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Most headphones used with portable electronics are low-impedance, around 32 ohms. This is because the power supplied by the device is limited due to it being battery powered, and the low impedance in the headphones allows higher volume levels.

From my basic electrical engineering courses, my instinct is that higher impedance headphones would also create a more level frequency response, thus being more true to the original signal. Is this true?

In relation to achieving optimal sound quality, is there any advantage to pairing high-impedance headphones with an amplifier for listening on an MP3 player or laptop, as opposed to just using low-impedance headphones?

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Weirdly enough, changing the number of turns of wire in a electromagnet doesn't change the magnetic field. Field is proportional to number of turns × current, so if you double the number of turns, you're also doubling the resistance and therefore halving the current, which means no net change. You're wasting less heat energy to produce the same magnetic field (which I think means higher sensitivity/efficiency). –  endolith Oct 8 '12 at 21:41
Very interesting. In my small experience I think that "AKG K141 Monitor" (1980-1990) are the best I have "listened to" so far. The high impedance (600 ohm) is still useable on my pc at full volume on my Soundblaster X-fi. I was wondering if lower impedance (55 ohm) headphones from AKG would have the same "uncolored" sound that the K141 Monitor have. I will go and test some. –  Zibri May 27 '13 at 13:46
Hi Zibri and welcome to AVP! 'Answers' to a question should be reserved for actually trying to answer the original question. I understand you don't yet have the rep to post comments, so I've converted your 'answer' to a comment. If you would still like to have your question answered, consider posting a new question. Cheers! –  JoshP May 27 '13 at 14:49
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5 Answers

High-impedance headphones are designed for studio-like applications where there may be multiple phones wired in parallel receiving an input signal from one source. Low-impedance headphones are designed to be plugged directly into a single source, and can more effeciently generate sound from the lower level input signal.

High-impedance headphones are a little more durable (electronically), but require higher signal levels to produce the same output level of low-impedance headphones.

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Multiple units wired in parallel? Wouldn't that short-circuit them? –  Gauthier Nov 24 '11 at 12:33
@Gauthier: No, it puts them in parallel. The total impedance drops, but not to zero. Putting 2 headphones in parallel halves the impedance. –  endolith Oct 9 '12 at 21:36
High-Z headphones are intended for use with passive mixers? –  ObscureRobot Oct 10 '12 at 12:48
@endolith: headphones, yes. But this answer says "receiving an input signal from multiple units wired in parallel", I interpret "units" as units with output, not headphones. If one unit's output want 1V while another one wants 0V, and they are connected... that's a SC. Where do I misunderstand? –  Gauthier Oct 11 '12 at 13:26
@Gauthier: Oh, I see. No, despite the wording, it's multiple headphones in parallel with a single source. :) "Phones in this impedance range may be directly plugged into the headphone jack routinely found on recording and playback equipment. Higher impedances, such as 600 ohms, are more useful in studio installations where many units may be wired in parallel for studio monitoring applications." akg.com/site/product_tipps/… –  endolith Oct 11 '12 at 13:44
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The power required to operate headphones is a function of the driver size and mass, whether the phones are open, closed, or in-ear, etc. The impedance of headphones is usually designed to get an acceptable volume level (power = voltage^2 / impedance) at the voltage level expected on the driving equipment. It's not necessarily a straightforward relationship of low impedance = cheap, high-impedance = pro.

Many really fine headphones have large drivers (more power), are open-air (more power), AND expect to be run from higher-voltage professional/amplified equipment... which sort of cancels out the impedance question from a design perspective. Apple earbuds are 23 ohms... my fave studio headphones, Audio-Technica ATH-M50s, are 38 ohms... one of the most common studio headphones, Sony MDR7506, are 63 ohms. So, more "pro" headphones are higher impedance, but that just means that you will get less power (lower volume) on a low-voltage audio source.

There are other good reasons to use an external amplifier... RF/EMI noise isolation, etc... but I think the main reason you might want to with better headphones is that the volume may be low with higher-impedance headphones.

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I think the key to my question lies in this part: "expect to be run from higher-voltage professional/amplified equipment". Everywhere I look, people say high impedance headphones are that way to match the high voltage amplifiers, and the amplifier people say they provide high voltage to power your high impedance headphones! It seems that the loop needs to stop somewhere, and it appears to me that there is a reasoning behind creating pro headphones with high impedance from 250-600 ohms. –  Cory Klein Jan 21 '11 at 21:39
@Cory: There is one kind of headphones that nobody has mentioned yet, and that is electrostatic headphones. Electrostatics are the only high-fidelity headphones that I would consider truly "high-impedance." The sound quality of electrostatics is unparalleled. But electrostatics are quite exotic; they require special high-voltage amplifiers, and are generally very expensive. –  Robert Harvey Jan 25 '11 at 18:23
"higher impedance → less power (lower volume)"? I don't think that follows, as you're not including sensitivity. Headphones convert electrical energy into sound energy and heat energy. A headphone generating more heat does not necessarily generate more sound. –  endolith Oct 8 '12 at 21:17
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In relation to achieving optimal sound quality, is there any advantage to pairing high-impedance headphones with an amplifier for listening on an MP3 player or laptop, as opposed to just using low-impedance headphones?

Yes, there is. In fact, there is an advantage to using an external amplifier for any headphones.

If you are resourceful, you could try building a CMOY amp in an Altoids box, like the picture below. The sound is awesome, and the cool factor is off the scale.

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Why do amps like this improve the sound? I could talk about slew rate, total harmonic distortion and a whole host of other factors, but the simple fact is that having a booster amp like this means that your original amplifier doesn't have to work as hard. Most small audio output (including the headphone amps in the vast majority of computers and laptops) only produce about 100 milliwatts of power, and that's just not enough to insure high fidelity.

Here's how impedance affects the performance of headphones: a lower impedance allows headphones to capture more power from the amplifier. All other things being equal, they are going to be louder than headphones with a higher impedance, because higher impedance requires a higher voltage level from the amplifier to achieve the same relative loudness. This is why earbuds typically have a much lower impedance than other headphones; it is necessary to get adequate volume, given the low voltages provided by batteries.

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Can you explain in what way high impedance headphones are superior? Why not just have low-impedance headphones with an amplifier? –  Cory Klein Jan 21 '11 at 21:41
+1 for Penguin mints! –  BenV Jan 21 '11 at 22:31
@Cory: I don't think high-impedance headphones are superior just because they're high-impedance. Their overall design is what makes them good headphones. –  Robert Harvey Jan 25 '11 at 0:44
I agree that just making some headphones high impedance isn't a catch-all to make them good headphones. But does the high-impedance contribute to superior headphones creating high fidelity sound? –  Cory Klein Jan 25 '11 at 18:14
@Cory: I don't see how; as long as your amplifier can handle the current needs of low-impedance headphones, it comes down to the quality of the headphone design. –  Robert Harvey Jan 25 '11 at 18:19
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It seems that the ratio of source impedance to headphone impedance, i.e. damping factor is primarily discussed in terms of effect on amplitude and frequency response. In addition, remember that a higher impedance circuit will likely exhibit a reduced slew rate and slower rise time. This will effect the clarity and openness of the sound and possibly dull transit response.

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Consider the difference between consumer and line level:

You need to match the impedance in order to preserve the condition of the gear, but pro line level (+4 dbu) is a hotter signal than consumer (-10 dbv). The reason that professional monitors use the hotter signal, is because it is higher fidelity.

I assume that the same applies to headphones. you get a wider dynamic range and more clarity in softer dynamics when you have a wider spectrum of amplitude, which is the property of the signal propagating through your resistors and cable.

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