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List of amps with a high damping factor

Discussion in 'General Audio Discussion' started by Noisypot, Jun 24, 2018.

  1. musichal

    musichal poet emeritus Subscriber

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    My Levinson int-amp spec is >400 @ 20khz.

    I noticed someone posted theirs with frequency @50hz.

    So is there a standard frequency involved with this spec? Appears not. Could the "K" be a typo? Is somebody just playing with numbers, and advertising the 'best' result? ???

    The comments about effects on bass seem to indicate that 20hz would be more relevant than 20khz.
     
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  2. BinaryMike

    BinaryMike Pelagic EE Subscriber

    The "K" is probably a typo. Most amplifiers have less loop gain and feedback at high frequencies, so their damping factors will be poorer at HF, but it's irrelevant in this context because tweeter performance isn't affected by amplifier DF. Any DF specification quoted at a frequency below that point where internal amplifier loop gain begins to roll off is adequate because it won't be different at other frequencies below that threshold. Well, unless the amp in question rolls off low frequencies inside the feedback loop, which would be rare in a SS model. A tube amp could easily have a DF sweet spot around 50Hz.
     
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  3. Audiovet

    Audiovet Well-Known Member

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    Mmmmm ..... this will not be a welcome post .... :(

    It appears to be forgotten how damping actually works.The formula regarding (load impedance)/(amp output impedance + cable impedance + whatever else) neglects one important factor. It is said that the electromagnetic 'braking' of the movement of a cone is controlled by the resistance/impedance in parallel with or shunting the voice coil at any stage/frequency. To put it in popular parlance: How big/(low-resistance) the short across the driver is.

    This seems to be the general concensus, but it is flawed - and which eventually made Fritz Langford-Smith, who seems/claims to have 'coined' the term, regrets his definiton somewhat later as misleading.

    The point (Ohm's Law): 'Braking' current in the voice coil is governed by the total resistance in the amplifier-driver circuit.

    Then what about the voice coil wire resistance??
    Why has that suddenly disappeared from the ohmic equivalent circuit? The lowest total series impedance that could ever exist in that circuit is the wire resistance of the driver voice coil alone, everything else being zero. (Here I am excluding electronically generated negative amplifier output impedance - that is a different story.)

    To sum up: Very generally the voice coil (wire) resistance of a driver happens to lie at some 60% of a driver's impedance; say around 5 ohm for an 8 ohm impedance voice coil (no empirical relationship; it just happens to turn out like that in practice).

    That makes the highest practical possible D.F of an amplifier-loudspeaker system around some 1,6*. (Now one can really go make this complex by referring to actually more accurately impedances, proceeding to phase angles, influence of cross-over networks etc.etc.)

    That the influence of (so-called, as defined) DFs upward of say 5 - 7 rapidly becomes irrelevant has been demonstarted by numerous practical tests and illustrated by as many graphs. Relevant articles are also plentiful; I normally refer to the popular 'westhost' site written by Rod Elliott. (This apart from the original article written by Langford-Smith .... rather long ago in an Australian magazine.)

    This is rather at a tangent to the thread subject; apology. But it should be considered. And to hasten to add, hence the *; I also do not discount effects on loudspeaker performance where l.s. impedances near the primary system resonance soars .... well, almost all over the place. My point is simply that, even more than Douglas Self intimated, so-called high DFs have no audible effect on the performance, mainly because of the wrong DFdefinition, and is simply of promotional value.

    Edit: Typo
     
    Last edited: Jun 26, 2018
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  4. charles 1973

    charles 1973 Super Member

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    My Bryston B100 SST integrated amp has a DF of 500 @ 20 hz.

    I have always wondered about the effects of DF considering some tube amps sound fine, Often great with DF in the 0 - 10 range. I'm guessing some speakers do work better with high DF's, and others work best with low DF's. I wouldn't base a purchase on that though unless I knew I had speakers that have a preference.

    Even amps with the same DF can respond far differently with the same set of speakers with respect to bass. Some are simply voiced toward the lean side, Like some Yamaha amps and receivers, While others, Like some NAD gear has a more full bodied sound with a broader bass response.
     
  5. sregor

    sregor AK Subscriber Subscriber

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    @Audiovet The voice coil is part of the "generator" of EMF and doesn't come into damping factor theory. If it were as you described, T/S parameters and acoustic suspension theory would be all wrong too. Self says that factor is not significant because of its negligible effects, not that the theory is flawed.
    Damping factor is way over rated. Once the system Q gets to .5, more damping just reduces bass. You can make a very good sounding very low going system if you vary the damping factor - either series resistance (wastes energy) or using current feedback. My 2 cents.
     
