Do all amplifiers sound the same?

Do all amplifiers sound the same?

Some time ago the now defunct stereo review had an interesting article
on blind a/b tests between different amplifiers - I saw a reprint
here;

http :// bruce.coppola.name/audio/Amp Sound.pdf

After a hiatus of many years I am now putting together a system and
every one I talk to tells me there is a difference between amplifier
sounds. I am sceptical and in a recent audition could not tell a Creek
EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
source).

Has any more work been done on this subject, esp. blind a/b tests?

Steve

Re: Do all amplifiers sound the same?

Steve <goldstarsteve@gmail,com > writes:

> Some time ago the now defunct stereo review had an interesting article
> on blind a/b tests between different amplifiers - I saw a reprint
> here;
>
> http :// bruce.coppola.name/audio/Amp_Sound.pdf
>
> After a hiatus of many years I am now putting together a system and
> every one I talk to tells me there is a difference between amplifier
> sounds. I am sceptical and in a recent audition could not tell a Creek
> EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
> source).
>
> Has any more work been done on this subject, esp. blind a/b tests?

I can't answer your question, but in my opinion, output impedance is one
of the most important distinguishing features. The lower the amp's
output impedance is over frequency, the better, although this (as
anything) can be taken to extremes. Unfortunately, I don't believe
many manufacturers publish their output impedance, especially over
frequency.
--
% Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven.
%% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and
%%% 919-577-9882 % Verdi's always creepin' from her room."
%%%% <yates@ieee.org> % "Rockaria", *A New World Record*, ELO
http :// www .digitalsignallabs,com

Re: Do all amplifiers sound the same?

On Tue, 25 Dec 2007 08:39:58 -0800, Randy Yates wrote
(in article <fkrbou01fjd@news1.newsguy,com >):

> Steve <goldstarsteve@gmail,com > writes:
>
>> Some time ago the now defunct stereo review had an interesting article
>> on blind a/b tests between different amplifiers - I saw a reprint
>> here;
>>
>> http :// bruce.coppola.name/audio/Amp_Sound.pdf
>>
>> After a hiatus of many years I am now putting together a system and
>> every one I talk to tells me there is a difference between amplifier
>> sounds. I am sceptical and in a recent audition could not tell a Creek
>> EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
>> source).
>>
>> Has any more work been done on this subject, esp. blind a/b tests?
>
> I can't answer your question, but in my opinion, output impedance is one
> of the most important distinguishing features. The lower the amp's
> output impedance is over frequency, the better, although this (as
> anything) can be taken to extremes. Unfortunately, I don't believe
> many manufacturers publish their output impedance, especially over
> frequency.
>

Output impedance is one of many criteria. Mostly, it affects damping factor
for the loudspeakers. The way I understand it is If a dynamic speaker is
looking down it's cable into the output stage of an amplifier and sees, what
is in essence, a dead short, the cone will stop instantly when the signal
stops, because of the back EMF being generated by the shorted voice coil in
the speaker's magnetic field (try this experiment: Get a raw driver and flex
the cone by hand at the dust cap. Then connect the terminals of the speaker
together with a jumper and flex the cone again. Notice how much more
difficult the cone is to move this time. That's the phenomenon behind
regenerative dampening) But even this is an oversimplification. In reality,
most speaker voice coils are looking into an inductor in the crossover and
the resistance of the speaker cable before it sees the output stage, so its
anybody's guess how much a low output impedance actually affects the overall
result.

Frankly, I think that the sound of an amplifier is more a result of the
complex load presented by the speaker system that it's driving than the
speaker's sound is influenced by the amplifier.

Re: Do all amplifiers sound the same?

Sonnova <sonnova@audiosanatorium,com > writes:

> On Tue, 25 Dec 2007 08:39:58 -0800, Randy Yates wrote
> (in article <fkrbou01fjd@news1.newsguy,com >):
>
>> Steve <goldstarsteve@gmail,com > writes:
>>
>>> Some time ago the now defunct stereo review had an interesting article
>>> on blind a/b tests between different amplifiers - I saw a reprint
>>> here;
>>>
>>> http :// bruce.coppola.name/audio/Amp_Sound.pdf
>>>
>>> After a hiatus of many years I am now putting together a system and
>>> every one I talk to tells me there is a difference between amplifier
>>> sounds. I am sceptical and in a recent audition could not tell a Creek
>>> EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
>>> source).
>>>
>>> Has any more work been done on this subject, esp. blind a/b tests?
>>
>> I can't answer your question, but in my opinion, output impedance is one
>> of the most important distinguishing features. The lower the amp's
>> output impedance is over frequency, the better, although this (as
>> anything) can be taken to extremes. Unfortunately, I don't believe
>> many manufacturers publish their output impedance, especially over
>> frequency.
>>
>
> Output impedance is one of many criteria.

