Tweakers' Asylum

thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . .

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walkstoslow

In Reply to: RE: Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . posted by Tre' on February 26, 2024 at 19:49:10

thanks for using the sansui as an example, the numbers are fascinating,
I will try to figure out the formulas these results came from.
hapoy listening

Follow Ups:

RE: thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - Lew 11:22:49 02/29/24 (1)
It's not sophisticated. The speaker "sees" the output impedance of the amplifier as the actual output impedance plus the resistance of the speaker wires. You just add the two values to get the net total. Then you divide the input impedance of the speaker (keeping in mind that no speaker has a constant input impedance, but we usually use a nominal value) by the net output impedance of the amplifier plus cables. When that ratio goes up, damping factor goes down, as you can easily see.
Since DF is mostly an indicator of how well the amplifier can "control" the speaker at low frequencies, you might want to use a speaker impedance value that most represents its impedance at low frequencies. The reason for this concern is that an electromagnetic speaker potentially produces a "back EMF"; when the woofer is moved forward or backward by the amplifier, it will naturally settle back to its original position and even overshoot the resting state. This overshoot causes its magnet and coil to move relative to each other, and this produces a voltage which is called "back EMF". If the DF is low, the amplifier will have a problem dealing with that spurious voltage coming back at it, and that can cause slurring of bass notes. Or so the story goes.
EDIT: So sorry, when the ratio of speaker impedance to net amplifier output impedance goes UP (which happens if speaker impedance along goes up or if amplifier output impedance goes down), DF goes UP (not down). I hope you can see that I was wrong above.

Edits: 02/29/24 02/29/24
- RE: thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - walkstoslow 12:41:17 02/29/24 (0)
  thank you again....

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