Amp Specs esp. DampFactor : Citation, Adcom, etc.

Aewhistory - don't base your decisions on specifications. High DF and low THD, IMD are most likely a result of deep negative feedback that increases TIM (Transient Intermodulation) causing unpleasant bright sound. I would even suspect that sound might be inveresly proportional to spects within given price range. Nothing will replace audition with your speakers. High DF might be not optimum for some overdamped speakers. There are excellent amplifiers with DF=1 (Atmasphere).

True enough, and I do appreciate the feedback especially as it is a good point, but all of the equipment I am considering is what most would call "classic" stuff. For instance, although I've got the Citations already, if I didn't there wouldn't be any place to audition them any longer. As it is, I'm mostly sticking to equipment that either I've owned in the past (I've had an Adcom GFA-545 and -555 years ago, but never with my current speakers) or equipment people close to me have owned. Essentially, Acurus, Aragon, Hafler, etc. I figure all of these are worth considering, and then I can try to mix and match with my needs (I have a pair of Duntech PCL-3s, Allison Fours, and a 7-channel Maggie system). If my experiment fails I can always resell the equipment, but I am hoping this will help make a more informed decision. The real problem is that with this equipment, and the equipment that I'm trying to match, an audition is almost always out of the question. You see my dilemma?

However, I will need ALOT of help discerning what the specs mean, or likely mean and how they might match this equipment.

Aewhistory,

Amount of gear sold here shows that problem is common. Maybe local dealer will lend you an amp or will let you bring your speakers (my did). Going by spects (especially DF) will be fruitless IMHO. Inductor in series with the woofer limits DF to about 100 anyway.

Hi Kijanki,

You make some good points. The dealer with whom I should have a good relationship--I've given him over $20k worth of biz--is a complete ass in my opinion, so I don't go there any longer, but there are some others I could approach.... I just don't have a working relationship with them. However, your suggestion got me thinking about another option: using some friends and other audiophiles for demos. This might be the way to go.

I do have a few questions, however, about specs. Some folks are passionately against using specs in judging equipment and others, albeit a smaller group IMO, are just a passionate that specs/performance should be measurable. Personally, I'm a military historian and tend to be analytical, so while I can appreciate both sides of the debate, the end result frustrates me. So my main question is in trying to understand the two sides, or rather how do I reconcile these two positions?

Another question I've got concerns the use of amplifier types for reg. speakers vs. subwoofers. Currently I use my Citations to drive two passive SVSs subs (one of the reasons for my fixation on DF), but I don't know if I should get a dedicated 'sub-type' amp such as the one designed for the buttkickers, should I keep my current setup (and I still need to experiment between regular vs. bridged as well), or get a couple large mono-blocks for the subs. This is the sort of problem/question I'm trying to figure out. But without listening, what sort of factors should I be looking for?

This is why I'm confused. I've been 'into' home theater for about fifteen years, I've read magazines, forums, etc., so I'm hardly a newbie, nor am I completely ignorant. Yet, I find information that consistently confuses me. Here is an example: I've just purchased an old Janis sub (haven't gotten it yet) to experiment with matching it with my speakers. It uses a tiny little 80watt amp to drive a 15" driver! However, I'm told that the DF for this amp is very high. How does this jive?

So on the one hand, everyone is always talking about major wattage to drive subs, meanwhile the Janis has this big driver and dinky amp with a high DF. So I'm stuck trying to reconcile all of this information and this is the genesis of why I asked for any other specs I could find to put together a spreadsheet.

BTW, I hope my ignorance isn't too frustrating. I'm just a little frustrated myself trying to make the right choices and digesting this information.

Thank you, Aaron

Aaron - I have Hyperion HPS-938 speakers that have very limited dealership in US. I bought it based on glowing reviews (6 month old dealer demo) without auditioning since I'm in Chicago and the closest dealer is in Pennsylvania. In worst case I would sell speakers but they turned to be absolutely great. Later I found that there is a website of Hyperion users that allow to audition in somebody's home.

I also, being an engineer, tend to over-analyze but I found things much more difficult (black magic?). I would even say that often amp with worse specifications has better sound. It has to do with how these specifications were obtained (negative feedback?) what is synergy with the rest of the system etc.
I tend to read editorial reviews but with a grain of salt. Stereophile reviews are always good and while they don't review non-advertisers they often compare gear. User's reviews and opinions here are great value to me (learning a lot).

