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Damping Factor

Aug 4, 2014 at 1:47 AM Post #16 of 168
silverears said:
 
Anyway, ok, the electrical damping in the case of resistive load is just power delivery issue.  That's good to know.
Click to expand...

 
But that's not true! Damping factor relates to how effectively an amplifier allows a speaker's back EMF to damp its mechanical response. Power delivery is a separate issue that is tangentially related to electrical damping. The type of load is not terribly relevant to whether or not the amplifier allows or hinders the driver's back EMF to generate currents that  damp the mechanical motion of the driver.
 
Cheers
 
Aug 4, 2014 at 6:30 AM Post #17 of 168
A significant amount of people uses 500 ohm in-lines for headphones with their speaker amps by the way.
 
Aug 4, 2014 at 9:51 AM Post #18 of 168
So...this conversation has been interesting. Here are my thoughts.

I think there is some truth to the idea that damping factor is "more important" for dynamic drivers than for planar magnetic ones as you depend a lot more on a mechanical mass-spring-dapener system, and the super-low mass of a planar's diaphragm shouldn't cause as much havok driving electrical signals backwards.

However...a planar's diaphragm is obviously reactive, so even if the mass is very small, you cannot assume that its movement will go unseen by the magnetic grids, and the lower the resistance of the driver, the easier it is to pass a current back through it (including a magnetically induced one).

Also keep in mind that those magnetic grids are supposed to be working together, and the diaphgram is going to alter the balance between the grids as it moves. If either becomes unbalanced, I would expect to see an induced current in the opposite magnet, and that would not only want to oscillate, but it would be resisting the desired effect in the diaphgram.

Lastly, follow the same dampening factor rules for power delivery. Even if it wasn't important for dampening the mechanical system, planar's tend to be power hungry, and you'll want to maximize your current in to get a good field generated. If you have a bad dampening factor, you are definitely wasting a lot of your amp's power.
 
Aug 4, 2014 at 10:49 AM Post #19 of 168
ab initio said:
  But that's not true! Damping factor relates to how effectively an amplifier allows a speaker's back EMF to damp its mechanical response. Power delivery is a separate issue that is tangentially related to electrical damping. The type of load is not terribly relevant to whether or not the amplifier allows or hinders the driver's back EMF to generate currents that  damp the mechanical motion of the driver.
Click to expand...

 
The damping effect appears as reactance when the driver is tested as a load, though. Otherwise, the amplifier cannot dampen resonances or distortion it has no way of knowing about. As these tests show, with low electrical damping, the same amount of frequency response error and increased distortion appear both on the voltage driving the headphones, and the actual acoustic output. If the driver is really purely resistive and linear, then a high source resistance could only change the acoustic frequency response and distortion if different sound could be produced from identical voltage and current input to the driver.
 
Aug 4, 2014 at 10:49 AM Post #20 of 168
ab initio said:
But that's not true! Damping factor relates to how effectively an amplifier allows a speaker's back EMF to damp its mechanical response. Power delivery is a separate issue that is tangentially related to electrical damping. The type of load is not terribly relevant to whether or not the amplifier allows or hinders the driver's back EMF to generate currents that  damp the mechanical motion of the driver.
Click to expand...


It's not about damping the simple mechanical motion of the driver, it's about damping the driver's electromechanical resonance.

http://en.m.wikipedia.org/wiki/Damping

"Damping" is meaningless outside the context of resonance.

Now, look at the impedance plot of a typical dynamic driver, whether it be a headphone driver or a loudspeaker driver. You'll notice they all share the same basic characteristic, a peak in the low frequencies. The center of that peak is the frequency of that driver's resonance. And it's the driver's resonance that determines it's low frequency response characteristics.

This resonance is characterized by its Q. A Q of 0.5 is called "critically damped." In this instance, the driver's low frequency response is ideal with no ringing or overshoot. Qs above 0.5 are called "underdamped." As you go above this, the low frequency response begins to get peaky, with increased ringing and overshoot.

Dynamic drivers are designed assuming they will be driven from an ideally zero source impedance in order to maintain the published Q for that driver and the expected low frequency response. As you drive it from a higher and higher source impedance, you will end up raising the effective Q, causing the driver to become underdamped resulting in a peakier low frequency response along with the associated ringing and overshoot.

