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Effects of damping factor on planar magnetics/orthodynamics ?

Discussion in 'Sound Science' started by frenchbat, Jul 10, 2012.
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  1. nigeljames
    My Master-6 with 1 ohm output impedance drives the HD800's exceedingly well  [​IMG]
  2. namhkim
    This is great, I am getting a few new cans, but I only have Schiit Vali to drive them. So I was worried with Vali's high output impedance. I guess it will be fine. Great thnx.
  3. namhkim
    So far, HE400 and HE400i has been really good without any ringing noise with Vali. But, some 60~70 Ohms dynamic coil headphones were rinigng... I guess orthos' impedance is really different from conventional coiled drivers' impedance..
  4. jcx
    so far the orthodynamics I've seen Z plots for look really flat - nearly pure resistors - which means they essentially shouldn't care about amplifier resistive output - its just a flat amplitude divider ratio without frequency response effects
  5. Steve Eddy

    Yeah, they don't have that resonance in the low end like dynamics. As jcx said, or those are virtually purely resistive.

  6. ninjaphone
    Just a tidbit of physics I feel like mentioning, and maybe you guys already know this, but anyway here goes.  The Yamaha manual stated "... absolutely no impedance change for any frequency..." and "there is also no inductance..."   It turns out the former is actually a direct result of the latter.  Any coil of wire has inductance, and with that comes a concept called reactance.  Reactance is essentially a variable resistance.  In an inductor,  the reactance is directly proportional to the frequency played through it.  The concept of inductance essentially only applies to dynamic headphones, as inductance is a property of coils.  So basically, in a dynamic headphone, the overall impedance (which takes into account the reactance of the voice coil) will be higher in the highs and lower in the lows. I believe this means that in reality the highs would be attenuated (albeit a small amount probably) and the lows would be kicked up in amplitude a little.  Again, because this only really applies to coils, planar magnetic headphones should have essentially no inductance --> no reactance --> and finally, an essentially flat impedance.  
  7. jcx
    the planar conductor does have low inductance - but there is still mass-spring resonance in any driver which is reflected to the electrical terminals by the electro-acoustic properties of the "motor" and mass and suspension of moving parts
    for electrodynamics there should still be the mass-spring resonance of the diaphragm but it isn't as easily visible at the electrical terminals in part because of the poor efficiency of most Orthos as electric "motors"
    and the diaphragm's resonant peak can also well damped in the mechanical-acoustic domain by the magnet structure and intentional added flow/acoustic resistive damping material
  8. impermanente
    Great answer, very concise and simple!
    By any chance do you know roughly in which range of frequency can be the mechanical resonance of a planar magnetic driver like the audeze LCD? As you pointed out since such a driver is like an harmonic oscillator (mass-spring system) then there must be an associated natural frequency (resonance frequency). I was wondering if the resonance was well outside the audible range, being the thin film diaphragm very light.
  9. jcx
    I'd still guess the underlying mechanical diaphragm drumhead resonance was low bass but I don't know, possibly it could be higher with circumaural headphones only driving a smallish mostly sealed cavity
    couldn't see a low bump even in the couple of high res impedance plots at http://www.innerfidelity.com/headphone-data-sheet-downloads that I looked at - maybe looking at more would give a hint
  10. castleofargh Contributor
    I always assumed that it was outside of the measured range. but now you make me wonder ^_^ .
    the mechanical damping should be very strong on a planar, as it's only the film stretched. so maybe it's just not visible because it follows an overdamped behavior and doesn't really have much time to oscillate and even less to keep a noticeable amplitude?
    anyway the more damped, the slower the frequency if I remember my stuff. so I would tend to agree with jcx that it could be a relatively low frequency.
  11. Mr Vicarious
    Very interesting discussion. Surprised that there isn't more known officially about the effect of output impedance on planar/orthodynamic headphones.
    From a purely subjective point of view, I have a Asus Xonar STU amp which has an output impedance of 10 ohms and a Hifiman 400s which has an impedance of 22 ohms. On paper (according to experience with dynamic headphones) this combination should sound awful! But the sound I'm getting is very good indeed - very well balanced, extended but refined upper frequencies and open, natural midband and deep, solid bass.
    Perhaps more user opinions might help bring about more serious, official attention to this issue? Anyone?
  12. reginalb
    The 400s has a super smooth impedance curve. It's more of an impedance flat http://www.innerfidelity.com/images/HiFiMANHE400S.pdf
    I have the Grado PS1000, they have around 30 ohm impedance, and even the what, I think 22 ohm? Hifiman HM-602 performs OK outside of this crazy impedance spike from those cans: http://www.innerfidelity.com/images/GradoPS1000.pdf 
    Then look at the output: 
    That treble roll always exists with the HiFiMan, so it's unimportant to my point. My point is that it's nowhere near the 8x rule, but it's actually fine, other than at that one spot where the impedance does something crazy, then the high impedance output goes a little nuts. Your HiFiMan cans don't have anything going on that might cause a crazy response change like that, so they're probably a little more forgiving to a higher output impedance.
    I'd also mention that if you aren't measuring it, it might not be terribly obvious what the source is doing. I can use the HM-602 with my Merlins, it still sounds like music. Accurate, no, but I mean, it's there, it plays music and honestly doesn't seem that bad paired with it. Though measured, you can see it goes a little nuts!
  13. Jon Sonne