That's why I said it's one of the most important distinguishing
features and not "it's the only distinguishing feature."

> Mostly, it affects damping factor for the loudspeakers.

I think damping factor was an attempt at simplifying output impedance,
so this is a little circular.

> The way I understand it is If a dynamic speaker is looking down it's
> cable into the output stage of an amplifier and sees, what is in
> essence, a dead short, the cone will stop instantly when the signal
> stops, because of the back EMF being generated by the shorted voice
> coil in the speaker's magnetic field

I have heard of this effect and admit I do not fully understand the
dynamics between back-EMF and output impedance. However, it seems that
such effects are secondary. What seems even more important is that the
correct output voltage is applied to the speaker. A zero output
impedance makes an amplifier an ideal voltage source, i.e., the correct
output voltage will be maintained up to the limits of the current-sourcing
ability of the amplifier.
--
% Randy Yates % "She tells me that she likes me very much,
%% Fuquay-Varina, NC % but when I try to touch, she makes it
%%% 919-577-9882 % all too clear."
%%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO
http :// www .digitalsignallabs,com

Re: Do all amplifiers sound the same?

On Dec 26, 11:57 am, Sonnova <sonn...@audiosanatorium,com > wrote:
> Output impedance is one of many criteria. Mostly,
> it affects damping factor for the loudspeakers.

Mostly, it does not at all.

> The way I understand it is If a dynamic speaker is
> looking down it's cable into the output stage of an
> amplifier and sees, what is in essence, a dead
> short, the cone will stop instantly when the signal
> stops, because of the back EMF being generated
> by the shorted voice coil in the speaker's magnetic
> field (try this experiment: Get a raw driver and flex
> the cone by hand at the dust cap. Then connect the
> terminals of the speaker together with a jumper and
> flex the cone again. Notice how much more difficult
> the cone is to move this time.

Unless you're moving the cone VERY fast, you're not
going to see any difference.

Now, try the experiment REALISTICALLY: Try doing
it and trying to sense the difference between a 0.4 ohm
resistor across the terminals vs a 0.1 ohm resistor
across the terminals.

> That's the phenomenon behind regenerative
> dampening)

There is no "regenerative damping." It's just damping.

> But even this is an oversimplification.

Yes, it is an oversimplification to the point of being
wrong.

> In reality, most speaker voice coils are looking into
> an inductor in the crossover and the resistance of
> the speaker cable before it sees the output stage,

And, in oversimplifying, you neglected the fact that
the single LARGEST resistance is ALWAYS there,
and that's the DC resistance of the voice coil. The
inductor might add a fraction of an ohm, same with
the leads, but the DC resistance of a typical niminal
8 ohm driver is in the realm of 6-7.5 ohms, and
THAT resistance completely dominates all others,
including the amplifier's output resistance, and it
is the voice coil resistance that essentially determines
the damping of the system.

> so its anybody's guess how much a low output
> impedance actually affects the overall result.

Actually, it's not guesswork at all. The series resistance
the voice coil dominates, and unless the other series
resistances are pathologically large and the so-called
damping factor is larger than 10-20, the amplifier's
output resistance will have NO appreciable effect on
the damping of the system.

> Frankly, I think that the sound of an amplifier is more
> a result of the complex load presented by the speaker
> system that it's driving than the speaker's sound is
> influenced by the amplifier.

That may be the case, but, again, it's something that
can be determined. If we have an amplifier whose
damping factor is "low" by contemporary standards,
say, 20 at 8 ohms, and we connect it to a speaker
whose impedance varies from 6 to 30 ohms. The
result is that the voltage at the speaker terminals
varies by 0.44 db between the minimum and maximum
impedance.

Now, get yourself an amplifier with an alledged damping
factor of, oh. 200. The resulting error is now on the order
of 0.05 dB. Do you think that you can hear the difference
resulting from a smooth change in broadband frequency
response of about 0.4 dB in a room with dynamically
changing music?

Re: Do all amplifiers sound the same?

dpierce.cartchunk.org@gmail,com writes:
> [...]
> And, in oversimplifying, you neglected the fact that
> the single LARGEST resistance is ALWAYS there,
> and that's the DC resistance of the voice coil. The
> inductor might add a fraction of an ohm, same with
> the leads, but the DC resistance of a typical niminal
> 8 ohm driver is in the realm of 6-7.5 ohms, and
> THAT resistance completely dominates all others,
> including the amplifier's output resistance, and it
> is the voice coil resistance that essentially determines
> the damping of the system.