I don't have any experience with subs but I'm sure others can help. One thing I noticed that extension is not automatically equal quality. My previous cheaper speakers had two 6" woofers while new ones have two 8" woofers in much larger cabinet but extension is worse (35Hz vs. 32Hz). What got better though, is bass quality - string attack and decay plus better tone and dynamics. I suspect that extension can be forced with extra driver and cross (like 2 1/2 crossover) or tuning of bass refleks. Bass refleks can also be tuned to minimize distortion (current speakers). Bass lower string is 42Hz while piano's is 27Hz but seldom used. For HT it is another story. My TV sound comes thru my system but the main purpose is music. I'm even afraid that sub might screw-up bass definition. There is also money allocation - good subs aren't cheap.

Some folks are passionately against using specs in judging equipment and others, albeit a smaller group IMO, are just a passionate that specs/performance should be measurable. Personally, I'm a military historian and tend to be analytical, so while I can appreciate both sides of the debate, the end result frustrates me. So my main question is in trying to understand the two sides, or rather how do I reconcile these two positions?

My feeling is that the proper reconciliation of those two positions is that an understanding and assessment of specs is both useful and necessary in RULING OUT component selections that would be poor matches to either other components in the system (e.g., impedance incompatibilities, gain or level mismatches, etc.) or to the listener's requirements (e.g., peak volume capability, deep bass extension, physical characteristics, etc.). That hopefully allows the potential candidates to be narrowed down to a manageable number, and may allow some expensive mistakes to be avoided.

The list of remaining candidates can then be further narrowed either by listening, or if that is not possible by careful assessment of reviews and user comments (with grains of salt liberally applied).

Best regards,
-- Al

I am sure that in future, the set of measurments will predict fully amplifier behaivor.

Today, however, many measurments are meaningless or obtained by using dubious techniques design to improve measurments results and not sound.

Today, there are very few measurments which can preedict accurately what to expect e.g. headroom, bandwidth, lowest impedance the amplifier is stable and may be a few more.
THD is not but distortion spectrum will tell me a lot.

At any rate, DF is the ratio of speaker input impedance to amplifier output impedance at given frequency (I think 100 Hz but not sure) and can be achived, as Kijanki said by using deep slow negative feedback. I saw amplifiers, mostly class D with DF > 6000 which could not drive difficult load speakers.

I would suggest to trust "a bit" professional reviewers but more the amplifier's owners review - however, critically i.e. to see what speakers were used, what front end was used etc.

Some folks are passionately against using specs in judging equipment and others, albeit a smaller group IMO, are just a passionate that specs/performance should be measurable. Personally, I'm a military historian and tend to be analytical, so while I can appreciate both sides of the debate, the end result frustrates me. So my main question is in trying to understand the two sides, or rather how do I reconcile these two positions?

This is actually fairly simple. The answer is that the specs were devised about 40-45 years ago, when very little was known about how the human ear perceives sound. A lot of research has been done since then, but none of it has been incorporated into the tradition of measurement, and so we have the experience of not being able to tell much of anything about the sound of the amp from its spec.

IOW, we don't measure what is important to the human ear.

This is what has led to the objectivist/subjectivist debate, although the issue is a bit larger and more complex than that. See
http://www.atma-sphere.com/papers/paradigm_paper2.html
for more information.

Just a FWIW, Damping factor is the least of your worries in any solid state amp. I would not worry about distortion either, Kijanki is correct in his initial post.

"we don't measure what is important to the human ear"

Atmasphere - absolutely true but how we can measure it? I don't know how to measure amp's music power or how to measure TIM distortion or how to guarantee synergy with the speakers. Is there anything we can do (new standards) or it will be always black magic?

I think there is. This is just my opinion of course, but I think we need a standard signal burst, one that last for about 1 second or so, that is completely non-repetative.

The instrument would then compare the amplifier's output to the original. The result would be examined for odd-ordered harmonics so a listener fatigue/brightness rating can be assigned. Then the lower ordered harmonics can be analyzed so a low-order coloration (warmth, caramel, syrupy) value can be assigned.

It would be nice to do this with a variety of test loads, both linear and nonlinear.

That's where *I'd* like to start anyway. I think there is no reason why such a test could not be devised- the compute power for that is pretty common these days.

Atmasphere, at the risk of sounding completely ignorant... why hasn't somebody done what you're proposing? This sounds brilliant, simple, and straightforward. In fact, I'd think that this sort of testing would supply much of the sort of information that I'm looking for.

