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Review and Measurements of Benchmark AHB2 Amp

cjm2077

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Interesting possibly switching supplies have internal HV, I would be hard pressed to to believe an ordinary PC trace spacing could be made to arc at 50V levels (see Paschen's law for air).

The standards are set with a lot of margin for error, and are spaced well beyond what you would get from a Paschen curve. I doubt they would have an intermediate voltage above the final bus voltage, but it's possible. I've never worked in an industry that requires active power factor correction, so it could happen there. I'd guess that the highest voltage is the 250Vac max on the incoming power lines, which is 350V peak.
 

etc6849

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Here's a comparison I did for using an AHB-2 to my now sold Emotiva XPR-1 monoblocks I used to drive some Klipsch P-17b bookshelf speakers. I don't have any speaker data for the P-39f drivers or I'd do similar calculations for them. The bookshelf speakers still have the factory crossover in them and sit in my office.

From: https://hometheaterhifi.com/reviews...fier/emotiva-xpr-1-monoblock-power-amplifier/
1590446777388.png


1590446115077.png



Emotiva XPR-1 monoblocks (max output and 1 watt output):
IMG_20200525_193630~2.jpg

IMG_20200525_193638~2.jpg


AHB-2 bridged mode (max output and 1 watt output):
IMG_20200525_193648~2.jpg

IMG_20200525_193656~2.jpg


Alternate method of calculating pressure for a given voltage to prove to yourself that Benchmark's rule of thumb makes sense (which it should provided the speaker specs are measured at 2.83Vrms):
IMG_20200525_200416~2.jpg


Note that for the noise SPL figure, it will likely depend on your environment.

A while back I did an accurate measurement of my room in this thread:
https://www.audiosciencereview.com/...hat-level-is-noise-heard-in-your-system.1013/

The spectrum below is for my room (measured with Earthworks M30, Benchmark MPA1, Benchmark ADC1 sending AES to my RME soundcard). Note that the room's inherent noise varies with frequency over the audible range by A LOT! My room is actually very quiet in the md-range.

1590452427417.png


@RichB
 

Pjetrof

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@etc6849
wow thx.
I wonder what the more experienced EE who believe amplifiers sound the same have to say to that post.
I used to believe amplifiers doesn’t sound the same.
Then I bought Harbeth and start reading Harbeth forum then this forum, and like I believed all the marketing magazine and tests that amplifiers have a sound, I started to believe the harbeth forum and this forum. That amplifiers sound the same.

now I m in doubt. Cause you re explanation is funded by science! So pls help me does amplifiers sound the same?
yes or no
 

JohnYang1997

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@etc6849
wow thx.
I wonder what the more experienced EE who believe amplifiers sound the same have to say to that post.
I used to believe amplifiers doesn’t sound the same.
Then I bought Harbeth and start reading Harbeth forum then this forum, and like I believed all the marketing magazine and tests that amplifiers have a sound, I started to believe the harbeth forum and this forum. That amplifiers sound the same.

now I m in doubt. Cause you re explanation is funded by science! So pls help me does amplifiers sound the same?
yes or no
This is exactly why one has to understand the science to interpret the result.
This work is essentially the same as if you play at 90dB the distortion needs to be under -90dB to be transparent. Or if you play at 115dB the distortion needs to be -115dB.
Where statistics and study showed that 0.03% is probably the best case audible distortion. Though majority of the listeners can't tell below 0.1% However study also shown that distortion under 1% is generally not noticeable.
Science can be right or wrong. Showing a piece of work is not the same as a legit proof.
Yes amplifiers will sound different if there's too little power which happens very often. And it will sound different if distortion is higher than threshold.
The most powerful and simple proof is an ABX test that's what's been said here.
 

Eetu

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@etc6849
wow thx.
I wonder what the more experienced EE who believe amplifiers sound the same have to say to that post.
I used to believe amplifiers doesn’t sound the same.
Then I bought Harbeth and start reading Harbeth forum then this forum, and like I believed all the marketing magazine and tests that amplifiers have a sound, I started to believe the harbeth forum and this forum. That amplifiers sound the same.

now I m in doubt. Cause you re explanation is funded by science! So pls help me does amplifiers sound the same?
yes or no

Keep in mind that @etc6849 's calculations show that thd+n are below room ambient while listening at loud levels (except at 1400W). As @JohnYang1997 said it's way harder to hear distortion with actual music so the calculations are a best (or should I say worst) case scenario. Both amplifiers also have flat frequency response so no audible difference there either.
 

