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destroyer X 20th March 2005 03:37 PM

Evaluating amps, a fair comparison blind testing.
A fair comparison blind testing, is an unfair testing method, as not entirelly precise.

As have one enormous fail, as use speakers, and some speaker can be better to amplifier A, helping the B amplifier to loose.

Of course, this is my idea, you can have another, and please, let me know.

Whe can jump to famous Speaker Monitors, made for Studio use, but you will see that each studio has it’s own preference…so…there’s nothing that can be easy called as reference speaker.

You can jump to headphones, this is a better idea, but….what is the best headphone? again a never ending discussion will start.

So, the fair method turn unfair, because of that, you have to elect one speaker, better to be something famous as legend, some JBL, some Altec Lansing and some English Speakers, as those Englanders are good to make wonderfull speaker systems .

That’s the reason why people use to measure using instruments, because it is hard to face those subjective decisions to take…. You have not high precision using people evaluation….and instruments give more precise informs of numbers…but do not can tell us the way the amplifier sounds.

Well, decide by some speaker, get a flat AKG microphone, (they say that it is flat) and put it in front of your test speaker, the one you elected….surrounded by heavy cloth, as you have not the correct sealed chamber to do that, some camping habitation can be good if you cover with heavy cloth…microphone 1 meter distance…check if generator of sinusoidal test signal can keep the same output voltage all over the audio range, inject that sound in a class A flat amplifier, alike the line amplifier used in Broadcasting television stations, or make some small JLH amplifier to drive the speaker under testing.

Now go changing frequencies and taking notes from a dB meter scale, related the microphone output, this microphone can be pre-amplified by a Shure amplifier or some class A single stage audio amplifier.

Now you will see that the speaker under test, the one elected, is not flat…other will not be flat too….no chance! they are all different, even 2 units, with a sequence of serial number, from same factory, have some small differences between them..hehe, world not perfect.

Those errors, can produce some judgment error, related the best amplifier, as this speaker will be used to reproduce both amplifier to make an A to B comparison testing.

The place to put the speaker must be hard as cement, may have some hard cloth under, may have some carpet only from the speaker to the hearing chair, a small carpet…the room sides need to be mufled with heavy cloth or some sound absorbing material, as foam, cotton or some sinthetic material…. Punch it!, if the material produces sound! good to use…they must aborb sound and never reflect sound, the sound we need is the one is produced by the speaker, and never a reflected sound.
Speaker have to be positioned 9 feet ahead, and have to be over some heavy and strong, non vibrating stand, to keep it the same side of your ears…. Use the tweeter center to adjust, as treble is more directional.

Behind the hearing chair, use a cloth too…heavy absorbing material…you will use one speaker only, two amplifier to be compared A to B, the speaker wiring have to be the same length and same material, the input sound must enter directly to power amplifier input, no tone controls can be used, better to cut the connection from pre to power amplifier.

The test input signal and music must be mono, both channels joined together, use poliester 4uF caps to join them….so, you have a little bit mufled sound, as some hi frequencies with opposite phase may be cancelled.

Both amplifier must be adjusted statically inserting a tone and measuring the voltage over the speaker, that voltage must be low and above the class A operation point, if an AB amplifier is used., normally 3 volts is enougth, this will produce a good sound, will never overdrive speaker and may be enougth to the speaker….check both amplifier with same steady tone…. The same voltage over the speaker… check with musical signal, dinamic signal…you will see differences….have to check now the sound pressure, using the microphone as a meter….. see the sound result of each amplifier using the microphone, and re-adjust if needed.

Check again with music signal…having the same result you can start your tests…of course, may use the best recording you can find (Graham Maynard can inform where to find them).

The people that will judge, good to be more than 10 persons, cannot know what amplifier is A and what amplifier is B, because visual impressions or some sonically agreable name, as Sony, can produce an unfair judgement…reduce ligth to minimum, to avoid losses to the evaluator attention, the chair must be very confortable, the other judgment people must be out…can hear nothing, cannot enter with some outside, already heard, sound impression…. Every man that finish their evaluation cannot talk with others, any word, have to go away immediatelly, and the switch operator can be the under test man, or, even better, one switch operator to take more precise notes, as the man in the position of evaluator can produce.

Same music sequence must be reproduced using amplifier A and B, and repeated many times, till the evaluator can decide by one of them, and many music styles must be used, better if unknown musics, from India, from distant places rithms to avoid errors…Indian music to relax are wonderfull for that purpose, and beautifull also. Enya, is one singer you can find as Indian relax songs in Kazaa…”Mai ia Hi” is interesting, but will be a terrible distraction. Go changing musics and styles, and wait the man have a decision…if delayed too much, and you feeling he has not sure….do not take his evaluation into account.

Alcohol, drugs to loose weigth, anti-depressive drugs, must be avoided as disturb attention.

So, go substituting evaluators, and adjust carefully the speaker position to each person, this adjustment is important!….speaker distance related to behind wall can be around 3 feet, if not, bass reproduction level will change.

And repeat testing another day, with all those guys…. And keep A and B in the same sittuation….see if they evaluate the same or not…if big differences, do it third time.

Carefull with the switch used to test….have to be professional heavy gauge switches, or some radio frequency coaxial switch. As you know, you will switch the amplifier output audio going to one single speaker…amplifier A to speaker, and amplifier B going to same speaker

The chair must be extremely confortable, the evaluator size must be adequated to the chair size, also you must ask him if he want water, food or go to the WC, he must feel confortable. Ask if a headache or some emotional problem…if nervous or something.

