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Headphone & Amp Impedance Questions? Find the answers here!

Discussion in 'Sound Science' started by proton007, Apr 25, 2012.
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  1. BrownBear
    Yeah, and actually I use my Pro/4AA at 250 ohms with my 5.5G iPod with good results as well. The iPod has a decent little amp in it, for the most part. 
  2. stv014
    Impedance alone is not a reliable indicator of how hard a headphone is to drive. For portable use, check the "Volts RMS required to reach 90 dB SPL" spec at InnerFidelity, you generally want it to be less than 0.1 Vrms. With similar values, the higher impedance headphone has the advantage, since most sources can output higher voltage to a higher impedance load, and it also reduces battery usage.
  3. proton007
    Thats what my main post is about, I already referred doublea71 to that but he wanted a more general solution.
  4. doublea71
    oy vey I still can't make heads or tails of this.
  5. firev1
    It should do alright with all custom IEMS in the market(is there any below 16 ohms?). As for your question, impedance matters not, it is the sensitivity or the IEM that counts. That being said, I don't know the max output power of the J3 but it should drive all IEMs in the market fine(with the potential exception of ER-4S) .
  6. doublea71
    I think the headphone out is 29 whatevers (Ohms?) per channel (L+R). 
  7. Chris J
    A typical headphone used in recording studios is the AKG K240 series. This is a 55 ohm headphone.

    A friend of mine used several in his recording studio.
    He drove them with a Bryston 2B power amp.
  8. proton007
    IEMs are made with portable sources in mind. Just use any IEM, it'll work perfectly fine with your J3.
  9. RexAeterna

    depends. i haven't found a portable device yet that can drive my 600ohm 240DF's well. then you also have impedance vs. frequency and what most people never mention is the need for reserve power for transients and dynamics. might get reasonable and comfortable enough in volume but there is still more to it. higher impedance headphones is only better for portable use cause of damping factor/output impedance(and like mentioned, to save battery life). that's why lot people mention even with low volume and restraint dynamics it still sounds clear and nice.

    i bypass all these limitations by using my headphones directly off of speaker outputs of my favorite and main power amps(limitless reserve of voltage/current, high damping factor/low output impedance close to 0/at 0ohms,ect.) and always have good results with all headphones i tried(even run my balanced Sony SA5000 off the speaker outs even though they are sensitive headphone. not problem though since i really don't have gain issues with my main amps and i listen what i consider normal volumes where i still can hear myself talk).
  10. proton007
    600 Ohms is pretty much the upper limit when it comes to portable amps.
    But if an amp can drive such a headphone to pretty comfortable volume, then I think there isn't much improvement to be had unless you're already reaching close to the amp's limits.
    And yes, a power amp will obviously have a lot more power than the headphone needs, but can also damage your headphones due to high Vrms if pushed too high.
    Thanks for the insight [​IMG]
  11. RexAeterna
    true. also depends on sensitivity. my DF's are 88db@1v@1khz(600ohms nominal@1khz). i think limit for portable players(not amps) is 1v max which for sensitive 600ohm headphone will get volume very reasonable and possibly loud enough to be enjoyable very much. i just said it depends really is all i meant. some headphones have higher spikes than others as well and then you got the music itself where when certain dynamic passages will require higher transient peaks here or there once in awhile requesting for more power. bit too complicated. so to keep it simple. plug it in, take a listen and if you like what you hear then that's awesome. enjoy the music. that's what it's all about.
  12. proton007
    I'm putting this in the main post. [​IMG]
  13. doublea71
    I've given up on trying to do the math to achieve perfect synergy btw the dap and iems - it's a task way above my payscale.
    ostewart likes this.
  14. Chris J
    Don't forget all that information is Highly Classified![​IMG]
  15. obobskivich
    Great guide, a few notes though:

    - Impedance is Z, Resistance is R; they are different things. Source impedance is therefore Zout or Zsource.

    - The damping factor section is largely marketing fluffies; for a variety of reasons including cable resistance, and the reactivity of loads (it will inherently vary with frequency). See here for more: http://www.butleraudio.com/damping1.php

    - Not all amplifiers decrease their output as Z increases; some are invariant (or nearly invariant) - the WA6 is a good example (it uses a transformer to accomplish this feat).

    - The actual power needs are dictated by sensitivity, as you note, but perhaps explain the log relationship between power and output. See here for more: http://trace.wisc.edu/docs/2004-About-dB/ Basically consider peaks and the dynamic nature of music instead of static demands; the easy way to do this is to figure out how dynamic the material you want to listen to really is, and then assume that is "top end" static demand and reference that to whatever output SPL you want. I think most people probably will target 60-70 dB but maybe I'm just weird like that (I get the sense I listen at VERY low levels compared to most people, based on the lengths I go to to reduce gain; perhaps I just have super efficient cans, I don't know). So if you're listening to modern pop, you probably only need 2-3 dB of DR, and that makes your continuous power requirements relatively high. If you're listening to old classical recordings, you might see 40 dB or more of DR (the highest I've ever documented is right around 40 dB, but I don't listen to much "very old" music and I hate doing vinyl restoration) - your continuous power requirements are very low, but the peak demands are going to be substantial. Especially if you want the continuous/base-line level at a "loud ish" point (like 70 dB).

    - Line out is not standardized. Pro and consumer gear targets different references (http://www.gearslutz.com/board/so-much-gear-so-little-time/403493-4dbu-versus-10dbu.html), and consumer gear has a tendency to be all over the place beyond that (I've seen fs spec'd anywhere between 1V and 5V). Some line drivers can actually run some headphones, some cannot. I've never seen a solid rule of thumb here (and it is not load invariant).

    Also in terms of "what you will hear" - it depends on the relationship between Zout and Zload and what the amplifier can actually do. If the amplifier can drive lots of volts into the load but has Zout (e.g. a receiver or otherwise "large" amplifier, you could probably even count some amplifiers like the Beyerdynamic A1 in here since Zout is around 100ohms) it will likely just mean attenuation or boost at various frequencies, if the amplifier cannot (e.g. "line out" on a soundcard), it will probably just mean roll-off. The former is perfectly okay, the later is not (the former means "coloration" or whatever else you like; the later is just things not behaving).

    Overall I think this is a great guide! :) And I agree with the "plug it in and listen" as well - just because you have something with high Zout doesn't mean it has to sound bad. I actually liked my HD 580s out of a receiver with 470ohm Zout more than any other amplifier I tried them on; it added "body" to the bottom end. So that's a preference. Of course there are also headphones with Zobels (or otherwise flat impedance curves), and that are very sensitive, that absolutely ignore this entire problem and sound the same out of anything (higher Zout just makes them quieter); they're relatively rare ime though (I can think of three Sony models, Grados, and Denons).
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