Dick,

I suppose it's difficult to improve the electromechanical system due to
the physics of the situation? E.g., enlarging the voice coil wire
diameter increases the driver mass, which then degrades the mechanical
damping.

What if you super-cooled the voice coil? Yeah, that's probably
expensive.

Or what if you used a small voice coil and a large magnet?
--
% Randy Yates % "Though you ride on the wheels of tomorrow,
%% Fuquay-Varina, NC % you still wander the fields of your
%%% 919-577-9882 % sorrow."
%%%% <yates@ieee.org> % '21st Century Man', *Time*, ELO
http :// www .digitalsignallabs,com

Re: Do all amplifiers sound the same?

dpierce.cartchunk.org@gmail,com writes:

> Actually, it's not guesswork at all. The series resistance
> the voice coil dominates, and unless the other series
> resistances are pathologically large and the so-called
> damping factor is larger than 10-20, the amplifier's
> output resistance will have NO appreciable effect on
> the damping of the system.

You're speaking in static, DC terms. What about dynamically? For
example, when the voice-coil is traveling and the back-emf is opposing
the amplifier's output voltage? Yes, there is still the DC resistance of
the coil in series, but the amplifier is working harder than under DC
conditions.
--
% Randy Yates % "I met someone who looks alot like you,
%% Fuquay-Varina, NC % she does the things you do,
%%% 919-577-9882 % but she is an IBM."
%%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO
http :// www .digitalsignallabs,com

Re: Do all amplifiers sound the same?

On Dec 29, 11:40 am, Randy Yates <ya...@ieee.org> wrote:
> dpierce.cartchunk....@gmail,com writes:
> > Actually, it's not guesswork at all. The series resistance
> > the voice coil dominates, and unless the other series
> > resistances are pathologically large and the so-called
> > damping factor is larger than 10-20, the amplifier's
> > output resistance will have NO appreciable effect on
> > the damping of the system.
>
> You're speaking in static, DC terms. What about dynamically? For
> example, when the voice-coil is traveling and the back-emf is opposing
> the amplifier's output voltage? Yes, there is still the DC resistance of
> the coil in series, but the amplifier is working harder than under DC
> conditions.

Think Mr. Thevenin.

That resistance is ALWAYS there, under ALL conditions.

There is absolutely NOTHING special about the
"back-EMF" that makes the situation in any way
unique. A mechanically resonant system with electrical
coupling behaves electrically exactly the same way
a straightforward parallel RLC resonant tank circuit
with a series resistance behaves.

The onl;y time the "back-EMF" exactly opposes
the amplfier's voltage is when the two are exactly
in phase, and that occurs at the fundamental
mechanical resonant frequency. At that point, the
electrical impedance is at its highest and dominated
by the series combination of the DC resistance and
the reflected mechanical and (to a very small degree)
acoustical losses.

And by "DC resistance" of the voice coil, I do not
mean that it's only valid at DC, rather that this
resistance, for the purpose of discussion, has no
appreciable frequency dependence. In other words
measure its value at DC and at, say, 100 Hz and you
will find no significant difference.

Re: Do all amplifiers sound the same?

"Randy Yates" <yates@ieee.org> wrote in message
news:fl5t9502qhb@news2.newsguy,com
> dpierce.cartchunk.org@gmail,com writes:
>
>> Actually, it's not guesswork at all. The series
>> resistance the voice coil dominates, and unless the
>> other series resistances are pathologically large and
>> the so-called damping factor is larger than 10-20, the
>> amplifier's output resistance will have NO appreciable
>> effect on
>> the damping of the system.

> You're speaking in static, DC terms.

Agreed, that the statement was couched in static terms, but it applies
equally well to the dynamic properties of a loudspeaker.

> What about dynamically?

Because the loudspeaker is a dynamic system, its AC properties differ from
its DC properties. However, the dynamic properties of a loudspeaker enhance
Mr. Pierce's argument. Because a loudspeaker is a passive system, its AC
impedance is *always* higher than its DC impedance.

Simple math shows that increasing the impedance of a load minimizes the
effects of the impedance of the source.

Therefore, the effects of the amplifier's output impedance are less in the
audio band than they are at DC.

> For example, when the voice-coil is
> traveling and the back-emf is opposing the amplifier's
> output voltage?