Inner Space

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I called Benchmark and asked about the altitude warning. Turns out that the German TUV test (Technischer Überwachungsverein, i.e. Technical Inspection Association) classifies cooling efficiency as reduced above 6,500 feet, hence the obligatory warning in compliance with that voluntary protocol. In the real world, however, Benchmark feels there will be no practical limitation, given the unit's general cool running and proper thermal protection.
 

RichB

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Keep in mind that @etc6849 's calculations show that thd+n are below room ambient while listening at loud levels (except at 1400W). As @JohnYang1997 said it's way harder to hear distortion with actual music so the calculations are a best (or should I say worst) case scenario. Both amplifiers also have flat frequency response so no audible difference there either.

Examining @etc6849 room noise floor measurements, it is clear that after 170 Hz the room is below 15 dB. In the range where our hearing is most sensitive, it is below 5 dB.

RoomNoise.png


- Rich
 

cjm2077

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I called Benchmark and asked about the altitude warning. Turns out that the German TUV test (Technischer Überwachungsverein, i.e. Technical Inspection Association) classifies cooling efficiency as reduced above 6,500 feet, hence the obligatory warning in compliance with that voluntary protocol. In the real world, however, Benchmark feels there will be no practical limitation, given the unit's general cool running and proper thermal protection.

Interesting, first I've heard of that one. But there is always another standard with some odd new twist to it.
 

Coach_Kaarlo

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Test conditions are typically steady state conditions (e.g. resistive loads only).

You can certainly test amps using a moving load and I would assume this was done internally by a manufacturer as serious with perfection as Benchmark. Benchmark's application notes do this with headphone amplifiers, can't remember if they have published measurements of the AHB2, I want to say they do somewhere.

https://benchmarkmedia.com/blogs/application_notes/12838141-headphone-amplifiers-part-1

Damping factor is the measurement for determining how well a woofer will be controlled. It is the nominal speaker impedance divided by the output impedance of the amplifier. However, as you point out, nominal speaker impedance isn't reality...

Driver control is another reason I tri-amped my speakers and will never go back. My old amps undeniably had better control of the woofers once they were wired directly to them.



Thanks for the response, deafening silence otherwise.

I read the (as usual) excellent Benchmark application notes you linked to. Seems like the logic applied to measuring the dynamic loads on head phones, and the subsequent clear results of how different dynamic loads are to static loads, indicate to me that measuring amplifiers in static conditions is almost utterly pointless. Not unlike using nominal impedance for speakers.


Honestly, in one breath knowledgeable members on this forum acknowledge the challenging dynamic requirements on the amplifier to drive a loudspeaker accurately - then in the next breath present endless measurements of static steady state conditions and loads as proof of what they are hearing or not hearing from an amplifier.

Am I the only one struggling here?! Maybe I am missing something obvious?

Edit [Benchmark quote: “The truth lies here: Specifications must be measured under typical operating conditions if they are to be useful in predicting audible differences.”]


I ask again, how can I measure the dynamic performance of the Benchmark AHB2 against other amps, with the same set of speakers?
 
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DonH56

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I worked 80+ hours last week and am not a speaker expert so take this FWIWFM.

Static testing up to full power is a reliable indication of performance though perhaps not of dynamic headroom if that is what you are asking. If the amp achieves excellent performance under steady-state conditions it is likely to do slightly better under dynamic conditions.

"Dynamic performance" is not really well defined; what exactly do you want to test?

Dynamic headroom uses a burst test on the bench but I would not subject a speaker to that sort of thing. It was a 20 ms burst per IHF; I think it is now an EIA standard but defined the same (not sure, have not really looked -- search for "IHF dynamic headroom test" or something like that). It is useful for assessing headroom beyond the steady-state power output but is not all that meaningful to me. More headroom can indicate a "looser" power supply that is not as well regulated, or perhaps an amp has lower steady-state performance due to limited thermal management or other limitations such as output device current limits and such. Without knowing more "dynamic headroom" does not really tell me much about the amp in comparison to other amps.