Now look at the impedance plot of a planar driver. They are ruler flat which means there's no sign of resonance and the driver behaves as a virtually purely resistive load (with a dynamic driver, to the left of the impedance peak it appears inductive, to the right of the impedance peak capacitive, and at the peak itself, resistive).

There being no apparent resonance, and the load being purely resistive, damping and the associated "damping factor" have no relevance.

se
 
Aug 4, 2014 at 11:38 AM Post #21 of 168
Yeah, if planars appeared inductive it should at least show up in the impedance measurements, isn't that the conclusion?
 
Aug 4, 2014 at 11:41 AM Post #22 of 168
Right now i think we did take this thread way off topic. However, i do think this is an important discussion to have. Can one of you guys start a proper thread so that people looking for answers to this question can find the discussion in the future.

That said, i think you guys have some of your fundamentals mixed up a bit and i think its important to flesh out the details and get the whole story of "damping factor" organized into a coherent storyline.

Cheers
 
Aug 4, 2014 at 11:47 AM Post #23 of 168
Should make a thread, yes. I won't make it though, don't know enough about the subject.
 
Aug 4, 2014 at 12:33 PM Post #24 of 168
steve eddy said:
It's not about damping the simple mechanical motion of the driver, it's about damping the driver's electromechanical resonance.

http://en.m.wikipedia.org/wiki/Damping

"Damping" is meaningless outside the context of resonance.

Now, look at the impedance plot of a typical dynamic driver, whether it be a headphone driver or a loudspeaker driver. You'll notice they all share the same basic characteristic, a peak in the low frequencies. The center of that peak is the frequency of that driver's resonance. And it's the driver's resonance that determines it's low frequency response characteristics.

This resonance is characterized by its Q. A Q of 0.5 is called "critically damped." In this instance, the driver's low frequency response is ideal with no ringing or overshoot. Qs above 0.5 are called "underdamped." As you go above this, the low frequency response begins to get peaky, with increased ringing and overshoot.

Dynamic drivers are designed assuming they will be driven from an ideally zero source impedance in order to maintain the published Q for that driver and the expected low frequency response. As you drive it from a higher and higher source impedance, you will end up raising the effective Q, causing the driver to become underdamped resulting in a peakier low frequency response along with the associated ringing and overshoot.

Now look at the impedance plot of a planar driver. They are ruler flat which means there's no sign of resonance and the driver behaves as a virtually purely resistive load (with a dynamic driver, to the left of the impedance peak it appears inductive, to the right of the impedance peak capacitive, and at the peak itself, resistive).

There being no apparent resonance, and the load being purely resistive, damping and the associated "damping factor" have no relevance.

se
Click to expand...

 
Well said.  Actually damping simply isn't a problem with headphones.  It is only a problem with speakers in the most extreme situations.  Headphone drivers are way too small to worry about damping.
 
Aug 4, 2014 at 12:45 PM Post #25 of 168
Yet smaller excursion produces much bigger sound pressure.
 
Aug 4, 2014 at 12:46 PM Post #26 of 168
ab initio said:
Right now i think we did take this thread way off topic. However, i do think this is an important discussion to have. Can one of you guys start a proper thread so that people looking for answers to this question can find the discussion in the future.

That said, i think you guys have some of your fundamentals mixed up a bit and i think its important to flesh out the details and get the whole story of "damping factor" organized into a coherent storyline.
Click to expand...


Ok, here's the thread. So what makes you think I have my fundamentals mixed up a bit?

se
 
Aug 4, 2014 at 12:46 PM Post #27 of 168
ab initio said:
Right now i think we did take this thread way off topic. However, i do think this is an important discussion to have. Can one of you guys start a proper thread so that people looking for answers to this question can find the discussion in the future.

That said, i think you guys have some of your fundamentals mixed up a bit and i think its important to flesh out the details and get the whole story of "damping factor" organized into a coherent storyline.
Click to expand...


Here you go.

http://www.head-fi.org/t/729314/damping-factor#post_10768643

se
 
Aug 4, 2014 at 3:53 PM Post #28 of 168
And the original thread is?
 
********************************************
 
The Dick Pierce page on Damping  Factor

Damping Factor: Effects On System Response

by Dick Pierce — August 30, 2004
http://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response
 
Aug 4, 2014 at 7:02 PM Post #29 of 168
 currawong if you're flying by (or another admin daring enough to venture into sound science), maybe you could take the last few post of this topic and move us into SE's?
I do think some interresting stuff have been written here that have indeed nothing to do with hd800.
 
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