It isn't that I disagree that each piece of equipment won't sound different, and I certainly agree that what sounds 'good' is subjective, but the methodology behind the sound reproduction should be measurable meaning that it should be possible to say something like: okay, you are looking for this sort of sound, for this sort of speaker, etc. Then you should be looking for amps with these characteristics.

The problem as I see it right now is that if none of these measurements have any value, then how can any of these judgments be made. This is why, at least in part, I think your idea is great.

One last note: about not measuring what is important to the human ear. I'm going to go out on a limb and say that this is likely not true. I can't say for sure, but in my field I research a fair amount of psychology regarding military deterrence and I am constantly impressed at how far the psychological and biological sciences have come in recent years. My point is that I would be shocked if no one has studied the interaction of the human brain, our in-built hearing, and how it interacts with music. Any study such as this would lead, inexorably, toward a better understanding of what appeals to the human ear (in general) and what does not. There are cultural issues here besides biological ones, but momentarily putting these aside, I believe you'd find that, in fact, what we hear, how we hear, and why we like certain things can be measured to a certain degree. To extrapolate, this would explain why certain types of sound reproduction--maybe using tubes?--remains popular even though arguably inferior technologically.

"...The result would be examined for odd-ordered harmonics so a listener fatigue/brightness rating can be assigned. Then the lower ordered harmonics can be analyzed so a low-order coloration (warmth, caramel, syrupy) value can be assigned. "

I believe that John Atkinson from Stereophile does this kind of measurments (his input signal can be subject of discussion) and looking on distortion spectrum - as you discuss above - I have some idea of the sound of the equipment - at least its midrange.

"A lot of research has been done since then, but none of it has been incorporated into the tradition of measurement, and so we have the experience of not being able to tell much of anything about the sound of the amp from its spec."

Simon Thacher from Spectron did study of the rlation between reproduction of musical peaks and listener fatique:
http://www.enjoythemusic.com/magazine/manufacture/0708/index.html

I beleive that Spectron amps are one of the best in that regard - of course, for easy load speakers you don;t need that amount of (distortion-free) power.

So, slowly but we still are moving along to understand relation between some measurments and some aspects of the sound.

Cheers

Atkinson's measurements are with steady-state signals. They tell you *something*, but how the amp behaves with a non-repetitive waveform is really much more important. In my opinion.

Aewhistory, you might be surprised to find out that research about the way the ear hears and how the audio system interacts with that, has really not been dealt with all that much in a way that is not classified.

I have heard of some research that has been done recently (in the last 3 years) that shows that if human hearing rules are not respected by the audio system, the process of analyzing the music by the brain moves from the one area to another. To be more specific, if the waveform is fast enough and lacking manipulation, the limbic system does the processing, but if too slow and certain harmonics are added, the processing is done by the cerebral cortex (emotional vs intellectual). I understand that they have hard numbers on that- on where the transitions occur. Fascinating stuff!

Hello Athmaspere,

LOVE your posts !!!!

I said that John Atkinson " input signal can be subject of discussion" and this is exactly what you did !

Even more interesting your comment: "... if the waveform is fast enough and lacking manipulation, the limbic system does the processing, but if too slow and certain harmonics are added, the processing is done by the cerebral cortex (emotional vs intellectual). "

Is exactly the same that Simon Thacher of Spectron wrote in the article I referred to:

"...The exploration of the origin of "listener fatigue" is extremely interesting, at least, for this writer. We believe that when our subconscious mind detects a small unnatural trace of distortion in reproduced acoustic music (which is not recognized yet as a very low level irritant by the analytical part of our brain) it activates a subtle alarm. This forces the listener into the tense or alert mode. Indirectly supporting this hypothesis is the common description we hear from Spectron users who utilize the two powerful monoblock amplifiers (7 kW peak power, each): "how relaxing" is my listening now "

Analytical part of the brain is the cortex, of course as you pointed out and emotional (or subconscious mind as Simon calls it) is our old reptilian brain

Its amazing - only from both of you I hear CLEARLY and bearly identically how audio engineering is related to our "undertsanding" of music

Seriously, I doubt that anyone could make serious progress in an audio design without understanding how the human ear/brain system works.

Some of this research is very new. The bit that I mentioned about how the processing moves from one part of the brain to another has only been done in the last 2-3 years. Intuitively, I think a lot of designers suspected something like that, hence some systems that invoke toe-tapping and the like; but its nice now to find out that the subjective experience is real and to have objective numbers to back it up.