If you want listening tests, my old sloppy clay-eared test was to use the Sheffield Drum Record or anything with large (percussive) transient signals.

HTH - Don
 

etc6849

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Full disclosure, that room noise measurement is for my theater, not my office. To get noise floor that low takes a lot of work, and definitely can't be done in an open room, etc... My theater has a lot of absorption on walls and ceilings at the first reflection points, plus I have 8 large bass traps.

@Pjetrof
The sound is absolutely world class with the AHB2's and they hold their value very well. I have no measurements to prove it, but IMD will be much lower with the AHB2 vs the Emotiva amps I had before (sold my last one's in 2019). For what it's worth, I remember hearing more detail in the background of tracks. Without passive crossovers, the Emotiva amps were useless for tri-amping as they had way too high of noise floor, and this hiss was easily audible at the main listening position.

Examining @etc6849 room noise floor measurements, it is clear that after 170 Hz the room is below 15 dB. In the range where our hearing is most sensitive, it is below 5 dB.

View attachment 65612

- Rich
 

Pjetrof

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@etc6849 thx for your replies.
I m in no doubt that the benchmark is a remarkable product, measurements prove it.
in my case living room is listening room, electronics are hidden in cupboard.
no Surround, just stereo normal spl level listening and singer songwriter music.
i ve harbeth 30.2 and was driving them with Accuphase e650.
that was underpowered for my speakers my spl level.
cause I Would lose so much money when I try to sell the amp, Not a year old and half the money, I was hesitated to spend mony again on the Accuphase 480, or benchmark or quad etc etc.
so I kept the Accuphase and bought for 179 euro a behringer A800.
comparing both not blind not level matched same room same speakers same music same ears.
the behringer edged it why the power uf course.
but when I was playing by ear same spl level I didn’t t hear a diffrence. So I’m sure if you do it blind and level matched no clipping no distortion you will not Be able to pick the right amplifier each time.
 

Aerith Gainsborough

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Here's a comparison I did for using an AHB-2 to my now sold Emotiva XPR-1 monoblocks I used to drive some Klipsch P-17b bookshelf speakers. I don't have any speaker data for the P-39f drivers or I'd do similar calculations for them. The bookshelf speakers still have the factory crossover in them and sit in my office.

Emotiva XPR-1 monoblocks (max output and 1 watt output):
View attachment 65464
In regard to @Pjetrof's question: I think, in order to put these measurements into a useful context, you need speaker data.
At 121 dB SPL, the distortion generated by small bookshelf speakers is most likely pretty extreme with them crying out for mercy, rendering the 41dB of the amp completely irrelevant. On top of that would be the question of whether human ears are be able to perceive any 41dB signal right next to a 110dB+ spike (assuming 3m listening distance @ -9dB).

I certainly couldn't because at these SPLs, I would cover them. I'd like to still be able to enjoy music 20 years from now. :p
 
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GXAlan

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@etc6849 thx for your replies.
I m in no doubt that the benchmark is a remarkable product, measurements prove it.
in my case living room is listening room, electronics are hidden in cupboard.
no Surround, just stereo normal spl level listening and singer songwriter music.
i ve harbeth 30.2 and was driving them with Accuphase e650.
that was underpowered for my speakers my spl level.
cause I Would lose so much money when I try to sell the amp, Not a year old and half the money, I was hesitated to spend mony again on the Accuphase 480, or benchmark or quad etc etc.
so I kept the Accuphase and bought for 179 euro a behringer A800.
comparing both not blind not level matched same room same speakers same music same ears.
the behringer edged it why the power uf course.
but when I was playing by ear same spl level I didn’t t hear a diffrence. So I’m sure if you do it blind and level matched no clipping no distortion you will not Be able to pick the right amplifier each time.

I am sure you can find sponsors to pay for sending the E650 to Amir. If you are the original owner, you may be able to have Accuphase wire it for 117v

I think the Accuphase is hurt by its limited power. When Amir measured the A800, he suggested that sensitive speakers may result in hiss.

