Review and Measurements of Benchmark AHB2 Amp

[RichB]

No, they are not. See also here including the following posts/test report: Link

There is a lot of discussion on ASR about damping factor (DF), that is worth a search, so recommended.

Your observations aside, for the moment, align with a DF, confirmed by Stereo.de.

Stereo.de AHB2 damping factor measurements is an outlier.

Dämpfungsfaktor an 4 Ohm bei 63Hz/1kHz/14kHz: 48/45/19

Here are the Benchmark AHB2 for damping factor:

DAMPING FACTOR​

• 350 at 20 Hz, 8-Ohms
• 254 at 1 kHz, 8-Ohms
• 34 at 20 kHz, 8-Ohms
• 7 at 200 kHz, 8-Ohms

Here are the DF measurements from SoundStage:

Damping factor is most important in bass frequencies but with these we can compare 1 kHz.
Stereo.de 48, Benchmark 254, and SoundStage 225.

I have no idea what Stereo.de is doing, and perhaps they don't either.

Concerning your observations, the perhaps 48 seems low but is still higher than necessary.
I observe no issues with the AHB2 and tight bass driving the Salon2s full range.

I have disconnected the upper section and listened to the bass 150 Hz and below on the Salon2s which that are -3 dB 23 Hz and this cannot be described as tight with any amplifier. I have driven there with Parasound amps with DF spec'ed at > 1100 and I find no audible difference in bass. If anything, the AHB2 is better, perhaps due to its tightly regulated power supply and minimal phase shift.

- Rich

 

[SIY]

There is a lot of discussion on ASR about damping factor (DF), that is worth a search, so recommended.

Your observations aside, for the moment, align with a DF, confirmed by Stereo.de.

Stereo.de AHB3 damping factor measurements is an outlier.


Here are the Benchmark AHB2 for damping factor:


Here are the DF measurements from SoundStage:

View attachment 231747

Damping factor is most important in bass frequencies but with these we can compare 1 kHz.
Stereo.de 48, Benchmark 254, and SoundStage 225.

I have no idea what Stereo.de is doing, and perhaps they don't either.

Concerning your observations, the perhaps 48 seems low but is still higher than necessary.
I observe no issues with the AHB2 and tight bass driving the Salon2s full range.

I have disconnected the upper section and listened to the bass 150 Hz and below on the Salon2s which that are -3 dB 23 Hz and this cannot be described as tight with any amplifier. I have driven there with Parasound amps with DF spec'ed at > 1100 and I find no audible difference in bass. If anything, the AHB2 is better, perhaps due to its tightly regulated power supply and minimal phase shift.

- Rich

Source impedance affects the frequency response, not just at bass but throughout the audible range. But... claims that consequent frequency response variations of hundredths of a dB are clearly audible are absolutely ludicrous.

 

[neutralguy]

Source impedance affects the frequency response, not just at bass but throughout the audible range. But... claims that consequent frequency response variations of hundredths of a dB are clearly audible are absolutely ludicrous.

I have measured the AHB2's frequency response variation (at least in terms of voltage) when driving real speakers in this post. The entire spectrum appears consistently tilted by about 0.15db 20hz-5khz, before the rolloff approaching 20khz. I wasn't able to hear a difference in my recordings vs an amp with lower output impedance (Topping LA90), but in Komamura 1983 they found that spectral tilts of about 0.1-0.2db/octave in bass or treble is audible, and one person even heard 0.08db/octave difference in symphony music. The AHB2's tilt has a lower slope than this, though it's across a broader region and there are bumps.

 

[617]

.015db is the difference between a speaker which is 3 meters away and one which is 3.005 meters away.

 

[peng]

.015db is the difference between a speaker which is 3 meters away and one which is 3.005 meters away.

You need a robot that can sit still in order to hear such minute difference consistently.

 

[neutralguy]

.015db is the difference between a speaker which is 3 meters away and one which is 3.005 meters away.

0.15db, not 0.015db.