That, IMO, is what the objective approach **should** be. Otherwise, the bench measurement rules amounts to the Emperor's New Clothes.

"Aewhistory, you might be surprised to find out that research about the way the ear hears and how the audio system interacts with that, has really not been dealt with all that much in a way that is not classified. "

That's disappointing to hear, although perhaps not surprising (and I shouldn't have presumed). With all the progress that the sciences have made, there is so much more to do; a fact made clear by our progress. If anything, our advances have really made it apparent how much of what we thought we knew we, in fact, do not know or have incomplete, need to rethink, etc.

However, thanks for sharing that snippet about something that has been done. Although this thread has gone completely in a different direction than I'd intended, I'm really quite happy with the discussion. I just wish I had something more to add, but I have been reading along consistently.

One last question/point: is there anything one might call research dealing with the linkage of critical listening and planar/electrostatic speakers? I might be totally off-base, but I remember hearing once that more than half of Stereophile readers had some sort of planar/eletrostatic speaker even though there are FAR more box-speaker manufacturers. I have little doubt that this is not representative of music listening in general; it must be representative of audiophiles and/or critical music listeners, right? Anyway, just wondering.

Atmasphere,

As I understand it, our brain works more in time domain than frequency domain. We cannot hear above 20kHz but recent research shows that people can still tell the difference between 20kHz and 50kHz bandwidth listening to music. All spacial clues are also defined by transients.

A lot of this information is lost or changed in digital processing. On one hand it is almost impossible to recover 20kHz sinewave when whole period is defined by two points of 44.1kHz (AFAIK Nyquist criteria protects only frequency information) on the other digital filtering alters step response making ringing to appear after (as it should be)and BEFORE pulse itself. Our hearing is sensitive to the shape of the wavefront. Newest filtering schemes (non-apodizing filters) used, for example, in Meridian CDP have (Stereophile review) normal looking step response and better, more natural sound.

Kijanki, would this explain why some have argued that keeping the signal above 20kHz is still necessary even though it isn't audible in the 'traditional' sense? Or is that what you're saying and I'm just repeating it? :-)

Thanks, Aaron

Aewhistory, I had impression that keeping bandwidth well above 20kHz prevents phase shifts within 20kHz but as research suggest it might as well improve transients that our brain processes.

Technical spects have no value to me. I'm not even sure what they mean. Is low THD amp better sounding than high THD amp? Same goes for DF.

To me, at least theoretically, a low THD should represent a cleaner signal path. Of course, this is theoretical, but what that spec. means to me is that the amplifier is not introducing outright distortion into the line. Of course, having said that, what constitutes distortion needs some definition.

This may seem completely unrelated, but in my field, history, the same types of arguments are made over trying to define terminology, categorizing, measuring, etc. And the results are no less frustrating. So while I can't claim to understand the finer aspects of EE, I do understand the academic aspects of the debate and appreciate them, despite my somewhat simplistic approach.

Yes, THD should represent a cleaner signal path but the problem is that amp design is a compromise - you want more of this you'll get less of that. THD is usually traded in SS amps for TIM and related odd order harmonics enhancement. Stereophile experimented with Cary CAD-805C amp that has adjustable feedback and found sound to be natural without the feedback (where THD is higher) and "Hi-Fiish" with deep feedback: http://stereophile.com/reference/70/

I'm not sure what can be useful in amps spects. RMS power ratings has some value but I can imagine two amps with the same RMS power rating where one can play music much louder (bigger overhead). It is like trying to classify a taste of wine. I'd like to know if it's red or white, dry or sweet but everything else is very subjective.

Aewhistory, for the most part I think you will find that a low THD indicates a greater amount of feedback (with it accompanying distortion of the 5th, 7th and 9th harmonics) rather than a 'cleaner' signal path.

IOW, if anything it appears that there is a loose correlation saying that higher THD will sound *better* not worse- and likely having a 'cleaner' signal path, hence less need for feedback. The 'cleanest' signal path will have no need for feedback. Note: this is neither a tube or transistor distinction.

Kijanki, IME wide bandwidth is important due to low phase shift, barring that, then gentle rolloffs as opposed to steep ones. I use an Alesis Masterlink in the recording studio for backup recordings. It can record at 88KHz, which is nice as when you use that mode, there is no brickwall filter. As a result the 44.1 KHz finished product does sound better on that account. I think things like this and what you just described are where the advances in digital are occurring- no doubt due to our improved understanding of how the ear works.