Tubes test very low for DF. My new MC275V is rated at only 14 but the soundstage and the sensation of airiness can be approached only by the fastest SS amps with DF's that easily exceed 200. It has to be in the way the two discharge and replenish energy but how? Thoughts?

I was under the impression Damping Factor had to do mostly with bass frequency control and tightness. The ability of an amp to start / stop the woofers real fast.

I could be wrong, though.

Jorge

Maybe this could help, and i quote:

"Like most specifications, damping factor does not tell you an amplifier is "good". It can't; no more than a tuner with a great image rejection specification is guaranteed to be a "good tuner". There is a lot more to good amplifier performance than output impedance. Frequency response, mentioned previously, is a good example; suppose the amplifier had a damping factor of 10,000 at 8 ohms, a stunning number (because it implies a very, very low output impedance)... but could only reproduce frequencies between 300 Hz and 1 KHz? Your music would sound pretty awful. Another is distortion: Suppose the amplifier distorts the music? What good is it then to have the speaker do more (even just slightly more) precisely what the amplifier says? Not much! So don't let damping factor go to your head, so to speak - it's one of many specs, one where higher numbers are better because they tell you that the amplifier has a lower output impedance, which is good. Read all the specs, try to learn what they all mean, and then you'll be able to get a good picture of amplifier performance.

The bottom line is, a really low damping factor can tell you an amp isn't going to be all that great with a highly reactive speaker (the larger a speaker driver is physically, and the more power it is designed to handle, the more likely it is to be highly reactive.) What's really low? Well, if we're talking about 8 ohm speakers, a damping factor below about 30 indicates it's going to have noticeably poorer control of a highly reactive load as compared to an amplifier with a damping factor of 100. How much? It works out to about 10% worse (because you have to factor in the speaker resistance.) As the damping factor goes lower, it gets worse yet. You can hear a 10% difference in speaker control. Trust me! "

From:
http://www.classic-audio.com/marantz/mdampingfactor.html

Jorge: A SS amp that can accurately reproduce bass will perform very well with midrange vocals and instruments as these elements have a bass component that gives them fullness and nuance. Accuracy should not be confused with quantity, which any amp can manage with liberal use of tone controls. Accuracy has to do with how well an input signal is reproduced and the best measure is with a 20 Hz square wave.

A full square wave test consists of 20 Hz, 1 kHz, and 20 Khz which broadly represents bass, midrange, and treble. The 20 Hz result is the hardest to get right because bass draws the most power and so the amp has to be fast to replenish energy quick enough not to degrade the signal. Amps that do well in the 20 Hz test do very well in the 1 kHz and 20 kHz tests.

Of the amps that I have seen that do well in the square wave test, there is a strong correlation with higher DF. Tubes do not follow this trend.

I don't think this guy has his facts straight. First off, amps have been able to generate all of the audible range frequencies since the fifties. And, THD's well below 0.1% has been standard since the beginning of SS. Even the lowliest of amps measure well below 0.1% THD. The threshold for hearing distortion is 1%.

I also think his highly reactive speaker example is not right. He is referring to speaker efficiency, which has to do with volume output for 1 watt and not with DF. A highly reactive signal has to do with how much attack and how much variation in frequency of the program.

Sam,

I think your initial post has led us through the wrong path. DF has got everything to do with controling the driver, particularly larger drivers like woofers.

What you describe as the soundstage and the sensation of airiness, has a lot more to do, IMO, with the way the different devices ( tubes vs. Transistors ) transfer audio signals and the type and amount of distortion they produce in the process. It is a well known fact that SS devices are less linear and produce high amount of distortion at lower outputs, whereas tubes will produce higher distortion closer to their rated outputs, though that distortion is kinder to the hear.

Back to your DF question, and trying to get a little deeper into it, here´s what I found over at Wikipedia, which seems to be pretty accurate:

In loudspeaker systems, the value of the damping factor between a particular loudspeaker and a particular amplifier describes the ability of the amplifier to control undesirable movement of the speaker cone near the resonant frequency of the speaker system. It is usually used in the context of low-frequency driver behavior, and especially so in the case of electrodynamic drivers, which use a magnetic motor to generate the forces which move the diaphragm.