    I also have the Hifiman HE-400s and I've experienced something entirely different. I've noticed that when I listen to my 400s when they are directly plugged into my macbook's hp-out, the sub-bass is a bit rolled off and the sub-bass is less dynamic/uncontrolled. The macbook pro has an output impedance of 22 ohms and the HE-400s, as you stated, also has 22 ohms of impedance, which means the dampening factor is only 1.

    In contrast, when I use the 400s with my Fiio Q1, the bass extends deeper and is nicely controlled and punchy. The Fiio Q1's output impedance is <0.3 ohms, resulting in a dampening factor of 73. I tried to match the volume by ear when I AB'ed the macbook and the Fiio Q1, and in my experience the difference is clearly audible, so I did not care to do a DBT.    

    I did not notice any difference in the sound other than the sub-bass, which makes sense since orthodynamic drivers have a ruler flat impedance response*.
    *From a post by Ab Initio: The output impedance of an amplifier acts in conjunction with the headphone impedance to form a sort of voltage divider. This impacts the power delivered to the headphone vs the power dissipated in the amplifier's output impedance. When the headphone impedance varies with frequency (as is very common in traditional voice coil dynamic drivers) then there is a frequency-dependence to the power delivered to the headphone.

    In theory, orthodynamic headphones should be affected by dampening factor since they act like microphones. Try it yourself: plug your planar magnetic headphones into a microphone input and see if you can record your voice. I did it with my HE-400s and it worked wonders.    

    Crown audio explains in very simple terms why a driver acting like a microphone can benefit from a high damping factor: 

    "Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing."

    "When the loudspeaker cone vibrates, it acts like a microphone, generating a signal from its voice coil. This signal generated by the speaker is called back EMF (back Electro Motive Force). It travels through the speaker cable back into the amplifier output, then returns to the speaker. Since back EMF is in opposite polarity with the speaker's motion, back EMF impedes or damps the speaker's ringing. The smaller the amp's output impedance, the greater is the effect of back EMF on the speaker's motion. An amplifier with low output impedance does not impede the back EMF, so the back EMF drives the loudspeaker with a relatively strong signal that works against the speaker's motion. When the speaker cone moves out, the back EMF pulls the speaker in, and vice versa. In short, the loudspeaker damps itself through the amplifier output circuitry. The lower the impedance of that output circuitry, the more the back EMF can control the speaker's ringing." 

    "Damping factor varies with frequency. As you might suspect, damping factor is most important at low frequencies, say 10 Hz to 400 Hz.

    NwAvGuy also mentions bass performance in his blog post about damping factor:

    "The bass performance of the headphones, as designed by the manufacture, may be audibly compromised if there’s insufficient damping. The bass might become more “boomy” and less controlled. The transient response becomes worse and the deep bass performance is compromised (the headphones will roll off sooner at low frequencies).

    Which fits nicely with my observation that the Hifiman HE-400s is compromised in bass performance when I use them with my macbook pro's hp-out.

    Of course, the need for electrical damping depends on the headphone design, as some headphones depend more on mechanical damping than electrical damping, so I am not claiming that every planar magnetic headphone needs a high damping factor to work properly. But in the case of the Hifiman HE-400s, high damping factor clearly improves (at least to my ears) the low frequency fidelity. 

    /Jon Sonne
  14. SilverEars
    Damping factor is often over used term here.  The term was first coined for speakers wasn't it?
    The term damping factor has mechanical wording to it, "damping," which makes us assume there is some control relation to the mechanical output.
    In general the ratio of the impedance is the factor.  Impedance we are familiar with is a magnitude(of real and reactive components). Can have reactive element to it.  
    If you look at the impedance graph of a headphone, it reveals if the headphone is reactive or not.  When the headphone impedance graph is not flat, and has significant curvatures, it's reactive.  Dynamics are reactive.  Planars are flat. Resistive.
    HE-400 is a planar.  Resistive.  Only factor is the drop in the power.  You will get more power delivery with the relatively low output impedance to the headphone. In this case, can we call it "damping factor?"  The meaning changes.
    Dynamics on the other hand, depending on how radical the impedance swings are, can be effected if the output impedance of the source is significant enough to change the FR as a whole.
    This is where the wording damping factor comes in for headphones with potential to change it's output do to significant enough output impedance effecting the headphone if it's reactive and there is comparable impedance on the output of the source.
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