Stereophile | January 2017 Issue

[Believe High Fidelity]

Driving is different from the speaker having the same oomph, mid bass, bass, drive, soundstage - some speakers come alive withe right muscle and sound lifeless but pleasant when driven be SETs. Now, I have no idea what power and control you used on the Vandy, but I have seen an AR 250 struggle to drive the Vandy 7 (83 db), and was acknowledged by the owner who was then looking for a change of amps.

65W SET. Should have distorted quite a bit given the claims made here but reviewers made no mention

PTA

Stereophile

 

[Argonaut]

A series of excellent posts from f1eng IMHO.

 

[microstrip]

What is considered to be efficient? What is considered to be a benign load?

Asking because we drove a 4/6ohm Vandersteen with an 87db sensitivity without any issues with distortion whatsoever

It is a complex subject because it implies EPDR (equivalent power dissipation resistance) versus frequency - see http://www.stereophile.com/reference/707heavy/index.html#Bt9VZ9v3mccmpJc9.97 and also depends on the speaker perceived subjective characteristics.

Unfortunately EPDR is not immediate from the usual impedance plots.

 

[LL21]

I agree that your first point is not open to discussion and is essentially fact.

What is open to discussion though is not what you have stated. What is open to discussion is the audibility of the distortion that SETs make vs. the audibility of the distortion that is made by other kinds of amplification types and it's detrimental impact on sound quality.

I do not believe there is such a thing as "euphonic" distortion. All distortion degrades. What has been clear though from about 60+ years of work is that not all distortion is created equal and its impact on audibility is exponentially connected to the order of the harmonic. The higher the order, the more objectionable the sound and the less it is masked from our ear/brain. Our ear/brain masks harmonics close to the fundamental so that up to fairly high levels they are inaudible. Content matters more than quantity. The question is where are those lines crossed.

This is where I disagree with you. Some distortion is harsh, some euphonic. SET amps produce lots of distortion but usually sound nice therefore the distortion they are producing is euphonic. If the distortion level is low enough it will effect the sound less, harsh distortion will always be objectionable.

Harmonic distortion must change the timbre of instruments.

The idea that there is some magic about SETs which makes them sound nice despite being non linear has made a renaissance, I don't buy it and I have never seen a convincing hypothesis as to why such magic could exist.

I am still convinced that people like SETs because of their distortion characteristic is changing the sound to their taste. I see nothing wrong with making such a choice btw.

I just admitted i could barely keep up with this discussion...but let me ASK a question. Is Morricab saying that the science that must be brought to the equation is how the human brain/ear actually take in sound and then process it?

In other words, the debate is not just about the fact that any distortion will change timbre...assume for the moment that this is a GIVEN...the question [i believe] is whether the human ear prioritizes/is as sensitive to one kind of distortion as the other. (e.g. in an extreme, would the human ear recognize 1.5% 2nd order with as much facility as only 0.2% of 3rd order?...therefore the level of distortion alone is not enough...we must then apply that to what matters to the human ear)

Do you buy into this? I have no knowledge either way...just asking.

 

[f1eng]

I just admitted i could barely keep up with this discussion...but let me ASK a question. Is Morricab saying that the science that must be brought to the equation is how the human brain/ear actually take in sound and then process it?

In other words, the debate is not just about the fact that any distortion will change timbre...assume for the moment that this is a GIVEN...the question [i believe] is whether the human ear prioritizes/is as sensitive to one kind of distortion as the other. (e.g. in an extreme, would the human ear recognize 1.5% 2nd order with as much facility as only 0.2% of 3rd order?...therefore the level of distortion alone is not enough...we must then apply that to what matters to the human ear)

Do you buy into this? I have no knowledge either way...just asking.

I believe that some types of distortion are euphonic and others unpleasant. I think it is not a question of the ear prioritising one over the other, just amps with euphonic distortion sound lovely, and so quite a lot of this distortion is not only tolerated but positively favoured. In the case of unpleasant distortion more will always be disliked.

 

[andromedaaudio]

Cool idea from stereophile bring a live performer and play a recording to compare on CES .

http://www.stereophile.com/index.html?page=2

If someone from stereophile is reading this , i am off curious who the winner was system wise, YG ???

