Tweakers' Asylum

Why would you want to reduce damping factor?

63.155.31.243

Brian H P

In Reply to: RE: Wire resistance is infinitesimal compared to speaker impedance. posted by Tre' on February 21, 2024 at 16:59:08

High DF is a selling point for many high powered SS amplifiers, which can take firm control of low-impedance speakers. Enough series resistance to audibly reduce it would result in mushy, uncontrolled bass (like you get with an SET amp). How could that be considered desirable?

Follow Ups:

reducing damping factor Is not desirable... - Tre' 10:31:23 02/24/24 (7)
You said "Tiny fractions of an Ohm don't matter." I say they do matter. They reduce the damping factor.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 02/24/24
- Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - Brian H P 15:06:43 02/26/24 (6)
  . . . by an infinitesimal amount. Nothing close to the 4 Ohms or more of a tube amp's output transformer.
  
  But I like fat cables (high purity OFC) anyway, just because.
  - RE: Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - Tre' 19:49:10 02/26/24 (5)
    A Dyna ST-70 tube amplifier has an output impedance of .5 ohms on the 8 ohm tap. Playing a 8 ohm speaker, that would provide a damping factor of about 16.
    
    walkstoslow has a SS Sansui from the 1970's with a damping factor of 70.
    
    The output impedance of his Sansui is .115 ohms.
    An amplifier with an output impedance of .115 ohms playing a 8 ohm speaker through wire with no resistance (I know there is no such thing) will have a damping factor of 70. Add speaker wire resistance of .115 ohms (a little less than 25 feet of 14 gauge) and the damping factor goes down to 35.
    
    My only point is, speaker wire resistance only causes a small reduction in power to the speaker but decreases the damping factor by much more. So the reason for large speaker wire is not more power but more control.
    
    Tre'
    
    Have Fun and Enjoy the Music
    "Still Working the Problem"
    - thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - walkstoslow 07:41:12 02/29/24 (2)
      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
      - RE: thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - Lew 11:22:49 02/29/24 (1)
        
        In Reply to: RE: thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . posted by walkstoslow on February 29, 2024 at 07:41:12
        
        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)
        
        In Reply to: RE: thanks, Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . posted by Lew on February 29, 2024 at 11:22:49
        
        thank you again....
    - RE: Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . - Lew 07:38:44 02/29/24 (1)
      Can you hear any difference between damping factors of 70 and 35? I don't think I could. I think DF only begins to make an audible difference when it goes below 10, or somewhere in that range below 10.
      - I think it depends on the speaker - Tre' 19:04:44 03/01/24 (0)
        
        In Reply to: RE: Rephrased for clarity: tiny fractions of an Ohm DO reduce damping factor . . . posted by Lew on February 29, 2024 at 07:38:44
        
        I think some speakers are pretty well mechanically damped and don't need much electrical damping. I think speakers with tight voice coil clearances make better use of whatever electrical damping there is.
        
        Others need more electrical damping. I believe cheap "sloppy woofers" with weak magnets and large VC gaps do better with an amplifier with the lowest output impedance.
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"

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