The back-EMF increases the impedance of the loudspeaker. Therefore, in some
sense it decreases the importance of the source impdedance of the amplifier.
In practice, it is the variation between the ranges where the speaker's
impedance is high and low that makes us prefer power amplifiers that provide
a low source impedance.

> Yes, there is still the DC resistance of
> the coil in series, but the amplifier is working harder than under DC
> conditions.

Actual laboratory observations show otherwise. If you observe an amplifier
*working*, you can externally determine that it is drawing power and making
heat. In some cases the output devices and some internal inductors may even
*sing* a little. These effects are almost always maximized when driving a
resistive load that is equal or approximate to the DC resistance of the
speaker. A counter-example would be a capacitor with low ESR, but in
practice these are rarely hung across the output terminals of a loudspeaker
without some series resistor in place.

When you hook up the speaker, these effects are usually appreciably
lessened. Similar effects can be observed when you monitor voltages and
currents inside the amplifier's circuitry. Therefore, a resistive load whose
resistance is the same or approximates the DC resistance of a loudspeaker is
generally, across the audio band, a tougher load for an amplifier to drive
than the speaker itself.

I say almost always only because there are a few loudspeakers that present a
high impedance to DC. Such speakers usually have built-in series capacitors
that can act to enhance low frequency performance in some cases.

Very few people have operated power amplifiers under maximum output
conditions into a loudspeaker, and not been in the acoustical field of the
loudspeakers. The acoustical field of the loudspeaker operated under these
conditions tends to distract most people.

Re: Do all amplifiers sound the same?

On Fri, 28 Dec 2007 08:59:42 -0800, dpierce.cartchunk.org@gmail,com wrote
(in article <fl3a1u01mqm@news4.newsguy,com >):

> On Dec 26, 11:57 am, Sonnova <sonn...@audiosanatorium,com > wrote:
>> Output impedance is one of many criteria. Mostly,
>> it affects damping factor for the loudspeakers.
>
> Mostly, it does not at all.
>
>> The way I understand it is If a dynamic speaker is
>> looking down it's cable into the output stage of an
>> amplifier and sees, what is in essence, a dead
>> short, the cone will stop instantly when the signal
>> stops, because of the back EMF being generated
>> by the shorted voice coil in the speaker's magnetic
>> field (try this experiment: Get a raw driver and flex
>> the cone by hand at the dust cap. Then connect the
>> terminals of the speaker together with a jumper and
>> flex the cone again. Notice how much more difficult
>> the cone is to move this time.
>
> Unless you're moving the cone VERY fast, you're not
> going to see any difference.
>
> Now, try the experiment REALISTICALLY: Try doing
> it and trying to sense the difference between a 0.4 ohm
> resistor across the terminals vs a 0.1 ohm resistor
> across the terminals.

Well, of course. That's what I was saying about "real world results" But
while one cannot tell the difference between an output impedance of 0.1 and
0.4 ohms. one can certainly tell the difference (in the bass) between an amp
with an output impedance of less than an ohm and one with an impedance of
output transformer!
>
>> That's the phenomenon behind regenerative
>> dampening)
>
> There is no "regenerative damping." It's just damping.

The damping occurs because of the regenerative back EMF.
>
>> But even this is an oversimplification.
>
> Yes, it is an oversimplification to the point of being
> wrong.

No, it's not wrong. It just isn't as great an effect as the classic
demonstration would have one believe.
>
>> In reality, most speaker voice coils are looking into
>> an inductor in the crossover and the resistance of
>> the speaker cable before it sees the output stage,
>
> And, in oversimplifying, you neglected the fact that
> the single LARGEST resistance is ALWAYS there,
> and that's the DC resistance of the voice coil. The
> inductor might add a fraction of an ohm, same with
> the leads, but the DC resistance of a typical niminal
> 8 ohm driver is in the realm of 6-7.5 ohms, and
> THAT resistance completely dominates all others,
> including the amplifier's output resistance, and it
> is the voice coil resistance that essentially determines
> the damping of the system.

I would have thought that was a given.
>
>> so its anybody's guess how much a low output
>> impedance actually affects the overall result.

I agree. I was merely explaining the "shorted turn phenomenon".

> Actually, it's not guesswork at all.

Not if you know all the factors, no. Then it becomes a simple matter of the
combination of the various DC resistances, and the various inductive and
capacitive reactances involved

The series resistance
> the voice coil dominates, and unless the other series
> resistances are pathologically large and the so-called
> damping factor is larger than 10-20, the amplifier's
> output resistance will have NO appreciable effect on
> the damping of the system.