 

[LL21]

I believe that some types of distortion are euphonic and others unpleasant. I think it is not a question of the ear prioritising one over the other, just amps with euphonic distortion sound lovely, and so quite a lot of this distortion is not only tolerated but positively favoured. In the case of unpleasant distortion more will always be disliked.

Thank you. Do you believe that the human can discern certain kinds of distortion better than others (ie, human ear can pick up 1% 3rd order distortion more easily than 1% 2nd order distortion)? Sorry for the remedial questions...just trying to follow this interesting debate.

 

[MPS]

Thank you. Do you believe that the human can discern certain kinds of distortion better than others (ie, human ear can pick up 1% 3rd order distortion more easily than 1% 2nd order distortion)? Sorry for the remedial questions...just trying to follow this interesting debate.

"THD is an average of a number of harmonics equally weighted, even though research performed decades ago identifies that lower order harmonics are harder to hear at the same level, compared with higher order ones. In addition, even order harmonics are said to be generally harder to hear than odd order. A number of formulas that attempt to correlate THD with actual audibility have been published, however none have gained mainstream use."
https://en.wikipedia.org/wiki/Total_harmonic_distortion

 

[KeithR]

Driving is different from the speaker having the same oomph, mid bass, bass, drive, soundstage - some speakers come alive withe right muscle and sound lifeless but pleasant when driven be SETs. Now, I have no idea what power and control you used on the Vandy, but I have seen an AR 250 struggle to drive the Vandy 7 (83 db), and was acknowledged by the owner who was then looking for a change of amps.

Thank you. A huge +1.

I want effortless sound with huge peaks in my system. I've heard a lot of the "it'll drive it" types and left dissatisfied while others were ok with it.

 

[Aries Cerat]

Good evening gents

Couple of questions to this debate.
1,Has anyone seen distortion measurements throughout the audible band, for coventional speaker/panels/hybrid?
Let us say at 95db.Not even talking about 100db.
How do these figures compare to any amplifier.Set or otherwise.

2...say that a dominant 2nd order harmonic is euphonic.Whould you be surprised to know that the overwhelming majority of speaker drivers produce 2nd harmonic dominantly? would not make this all speakers inherently euphonic?

3.Would not the level of these even order speaker distortions, a magnitute higher than the distortions present throught the electronic chain, dictate how euphonic the sonic result is?or not

4.A chip amplifier with 40db feedback will be virtually distortionless at steady state.Combined with a speaker producing 2% distortion at 100Hz would it have more correct timber than the same speakers driven by a set with 0,1% distortion?

5.If a set can change the timber of an oboe then why do the 99% of the speakers in the market do not produce indistinguishable blabber noise instead of music.Mind that you must first answer #1

6.An amplifier with a major 2nd harmonic distortion will cancel the speaker's 2nd harmonic thus producing third harmonic.If connected in phase it will amplify the second hamonic.If we follow your logic, then just connecting the speakers out of phase would make the set sound like PP and the opposite.Apparently it does not.


Please take these in a friendly tone.
Cheers
Stavros

 

[Mike Lavigne]

Thank you. A huge +1.

I want effortless sound with huge peaks in my system. I've heard a lot of the "it'll drive it" types and left dissatisfied while others were ok with it.

absolute power corrupts absolutely.

I love to be corrupted.

 

[FrantzM]

Thank you. A huge +1.

I want effortless sound with huge peaks in my system. I've heard a lot of the "it'll drive it" types and left dissatisfied while others were ok with it.

absolute power corrupts absolutely.

I love to be corrupted.

Add me to that list ...

 

[NorthStar]

absolute power corrupts absolutely.

I love to be corrupted.

:b

 

[LL21]

Thank you. Do you believe that the human can discern certain kinds of distortion better than others (ie, human ear can pick up 1% 3rd order distortion more easily than 1% 2nd order distortion)? Sorry for the remedial questions...just trying to follow this interesting debate.

