• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Review and Measurements of Benchmark AHB2 Amp

josh358

Senior Member
Joined
Jun 13, 2017
Messages
493
Likes
387
I would be interested to read what other amplifiers you compared it to (apart from the Parasound) and how you determined any differences.
Different methods, of necessity -- I'm largely retired at this point and do only the occasional consulting gig, so I no longer hear much outside of the occasional show or visit to a dealer. So I've compared some amps formally here -- besides the A21, off the top of my head, Yamaha and Crown pro amps, an old Hafler, a Vidar, an Emotiva -- none of which are exactly state of the art (the Vidar is the best of them, followed by the Emotiva) -- and otherwise I have to rely on memory of the amps I've listened to over the years at home, in the studio, and so forth. So I've never had a chance to A/B it with something like a Pass, never mind something like a VAC!

When I have an amplifier here, I level match and do a comparison with an A/B switcher that I built for the purpose, using both short-term A/B listening to circumvent aural accommodation and long-term listening to circumvent the shortcomings of short-term auditory memory. Then I listen to a variety of tracks that I've found useful for evaluation and with which I'm intimately familiar. So I'll listen to choral and orchestral music, and piano -- the most demanding and revealing -- and also smaller chamber works. I'll supplement that with some jazz and rock, which have their own demands. I find that the difference between good amplifiers is subtle, and while some things stick out right away (the Parasound, for example, has very rich midbass), others are subtle and require long-term listening (forex, a cymbal on the Parasound sounds like noise, while on the AHB2, it sounds like, well, a cymbal -- it rings). Listening is on my Tympani IVA's, which present the amps with an easy non-reactive load but are inefficient so likely to force them into Class B or even clipping and are among the more revealing speakers -- more revealing than most dynamics, less than 'stats (which however are a very reactive load so perhaps not the best for amplifier comparisons). (To put this in perspective, the Parasound, which is a high bias AB amplifier, would with the Tympanis go into Class B at something like 94 dB SPL.)

Finally, if a difference isn't obvious, I'll seek outside confirmation, either by asking someone to listen and getting their unprompted comparison, or by reading what others have heard, e.g., looking at reviews. Typically it matches up -- occasionally I find that I've fooled myself!

That said, I'm not a critic and I don't have an opportunity to hear a wide variety of equipment under controlled conditions as I did in the studio. So while I think I can do a valid A/B comparison if I have the gear here (I've been doing some interesting DAC comparisons lately) I haven't heard a lot of what's out there today under good conditions, as opposed to at shows and dealers, where it's hard to determine what's due to what.

In any case, my characterization of the AHB2 as the cleanest amp I've ever heard is based on years of experience with a large number of amplifiers, but shouldn't be taken as some kind of formal review, it's just my impression -- though if you look at reviews, you'll find that others have independently reached similar conclusions.
 

maty

Major Contributor
Joined
Dec 12, 2017
Messages
4,596
Likes
3,161
Location
Tarragona (Spain)
@JohnPM

Simple questions: Do you get excited when listening to certain recordings? How many times does it happen in a week when listening to music?

For me it is a crucial factor. Not long ago the same recordings did not get excited or did not do it with the same intensity.

https://www.diyaudio.com/forums/music/6958-playing-listening-post5796227.html

Now some of them drive me crazy, I become the conductor of the orchestra, I sing with the choir ... that is what I am looking for and I have achieved with my second audio system.
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
493
Likes
387
Oh, I wholeheartedly agree, there is no substitute for listening........................as long as you don't know what you are listening to.
That's why (since it isn't practical for me to do blind tests) I always seek verification for my subjective impressions, either by having a non-audiophile who knows live music listen and tell me what they've heard, or reading reviews *after* I listened to see if the reviewer heard what I did. In my experience, they almost always did, although we don't always agree on what we like.
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
493
Likes
387
Another simile.

In a recording studio, to detect the quality of the audio we want a loudspeaker that gives the frequency response as flat as possible, and an amplifier that is very transparent, like the Benchmark.

But if we want to enjoy music at home, such a flat response can cause auditory fatigue in a short time. From there many search speakers with very flat response and few oscillations but with a negative slope.