Modern Solid state amps can have damping factors of greater than 200.

>> Frankly, I think that the sound of an amplifier is more
>> a result of the complex load presented by the speaker
>> system that it's driving than the speaker's sound is
>> influenced by the amplifier.
>
> That may be the case, but, again, it's something that
> can be determined. If we have an amplifier whose
> damping factor is "low" by contemporary standards,
> say, 20 at 8 ohms, and we connect it to a speaker
> whose impedance varies from 6 to 30 ohms. The
> result is that the voltage at the speaker terminals
> varies by 0.44 db between the minimum and maximum
> impedance.
>
> Now, get yourself an amplifier with an alledged damping
> factor of, oh. 200. The resulting error is now on the order
> of 0.05 dB. Do you think that you can hear the difference
> resulting from a smooth change in broadband frequency
> response of about 0.4 dB in a room with dynamically
> changing music?

I'm not arguing about broadband frequency response, I'm talking about the
amp's ability to damp (or stop) a large, high mass magnetic bass driver
abruptly when the signal stops. This determines, to some extent, the quality
of the bass in a system.

Re: Do all amplifiers sound the same?

On Dec 30, 11:55 am, Sonnova <sonn...@audiosanatorium,com > wrote:
> On Fri, 28 Dec 2007 08:59:42 -0800, dpierce.cartchunk....@gmail,com wrote
> (in article <fl3a1u01...@news4.newsguy,com >):
>
>
>
> > On Dec 26, 11:57 am, Sonnova <sonn...@audiosanatorium,com > wrote:
> >> Output impedance is one of many criteria. Mostly,
> >> it affects damping factor for the loudspeakers.
>
> > Mostly, it does not at all.
>
> >> The way I understand it is If a dynamic speaker is
> >> looking down it's cable into the output stage of an
> >> amplifier and sees, what is in essence, a dead
> >> short, the cone will stop instantly when the signal
> >> stops, because of the back EMF being generated
> >> by the shorted voice coil in the speaker's magnetic
> >> field (try this experiment: Get a raw driver and flex
> >> the cone by hand at the dust cap. Then connect the
> >> terminals of the speaker together with a jumper and
> >> flex the cone again. Notice how much more difficult
> >> the cone is to move this time.
>
> > Unless you're moving the cone VERY fast, you're not
> > going to see any difference.
>
> > Now, try the experiment REALISTICALLY: Try doing
> > it and trying to sense the difference between a 0.4 ohm
> > resistor across the terminals vs a 0.1 ohm resistor
> > across the terminals.
>
> Well, of course. That's what I was saying about "real world
> results"

Well, here you harp about "real world results" after someone
objects to your experiment which has nothing to do with
"real world result."

> But while one cannot tell the difference between an
> output impedance of 0.1 and 0.4 ohms. one can
> certainly tell the difference (in the bass) between an
> amp with an output impedance of less than an ohm
> and one with an impedance of output transformer!

And with the exception of some degenerative, patholoigcally
bad designed tube amplifiers, the typical tube amplifier with
it's output transformer exhibits effective output resistances
of an ohm or less.

> >> That's the phenomenon behind regenerative
> >> dampening)
> > There is no "regenerative damping." It's just damping.
>
> The damping occurs because of the regenerative back EMF.

There is no "regenerative." You are either misusuing the
term or misunderstanding the concept.

> >> But even this is an oversimplification.
>
> > Yes, it is an oversimplification to the point of being
> > wrong.
>
> No, it's not wrong. It just isn't as great an effect as the classic
> demonstration would have one believe.

No, your oversimplification is ORDERS OF MAGNITUDE
off the mark, enough that your suggested demonstration,
which you implicitly admit is far from "real world," simply
does not reflect the real world AT ALL.

> >> In reality, most speaker voice coils are looking into
> >> an inductor in the crossover and the resistance of
> >> the speaker cable before it sees the output stage,
>
> > And, in oversimplifying, you neglected the fact that
> > the single LARGEST resistance is ALWAYS there,
> > and that's the DC resistance of the voice coil. The
> > inductor might add a fraction of an ohm, same with
> > the leads, but the DC resistance of a typical niminal
> > 8 ohm driver is in the realm of 6-7.5 ohms, and
> > THAT resistance completely dominates all others,
> > including the amplifier's output resistance, and it
> > is the voice coil resistance that essentially determines
> > the damping of the system.
>
> I would have thought that was a given.

No, in your discussion, it most assuredly WAS NOT a
given. If it was, you would have realized and hopefully
discussed the fact that the other resistances you cite are
simply insignificant by comparison.