"THD is an average of a number of harmonics equally weighted, even though research performed decades ago identifies that lower order harmonics are harder to hear at the same level, compared with higher order ones. In addition, even order harmonics are said to be generally harder to hear than odd order. A number of formulas that attempt to correlate THD with actual audibility have been published, however none have gained mainstream use."
https://en.wikipedia.org/wiki/Total_harmonic_distortion

Thank you...that was where I was going with this. I do not know if the audibility of different orders of harmonics are harder to hear or not...but if it IS the case, then clearly, this ought to be factored into designing and evaluating an amp (among many other things).

 

[LL21]

Good evening gents

Couple of questions to this debate.
1,Has anyone seen distortion measurements throughout the audible band, for coventional speaker/panels/hybrid?
Let us say at 95db.Not even talking about 100db.
How do these figures compare to any amplifier.Set or otherwise.

2...say that a dominant 2nd order harmonic is euphonic.Whould you be surprised to know that the overwhelming majority of speaker drivers produce 2nd harmonic dominantly? would not make this all speakers inherently euphonic?

3.Would not the level of these even order speaker distortions, a magnitute higher than the distortions present throught the electronic chain, dictate how euphonic the sonic result is?or not

4.A chip amplifier with 40db feedback will be virtually distortionless at steady state.Combined with a speaker producing 2% distortion at 100Hz would it have more correct timber than the same speakers driven by a set with 0,1% distortion?

5.If a set can change the timber of an oboe then why do the 99% of the speakers in the market do not produce indistinguishable blabber noise instead of music.Mind that you must first answer #1

6.An amplifier with a major 2nd harmonic distortion will cancel the speaker's 2nd harmonic thus producing third harmonic.If connected in phase it will amplify the second hamonic.If we follow your logic, then just connecting the speakers out of phase would make the set sound like PP and the opposite.Apparently it does not.


Please take these in a friendly tone.
Cheers
Stavros

thanks for taking the time to participate. I have also enjoyed your others posts...i would say they share a similar very educational tone to Atmasphere (Ralph Karsten) who also has done years and years of actual designing, production (very successfully) in the top tier of audio.

 

[morricab]

I believe that some types of distortion are euphonic and others unpleasant. I think it is not a question of the ear prioritising one over the other, just amps with euphonic distortion sound lovely, and so quite a lot of this distortion is not only tolerated but positively favoured. In the case of unpleasant distortion more will always be disliked.

The science is clear: Masking of low order harmonics is a phenomenon that has been known for a long time. Masking is greatest for harmonics that are closest to the fundamental. Also known for quite some time is the ear's self-generated harmonics that also result in a a masking effect and is amplitude independent. Go above these thresholds and the changes from harmonic distortion will be audible, stay below and they will be inaudible, regardless of whether there is an objective timbre change or not. So, there is clear prioritization for the masking of low order harmonics, which occur in nature, and high order harmonics, which occur only in synthetically produced situations like Class AB, push/pull amps with negative feedback.

Amps that you say sound lovely due to EUphonic distortion in fact sound lovely because the distortion they are producing is largely inaudible and your brain hears it as pure. You are so used to the synthetic rendition that you have mistakenly placed this as the "neutral" reference. I know quite a few classical musicians, who once they hear it, recognize the reality right away.

 

[morricab]

Thank you. Do you believe that the human can discern certain kinds of distortion better than others (ie, human ear can pick up 1% 3rd order distortion more easily than 1% 2nd order distortion)? Sorry for the remedial questions...just trying to follow this interesting debate.

Yes, this has been shown and the higher the order the more sensitive you are to it and the more harsh it is. Read the discussion in Cheever's intro and his discussion of aural harmonics. It is similar to what Jean Hiraga was talking about 30 years ago as well. Geddes research papers indicate along the same lines.

This is why zero crossing distortion in Class AB, push/pull amps is an issue. This discontinuity as the signal passes zero volts (where the two transistors hand off one to another) causes a burst of high order harmonics, is very audible and cannot be eliminated with negative feedback. It is the elimination through use of Class A amps that is one of the big advantages of Class A.

The problem with push/pull amps is that they purposely cancel even order harmonic distortion and therefore A) destroy a pattern that is recognized as natural by the ear/brain and B) leave the less pleasant sound odd harmonics. Now, it seems lately some designers have been purposely designing their PP amps so that they do not cancel out so much even harmonic, which must mean they have unbalanced the PP symmetry in some way because the cancellation of even harmonics is INHERENT in a PP design where the two sides are as symmetrical as possible.

