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AHB2 Mono v Stereo - what is audible?

Coach_Kaarlo

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I am genuinely interested

I understand that you think I'm manifesting the "ASR way", but that isn't the case. For me this isn't a matter of dogma, it's about a rationally constructed method of truth-testing. If you can hear the difference between 2 amplifiers, then that's great. That is true. That is your experience. For it to be objectively true then this truth needs to exists outside of your subjective experience. Double blind testing isn't blind dogma, it's a tried and tested scientific method used to uncover to location of the difference that a person might experience. If you experience subjective differentiation and then can replicate this under blind conditions then there may be an objective verifiable reason as to why this occurs.

Now, if said double blind testing is undertaken, for it to have the type of validity that I mention above, one's methodology needs to be scrutinised. What equipment was used? Did you volume match? What equipment did you use to volume match? Again, this is not blind dogma, but tried and tested scientific methodology involving experiment control.

Unfortunately recording your set up and posting it for a poll wouldn't meet this methodology. I can't help but think that you already know that and are perhaps being deliberately provocative. But, of course, I might be wrong.


Dogma is not being able to consider rational alternatives. Rationally if only a few people can hear a difference no big deal, carry on.

However, if a large portion of listeners hear the same difference then we can start the science.....blind tests etc......because there may be some basis to the hypothesis. Rare that it is ever done the other way around in the real world.....apart from on ASR in the endless discussions of what is audible etc etc etc etc.....


My hypothesis: the real world addition of Revel F208 speakers to my system (see signature) produces audible differences in sound reproduction between the mono and stereo settings when using the AHB2 amplifier.


My simple experiment:
  1. same source content (Stevie Ray Vaughan live in Montreux - Texas Flood https://tidal.com/browse/track/1217)
  2. playback via Tidal into PC into DAC 2 then AHB2's into Revel F208's
  3. levels matched using random pink noise - full range (delta wave does show a small difference in level - oops just adjust in playback see edit below)
  4. [edit: the levels are off apologies, adjust File 1 =+0.67dB / File 2 = +4.00dB]
  5. REW version 5.20
  6. MiniDSP Umik-2 with 90 deg calibration file - positioned at 1050mm high, on the centre LP
  7. speaker CRS 2100mm
  8. same AHB2 amplifiers (switched between mono and stereo, and channel 2 interconnect and speaker cable connected to stereo position)
  9. same length speaker cable (damping factor not affected, cable capacitance and resistance unchanged)
  10. room effects removed by listening outdoors in free field conditions - see measurements below

The test - what is audible?
  1. file #1 was recorded with amplifiers set to mono or stereo
  2. file #2 was recorded with amplifiers set to mono or stereo
  3. files are identical and this was a bias test not a listening test (ie. I tell you they are different but you believe / hear they are not)

Links:

File 1 = https://drive.google.com/file/d/1Xyn_yQ2LbrVZE4KAmUiLrvBBsVxKDj2f/view?usp=sharing

File 2 = https://drive.google.com/file/d/17GHit4JTZbAzXAb4QNxEj8zkAqkh1XWB/view?usp=sharing

Record your results here = https://docs.google.com/spreadsheets/d/1TBzr7uOlnReLAC-NVYUcfFqvnZUQ5Hy_Dz1QSPPzpIw/edit?usp=sharing


Measurements below taken from the LP (recording point), with everything setup as recorded;

TEST - WATERFALL.jpg


TEST - DECAY.jpg


TEST - SPECT.jpg




This is an imperfect, and overly simplified test = yes! But not everything of import needs to be the subject of extensive blind testing or published scientific peer reviewed papers. Some things are so blatantly obvious that they require no such benchmark - for example speakers with correct phase versus out of phase incorrect wiring........

This is a bit of fun to see what can be heard. Don't cheat yourself, listen and vote.
 
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restorer-john

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1st attempt. ABXd with Foobar, focusrite 2i2v2 and my AKG-702s.

1616980564239.png


Note the auto gain adjustment was significant...