In short, that a little imperfection can be the panacea. Another thing is what usually happens, with very imperfect sound systems but that enchants its owners for a while until they spend more money on changing components again and again, without rhyme or reason, ignoring the available specifications and measurements, only attending to subjective evaluations of other people.
In all fairness, the use of a declining house curve isn't an imperfection, or rather, it compensates for some known imperfections in two channel stereo, namely that, if you want the balance from your monitor speakers to sound like what you hear in the hall, you need a declining curve. But as J. Gordon Hold noticed years ago, this isn't true with multichannel.

I know of two possible explanations for this. One that I've read is that it has to do with the HRTF (head-related transfer function) -- the speakers are at +/- 30 degrees, and the declining curve compensates for the response of the ear at that angle. The other is just that cardioid microphones pick up what's in front of them, which is mostly direct sound (particularly since they're generally located close to the orchestra or in multimiked recordings even right above it). Whereas in a hall after the first few rows you're in the far field and hear more reverberation than direct sound, and the reverberation has attenuated highs. In support of that, I've noticed that recordings made with spaced omnis and Blumlein (crossed figure eight) have a more natural balance than recordings made with cardioids or close miking. Both theories would be consistent with Holt's observation that the house curve is unnecessary with multichannel.

But here's another imperfection for you -- the acoustics in studios are quite dry, because you have to able to hear every detail, every glitch. But Floyd Toole pointed out that recording engineers prefer a wetter acoustic at home. This is in a sense less accurate, but the added reverberation is necessary because two channel stereo doesn't sound convincing on its own -- it needs room reverb. So you're basically adding artificial reverb to make up for the missing reverb in the two channel recording. (Multichannel, by way of contrast, works best with a lower RT60.)
 

Juhazi

Major Contributor
Joined
Sep 15, 2018
Messages
1,717
Likes
2,897
Location
Finland
Nice but a bit strange discussion about distortion...

I think that the sound system at home should not add anything to the original "data" on the media. But we live in an imperfect world. The greatest source of distortion is the loudspeaker, no doubt. But still we can hear and measure distortion and other faults of other gadgets between source and the speaker too. Loudspeaker is a very unlinear device with many problems, of which distortion is not the greatest. When we measure it's acoustic performance one big problem is noise floor - at low spl it masks all distortion. Distortion % is not constant, it gets bigger when spl is raised, and this is nonlinear.

I can hear differencies in amplifiers sometimes, even with moderate spl and mid-quality speakers. I don't know where it comes but one of my suspects is the amount and type of feedback used. Power rating and distortion specs don't tell it, unless there is something really strange like most tube amps have.

I understand Kal well and respect the honesty! Sorry, I always skip the impressions text of reviews in S'phile and check Atkinon's measurements and comments first. Then I look at Specs and price. Then only sometimes I read the conclusions/final words of the review and usually get surprised or confused.
 
Last edited:

daftcombo

Major Contributor
Forum Donor
Joined
Feb 5, 2019
Messages
3,687
Likes
4,068
the use of a declining house curve isn't an imperfection, or rather, it compensates for some known imperfections in two channel stereo
Do you know what should be the slope?
Does it depend on the room size? Listener distance? RT60?
Should the slope be applied to the speaker response or measured at the listener spot?
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
493
Likes
387
Do you know what should be the slope?
Does it depend on the room size? Listener distance? RT60?
Should the slope be applied to the speaker response or measured at the listener spot?
You could start with 1 dB/octave, but different authorities have different opinions on the slope and where to apply it. (It may be that there's no ideal curve, because of differences in recording technique and venue.) Then you want to measure near your listening seat, with spatially averaged readings if possible. RT60 and room size will affect it as you surmise, as well as loudspeaker response, and that will show up in your measurement. So you tune it so that the measurement is where you want it. Then you listen and fine tune by ear.

Here's a discussion if you're curious:

https://www.innerfidelity.com/content/acoustic-basis-harman-listener-target-curve
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
493
Likes
387
I do agree with this statement and that is why I bought them. However,.....

I also agree, to a degree, with these comments based on comparison with the similar Parasound A31. It is no so much that the Benchmark robs the music of excitement but that the Parasound and Benchmark provide different types of excitement.
That's a good point. I was listening to a high res file on the Benchmark the other day and the sound was so beautiful that I couldn't stop listening. Like a forest pond on a windless day.