> >> so its anybody's guess how much a low output
> >> impedance actually affects the overall result.
>
> I agree. I was merely explaining the "shorted turn
> phenomenon".

And you neglected to then point out that almost every
amplifier on the planet provides that "shorted turn,"
given that it is NOT a significant source of loop resistance.

> > Actually, it's not guesswork at all.
>
> Not if you know all the factors, no. Then it becomes a
> simple matter of the combination of the various DC
> resistances, and the various inductive and capacitive
> reactances involved

The inductive and capacitive reactances have no effect
on damping resonance.

> > The series resistance
> > the voice coil dominates, and unless the other series
> > resistances are pathologically large and the so-called
> > damping factor is larger than 10-20, the amplifier's
> > output resistance will have NO appreciable effect on
> > the damping of the system.
>
> Modern Solid state amps can have damping factors of
> greater than 200.

Try it again, a damping factor of 20 or so is sufficient
to control all resonances in a speaker. 200 will NOT
damp ten times better than 20, in fact, in most cases,
the difference is nearly unmeasurable.

> >> Frankly, I think that the sound of an amplifier is more
> >> a result of the complex load presented by the speaker
> >> system that it's driving than the speaker's sound is
> >> influenced by the amplifier.
>
> > That may be the case, but, again, it's something that
> > can be determined. If we have an amplifier whose
> > damping factor is "low" by contemporary standards,
> > say, 20 at 8 ohms, and we connect it to a speaker
> > whose impedance varies from 6 to 30 ohms. The
> > result is that the voltage at the speaker terminals
> > varies by 0.44 db between the minimum and maximum
> > impedance.
>
> > Now, get yourself an amplifier with an alledged damping
> > factor of, oh. 200. The resulting error is now on the order
> > of 0.05 dB. Do you think that you can hear the difference
> > resulting from a smooth change in broadband frequency
> > response of about 0.4 dB in a room with dynamically
> > changing music?
>
> I'm not arguing about broadband frequency response,
> I'm talking about the amp's ability to damp (or stop) a
> large, high mass magnetic bass driver abruptly when
> the signal stops.

And that was PRECISELY what I was talking about
earlier. Your dismissive comments that the
DC resistance "was a given," your inclusion
of inductive and capacitive reactances and your claim
that it is all"guesswork," clearly indicates
you're not grasping the true nature of "damping" in
it's formal electromechanical sense. And that very
mature is central to the operation of loudspeakers.

The damping of the entire system is determined
PRIMARILY by the DC resistance of the voice coil.
The output resistance of the amplifier has, at most
a MINOR effect.

In fact, if you look at the reciprocal of the damping
factor, THAT number gives a good indication of how
much of the electrical damping is provided by the
amplifier.

So take an amplifier with a damping factor of 10: only
1/10 of the total electrical damping of the system is
controlled by the amplifier, 90% is controlled by the
DC resistance of the speaker.

How about a damping factor of 100? Well, 1% of the
damping is provided by the amplifier, 99% is by that
DC resistance of the voice coil

In other words, the higher the damping factor, the LESS
the amplifier contributes to the damping of the speaker.
This is why the "damping factor" is such a useless
specification. It was born PURELY out of marketing.

And all this discussion ignored the fact that the
mechanical losses in the system provide more
damping than even the worst amplifier. Given that
in most high-quality electrodynamic woofers, the
mechanical losses are on the order of 1/5 to 1/2
the electrical damping due to the voice coil, it
further diminishes the contribution of the amplifier
output resistance.

Take a typical speaker with a Qt of 2 and a Qe of
0.7, and now we find that the amplifier with a damping
factor of 10 contributes only 5% or so of the total
damping.

At your leasure, try the following:

www .cartchunk.org/audiotopics

You can also google for my ame and "damping factor."

To reiterate: It is the voice coil DC resistance and
NOT the amplifier output resistance that determines
the damping of the VAST majority of amplifier and
speaker combinations "Experiments" such as trying
to see the difference between an open circuit and a
short circuit in terms of "observing" damping are
wholely unrealistic and flawed because they represent
comparisons that wuill NEVER occur in the "real world."
And all of this is quite well understood and not subject
to any guesswork at all, assuming the appropriate
compcepts and models are being used.

If not, then any guess is as bad as any other.

Re: Do all amplifiers sound the same?