And my result was pretty poor, not much better than 50:50. But look at the result harder. I worked out what difference I was hearing after the 6th trial and only made one mistake in the next 10 ABXs.

I'll try again tonight with my listening ears on (and a wine or two). ;)
 
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Coach_Kaarlo

Coach_Kaarlo

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1st attempt. ABXd with Foobar, focusrite 2i2v2 and my AKG-702s.

View attachment 120890

Note the auto gain adjustment was significant...

And my result was pretty poor, not much better than 50:50. But look at the result harder. I worked out what difference I was hearing after the 6th trial and only made one mistake in the next 10 ABXs.

I'll try again tonight with my listening ears on (and a wine or two). ;)

Thanks @restorer-john , clearly I am operating out of my area of competence.

I think I set levels when something was noisy in the background, then recorded when it was not....perhaps....hard to explain such a big difference otherwise.
 
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RobS

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Did you only increase in gain with the mono AHB2 (should be +6db)? Or was there more to the performance of it in mono? Sorry not sure what we should be looking for.
 
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Coach_Kaarlo

Coach_Kaarlo

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Did you only increase in gain with the mono AHB2 (should be +6db)? Or was there more to the performance of it in mono? Sorry not sure what we should be looking for.

I matched the levels (aiming for 90dB) with REW each time before recording, however I live in a penthouse apartment with a large external uncovered balcony, which means some background noise. That is the only reason I can think of why the recording levels differ. However based on John's feedback I edited the post with his gain adjustments.

The test is to see if there is any audible difference between the two files.
 

RobS

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Ah gotcha. Listening via HD800 and track 2 sounds duller, less oomph in the bass. Track 1 is more dynamic, open and more present bass. I think it's pretty obvious track 1 is mono, lol.

BTW what gain setting on the back do you have on the AHB2 for both mono and stereo?
 
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Coach_Kaarlo

Coach_Kaarlo

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Ah gotcha. Listening via HD800 and track 2 sounds duller, less oomph in the bass. Track 1 is more dynamic, open and more present bass. I think it's pretty obvious track 1 is mono, lol.

BTW what gain setting on the back do you have on the AHB2 for both mono and stereo?

Ran them both with the switch all the way down - as per Benchmark. But your advice was good - they sound much better with the middle setting.

Will wait awhile before confirming or denying the result.
 

RobS

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It probably has to do with less feedback with the higher gain settings. I’ve been on the lowest gain setting for awhile now trying to get more acquainted with it. I fixed the gain structure of my system so it didn’t sound as bad as before. I think it’s important for people to know that you really should be sending a +22dbu signal to the AHB2 when it’s in its lowest gain mode. If your balanced source is only outputting 4VRMS it’s best to stick to the middle gain setting or even the top one.
 

RobS

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BTW can you tell me what the output is of your DAC/Pre? 2VRMS? 4VRMS? Higher? I’m curious.
 

restorer-john

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@Coach_Kaarlo The recording sounds pretty dull and lacking dynamics to me. I don't know the recording or the music however. Is it just like that? Or did you just burn out the tweeters? ;)

As a comparison, here's a recording I made in my loungeroom (several months ago) just with an inexpensive handheld (you can hear my hand move at one point) Tascam DR-05, approximate listening position. 90 degree internal omnis.

https://drive.google.com/file/d/15fXEeo7PshuxgijK97mVCJ1CZfcSdw1U/view?usp=sharing

Vintage TOTL 1989 Sony ES gear.
Sony CDP-X7esD
Sony TAE-77es
Just one Sony TAN77es Rated 270+270W (continuous 20-20k) @4R- dynamic (EIA/EIAJ 520W/[email protected])
into a pair of little Jamo E800s (165mm two way) sitting on 600mm stands.

These puppies:
IMG_4136 (Small).jpeg

IMG_4137 (Small).jpeg


Sure, the sound is a little live (polished wooden floors in the kitchen/family adjacent), but full of dynamics.

