Thanks for trying. I'll be seeing Jeff Rowland in the next few weeks, so I'll ask him about it.
Dave |
Hi Dave, the distortion I'm talking about is the kind that you get without the amplifier clipping, but from what you are describing I can't help but wonder if the lower-powered amps you were auditioning were simply being driven too hard.
Once you get over damping factors of 20 or so, there is no audible artifact that can be attributed to 'damping factor'.
Power supplies can have a big effect on how the amp plays bass too. Inadequate supplies can cause the amp to have a dirty or muddy bass quality when the amp is working hard, without the amp clipping. BTW this would have little to do with the output impedance of the amp ('damping factor' is 8 ohms with relation to the output impedance of the amp, BTW; a damping factor of 20:1 is thus an output impedance of 0.4 ohms).
IOW I would be **very** hesitant to attribute any of what you heard to 'damping factor'. The possibilities I mentioned above are far more likely, though by no means the only explanations. |
03-31-08: Atmasphere said:
"Dave, its likely something else, in this case power and distortion. Audiophiles like to think that 'damping factor' is what they are hearing when the bass is better, and a lack of 'damping' when the bass is muddy. What is really happening is that an amplifier with clean bass is not making distortion. The amp that has muddy bass is making a lot of distortion. It really is that simple."
Well, that doesn't explain why one Jeff Rowland amp with 100 watts (into 4 ohms) of power sounded so much better in the bass than another Rowland amp with 275 watts into the same load, but with similar IM and harmonic distortion numbers.
There WAS distortion, but it seemed to be introduced by the woofers, not the amps. One amp controlled the woofers better than the other. (I'm a musician, so I know "real" bass. There were "Poster board" images of instrument in this case).
The least controlling amp was a relatively low powered Primare. Some might say it's bass had more "bloom", but I would have said it was "bloated". The lower powered Rowland improved the bass by a couple of orders of excellence, but the Rowland monoblocks really brought us very close to real bass.
When you speak of distortion, are you speaking of the entire system, including any uncontrolled resonance of the speakers' drivers? I heard that distortion and it's very real and obvious. The publish distortion numbers of amps are not measure with a big woofer on the other end of the wire. If we include that distortion, then it seems like damping and power will decrease system distortion given equal measurement of the amps under test loads without speakers attached.
Thanks for continuing to try to help Duke.
Dave |
Atmasphere's description here is EXACTLY what I heard with Wolcott amps as I turned the damping factor control up higher and higher. The loudspeakers were SoundLab fullrange electrostats:
"...[One] of the first things to go is the low frequency ambiance in the recording. Further reduction of definition [raising of damping factor] results in 'poster board' images of instruments in the soundstage."
Duke |
Dave, its likely something else, in this case power and distortion. Audiophiles like to think that 'damping factor' is what they are hearing when the bass is better, and a lack of 'damping' when the bass is muddy. What is really happening is that an amplifier with clean bass is not making distortion. The amp that has muddy bass is making a lot of distortion. It really is that simple.
If you have ever spent time around instruments that actually make bass (bass drums, bass guitar, string bass, organ pedals) one thing you learn real quick is that there is no such thing as 'tight bass' in real life. 'Tight' bass only exists artificially.
Amps that exhibit 'tight' bass often have lots of feedback, which is there to reduce distortion. Unfortunately a price is paid: loop feedback at low frequencies can behave as a sort of dynamic compression, and has the ability to cause the amplifier to loose soundstage definition (the 'air' around instruments that flesh out the body of the instrument as well as its ambient signature). Often 'tight' bass is as a lack of definition at low frequencies.
