 (Load) = -0.85 dB

Based on DF and linearity into the load, the AHB2 should perform better into more difficult loads by .30 dB minimum (greater than the .1 threshold).

I agree, that dynamic measurements into load would be a useful addition but the AHB2s power supply holds up better for difficult loads so should do better at such a measurement.

There is no evidence (or math) that supports audible improvements from amplifiers effective damping factors > 100.

- Rich

 

[pogo]

• Damping Factor 130 at 20Hz with published curve
• DB loss into 4 Ohms up to 2 kHz: 0.2 dB
• DB loss into 2 Ohms up to 2 kHz: 0.25 dB

DB loss is not the real problem, but the undesired higher swing out amplitude, i.e. the input signal is not properly followed, which leads to a washed-out bass range with complex music signals.

 

[RichB]

DB loss is not the real problem, but the undesired higher swing out amplitude, i.e. the input signal is not properly followed, which leads to a washed-out bass range with complex music signals.

Failure to control the bass drivers would most likely result in dB gain.

The Stereophile measurements into their simulated speaker load indicates that the A21 (DF 1100) and AHB2 (DF 350) clearly that DF is not the most important factor in tracking the the input signal (frequency response).

The A21 clearly has more difficulty maintaining the voltage into a 4 Ohm and 2 Ohms load.
That means it will not track the input signal as well as the AHB2, confirmed by measurements.

Thus completes my discussion. Life awaits, enjoy.

- Rich