Damping factor.

discussion of magnetic volume control design for both line and speaker levels.

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dave slagle
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Joined: Sat Jan 22, 2005 3:54 am
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Damping factor.

Post by dave slagle »

People go on and on about damping factor and I continue to be astounded how they only consider the ratio of the output impedance of the amp to the input impedance of the "speaker". In truth the load presented by the "speaker" is actually the impedance of the crossover and everyone ignores the source impedance to each individual driver. I recently simmed one of bruce edgars crossovers for a friend and figured this would be a good point to jump into this topic so here is the crossover in the frequency domain.

Image

In the sim, the Output Z of the amp is 0.5Ω and the load presented by the speaker as a whole is a pretty benign 8Ω load for a damping factor (DF) of 16.

Image

The thing that always gets ignored is the actual source impedance to each individual driver which is a far different picture that the relatively benevolent plot above.
Screen Shot 2021-07-17 at 9.05.25 AM copy.png
Screen Shot 2021-07-17 at 9.05.25 AM copy.png (27.54 KiB) Viewed 3218 times
the solid colored bars at the bottom represent the frequency range covered by each driver and this tells a very different story about damping factor and what it really controls. As a final thought experiment simply consider the same speaker above tri-amped with a line level crossover where the theoretical 0.5Ω output Z of each amp were connected directly to each driver.... suddenly the world makes sense again.

dave
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dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Re: Damping factor.

Post by dave slagle »

Didn't have much time to ponder things since I already had a solution in hand.... Ditch the L-pad on the 2441 and replace it with an autoformer. Here is the big picture of the change showing the Lpad being replaced with an autoformer and the frequency domain plots clearly overlap.
Screen Shot 2021-07-17 at 10.07.11 AM.png
Screen Shot 2021-07-17 at 10.07.11 AM.png (56.57 KiB) Viewed 3216 times
the load presented to the amp also is close enough for gov'ment work.
Screen Shot 2021-07-17 at 10.08.47 AM.png
Screen Shot 2021-07-17 at 10.08.47 AM.png (54.64 KiB) Viewed 3216 times
The key change here is the drive impedance to the 2441 where you can see that the autoformer substantially reduces the drive to the 2441.
Screen Shot 2021-07-17 at 10.25.19 AM.png
Screen Shot 2021-07-17 at 10.25.19 AM.png (51.94 KiB) Viewed 3216 times
Of course a better solution would be to biamp and drive the bass with its own amp and a line level crossover but that opens up another can of squiggly things.

dave
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www.hifiheroin.com
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