It was an early 1980s Tom Scott, live to two track digital recorded on the Soundstream digital recorder. No analog steps, no overdubbing, all musicians in the one studio at the same time- something novel these days.

But Amir will chastize me for using stereo... :)
 
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Coach_Kaarlo

Coach_Kaarlo

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BTW can you tell me what the output is of your DAC/Pre? 2VRMS? 4VRMS? Higher? I’m curious.

Not sure of the top of my head - std DAC2-HGC output - jumpers unchanged from factory.
 
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Coach_Kaarlo

Coach_Kaarlo

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@Coach_Kaarlo The recording sounds pretty dull and lacking dynamics to me. I don't know the recording or the music however. Is it just like that? Or did you just burn out the tweeters? ;)

As a comparison, here's a recording I made in my loungeroom (several months ago) just with an inexpensive handheld (you can hear my hand move at one point) Tascam DR-05, approximate listening position. 90 degree internal omnis.

https://drive.google.com/file/d/15fXEeo7PshuxgijK97mVCJ1CZfcSdw1U/view?usp=sharing

Vintage TOTL 1989 Sony ES gear.
Sony CDP-X7esD
Sony TAE-77es
Just one Sony TAN77es Rated 270+270W (continuous 20-20k) @4R- dynamic (EIA/EIAJ 520W/[email protected])
into a pair of little Jamo E800s (165mm two way) sitting on 600mm stands.

These puppies:
View attachment 120901
View attachment 120902

Sure, the sound is a little live (polished wooden floors in the kitchen/family adjacent), but full of dynamics.

It was an early 1980s Tom Scott, live to two track digital recorded on the Soundstream digital recorder. No analog steps, no overdubbing, all musicians in the one studio at the same time- something novel these days.

But Amir will chastize me for using stereo... :)


Re tweeters and the tonality of the recording, here is an on-axis measurement the same afternoon I made the recording.

TEST - AXIAL RIGHT.jpg
TEST - AXIAL LEFT.jpg



Highs seem good on the axial measurements, I think what we hear is the lack of reflections, and the off axis sound drops away so much at the LP.

The tonality compared to the original track is quite different from an accuracy / reproduction POV when listening through headphones, but I guess there is sufficient detail to hear any difference that may or may not exist.

TEST - WATERFALL.jpg


Probably the Revel's themselves ;)
 

Blumlein 88

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Just a suggestion. For level matching best practice is to use a tone 440 or 1 khz is usually good. And set by the voltage level at the speaker input terminals. You'll be able to get precise level matching that way. Listen one way and set levels. Play your tone and record voltage. Then you can set the second way to the same voltage.

I've not listened to your files yet, but it wouldn't be surprising for bridge and stereo to be just a little different due to gain structure and changes in output impedance.
 
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Coach_Kaarlo

Coach_Kaarlo

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Coach_Kaarlo

Coach_Kaarlo

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Just a suggestion. For level matching best practice is to use a tone 440 or 1 khz is usually good. And set by the voltage level at the speaker input terminals. You'll be able to get precise level matching that way. Listen one way and set levels. Play your tone and record voltage. Then you can set the second way to the same voltage.

I've not listened to your files yet, but it wouldn't be surprising for bridge and stereo to be just a little different due to gain structure and changes in output impedance.

Thanks for the advice - gratefully received - will purchase a meter so I can set levels with voltage (ambient SPL near an airport turns out to be much less accurate).

Also interested to see what you hear.
 

RobS

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Do any other AHB2 owners hear a difference between the mono and stereo units besides the extra +6db the monoblock nets you?
 

RichB

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Do any other AHB2 owners hear a difference between the mono and stereo units besides the extra +6db the monoblock nets you?

I have not tried. Let's see how this plays out.
The Poor Audiophile review mentioned bazookas driving the Salon2s in Mono mode, but I expect this was the added gain and perhaps the ability for more output

I have two friends with Salon2s, 1 bi-amps (like me) and the other bridges because he likes the occasional loud demo.

- Rich
 
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Coach_Kaarlo

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