  6. Roadrash

    Roadrash AK Subscriber Subscriber

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    Just out of curiosity, what exactly is considered to be a high damping factor? Anything over a DF of 100, 200, or more?
     

     

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  7. damacman

    damacman Blown and Injected Subscriber

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    This is absolutely spot on. No, it won’t ever be accepted by the masses because marketing and conjecture trump physics 1000 fold in audio.
     
  8. sregor

    sregor AK Subscriber Subscriber

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    Although I agree that DF is mostly Hype, I fail to see any real physics here....
     
  9. sqlsavior

    sqlsavior AK Subscriber Subscriber

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    If one listens intently enough, it is possible to totally ignore damping factor as a meaningful statistic. That puts it in crowded company, for me, anyway.

    Apologies for the un-asked for contribution.
     
  10. damacman

    damacman Blown and Injected Subscriber

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    You took my reply too literally.
     
  11. sregor

    sregor AK Subscriber Subscriber

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    Should have read this post first? :)
     

     

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  12. Audiovet

    Audiovet Well-Known Member

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    With respect, Sregor,
    if I have Thevenin's Law correct, in a basic electrical circuit all resistances operate accorcing to their degree, whether part of the generator or the load (current can only flow in a closed circle). That is why one can consider a simple battery or rather a cell, as an 'ideal' constant voltage source with infinite current ability, in series with (an internal) resistance. In the case of damping factor, the movement of the voice coil in a magnetic gap is the emf generator, with all resistance 'attached' to it serving to limit the output current or rather circuit current as a result of the emf, at any time.

    In our case such resistance is the total sum of: the amplifier output impedance plus the cable impedance, plus if one wishes to be pedantic any terminal clamping resistance, plus the voice coil impedance. As said, the latter does not suddenly disappear from the mix! This is universal electricity long before one comes to specific applications. Negligible effects (Self et al) are literally because of the flawed definition or perhaps more accurately the flawed application of the current definition. As said, Langford-Smith himself recognised this in an Australian magazine of the time after having coined the term (if my information is correct).
     
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  13. drumbum

    drumbum Super Member

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    Can't remember where I saw this, but AR stated the AR3, being sealed, needed an amp with a damping factor of 1.
     
  14. EngineerNate

    EngineerNate AK Subscriber Subscriber

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    It would seem to be that df would be less important in an acoustic suspension design because the driver's movement is damped by the air spring created by the sealed box.

    We should also note that the design of the suspension in a driver has a large contribution as well. Drivers are often designed with a specific application in mind-sealed vs. ported, though most available to the DIY market have a Qtc somewhere in the middle to catch designers of many configurations eyes.
     
  15. E-Stat

    E-Stat AK Subscriber Subscriber

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    AR conducted their "Live vs Recorded" demos using Dyna MKIIIs with a DF of 15.

    ardyna.jpg

    By contrast, My New Advents are a poor match for tube amps sounding dull and heavy. For grins, I once drove them using the big VTL monoblocks. Not pretty.

    They were voiced using SS amplification.
     
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  16. Gibsonian

    Gibsonian Super Member

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    Most of us could save alot of dough and get sound that can't be differentiated from live with some Old AR3s and Dynaco tube amps!

    If that is the case new materials and modeling etc really won't help us today to improve as duplication of "live" achieved many moons and technological advances ago!
     

     

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  17. E-Stat

    E-Stat AK Subscriber Subscriber

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    You cannot argue with blind test results. ;)
     
  18. Gibsonian

    Gibsonian Super Member

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    That's right!
     
  19. sregor

    sregor AK Subscriber Subscriber

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    The problem is - speaker is not a resistor. There is an EMF generator, acoustic output, mechanical resistance and mechanical energy storage (weight and springs)

    [​IMG]
    Diagram from http://audiojudgement.com/speaker-equivalent-circuit/

    Bottom line: Small, Thiele and predecessors developed verifiable models which show how amplifier output impedance can and does affect sound.

    Edit: this is starting to get off topic and apologize for letting it get out of hand.
     
    Last edited: Jun 27, 2018
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  20. sregor

    sregor AK Subscriber Subscriber

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    A related story - supposedly AR had to partially demagnetize the magnets or the AR because the system was overdamped and they got more bass with a weaker "motor"
    There also is the damping switch on the back of the Cizek 1. Again oversized magnet structure The switch inserted a resistor in series with the woofer which changed the system Q to .5 and extended and smoothed out bass end. I believe the Idea was given to them by Dick Pierce of BAS and Suffolk Audio.
     
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