 

[tmtomh]

I apologize for not being able to lay my hands on the source at the moment, but my understanding is that studies have shown that 0.2dB appears to be the minimum volume difference that humans can detect, and only in very specific circumstances - and such small volume differences are not even necessarily perceived as differences in volume (but rather in some kind of detectable difference that people cannot necessarily describe).

It's a strange aspect of how some discussions seem to go here at ASR: a performance metric is considered adequate - excellent even - but then all of a sudden someone discovers or proposes a new cause or reason that this metric could be affected, and people kind of lose their marbles over it.

In other words, a variation of frequency response of 0.15dB is trivial and essentially flat - in many FR measurements (including some of Amir's depending on the scale he uses), 0.15dB is not even visible.

Yet when someone proposes that maybe a device might have 0.15dB variation in FR because of damping factor in particular, people start obsessing over it.

I don't know; it just seems strange to me and, with respect, kind of pointless.

 

[JP]

You clearly don't hold your head in a vise when you listen....

 

[dlaloum]

AHB2 took the advantage of THX technology, is good/great but far from perfect. It's a shame not to expand further based on that THX.

From business perspective, esp. for tech-related companies, not continue developing/improving new product is a path to death and competition will soon catch up. Is it just to make $$ and forgot about the original passion to audio technology?

From consumer point of view, I'd think twice of buying products from such companies because it means no future upgrade path and investment will be obsolete, forget about "classic".

Seems to me that the "THX Technology" is just a newer spin on Peter Walkers Current Dumping...

 

[restorer-john]

I apologize for not being able to lay my hands on the source at the moment, but my understanding is that studies have shown that 0.2dB appears to be the minimum volume difference that humans can detect, and only in very specific circumstances - and such small volume differences are not even necessarily perceived as differences in volume (but rather in some kind of detectable difference that people cannot necessarily describe).

Let's talk about that for a second.

0.2dB came up the other day actually. Since the early 1970s when my father brought home a Marantz 1060 amplifier, plugged it in, listened to one his many classical test pieces and instantly proclaimed it was left sided, both him and I can easily hear the imbalances (volume differences) between the channels of any amplifier when played in a room you know. I think you can do that too and probably do it all the time either consciously or unconsciously.

The level difference on that actual amplifier was measured by me just last week and is 0.2dB louder on the left channel. Just 0.2dB. There is nothing wrong with any of the active stages- they are all identical in gain. It is the balance pot, which sits up front of everything and had an approximate 10% difference in taper resistance either side on the centre wiper point. The source is seeing a small variance in combined loading (bal and vol pots).

Many times when people here on ASR have posted excerpts for ABX testing, it is the relative channel levels with respect to one another (the image balance) that is the giveaway. A tiny movement of the image is a direct result of level changes in channels. We can easily hear that, and I would wager we could easily hear well below those numbers reliably when listening to stereo content with specific instrument placement.

 

[F1308]

So we have that humans are detecting 0.2 dB in volume difference and 5 cents in pitch, known as JND and meaning just a mere 0.08 Hz when attending the 27.5 Hz range, 1.27 Hz when in the 440 Hz range and 10 Hz in the 3520 Hz range.

 

[dlaloum]

Let's talk about that for a second.

0.2dB came up the other day actually. Since the early 1970s when my father brought home a Marantz 1060 amplifier, plugged it in, listened to one his many classical test pieces and instantly proclaimed it was left sided, both him and I can easily hear the imbalances (volume differences) between the channels of any amplifier when played in a room you know. I think you can do that too and probably do it all the time either consciously or unconsciously.

The level difference on that actual amplifier was measured by me just last week and is 0.2dB louder on the left channel. Just 0.2dB. There is nothing wrong with any of the active stages- they are all identical in gain. It is the balance pot, which sits up front of everything and had an approximate 10% difference in taper resistance either side on the centre wiper point. The source is seeing a small variance in combined loading (bal and vol pots).

Many times when people here on ASR have posted excerpts for ABX testing, it is the relative channel levels with respect to one another (the image balance) that is the giveaway. A tiny movement of the image is a direct result of level changes in channels. We can easily hear that, and I would wager we could easily hear well below those numbers reliably when listening to stereo content with specific instrument placement.