Speaker diaphragms have mass, and their surrounds have stiffness. Together, these form a resonant system, and the mechanical cone resonance may be excited by electrical signals (e.g., pulses) at audio frequencies. But a driver with a voice coil is also a current generator, since it has a coil attached to the cone and suspension, and that coil is immersed in a magnetic field. For every motion the coil makes, it will generate a current that will be seen by any electrically attached equipment, such as an amplifier. In fact, the amp's output circuitry will be the main electrical load on the "voice coil current generator". If that load has low resistance, the current will be larger and the voice coil will be more strongly forced to decelerate. A high damping factor (which requires low output impedance at the amplifier output) very rapidly damps unwanted cone movements induced by the mechanical resonance of the speaker, acting as the equivalent of a "brake" on the voice coil motion (just as a short circuit across the terminals of a rotary electrical generator will make it very hard to turn). It is generally (though not universally) thought that tighter control of voice coil motion is desirable, as it is believed to contribute to better-quality sound.

A high damping factor indicates that an amplifier will have greater control over the movement of the speaker cone, particularly in the bass region near the resonant frequency of the driver's mechanical resonance. However, the damping factor at any particular frequency will vary, since driver voice coils are complex impedances whose values vary with frequency. In addition, the electrical characteristics of every voice coil will change with temperature; high power levels will increase coil temperature, and thus resistance. And finally, passive crossovers (made of relatively large inductors, capacitors, and resistors) are between the amplifier and speaker drivers and also affect the damping factor, again in a way that varies with frequency.

For audio power amplifiers, this source impedance Zsource (also: output impedance) is generally smaller than 0.1 ohm (Ω), and from the point of view of the driver voice coil, is a near short-circuit.

Imo, damping factor is only one of the many performance aspects of an amplifier and not the most important factor to dterminate the amplifier quality and effeciency. If in fact it was, what about the example you’d posted in your first post…?! And i quote: “….My new MC275V is rated at only 14 but the soundstage and the sensation of airiness can be approached only by the fastest SS amps with DF's that easily exceed 200.”

In fact, nearly all valve amplifiers have a low damping factor, caused by a relatively high output impedance. Speakers must be very well damped indeed to work well with any valve amp, or the bass will become poorly defined, and crossover networks (which rely on a very low amp impedance) may not work as well as intended.

BTW, about the link i'd posted above.
Do you think Ben Blish is not accurate in what he says and writes?

http://www.classic-audio.com/

Blish's use of THD and limited spectrum amplifiers are intended for the uninformed. These are Bose level arguments that IMO will not hold water with anyone with even a limited knowledge of specs let alone more experienced enthusiasts. I have never seen an amp that "could only reproduce frequencies between 300 Hz and 1 KHz" and in fact, I would imagine the FTC would do something to prevent something like this from ever hitting the market.

True, DF is one of many specs that make an amp. Having heard dozens of amps with varying performance, IMO there is a strong correlation between faster amps and greater accuracy. Again, I must repeat that many including yourself confuse input/output accuracy with sound quality which has a subjective component. The objective definition of input/output accuracy is how much the amp changes the input signal and this is measured using the square wave test.

SS with high DF does very well with this test but tubes do not and yet tubes have a magical sound that cannot be denied. What I am trying to understand is why. And I am trying to understand the empirical evidence of why DF metrics differ for SS and tubes.

DF applies to bass but it also applies to the rest of the frequency spectrum. For any amplifier, all frequencies have attack and decay that can be tested for and measured. Attack and decay have everything to do with clarity.

How and why is this true?

SS distortion is measured at full rated power so how is the non-linear distortion you mention audible?

Let’s clarify some of these issues.

About Damping Factor:
In simple terms, damping factor is simply a measure of an amplifier’s ability to drive and control a speaker.
The damping factor in an amplifier depends greatly upon the speaker to which it is connected, the wire connecting the speaker to the amplifier, the signal frequency that the amplifier is sending to the speaker, and the power level at which the amplifier is operating, among other things. Damping factor is most critical at low frequencies, generally 100 Hz and below (i.e. frequencies that a woofer reproduces). At such frequencies, a high damping factor is desirable in order to maintain a "tight" sound. If an amplifier/speaker pair has a low damping factor, the bass response is likely to be "boomy", "uncontrolled", and "loose" sounding.
Sorry, but imo if you understand a little what damping factor is you should know by now that it’s more difficult for an amplifier to drive and control a larger mass like a woofer-driver than a lighter mass like a tweeter….