Finally, negative feedback is used to lower overall distortion in a circuit but it has the effect of reducing low order harmonics and multiplying high order harmonics. THis has been shown by Crowhurst, Baxandall and recently in a white paper by Pass.

The sensitivity to the high order harmonics is anything but linear...it is in fact exponential and why high orders SHOULD be avoided at all costs...but they are not and in fact most amps have copious amounts...they all sound different and nearly all sound wrong.

All of these "innovations" has led to a reduction in THD and IMD but has made a pattern that is unrecognizable in nature and therefore audible even with very low levels and not a natural but synthetic sound...kind of like looking at hyper resolution 4K that has a lot of low level digital artifacts... I sure looks sharp but utterly fake.

 

[LL21]

Wow...thanks for that! Very interesting, Morricab. I respect your views on SS, though based on your description, Gryphon's pure Class A focus with no negative feedback seems a good start.

 

[morricab]

Thank you...that was where I was going with this. I do not know if the audibility of different orders of harmonics are harder to hear or not...but if it IS the case, then clearly, this ought to be factored into designing and evaluating an amp (among many other things).

It is harder to hear low order:

D.E.L. Shorter from the BBC in 1950 came up with the weighting of N*N/4, where N is the order of the harmonic. That means the harmonic has a squared effect.

However, later investigators found that was not drastic enough.
From CHeever:

"For rising S.P.L.’s the ear creates a monotonically reduced steepness pattern. We cannot disregard this function of the ear. For example, if the ear is presented with an auxiliary sound distorted with a set of harmonics that are consonant with the aural harmonics at 100 dBA but the actual sound pressure level of the fundamental is say 10 or 100 times (10 or 20dB) less, it will be perceived distorted. The Eq. 2-1, below, I derived myself from the Olson data takes this into account and application rationale follow. It is a mathematical expression relating the percentage of the fundamental S.P.L. of the ears self distortion, per harmonic, relative to the sound field S.P.L.
1.35*10(dBA) %Fn = 22
Eq. 2-1 Individual Aural Harmonics
Where: %Fn= Aural Harmonic Amplitude in % of Fundamental for the nth harmonic.
dBA = Decibels “A” weighted Sound Pressure Level resultant from the Fundamental.
n = The harmonic number. f = nFf where f is frequency, Ff= fundamental frequency

The power of the exponentiation may seem high but the fit is excellent, shown following in Fig. 2-7. The solid data points are the data taken directly from the Olson figure reproduced earlier as Fig. 2-2. The hollow data points are calculated from Eq. 2-1. Fig. 2-7 Showing fit of Eq. 2-1 versus Olson aural harmonic test data[28]. For the highest SPL's a compression of the 2nd aural harmonic is not taken account for. For normal music levels of 90dBA peak the fit is very good to 0.0001% of fundamental, or about 30dBA, which is below the noise floor of a normal listening environment. An ideal amplifier would contain no harmonics that do not conform to this aural harmonic envelope. The relative deviation between an amplifiers distortion harmonics and the aural harmonics, per harmonic, must better quantify the subjective sound quality of an amplifier. In reviewing many different amplifiers I found that their harmonic signature did not follow the aural harmonic envelope. Universally the distortion has high order harmonics without the next lower order harmonics’ complementary level. Contrary to the history and evolution in audio design, high order harmonics, if they appear, MUST be joined by a family of lower order harmonics that follow the aural harmonic envelope. In calculating the magnitude of an amplifiers deviation for the aural harmonic envelope I propose that each harmonics deviation be on a relative basis (% of reading, referenced to the level of the nth aural harmonic derived from Eq. 2-1), rather than on the absolute percentage referenced to the fundamentals level. "

 

[morricab]

Wow...thanks for that! Very interesting, Morricab. I respect your views on SS, though based on your description, Gryphon's pure Class A focus with no negative feedback seems a good start.

Most PP tube amps basically have the same problems...plus issues with output transformers that SS doesn't have.