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Old 24th November 2004, 11:21 AM   #1
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Default Amplifiers, AB comparative testing, a blind test method.

Here is the text of AB blind tests to amplifiers comparison
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Old 24th November 2004, 11:22 AM   #2
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Default AB blind test to compare amplifiers

AB comparison test of amplifiers

To be a blind testing is a need, as no blind testing have not scientific value.

Many things can influence the value you can give to some amplifiers, its appearance, color, shape, your own mood, the ambience and your spectations.
Also when speaker is big, you will wait for a big sound, and the opposite are also true.
The louder the speaker is reproducing, the best you will evaluate it... and we can spend pages talking about Psycho - acoustival subjective evaluations...and this is the damn hell to evaluate.

First problem.... Impeachment or not impeachment to evaluate... do you like very much the amplifier factory, constructor, team of Marketing pappers?

How long time have you been watching that special brand?

Some of your good friends have that amplifier?

Well, those things reduce the AB comparison testing precision, and that test is not either precise.

We have the idea that we hear with our ears...wrong.... This is only the transducer that will send informations to your brain..... and all informations, are electrical pulses, and those are created as result of sensorial cells pression.... Are electro-chemical energy that have its own delay, have its own ressonances and has a "curve" or hearing that you need to make visiting a Doctor.

Yours ears/brain, do not have equal characteristics, so, monaural testing are better than stereo testings.... Better separation will be understood as better sound..

The louder amplifier will be easy evaluated as better, also the unbalance one, that have some "loudness" tendency will be better evaluate in low levels.

Some distortions are perceived as crispy highs, so, you need to compare sounds alike bells, marimba, rain with claps and gun shots compared to drumshots.

Speaker must be some good brand, recognized as good by the biggest parcel of your audiophile community... forget those bise, bozo and those "exotic" transducers....run to majority of people, this will be more safe to avoid mistakes.

So, having one speaker sample, 2 units exactly the same.... Check it if 1 volt of 1 Khz sinusoidal audio will produce the same "air pressure" captured by some good microphone, as AKG, Senheiser, Shure. To measure that use a wave form monitor or use some tape deck observing VU meters, less precise, but can be a good helping hand....Avoid bargraph meters for that, as they are too much crazy, and can be easily misadjusted.

Now you have fixed one important variable...the speaker.... Using the same.....the same volume, the same quality....of course, better if you can use many brands, matched pairs, as some amplifiers sound great with one and terrible with other....the speaker can unvalidate all your efforts.

I am talking to an AB comparison blind testing, using ears, not instruments.

Blind, because you cannot see the amplifiers, the vision influences must be diminished, reduced the more you can...if a dark room can be reached, better, as you have not vision inputs to your brain microprocessor.

Test alone that is much better to precision, and test it in group, as can be interesting to increase precision...but call the guys one each testing time....the chair, the listening place is important, also the chair, make it confortable, and tried to evaluate the listener mood...do not do that if the one is hungry, angry, bad mood, sick, worry about someone sick, with marriage problems....so, people must be carefully selected, and all them have to visit Doctor to obtain his own hearing curves.

The test must be repeated an other day...this will increase evaluation precision.

You must use sound effects and music, and this is a terrible problem, as if you like some music, you will have some positive tendency, some tolerant mind that will reduce evaluation results.... The amplifier must be switched many times inside some musical sample, and use all rithms you can find, and sound effects too...but all them monaural, not stereo sounds!

The speakers must be in the "traditional" triangle position, beeing the tester in one triangle corner.... The high must be exactly your ears....the tweeter must be aligned horizontally and vertically related your ears.....put some 14 Khz tone, half watt, and turn the right speaker slowly till he "tester" man will say that could hear easy and loud. Repeat to the other speaker, the left one...each man, a level adjustment.

Both amplifier under test must be hidden, also covered not to have modulation lamps when driven, the power must be low.... From 2 to 8 watts, depending the room size, to avoid speaker distortions or amplifiers distortions...here you have a problem...one of them may work in class A , when the other are running AB class!.... so, take that into your account.

One person will operate the switches, but you have to make some cross testing...inverting speakers.....because of ears differences. Use some radio frequency hard switch, with good mechanical pressure over contacts or use some good relay to swith speakers.... The speaker wire must be good in diameter and exactly the same length.

The amplifiers must be pre-adjusted to same power over the speakers....and the measurement is not electrical....is acoustical measurement....make it with microphones and meters.

Behing the listener you must have some anecoic plastic material, the sound absorbers material you know very well, that one expensive or something equivalent.

At you right side, right ear, and left side, left ear.... The same reality....if a wall, make it the same the other one...remove any objects....or use some sound absortion material....the interest is the direct sound, not the reflected sound.

In the test table, the bottom must be exactly the same to both speakers....also the right side...if one has a door 1 meter distant....put some absortion material over the door and make the same the other side.

The listener must be instructed to try to make differences between applause and rain falling in your ceiling or in your garden, or even cement surfaces.

Also to identify a Marimba and small bells, and bottles with watter.... And questions must be made.....What is this..... with side re-created that sound better....and them...invert amplifiers.

When finished, observe that you have a reasonable result related that speaker....you have to try others and repeat again.

This is a damn hard work, takes time, and you will be learning everyday.

People cannot know if tube or transistor, or Jfets are beeing evaluated...they will be ready to see differences, when sometimes there are no difference, only illusions.