IME, when you start to loose definition, the of the first things to go is the low frequency ambiance in the recording. Further reduction of definition results in 'poster board' images of instruments in the soundstage. Initially, this might sound as if the amp is more focused, but after a while the lack of ambient signatures (hall reflections and the like) let you know what is really going on. |
That Duke, I appreciate your thoughts. However, this makes me wonder what I was hearing as both damping factor and power went up and ringing went down. This was in the DALI Helicon 400Mk.2. The difference wasn't subtle at all. All were SS amps and the bass was out of control with the low powered amp, tighter with the medium power stereo amp and the best with 500 watt mono-blocks. Do you think this was not so much due to damping, but more so to the power guiding the woofers? Or, is it something else?
Dave |
Dcstep, I don't know how much of a difference greater amplifier power makes. In my experience if the amplifier and speaker work well together, it doesn't really matter what the amplifier's damping factor is.
I used to think that a speaker would ring like a bell if the amp didn't have a high damping factor, but I no longer believe that. The voice coil is powered all the way through its cycle. In a properly designed speaker, the voice coil never has to depend on the amplifier's low output impedance to "put on the brakes" and stop unintended oscillation.
I have owned two amplifiers (Berning ZH-270 and Wolcott Presence P220M) that had variable damping factor controls, which imho was a useful feature for pairing up with different speakers. With neither amp did I ever encounter a speaker that sounded best with the damping factor at the highest setting.
I tend to like zero-global-feedback tube amps, which inherently tend to have a very low damping factor. This does limit speaker choice somewhat, but once I put on my speaker designer hat I see opportunity there instead of limitation.
Duke |
Duke, is an amplifier's ability to damp a speaker a function of several things including damping factor, amplifier power, the resistance of the speaker and resistance in the cable?
All other things being equal, wouldn't an amplifier with 500 watts into 4-ohms and a damping power of 1000, for instance, have a much higher damping ability than a 50 watt amplifier into the same load with the same damping factor?
Dave |
Gs5556, the net effect of low damping factor on SPL is not the same as having a resistor in series. The modification of Qe is the same, but because there is in fact no resistor in series that is soaking up power there is no corresponding loss in SPL.
Once again, a real-world example: The low damping factor OTL amplifier I use delivers about twice the wattage into my speaker's high impedance in the bass region as it does into the 8-ohm load they present across the rest of the spectrum. That extra wattage in the bass region is indeed a free lunch.
Just for the record, note that the wattage output of a high damping factor amplifier is also modulated by the speaker's impedance curve, but in the opposite direction.
Duke |
Duke, I agree that using speaker equations can show that the lower cutoff frequency is a function of Qe. For example, if you assume a speaker design with a Qt of 0.707 with a driver that has a voice coil resistance of 5 ohms, a Qm of 3, 8 ohm impedance, and a Fs of 40 hz, then Qe at a DF of 1000 or greater will be 0.925 and give a lower cutoff of 40 hz. If you go down to a DF of 10, Qe is 15% higher and the lower cutoff drops 3 dB to 36 hz. But that's not a free lunch...
What you have to take into account is that the SPL ultimately depends on pressure generated by the driver. The factors affecting pressure are the driver magnet force factor, piston area, voice coil resistance and mechanical compliance. The SPL using these factors is inversely proportional to voice coil resistance. So decreasing the DF has the same effect as increasing the coil resistance so any -dB frequency drop by increasing Qt is offset by the reduction in SPL which is a wash. Otherwise, you could simply place a variable resistor in line with the driver which you can then adjust Qt to play with the frequency response in your room, independent of amplifier power. |
Gs5556, I agree with you that the primary low-frequency effect of amplifier output impedance (or damping factor) is on driver electrical Q. And the lowest possible value of Qe is not necessarily ideal.
Let me give an example of a speaker that would be suited for a low damping factor (high output impedance) amplifier. Suppose you have a very low-Q fullrange single-driver speaker whose frequency response (measured on a high damping factor amplifier) shows a gentle rolloff starting in the upper bass region, with the low bass being pretty weak. This speaker will sound thin and gutless without help in the bass region.
