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Does damping factor matter?


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Benchmark says it does:

 

https://benchmarkmedia.com/blogs/application_notes/audio-myth-damping-factor-isnt-much-of-a-factor

 

Yet, tube amps can sound glorious in spite of their typical low DF, one example being the Spudkit (very low DF as it does not employ any negative feedback) which continues to be highly praised when used with Klipsch speakers.
 

 

Maynard 

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On 4/30/2021 at 6:34 AM, tube fanatic said:

Benchmark says it does:

 

https://benchmarkmedia.com/blogs/application_notes/audio-myth-damping-factor-isnt-much-of-a-factor

 

Yet, tube amps can sound glorious in spite of their typical low DF, one example being the Spudkit (very low DF as it does not employ any negative feedback) which continues to be highly praised when used with Klipsch speakers.
 

 

Maynard 

Yes and No

 

If a speaker existed that was absolutely flat in resistance and frequency response

Then we wouldn't need equalizers and tone controls, but we do.

 

Should the output of an amp be linear connected to the ideal load?  YES

 

THX has a set of tests and measurement for a lot, maybe 150+, parameters for amps

to characterize how they behave in all kinds of situations

My experience in electronics, is how a unit behaves in error, failure, attached equipment failure etc separates the men from the boys. All semi competent designs work well in ideal conditions.

 

I saw a brilliant mathematical analysis on damping specs

and quickly forgot most of it.

What I do recall is that 20 is the magic number

and above that doesn't do much.

 

My MC2205 has a factor of 12, and sounds great

The excursion on the LaScalas is minimal

The amp is pushing and pulling the speaker coils, the tighter tolerances the better

Electricity wants to flow to the lowest resistance, ground.

 

I'll leave it to someone else

but if I recall correctly

Tube amps and McIntosh with the giant output transformers

the load the amp sees is the giant linear transformer, not the speakers

The taps are labeled for the load they connect to aka 4,8,16 Ohm

Not labeled with the resistance of the amp at the tap.

 

Capacitance changes with frequency

Coax spec sheets and white papers show little to no value to much over 16GA lamp cord.

The world's greatest cable is coax, Belden copper core

https://www.belden.com/products/cable/coax-triax-cable

 

PS I usually associate negative feedback with op amps, the better the op amp the less NF required.

I also understand some, most?, tube designs employ NF to flatten frequency curves.

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I've come to understand negative feedback as an Error Correction, and the fewer errors it has to correct, the better.

 

Damping factor? Just need 'enough', and your cables degrade it. Functionally, it's a log curve, amps that claim to be out in the flat part usually end up on the curved part after speakers and cables are hooked up, and beauty is in the ear of the beholder.

 

Aren't the Subjective Art Hobbies fun?

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31 minutes ago, Shiva said:

I use a Crown K2 on my mains.  Damping factor of 3000.

Yeah ... K1 here with a similar damping factor. Dramatic difference with my previous amp :) 

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^^

Both amps claiming to be waaay out on the flat part of the curve. 

How much resistance between there and the driver itself? Or even to the inputs at the crossover?

What's the actual delivered damping factor? Probably way less than 3K.

 

 

Either way, I'm jealous and I want one of those. 😁

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1 hour ago, Emile said:

Yeah ... K1 here with a similar damping factor. Dramatic difference with my previous amp :) 

Either of you using the Crowns with passive XO?  I’m sure the bass is solid and plentiful, how’s mids? Any harshness,, edginess? Any comparisons to a class A amp in same system? Paired with tube preamp? Thanks

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I find the Crown very smooth sounding and transparent as well.  Neither harsh nor edgy.   Even though the K2 is rated at 500 watts a side, it had to sound good putting out less than a watt as well and it does.  Listening to it now, Tidal from an iPhone, into my SMSL SU-8 Dac, that has XLR outs and works as a preamp, into the Crown. 

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I find the Crown very smooth sounding and transparent as well.  Neither harsh nor edgy.   Even though the K2 is rated at 500 watts a side, it had to sound good putting out less than a watt as well and it does.  Listening to it now, Tidal from an iPhone, into my SMSL SU-8 Dac, that has XLR outs and works as a preamp, into the Crown. 
Best sounding pro-amp I've owned besides a Macrotech. My tech bench tested it at 580 wpc @8 ohms.