Now what we need is an amplifier that does everything. Maybe it's time for an AHB3? :)
 

GrimSurfer

Major Contributor
Joined
May 25, 2019
Messages
1,238
Likes
1,484
Interesting discussion. Subjectivists usually say that it is impossible for live music to be reproduced faithfully. This makes limited sense because there are all kinds of things that may colour live performances -- from concert hall (acoustic space effects for symphonic performances) to amplification effects (amplifier distortion in contemporary performances).

I tend to lean the other way... give me sources, preamps, and amps that allow the least possible colouring and work with loudspeakers and spaces to achieve the necessary effect. The ABH2 fits within this model nicely, whereas a great many tube and solid state consumer and so-called pro shite do not, according to objective measurements.

The measurements taken by Amir and others elsewhere on the web demonstrate that Benchmark has done a very credible job designing and building the ABH2. Since these measurements are pretty much irrefutable at this stage, one may conclude that Benchmark has come closer to reaching amplifier excellence than a great many manufacturers of audio equipment (past or present).

If transparency is not the goal, then perhaps there's room for another conversation like source selection, decoding, room set-up, equalization etc. But these lie outside the role of an amplifier, which is to provide gain and gain only, to an audio signal.
 
Last edited:

GrimSurfer

Major Contributor
Joined
May 25, 2019
Messages
1,238
Likes
1,484
That's a good point. I was listening to a high res file on the Benchmark the other day and the sound was so beautiful that I couldn't stop listening. Like a forest pond on a windless day.

Now what we need is an amplifier that does everything. Maybe it's time for an AHB3? :)

Interesting points, josh.

First, I'm jealous of your Benchmark. Wish I had one myself.

Second, I'm delighted to hear that you're enjoying yours so much.

Third, I think that one of the biggest problem in the industry at the moment is trying to do everything adequately at the expense of doing one or two things very well.

The consumer electronics industry loves designing, building, and selling such gear at various price points. They're not so good at doing one or two things very, very well.

If we allow the qualitative aspect to be removed from audio, then the whole thing either turns into a checklist or devolves into the ridiculous assertion that all amps etc. sound the same.

I'm in no way suggesting that's what you meant by the last bit of your post.. I'm just highlighting one of the hazards of placing features ahead of quality, which I've always seen as something that has dumbed down the hobby.
 

josh358

Senior Member
Joined
Jun 13, 2017
Messages
493
Likes
387
I have a love for the big amplifiers made at the end of the 80s. Specifically the Sony ES series. I like the soundstage, and the way in which they make me able to hear the air between the instruments. You can almost touch it. They place another acoustical room inside your room. Alas, my 30 year old amplifier is currently broken, again and I'm looking for something more reliable.

Given your experience with the AHB2, do you think it would be good fit for me?

For the last couple of days I've been going back and forth between the Hyper NC400 DIY modules, a boutique NC500 amp, the NAD M22 or the Benchmark. I'm quite disappointed the tech specs of most current amplifiers, when I compare them with what was possible 30 years ago, it's often a joke what you get today.
It's hard for me to know since I don't know your listening habits and equipment. That said, the AHB has imaging and detail in spades, without being hyped. This is an amplifier for people who don't like distortion, whether it's something like crossover notch distortion that takes your ears off or the kind that prettifies the sound with second harmonic distortion, and it's a bargain by high end standards as well. That I think highly of it is evidenced by the fact that I own it.

What I'd suggest you do is take advantage of Benchmark's 30 day trial, there's really no substitute for auditioning something with your equipment and musical selections.
 

Shadrach

Addicted to Fun and Learning
Joined
Feb 24, 2019
Messages
662
Likes
947
Another simile.

In a recording studio, to detect the quality of the audio we want a loudspeaker that gives the frequency response as flat as possible, and an amplifier that is very transparent, like the Benchmark.

But if we want to enjoy music at home, such a flat response can cause auditory fatigue in a short time. From there many search speakers with very flat response and few oscillations but with a negative slope.