Better if you have hearing tests made produced by audiometers and Medical Doctors, but having not, ask him when using telephone if he prefer some ear… he will prefer one…ask him the preference reason…if the preference was volume, no trouble!…but if preference is tone….there’s a trouble in the man’s hearing.

Never used stereo signal to evaluate nothing, as the best stereo separation will impress the evaluator….the best separation unit will be always the best amplifier.

Also the loudest amplifiers will be sometimes the prefered.

Interesting, I had the experience that the distorted ones are prefered related the top quality ones….this is alike transistor construction…must be clean perfect silicon…an them you inject some dust material to make it work good….some injection of harmonics are sometimes interesting.

Find any hum in the system, as this will disturb evaluation….the hum unit will sound warmer to some evaluators.Warmer to some evaluator can means better or worst, so, will disturb.

The switch operator, the man in charge to make the test, better that YOU do that, cannot be watched by the evaluator…as your smile or face expressions can influence…better to be hidden and cover peak meter ligths or something that can appear pretty related the other amplifier, the amplifiers cannot be watched, their names, brands or details not informed, you cannot talk anything about that…only the basic instructions to the test…be kind, if the evaluator is nervous, do not use his evaluation.

Ask the evaluator about his day….some big problem?… some family sick…unemployed?… in other words, check if he is on troubles…if positive, on troubles, do not use his evaluation results.

Using that kind of test results will be good, if have something to include or correct, please inform… I have beein using this test, a long time, but I can be making a long time mistake too…perceiving something wrong…please!, let me know.

If you can, use JLH or Graham unit to compare with other class A, and AKSA to compare with other 50 to 100 watts AB….if you find some better than those three….please, let me know.


breez 20th March 2005 03:46 PM

But how do you evaluate things like soundstage if the test is done as mono?

destroyer X 20th March 2005 03:49 PM

This is some fail of mono test method.
Cannot evaluate that this way.

thank you,



anatech 20th March 2005 06:05 PM

If it sounds good in mono, it will sound great in stereo. It's very instructive to listen to amps and speakers in mono.

Destroyer X, we Canadians make great speakers too. We have a government facility for speaker development called the NRC. There they correlate listening tests to measurements. Neat concept. The scarry thing is that they are able to predict listening tests by looking at data first.


destroyer X 20th March 2005 07:18 PM

In my personal point of view, Canada is more advanced that USA in many aspects.
So, having the more clean world towns, best organized public service and many wonderfull things, you do not use to make noise about that, maybe some internal division turn your country a little bit shy to exibition of your power and organization, as will have internal resistances.

If you can send me some links where i can find Canadien products, i will be more instructed to see, and more happy to learn more things... i am alike a sponge, i want to learn everything that life can offer to me, and i use to read from books of medicine to Orient Meditation techniques...nothing is foolish for me, except some humans, and in special, those that never accept their own foolishes.

I will be happy to surf the WEB finding Canada things, as i tried once but could not find too much things, i tried Italy and i finded only Tube amplifiers, tried france and found almost nothing related audio amplifiers, the amplificateurs du puissance d'audio et du son.

I will thank you, in advance, the links you post here, or, if you prefer by any reason:


anatech 20th March 2005 08:15 PM

Hi Carlos,
We aren't American, we aren't British. I guess that's where our minds are at. Canada is just a place with it's own problems and good things, like anywhere else.

Here is a link to the NRC, the whole thing. Might give you an idea how the government works. I haven't tried, but search under acoustics or audio. Dr. Floyd Toole set it up and ran it for a while.

A google search for Canadian audio may help you learn what's going on here. I don't know if Google will give you . It may default you to another search engine in your area.

We have snow ..... evil white stuff. Remember that.:down:


anatech 20th March 2005 10:30 PM

Hi Carlos,
Did some poking around on the NRC site. Here's a link into the acoustics area
This may give you an idea as to what Canadians do when it's too darn cold to go outside.;)


destroyer X 20th March 2005 11:33 PM

We are never satisfied, that's human problem, and quality too, because push us to
Develop and increase the things. You may need hot, and i need cold...the neighboor's chicken is always more fat and delicious related our own chicken... some brazilian say...may be Universal that idea, with other words.

Here is damn hot....i am having many showers each day, and using soap because needed, as too much hot those hair is starting to fell down, so many showers...turning dry.

Oh! my god! dream now is to have in a zero degree place.... oh wonderfull!, you put coats, gloves, good boots and go, you take all you clothes off and even nude you go feeling bad, in special when people is laughing in the front building because my with Bu- .
I live in front of the beach, and wind is flowing all the time...but with 29 degrees celsius, this air cannot be so conditioned is running....and i am turning sick because those things remove all humidity from the air...throat dries and crack.

thank you by the links, i will visit them all very slowly, will try also.

I love to do that...sometimes i type some country to go surfing...wonderfull this world, so many differences!

I think they will close this thread, people not interested and they are very fast using the trigger those days



Burnedfingers 20th March 2005 11:35 PM


This may give you an idea as to what Canadians do when it's too darn cold to go outside.

Hey Chris you guys only have about 30 days a year that its above zero. Just kidding.


destroyer X 20th March 2005 11:42 PM

Good to see neighboors kidding in perfect harmony
But our party will finish guys, moderators will block because low quantity of people visiting, only 120 in many hours.

And we are having fun...hehe, the way i like, but scaping from the thread subject...they will pull the trigger and Booom!

till the next thread.

If no one appear here, to a start a big discussion, telling something hard and strong alike

All this written here is a dam bull ----!

If not, i am afraid thread will not survive. And people may have not too much to discuss, as this method is old as the tube age.


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