Steve wrote:
> Some time ago the now defunct stereo review had an interesting article
> on blind a/b tests between different amplifiers - I saw a reprint
> here;
>
> http :// bruce.coppola.name/audio/Amp Sound.pdf
>
> After a hiatus of many years I am now putting together a system and
> every one I talk to tells me there is a difference between amplifier
> sounds. I am sceptical and in a recent audition could not tell a Creek
> EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
> source).
>
> Has any more work been done on this subject, esp. blind a/b tests?
>
> Steve

Amplifiers do not all sound the same.
Some may.
Some do not.
They certainly do not measure the same.

The THD or IM specs do *not* tell the story.

Those who are still doubters, may review Dr. Earl Geddes research on
this subject. It provides the necessary scientific and engineering
basis for the above assertion.

There are a few other 'confounding" factors to account for when
an individual is trying to decide these things:
- there may be masking effects from other parts of the system
(for example a perfectly blameless amp could not be discriminated
from one that was not blameless, if there was sufficient "objectionable"
harmonic signature produced by another element in the system).
- the listener may or may not have physical deficits that prevent
such a discrimination.
- the listener may never have heard a system without many of the
typical "objectionable" artifacts (no basis for comparison).
- there may be other factors, including subsonic sound and ultrasonic
sounds in the environment, excessive reverberation, etc. that
interfere.

As far as "A/B" or "ABX" tests, they are usually valid for the specific test
condition, as made. Suitability of those tests for generalized
application, if they lack controls for at minimum the above factors, and
some others (such as basic THD, IM, polar response, room reverberence,
noise floor, etc...) makes the ones that I have seen published
so far - that is a preponderance of those I am aware of - not meaningful.

Others will disagree, I am sure.

The key to assembling a system that one enjoys listening to depends on
one's thresholds for certain types of "irritants" (and avoiding them),
a bit of luck, serendipity, and in some cases knowledge of matters
technical and acoustic. Money, per se, does not play the major role
in this respect, since there is lots of excellent used gear, and the
possibility of DIY... : )

- -bear

Re: Do all amplifiers sound the same?

bear <bearlabs@netzero,net > wrote:
> Steve wrote:
> > Some time ago the now defunct stereo review had an interesting article
> > on blind a/b tests between different amplifiers - I saw a reprint
> > here;
> >
> > http :// bruce.coppola.name/audio/Amp_Sound.pdf
> >
> > After a hiatus of many years I am now putting together a system and
> > every one I talk to tells me there is a difference between amplifier
> > sounds. I am sceptical and in a recent audition could not tell a Creek
> > EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
> > source).
> >
> > Has any more work been done on this subject, esp. blind a/b tests?
> >
> > Steve

> Amplifiers do not all sound the same.
> Some may.
> Some do not.
> They certainly do not measure the same.

> The THD or IM specs do *not* tell the story.

> Those who are still doubters, may review Dr. Earl Geddes research on
> this subject. It provides the necessary scientific and engineering
> basis for the above assertion.

Hopefully it provides the blind test results to demonstrate audible
difference.

> There are a few other 'confounding" factors to account for when
> an individual is trying to decide these things:
> - there may be masking effects from other parts of the system
> (for example a perfectly blameless amp could not be discriminated
> from one that was not blameless, if there was sufficient "objectionable"
> harmonic signature produced by another element in the system).
> - the listener may or may not have physical deficits that prevent
> such a discrimination.
> - the listener may never have heard a system without many of the
> typical "objectionable" artifacts (no basis for comparison).
> - there may be other factors, including subsonic sound and ultrasonic
> sounds in the environment, excessive reverberation, etc. that
> interfere.

or, the two amps really do not sound different, when used within their
limits.

> As far as "A/B" or "ABX" tests, they are usually valid for the specific test
> condition, as made. Suitability of those tests for generalized
> application, if they lack controls for at minimum the above factors, and
> some others (such as basic THD, IM, polar response, room reverberence,
> noise floor, etc...) makes the ones that I have seen published
> so far - that is a preponderance of those I am aware of - not meaningful.

Double Blind tests have been and continue to be used by Harman for
generalized application in loudspeaker development.

And amplifier (and cable, btw -- mentioned because you sell 'high end'
cable that you claim sounds better than plain cable) difference tests have
been done where the listener who claimd to hear difference between *his*
gear and others, was tested with his gear, against other gear. And failed
the test.

> Others will disagree, I am sure.

> The key to assembling a system that one enjoys listening to depends on
> one's thresholds for certain types of "irritants" (and avoiding them),
> a bit of luck, serendipity, and in some cases knowledge of matters
> technical and acoustic. Money, per se, does not play the major role
> in this respect, since there is lots of excellent used gear, and the
> possibility of DIY... :_)

Have you ever ABX'd differences in amps, and if so, under what conditions,
and what scores did yuou obtain?