The other difference will likely be in more complex musical passages than singer/songwriter type music. (if a difference is to be heard). You may also notice a bigger difference when using more sensitive speakers.

But if the e650 doesn’t sound any better than the A800 to you, you should sell the e650. Although you take the hit in depreciation, it will only get worse over time.
 

Pjetrof

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@Aerith Gainsborough
My speakers are harbeth 30.2
When the Accuphase was driving the speakers I phoned several shops, where I was a regular customer, telling them the Accuphase the feeling I had was under powering. Each sales Man couldn't t believe it. They knew my system and my place, my choice of music,but where happy to sell me pre power a class from Accuphase or high power class ab Accuphase.
I play most of time singer song writer so no complex music at reasonable level.
then I discovered harbeth user group they say don’t pay to much on electronics Just make sure you have enough watts.
still didn’t believe it. I heard from benchmark, at harbeth they like quad was thinking tubes Luxman hegel anyway walking in circles and spending stupid money!
then I discovered this forum!!
out of curiosity I bought the behringer a800 ....... the rest is history
5C84F773-7CA6-40E1-89DD-67A3FE6764A5.jpeg
 
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Pjetrof

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@GXAlan
see post above
In the mean time I sold the Accuphase and took the hit!
and was thinking buying benchmark .... but why should I?
for the better measurement?
its inaudible?
plus the behringer has more power!
no gonna buy matrix dac,
and After Corona a nice holiday.
i m finished with spending lots of money on electronic.
uf course the accu or Luxman or tubes had primaluna feel luxurious solid etc but that is not the reason I bought
those machines, they have to amplify a signal!
nothing more nothing less.
in my case hidden in a cup board.
image.jpg
 

Eetu

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@GXAlan
see post above
In the mean time I sold the Accuphase and took the hit!
and was thinking buying benchmark .... but why should I?
for the better measurement?
its inaudible?
plus the behringer has more power!
no gonna buy matrix dac,
and After Corona a nice holiday.
i m finished with spending lots of money on electronic.
uf course the accu or Luxman or tubes had primaluna feel luxurious solid etc but that is not the reason I bought
those machines, they have to amplify a signal!
nothing more nothing less.
in my case hidden in a cup board.
View attachment 66195
Yes, as you've noticed the 30wpc at 8 ohms of the Accuphase wasn't probably enough to drive your rather ineffecient Harbeths.

There's a lot of options other than the A800 and the Benchmark though! I would look into Purifi & Hypex-based amps that have similar rated power as the A800 but a lot lower THD + N (AND price compared to the AHB2).
 

Pjetrof

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Yes I know but would it be audible?
hypex nc 400 is 1200 euro
purify i don’t know for sure around 1500
the Behringer is 179 euro
and if so
would it be 10 times better.
i know the Accuphase is 60 times the price.
at low level so well beyond clipping the sound is not different
my speaker are only 86 dB.
so why buy the recommended amps
i can buy every 2 year when warranty finish a new one for almost 20 years
and Spend the same
i believe in class d Efficiency now with global warming etc but I also believe the technic will improve every year.
 

Pjetrof

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And all this thx to Amir and his Site

it was not long ago if an amp didn’t weigh 40 pound I would not listen to it.
if it was not expensive it couldn’t be good.

anyway we make mistakes we re humans.
i wish I discovered the internet earlier.
and more this forum.
I would have spend money much wisier!
 

Aerith Gainsborough

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Yes I know but would it be audible?
Hmm honestly I'm not sure about that one.
If I remember correctly, the Behringer had it's highest harmonic at -80dB?

Typically, people here laugh at AVRs that have sinads in the 85-90 range, calling them "insufficient".
Keep in mind, gear like the Behringer is designed for professional use in venues / PA systems. You rarely get quiet rooms in these settings, so THD/noise might not matter as much there.

If you have a good headphone setup, it would be easy for you to compare the two and assess whether YOU are able to hear the noise floor / distortions. If you can't, then don't give the numbers another thought and get back to enjoying the music.
 
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