Okay, let's look at what happens when this speaker is driven by a tube amp with a very low damping factor, let's say a damping factor of 1 (output impedance of 8 ohms). This would be like doubling the driver's electrical Q. So in effect we would be getting a "free lunch" - about 3 dB or so of bass boost. This will probably make the speaker's tonal balance acceptable without having to add a subwoofer.
To give a real-world example, I build a speaker that is -3 dB at 35 Hz and -6 dB at 32 Hz with a solid state amp. With a low-damping-factor tube amp, this same speaker is -3 dB at 30 Hz and -6 dB at 24 Hz (this assumes appropriate re-tuning of the port.) As you can see, there is a significant "free lunch" here as well: the -6 dB point (which often predicts the actual in-room bass extension) moves about half an octave lower with the low damping factor amp. And, the response is actually smoother (less ripple) with the low damping factor amp.
I just gave away one of my secrets. Since it's over here under "Amps Preamps" instead of under "Speakers", maybe no one will notice.
Duke |
Duke, I am confused. Can you please explain how one can tell by looking at a speaker response curve if it has a solid state or tube amp in mind? I always thought that those curves were amplifier-independent and any off-bass responses were the result of an amplifier's inability to keep up current at low impedances or room effects.
My understanding of speaker design tells me that the amplifier's output impedance affects the electrical Qe, which in turn, affects the speaker's Qt. If the damping factor is infinite (zero output source impedance) then the electrical Qe is just the voice coil and crossover resistances. Would this not be the ideal, the smallest possible value of Qe?
My view is that damping factor is way misunderstood. I think some envision the amplifier physically starting and stopping the speaker cones. It's the magnet that does that. The motion of the cone is the same no matter what the damping factor. What a high DF does is minimize the effect of any back emf, reducing distortion. Its measure also indicates the amplifier's ability to put out higher current at lower speaker impedances.
I would not even consider damping factor in choosing an amplifier, period. If an amp/speaker combo is not meant to be, you will hear it. |
Coming at this issue with my speaker designer hat on, in my opinion it is possible for a speaker to be either overdamped or underdamped by an amplifier. Most speakers today are designed with high damping factor solid state amps in mind, but then those speakers may be underdamped (too much bass) when driven by a low damping factor specialty tube amp. On the other hand, a speaker designed to work well with a low damping factor specialty tube amp may be overdamped (not enough bass) when driven by a solid state amp.
Blame for a mismatch (resulting in too much or too little bass) is often incorrectly attributed to the amp or to the speakers, when really it's a component compatibility issue.
To zero in on your second question, a higher damping factor is not always a good thing - it depends on the speakers. My speakers can be tuned for either type of amplifier, but in my opinion they perform best with a low damping factor amplifier.
Duke
dealer/manufacturer |
Thanks for the replies.
Of course making decisions based solely on damping or specs is foolish. But the more information I have, the more I can whittle down my huge list. Funny though, the list is getting bigger, not smaller. Now I'm looking at Bel Canto's line of e.one amps. Particularly the 300 series. |
Looking at the specs on the Totem I think you'll have no problem. The little boogers are 4 ohm and fairly low efficiency. The 4 ohm resistance actually lowers the effective damping of the whole amp/cable/speaker system. In general, damping is less important with a smaller number of smaller drivers, but it'll still be a positve.
The Belles' 500 watts into 4-ohm is not an issue. Just set the volume by ear and you won't blow anything up or fry your tweeters.
I'm sure you've thought of this, but you'll need excellent sources and cables or that setup will reveal any shortcomings.
Let us know how you like it after you've got it set up.
Dave |
In the purely hypothetical sense, no. Damping factor is like distortion . . . in absolute terms, there are specs that are better and there are specs that are worse . . . in the case of damping factor, higher is better, and in the case of distortion, lower is better.
But they are both woefully inadequate in terms of measuring an amplifier's sound quality, and completely worthless as published specifications. There are both great-sounding and terrible-sounding amps with high damping factors and with low damping factors. |