Sent from my SM-G950U using Tapatalk

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Impedance variations can cause significant changes in the frequency response at the amplifier output if the amplifier's output impedance is too high. If the amplifier output impedance is very low (high damping factor), the resistive, inductive and capacitive portions of the speaker impedance will have little impact on the amplitude or phase response at the output of the amplifier.  If the amplifier output impedance begins to approach that of the speakers (damping factor of 1), the resistive, inductive and capacitive portions of the speaker impedance will have a major impact on the amplitude and phase response at the output of the amplifier.

 

Simply put, it depends on your speakers and your amplifiers in combination with each other. Enough is enough, and too little is an audible concern. Functionally, In most common use cases, one amplifier with a damping factor of say (10) will in most cases not result in more than about 2db of audible change from another amplifier with a damping factor of say (3000). Unless you have like 1/2 ohm 12V car audio subwoofers or something weird going on. My speakers have a significant impedance dip and severe phase angle change at a specific low frequency. A higher damping factor can perform a function that will kind of assist the amplifier allowing it to sort of ease through those sudden swings. Or you could also add more amplifier headroom. I do both.

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12 hours ago, Shiva said:

I use a Crown K2 on my mains.  Damping factor of 3000.  Carry on.😀

Crown amps are beasts---------slamming hard bass -

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19 hours ago, VDS said:

Either of you using the Crowns with passive XO?  I’m sure the bass is solid and plentiful, how’s mids?

Using the K1 with passive XO on KPT-904's with K-510 horns.  (Used to have a Marantz 2270 on these.) Bass is awesome; mids/highs are stellar :)

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I have to ask what are you mega watt SS guys doing posting in the Tube section 🤷‍♂️... Us tube guys all know you have long ago burned all the hairs out of your ears to know what sounds good :) 

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6 hours ago, NOSValves said:

I have to ask what are you mega watt SS guys doing posting in the Tube section 🤷‍♂️... Us tube guys all know you have long ago burned all the hairs out of your ears to know what sounds good :) 

a bit of fun never hurts 

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  • 2 weeks later...
On 4/30/2021 at 6:34 AM, tube fanatic said:

Benchmark says it does:

 

https://benchmarkmedia.com/blogs/application_notes/audio-myth-damping-factor-isnt-much-of-a-factor

 

Yet, tube amps can sound glorious in spite of their typical low DF, one example being the Spudkit (very low DF as it does not employ any negative feedback) which continues to be highly praised when used with Klipsch speakers.
 

 

Maynard 

The "damping factor," as usually defined, is the speaker impedance divided by the output impedance of the amplifier.  Since, probably, a manufacturer typically assumes an 8 ohm speak impedance when quoting a damping factor, this means that what is being stated is just a slightly convoluted way of saying what the output impedance of the amplifier is.  That is, Output Impedance = 8 divided by Damping Factor.

 

I think the concept of damping factor as a "figure of merit" is highly misleading.  Figure 1 shows a simplified effective circuit for an amplifier (the left-hand box) connected to a loudspeaker  (the right-hand box).  The amplifier is modelled as an ideal (zero impedance) voltage source in series with a resistor R0 (the output impedance).  The loudspeaker is modelled as an ideal (zero DC resistance) inductor in series with a resistor Rs (the DC resistance of the loudspeaker). The ideal inductor has an impedance Z, which is, of course, highly frequency dependent.  The loudspeaker model here is very crude; better models look something like what is depicted in Figure 2.  In each case, it is a resistor Rs in series with the rest of the model.

 

If we stick with the very simplified model in Figure 1, and furthermore if we make the rough approximation that we can just add Rs and Z to get the net "speaker impedance" (i.e. we neglect the complications of the need to take into account the phase angle for the inductive reactance of the speaker coil), then the usual so-called damping factor DF is calculated as

 

               DF = (Rs + Z)/R0,

 

which can get impressively (and deceptively!) large if the output impedance of the amplifier, R0, is very small.

 

But it is clear from the circuit in Figure 1 that R0 and Rs are simply two resistors in series, and they both represent lossy components that tend to prevent the amplifier signal from controlling the speaker cone.  A much more accurate measure of how effectively the amplifier controls the cone is to calculate Z divided by the total series resistance.  Thus we can defined the "true damping factor" TDF as

 

          TDF = Z/(R0 + Rs).

 

The crucial point is that the speaker resistance Rs should be in the denominator in this calculation, not in the numerator!  It is completely misleading to do what is normally done when calculating the damping factor, and adding in the speaker DC resistance (which is typically of order 6 ohms) in the numerator.  The speaker DC resistance totally overwhelms any resistance in the speaker connecting leads, and in a solid state amplifier it totally overwhelms the output impedance of the amplifier.  It even overwhelms the output impedance of many tube amplifiers.