In short, that a little imperfection can be the panacea. Another thing is what usually happens, with very imperfect sound systems but that enchants its owners for a while until they spend more money on changing components again and again, without rhyme or reason, ignoring the available specifications and measurements, only attending to subjective evaluations of other people.
tenor.gif
 

Kal Rubinson

Master Contributor
Industry Insider
Forum Donor
Joined
Mar 23, 2016
Messages
5,273
Likes
9,794
Location
NYC
I understand Kal well and respect the honesty! Sorry, I always skip the impressions text of reviews in S'phile and check Atkinon's measurements and comments first. Then I look at Specs and price. Then only sometimes I read the conclusions/final words of the review and usually get surprised or confused.
Me, too.
 

Kal Rubinson

Master Contributor
Industry Insider
Forum Donor
Joined
Mar 23, 2016
Messages
5,273
Likes
9,794
Location
NYC
Kal, I think you mentioned you have 3 of them. How are you using the 3 if you don't mind (bridged mono-blocks, biamping/triamping, multiple systems, etc.) ?
Bridged mono-blocks, one for each of my front three speakers.
 
  • Like
Reactions: Pio

edechamps

Addicted to Fun and Learning
Forum Donor
Joined
Nov 21, 2018
Messages
910
Likes
3,620
Location
London, United Kingdom
Harman developed an algorithm that they say correlates subjective impressions of speaker quality with on axis and polar response, but while Stereophile does some of these measurements we don't have that algorithm

Are you referring to that paper, written by Sean Olive under Harman? If so, it is publicly accessible, though sadly behind a paywall, so I'll paraphrase it. Here's the equation:

Sean E. Olive said:
Pref. = 12.69 − 2.49 * NBD_ON − 2.99 * NBD_PIR − 4.31 * LFX + 2.32 * SM_PIR

The paper defines NBD_ON as "On-axis frequency response Average Narrow Band Deviation (dB) in each ½-octave band from 100 Hz-12 kHz". NBD_PIR is the same for the predicted in-room response (which itself is derived from on-axis and off-axis measurements). LFX is "Low frequency extension (Hz) based on -6 dB frequency point transformed to log 10", and SM_PIR is "Smoothness (r²) of predicted in-room response based on a linear regression line through 100 Hz-6 kHz".

The above equation can predict the subjective preference score that human listeners gave while blind testing the 70 loudspeakers in the study with a coefficient of determination of 89%. The nitty-gritty details of these metrics and how to compute them are described in the paper.

I would find it highly valuable if people doing loudspeaker measurements also provided the result of this equation, as it condenses most of what matters into a single, easily comparable number (similar to how @amirm likes to use SINAD to score electronics).

There's also a published formula for the audibility of harmonic distortion components

I never heard of that one. I'd be interested in learning about studies on that topic - accurately quantifying the audible impact of non-linear distortion is still a somewhat unsolved problem, as far as I know. 15 years ago Geddes and Lee proposed a new metric that seems better than THD but it doesn't look like it caught on.
 

tktran303

Addicted to Fun and Learning
Forum Donor
Joined
Mar 27, 2019
Messages
683
Likes
1,181
Really interesting post, thanks for sharing. I guess you're referring to "Near field HD spectrum (20 mm distance)" from https://hificompass.com/en/speakers/measurements/accuton/accuton-s280-6-283n. I should probably give it a try myself too, but @RayDunzl is the man for such measurement, in case he haven't done it already. It would be nice to check H2...H5 for 90dB at 2-3 meters in front of speakers (listening point), of course...sinewaves (-1dBFS maybe).

Thank you!

The 20mm measurement is only accurate up to approximately 400Hz for this large 11” woofer.

I’m talking about the 315mm measurement, which is valid for higher frequencies.

One can freely peruse all the other woofers, midranges and tweeters on that site to see the harmonic distortion of many drive units.

The science of transducers measurements interpretation is beyond the scope of this thread.

My point is, the Benchmark is a fine amplifier, and offers superb measured performance. As far as a class A/B amplifier is concerned, I haven’t seen else measure like this for almost 2 decades.

The fact that it is A) not silly money B) manufactured in the country of origin ie not outsourced C) isn’t the size of a fridge should make it on the top of everyone shopping list.
 

gvl

Major Contributor
Joined
Mar 16, 2018
Messages
3,427
Likes
3,982
Location
SoCal
Really isn't there something in the measurements done here that can account for that on your system?

I really don't know. This time I'm annoyed to the point I actually plan to do a blind level matched test as the differences seem to be pretty obvious, but if I fail then it's my brain playing tricks on me.
 
Top Bottom