Some things we are more sensitive to than others.... I haven't seen a study on horizontal location cues vs frequency/level sensitivity...

My personal testing was messing with a few tracks, trying to see how sensitive I am to frequency response variations, and how close the F/R had to be on two identical tracks (ie two tracks where light EQ was applied to differentiate them before testing - so they were the same track, edited).

I didn't experiment with channel balance, or even more tricky - varying the F/R between the channels of the same track,

my result was that 0.2db F/R difference was not identifiable - 0.5db was identifiable.

 

[SIY]

Interchannel level differences are not the issue here.

 

[tmtomh]

Let's talk about that for a second.

0.2dB came up the other day actually. Since the early 1970s when my father brought home a Marantz 1060 amplifier, plugged it in, listened to one his many classical test pieces and instantly proclaimed it was left sided, both him and I can easily hear the imbalances (volume differences) between the channels of any amplifier when played in a room you know. I think you can do that too and probably do it all the time either consciously or unconsciously.

The level difference on that actual amplifier was measured by me just last week and is 0.2dB louder on the left channel. Just 0.2dB. There is nothing wrong with any of the active stages- they are all identical in gain. It is the balance pot, which sits up front of everything and had an approximate 10% difference in taper resistance either side on the centre wiper point. The source is seeing a small variance in combined loading (bal and vol pots).

Many times when people here on ASR have posted excerpts for ABX testing, it is the relative channel levels with respect to one another (the image balance) that is the giveaway. A tiny movement of the image is a direct result of level changes in channels. We can easily hear that, and I would wager we could easily hear well below those numbers reliably when listening to stereo content with specific instrument placement.

An interesting point, John, and one that makes a lot of sense - L-R channel imbalances are no doubt much easier for humans to detect because the center image moves, or more generally because evolutionarily human hearing appears to have evolved to be quite sensitive to left-right ear differences as a way to pinpoint the location of things in the world.

But as @SIY notes, that's not the issue being discussed here. Fine to bring it up in the thread, but it's irrelevant to the question of whether or not 0.15dB variance in frequency response caused by damping factor (or anything else) is an audible concern.

 

[dlaloum]

An interesting point, John, and one that makes a lot of sense - L-R channel imbalances are no doubt much easier for humans to detect because the center image moves, or more generally because evolutionarily human hearing appears to have evolved to be quite sensitive to left-right ear differences as a way to pinpoint the location of things in the world.

But as @SIY notes, that's not the issue being discussed here. Fine to bring it up in the thread, but it's irrelevant to the question of whether or not 0.15dB variance in frequency response caused by damping factor (or anything else) is an audible concern.

To be fair, no one was specific as to where and how the db variance was...

My comments were based on F/R variance only - no channel imbalance variances were tested.

But yeah - I think different aspects may have different audibility thresholds

 

[pogo]

Stereo.de AHB2 damping factor measurements is an outlier.

Why, I have not seen another measurement at 4ohms!?
Here is an answer from the Stereo Team:
We measure the damping factor on a resistive load (4 ohms). It is calculated from the ratio between the no-load voltage and the terminal voltage under load.

 

[restorer-john]

Why, I have not seen another measurement at 4ohms!?
Here is an answer from the Stereo Team:
We measure the damping factor on a resistive load (4 ohms). It is calculated from the ratio between the no-load voltage and the terminal voltage under load.

Damping factor is traditionally measured at 1W (2.83V@8R).

 

[pogo]

Isn't it important to look at the other operating conditions as well?

 

[restorer-john]

Isn't it important to look at the other operating conditions as well?

Not sure what you are asking.

The output impedance of an amplifier varies vs frequency and output voltage/current. It is not a single number.

 

[peng]

0.15db, not 0.015db.

Okay that's better but still, I think moving your body even a few inches would have comparable effects. While someone could actually detect such small variations even when listening to music and movies, practically speaking it may not be significant enough for them to consistently prefer one amp over the other. More studies on such things would be good.