 

As long as the output impedance of the amplifier is small compared to the 6 ohm or so DC resistance of the speaker, then it isn't going to matter too much what it is.  The difference between 1 ohm output impedance and 0.001 ohm output impedance is almost negligible, as far as the control of the speaker cone is concerned.

 

I made simplifying approximations to keep the discussion easy, but the basic point remains the same if one does things more precisely.  The essential thing is that the DC resistance of the speaker is directly in series with the output impedance of the amplifier, and it is the sum of those two that represents the net effective "resistive loss" that characterises how well, or badly, the amplifier is getting its signal to the speaker cone.

DF1.jpg

DF2.jpg

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  • 3 weeks later...
Posted (edited)
On 5/15/2021 at 1:52 PM, Backfire said:

But it is clear from the circuit in Figure 1 that R0 and Rs are simply two resistors in series, and they both represent lossy components that tend to prevent the amplifier signal from controlling the speaker cone.

 
Nailed it. Good illustrations too. : )

 

Amplifier damping factor is wildly misleading. There is so much additional resistance in the round trip from amplifier to loudspeaker that even an amplifier output impedance of zero (infinite damping factor) is useless for increased driver damping. Good amplifier design will nevertheless minimize output impedance (increase damping factor), BUT the benefit of that lies behind door #2!

 

The damping of a moving coil loudspeaker diaphragm is almost totally in the hands of the driver design and the box design. Stated differently, how long it takes a driver to stop moving after a pulse has little to do with the amplifier's output impedance (a.k.a. damping factor). Horn-loaded passbands (all of them in the case of the Klipschorn) provide huge amounts of stopping force (damping) after a pulse due to the vastly increased acoustic impedance on the front side of the driver. Well designed horn-loaded subwoofers (Danley's tapped horns for example) are so realistic that they often aren't acceptable in concert work because people are used to the sloppy "BOOOOMMM" of a kick drum from ported designs.

 

Since damping factor is calculated by dividing 8Ω by the amplifier's output impedance, and since we know that even a zero output impedance won't help damp the loudspeaker, let's stop talking about "damping factor" and just talk amplifier output impedance.

 

So what's behind door #2? Voltage Division! (and trying to avoiding it)

 

Think about two equal value resistors that cut the voltage coming from the amplifier to the loudspeaker in half. That's a 6dB reduction is SPL. Huge. We generally perceive a 9dB reduction as half the loudness and +9dB as twice the loudness. I easily hear 0.5dB volume differences in quiet listening rooms and I ain't no spring chicken.

 

The rocket-science equation (tongue in cheek) is: Rg/(Rs+Rg).

 

Rg = loudspeaker driver.

Rs = total round-trip resistances before the loudspeaker driver.

 

1699556891_VoltageDivision1.png.aa72d9f9602373bd253e7c0e21eab7db.png

 

Now what if the total round-trip resistances before the loudspeaker decreased to 0.1Ω? (damping factor of 80 (8/0.1)

 

1219428384_VoltageDivision2.png.980b457c70402fdd3d65394a234e499e.png

 

No audible reduction in volume! What if Rg (the loudspeaker) doesn't have a constant impedance? Answer: a tube type amplifier with a high output impedance will drive the loudspeaker at different volumes DEPENDING ON FREQUENCY. Not good. Probably.

 

Now a real world example. This is the impedance plot (Rg) of a Danley SM100.

 

1691447201_SM100Z.thumb.png.2e67beb7acb1b1455a5332c3a280d04c.png

 

Now let's look at the varying frequency response of the loudspeaker CAUSED BY a high amplifier output impedance.

 

1139933069_SM100MC275CE.thumb.png.0bb69005b522c5ad43448a8d6a847fae.png

 

"Oh, but my tube amp sounds so much better than my solid state amp". I believe you, but the main reason is the variable EQ the tube amp is providing through voltage division with the varying impedance of the loudspeaker.  Different loudspeaker cables may vary this EQ further. If you want to do a fair shootout between tube and solid state amps, you need to use loudspeakers with very flat impedance curves. @Bubo implied this in his post and @314carpenter explained the voltage division issue perfectly. I hope the plots of the effect on a real loudspeaker are helpful.

 

God bless you and your precious family - Langston

Edited by Langston
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