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Can someone explain damping factor
Can someone explain damping factor
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Old 8th February 2018, 02:21 AM   #11
planet10 is offline planet10  Canada
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Can someone explain damping factor
Damping factor is a very misleading spec and not nearly as useful as knowing the output impedance (Z(source), the speaker impedance (Z(load)) and how well damped the LF alignmnet of the speaker is.

There is an appropriate output impedance for any speaker. Most modern commercial loudspeaker is designed assumming a low output impedance (ie voltage source), but in the diy world we have a lot more choice.

Since a speaker is driver is a current controlled device (not a voltage controlled one) there are advantages to amplifiers with high output impedance (current amp).

What is appropriate in the amplifier is very much dependent on the speaker to be used with it. They should not be considered separately.

dave
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Old 8th February 2018, 02:33 AM   #12
Koonw is offline Koonw
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Can someone explain damping factor
This article may have the answers to your questions, noted the effect on frequency response of various damping. Once you have determined the critical damp factor of the speaker then you can adjust NFB for amp to lower or raise output impedance to match the critical damping so that the frequency response becomes flat. The output impedance of the amp and speaker damping factor need to be found out separately of course.

Last edited by Koonw; 8th February 2018 at 02:37 AM.
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Old 8th February 2018, 02:38 AM   #13
dotneck335 is offline dotneck335  United States
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Quote:
Originally Posted by CharlieLaub View Post
If your driver has Re= 1 Ohm and your Damping factor is 15 then you can expect frequency response abnormalities. Why? Because the output impedance = 1/15 ~ 0.7 Ohms is on the order of the driver impedance. The amp and driver appear in series, and act like a voltage divider.
Methinks your math is in error. 1 ÷ 15 = 0.066Ω, not 0.7Ω.
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Old 8th February 2018, 02:44 AM   #14
cnpope is offline cnpope  United States
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Quote:
Originally Posted by planet10 View Post
Damping factor is a very misleading spec and not nearly as useful as knowing the output impedance (Z(source), the speaker impedance (Z(load)) and how well damped the LF alignmnet of the speaker is.

dave
Yes, indeed, I agree with you about that. But also, as I was saying, the purely resistive component of the speaker's impedance should really be adding into the denominator, not the numerator, in the ratio defining the damping.

One could roughly model the speaker as having an ideal zero-resistance coil (e.g. made of superconducting wire), in series with a resistor R(load). The measure of how well damped it will be is then given essentially by Z/R(tot), with R(tot)=R(load)+R(source), and Z being the impedance (highly frequency dependent) of the superconducting coil in its dynamical environment as it moves, on the speaker cone, in the magnetic field of the speaker magnet.

I just measured the DC resistance of one of my Lowther DX3 speakers, and it is about 7 ohms. Looking at the impedance plots for the DX3 there is a huge peak, of order 100 ohms or more, at about 60 Hz. Outside the range 30 - 130 Hz, the impedance is about 10 ohms or less. So outside the 30 - 130 Hz range, the resistance of the coil accounts for most of the impedance of the speaker. This means the "true" damping factor over most of the audio range will never be more than about 2 at the most, even if the source has virtually zero output impedance. And whether the source has 0.01 ohms or 1 ohm output impedance hardly affects the damping at all.
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Old 8th February 2018, 07:21 AM   #15
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by EL34Dave View Post
But how would one determine how much is needed?
Get a solid state amp (it has oodles of damping factor). Now add some resistance in series with the output, and listen. Do you like the sound? Try a different value. Eventually you will find a value that suits your speakers and your ears, and you can try to emulate that value in the next amp you build.
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Old 8th February 2018, 08:06 AM   #16
globalplayer is offline globalplayer  Germany
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Quote:
Originally Posted by EL34Dave View Post
But how would one determine how much is needed.
On high powered subs about as high a df as you can get.
(at least 300, better 500 - 2000+).

Use "thick wire" also.

Some will say it doesn`t matter but clearly they didn`t experiment themselves.
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Old 8th February 2018, 08:44 AM   #17
traderbam is offline traderbam  Europe
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Quote:
Originally Posted by Merlinb View Post
Get a solid state amp (it has oodles of damping factor). Now add some resistance in series with the output, and listen. Do you like the sound? Try a different value. Eventually you will find a value that suits your speakers and your ears, and you can try to emulate that value in the next amp you build.
Except that you may be altering that amplifier's stability as you change the resistor, so what is heard may be a combination of the two. But I think this is a good way to see just how unimportant very high DF is.
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Last edited by traderbam; 8th February 2018 at 08:47 AM.
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Old 8th February 2018, 08:46 AM   #18
scottjoplin is offline scottjoplin  Wales
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Thanks Koonw, that's a very interesting article that actually answers the question
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Old 8th February 2018, 08:50 AM   #19
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by traderbam View Post
Except that you may be altering that amplifier's stability
Yes I suppose so, although the resistance you use will probably be only a fraction of the speaker coil resistance, so I suspect the stability change won't be very much in most circumstances.
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Old 8th February 2018, 08:50 AM   #20
globalplayer is offline globalplayer  Germany
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I am missing measurements of group delay, distortion and impulse response in that article.
FR alone isn`t telling the whole story.
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