___
-S
"As human beings, we understand the world through simile, analogy,
metaphor, narrative and, sometimes, claymation." - B. Mason

Re: Do all amplifiers sound the same?

On Tue, 25 Dec 2007 08:44:45 -0800, bear wrote
(in article <wuSdnXCWiP7gruzanZ2dnUVZ_veinZ2d@pghconnect,com >):

> Steve wrote:
>> Some time ago the now defunct stereo review had an interesting article
>> on blind a/b tests between different amplifiers - I saw a reprint
>> here;
>>
>> http :// bruce.coppola.name/audio/Amp_Sound.pdf
>>
>> After a hiatus of many years I am now putting together a system and
>> every one I talk to tells me there is a difference between amplifier
>> sounds. I am sceptical and in a recent audition could not tell a Creek
>> EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
>> source).
>>
>> Has any more work been done on this subject, esp. blind a/b tests?
>>
>> Steve
>
> Amplifiers do not all sound the same.
> Some may.
> Some do not.
> They certainly do not measure the same.

That is true.
>
> The THD or IM specs do *not* tell the story.

That is correct. Up to a certain point, both seem to be relatively
unimportant. Research has shown that humans aren't very sensitive to the
harmonic and IM distortion produced by amplifying devices. Back in the
"golden era" of tube hi-fi, manufacturers would outdo themselves trying to
get the most zeros between the decimal point and the numbers. This made them
bias their tubes far into the linear portion of the tube's transfer curve.
This lowered distortion all right, but it made the tubes run very hot and
self-destruct with alarming rapidity. After it was found in double-blind
tests that levels up to over 1% in amplifiers were undetectable by humans,
manufacturers started backing off on output bias. over the last thirty years
or so, we have seen the life of output tubes increase dramatically from a
mere few hours to many thousands of hours over a number of years. Of course,
the tradeoff is that harmonic and IM levels have gone from 0.001% to 0.1% or
even higher. Nobody notices.

Re: Do all amplifiers sound the same?

On Dec 26, 11:58 am, Sonnova <sonn...@audiosanatorium,com > wrote:
> On Tue, 25 Dec 2007 08:44:45 -0800, bear wrote
> (in article <wuSdnXCWiP7gruzanZ2dnUVZ vein...@pghconnect,com >):
>
>
>
> > Steve wrote:
> >> Some time ago the now defunct stereo review had an interesting article
> >> on blind a/b tests between different amplifiers - I saw a reprint
> >> here;
>
> >> http :// bruce.coppola.name/audio/Amp Sound.pdf
>
> >> After a hiatus of many years I am now putting together a system and
> >> every one I talk to tells me there is a difference between amplifier
> >> sounds. I am sceptical and in a recent audition could not tell a Creek
> >> EVO from a NAD 325 BEE (through EPOS M12.2 speakers with a Creek cd
> >> source).
>
> >> Has any more work been done on this subject, esp. blind a/b tests?
>
> >> Steve
>
> > Amplifiers do not all sound the same.
> > Some may.
> > Some do not.
> > They certainly do not measure the same.
>
> That is true.
>
>
>
> > The THD or IM specs do *not* tell the story.
>
> That is correct. Up to a certain point, both seem to be relatively
> unimportant. Research has shown that humans aren't very sensitive to the
> harmonic and IM distortion produced by amplifying devices. Back in the
> "golden era" of tube hi-fi, manufacturers would outdo themselves trying to
> get the most zeros between the decimal point and the numbers. This made them
> bias their tubes far into the linear portion of the tube's transfer curve.
> This lowered distortion all right, but it made the tubes run very hot and
> self-destruct with alarming rapidity. After it was found in double-blind
> tests that levels up to over 1% in amplifiers were undetectable by humans,
> manufacturers started backing off on output bias. over the last thirty years
> or so, we have seen the life of output tubes increase dramatically from a
> mere few hours to many thousands of hours over a number of years. Of course,
> the tradeoff is that harmonic and IM levels have gone from 0.001% to 0.1% or
> even higher. Nobody notices.

Part of the reason could be coming from the other end: the source has
gotten much cleaner. Before it was vinyl and cassette recordings with
distortion levels magnitudes higher than with digital lossless files
we play today.

On a slightly different note, I found one way to easily distinguish a
lossy audio file from its lossless counterpart: distortion. The
Lossless file will play much louder and cleaner than the lossy file on
the same system.

CD