About Harmonic Distortion:
Harmonic distortion (although certainly undesirable) is imho, one of the more tolerable types of distortion as long as it is kept reasonably low. The reason that a seemingly high value of THD is acceptable for music is partially because many sounds in nature are rich in harmonics. Also, most decent cassette decks (which most people agree sound pretty good) have THD (off the tape that is) of several percent…. Worse, even good speakers can have THD up to 10%, especially at low frequencies! All in all, the human ear can tolerate a fair amount of THD before it becomes objectionable.

About transistors and tubes:
The signal path in a tube amplifier undergoes similar processing as the signal in a transistor amp, however the devices and voltages are quite different. Tubes are generally "high voltage low current" devices, where transistors are the opposite ("low voltage high current"). One of the biggest differences between a tube amplifier and a transistor amplifier is that an audio output transformer is almost always required in a tube amplifier (this is because the output impedance of a tube circuit is far too high to properly interface directly to a low impedance loudspeaker). High quality audio output transformers are difficult to design, and tend to be large, heavy, and expensive. In valve amplifiers the output transformer isolates the speaker from the amplifier electronics.
Transistors drive the speakers directly. The output of a solid-state amplifiers is directly connected to 2 DC power supplies through the output transistors. The instantaneous non-symmetry within the music waveform (particularly from the bass notes) is averaged as a modulating DC offset. This modulating offset is small, but it varies the efficiency of the speaker, introducing inter-modulation distortion, amplitude modulating the music.

About input/output stages
Only the output stage of an amplifier interfaces to the speakers.

About Speakers
Amplifier efficiency is generally assumed to be stated for resistive loads, however speakers are reactive loads, meaning they are basically a resistance with the added characteristic of inductance or capacitance (one or the other at any given time). A speaker will never be totally reactive (meaning it will never be totally inductive or total capacitive, it will always have a resistive component). Ideal inductors and capacitors dissipate no power (these devices store electrical energy), however they DO allow current to flow.
Just for curiosity:
Most loudspeakers are actually very inefficient transducers; only about 1% of the electrical energy sent by an amplifier to a typical loudspeaker is converted to acoustic energy, some say that most speakers are only about 5% efficient… The remainder is converted to heat, mostly in the voice coil and magnet assembly.

About Ben
I don’t even try to answer you, Sorry. His site is so explicit in so many ways that imo no words are necessary.

In resume
Do not be terribly concerned with damping factor when dealing with quality equipment. Most of the good amplifiers and speakers available today will yield excellent sound when used together.
In fact I believe that in some amps the problem is excessive damping or over-damping(which reduces efficiency, limiting responsiveness and resulting in excessive loss of bottom end – not allowing the woofer “to breath”…) and not the contrary……

A final note (from Nelson Pass ):
A solid-state guy probably starts fixing his audio setup response with a parametric equalizer and the tube guy enjoys his music with a nice glass of wine...

Having talked to circuit designers who worked at major manufacturers, IMO Blish's approach is not totally scientific and there is more than a whiff of marketing in his work. I do appreciate his effort to post his thoughts.

True, THD can be SUBJECTIVELY desirable in gear. In fact, tubes do not test well at all but the harmonic distortion is the tubey goodness that makes my MC275V so enjoyable. THD in speakers can be startlingly high. JBL used to test their own speakers and also the competition. The better JBL's tested to 7% THD while others like the Bose 901 were a laughing stock at over 20%. However, there are numerous rabid Bose fans who will defend the 901 to the end.

I don't pay too much attention to the subjective because preference is intensely personal and inherently biased. I prefer to look at objective measures and how things work, which your info sheds some light.

I disagree with your "In Resume" conclusions, particularly your statement "Most of the good amplifiers and speakers available today will yield excellent sound when used together." I've heard boutique amps and speakers that cost more than some new cars and didn't like the sound at all. OTOH, I'm always interested in finding a better sound and also in how things work.

As you said, you dont pay attention to the subjective, I would say that most of us on this forum are only subjective listeners, and not bound by a square wave test. I could care a less about the numbers, Years ago I used to get caught up in the numbers, an example, My teac cassette deck had some very good numbers, but I think the little 2 head Nak that I got from speakerman sounds better and it has worse numbers. but hey, the numbers dont lie, or do they.

elroy

As I noted earlier, subjective is problematic because of bias. Not saying that is good or bad.

you are correct, I may think something sounds good, but it may be crap, or I just cant hear the difference between an emerson cd player and a rega. but I do have pretty good ears, I think anyway.

elroy

So why not qualify your subjective statements? There must be a reason why you run the superb CX/MX-2000 set other than it sounds good.