Some old guy, that loved Tubes all life, believing that tubes are the best!.... so, passed all his life believing that, and talking about that, this one will have problems to evaluate bad some tube amplifier.... He will say "that one" is bad, only "that one!"..... that the switch was wrong...will say:
- "Hey, come on!...check that damn switches!"

If the tube was something alike "his life".... He will fell as killed with that notice... will be very hard to him...this way, do not inform before....and maybe, if possible, do not inform after.

Can you imagine, if someone realized, that all his life was hearing trash, and saying that was wonderfull...the size of this idiot...or, the feelings involved?

I am not talking nothing against tubes...this is one example only.

I am thinking how easy some people say this one is good, this one is bad....normally the things they own are better.....many never compared nothing with nothing.... Compared but not simultaneously, believing musical memory is enough to judge.... This is not true...must test under controlled situations, a blind testing.

When some Australian circuit win JLH, people ask to repeat many times..as they could not believe... was hard to evaluate, differences too small they are for one and bigger to others.

Of course I do not remembered everything, but I am not hidden nothing...if I forgot something...came to include, to correct, to validate or came to say that this is a bull ----

I will not turn nervous, as this is an observation and analysis result of more than 30 years testing.

The amplifier my group say it is better than this other one...you can run to buy....precision is very reasonable...and take the "sound" into account.

We have censor inside our brain.....the one work with tubes, for long years, will not evaluate bad tubes, this is impossible...this will break the Brain protection against hard frustration...knowing the tube amplifier is playing now....this one he will evaluate as better...this way, only blind testing can work.

Regards,

Carlos
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Old 24th November 2004, 12:24 PM   #3
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Blind Testing


Well, Carlos you might just as well close your eyes and flip a coin because either way you have a 50/50 chance on the outcome.

What does blind testing prove? Not a damn thing so why bother?
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Old 24th November 2004, 01:19 PM   #4
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Default Blind

If you ask nicely to your local blind society. I am sure they can provide you bus load of music lovers to do the blind test for you!

The Butcher

PS Donate a Trained Golden Retriever to them for their effort would be nice!
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Old 24th November 2004, 04:58 PM   #5
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Quote:
Originally posted by burnedfingers

What does blind testing prove? Not a damn thing so why bother?
So you say all amps sound the same, listeningtests unnecessary ?
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Old 24th November 2004, 06:06 PM   #6
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Default Yes boys, this is a sensitive idea, and put reality clear, some people do not like.

That some amplifier win other related sound reproduction.

Those guys, can feel bad when discover that paid a lot of money and result was not the expected, this may turn unconfortable.

The blind test is made to avoid "passion", and must be made to people that can see, and maybe to the others that cannot "see" too.

When in doubt, what amplifier is best...it can give you an answer.

Just that.

Carlos
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Old 24th November 2004, 08:10 PM   #7
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Some amplifiers or products have obvious audible differences, but in cases where they are extremely close, I believe that "blind testing" can be useful.

By "blind testing" I mean listening to two seperate devices and making a choice between the two without knowing which one I am choosing. I do not believe that it is necessary to close one's eyes and listen in darkness. I find that very annoying and it seems that I end up missing things.

I believe it is because my senses and perceptions are accustomed to working together as a whole, and abruptly removing one of those senses throws everything off. Perhaps if I always listened to music with my eyes closed, it would be a different matter.

It is also hard for me to form an image of the music in front of me without seeing objects in the room to give a sense of scale and distance--my imagination needs a few real physical boundaries with which to work, otherwise I'll be concentrating too much on other things and not the evaluation at hand.

To each his own I suppose. I find that my method for listening and evaluating equipment serves me well and is no better or worse than another person's preference.

The key thing that many people forget is objectivity. Don't dismiss something simply because of how it is designed or what parts are used in it. People screw this up very often with things like capacitors and op-amps. It is okay to have expectations but always try to clear your mind and keep it open.
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Old 24th November 2004, 08:35 PM   #8
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Well put JFET. I'd like to add that to really do this right, you need more than just an A is better than B or B is better than A comparison. You also need A is the same as B. And coupled with this a 2nd party who will wire without your knowledge the amps to A and B in any order including using the same amp on both. Run the test multiple times and see if the results are consistent.
--
Danny
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Old 24th November 2004, 11:48 PM   #9
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Quote:

So you say all amps sound the same, listeningtests unnecessary ?

Did I say that? Please go back and re read my post.

What I am saying is this... While we the informed and educated listeners can and do hear a difference in MOST cases the same cannot be said for others. I conducted blind tests over 30yrs ago with very annoying results that proved its still a 50/50 chance. I have seen a $200 pioneer STK module amp win out over much higher priced equipment. Mind you this was by people who surely should have been able to tell the diference. Flip a coin or conduct the same tests day after day and end up with different results.
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Old 25th November 2004, 12:47 AM   #10
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Default Happy to see the Christmas hat, and snow, and you here changing ideas...

This is great!

Someone used the perfect word, consistency...that's the whole thing...and avoiding the tricks we make with ourselves all the time.

If the darkness is a problem, so go with ligths on!, no problem!, the reason is to avoid distractions seeing objects and not imerging in the music dream....something can wake up you to sensorial reality, dividing atention with vision and hearing...the idea is to reduce all stimulum.... to reduce fatigue, cannot he hungry, a confortable and good place to sit.

All those things, can contribute to a better precision related the attention someone can have.

But people are individual, your case, we turn ligths on...no problem, just do that and tell us something, will be great, as this kind of evaluation, since well made, give some results you can trust with reasonable confidence.

regards,

Carlos
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