Headphone Impedance question (for super techy nauts)

The Lounge General Discussion
#1

So I’ve got a pair of Audio Technica ath-m50’s ( the older ones, not the ath-m50x) and just recently I realized that there impedance (38ohm) is lower than the rytms headphone output impedance (55ohm), and my mixers (120ohm), and not sure about OT (not stated but am guessing it’s similar to rytm).
From what I understand in audio things usually travel from lower impedance to higher.
After doing a bunch of research, it is generally recommended for a headphones impedance to be 8 times higher than the source output.
So what about these phones being actually lower impedance than the source output?
From my research it seems that what happens is the electrical dampening of the audio no longer takes place and instead the phones are dampened according to there own impedance curve, changing the frequency response.
What I can’t find out is if these phones were designed knowing this and still perform optimally with higher impedance outputs.
Some info even suggests amplifier damage by plugging in phones of too low impedance to higher impedance outputs.
With the ath m50s being so popular it seems like all this would have been thought about, but I’m curious to understand.
Anyone?

Edit: As I was typing this I realized I should just email Audio Technica, but still something to chew on and I can post back with thier answer…

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Octatrack headphone output impedance? 80ohm-250ohm
Octatrack headphone output impedance?
#2

I imagine you’ll be fine in any case. If you want to read about it - here’s a guy who really seems to have done the research.

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#3

Read that plus a lot more last night, still didn’t answer my specific question…
Thanks though!

#4

That page even suggests that the Behringer UCA202 with a 50 ohm output impedance struggles with some 16 - 32 ohm headphones, which would make me feel that using my 38ohms with the Rytm’s 55ohm output would be a bad idea, but I’m having a hard time believing that seeing how popular these phones are and that they should just be “plug n play”…

Edit: it even says “some 16-32 ohm headphones” implying that some are different and would be fine running off of the higher impedance output. This is the area I’m seeking info about…

#5

I’ve let myself be told (mostly by the nwavguy) that a good rule of thumb is that the output impedance of your thing should be 1/8th of that of your headphones.

I don’t have that situation, I have an output impedance of “less than 50” vs. 300 ohms on my headphones - that’s probably not 1/8.

I dug around a lot and eventually some dude on Reddit said that it’s probably no problem, with enough conviction. Been happy ever since.

I believe the differences are pretty negligible (some nwavguy’s charts show differences that are really small), but I’m no expert, I just read some stuff about it.

#6

Yeah, I’m just curious because mine are actually lower than the output. I know I could just forget about this but for me I actually enjoy learning all sorts of finicky little details about audio and electricity. I like to understand how and why things work, and that knowledge makes me happy, so it’s really no bother for me to learn the nitty gritty of all this and is a pleasure not a bore… For every little tangent I go off and explore I gain a better understanding of not only audio, but electricity itself… fascinating…

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#7

There is a linked article, which puts the focus on the headphones:

It seems to me that low impedance headphones are optimized for all of our mobile gear like iPods, iPhones etc., which can provide low output impedance for technical reasons only. If plugged in to studio equipment, which often provides high output impedance, low impedance headphones might tend to non-linearity of frequency response or distortion. Maybe it’s an audiophile issue only?

#9

Alright, just sent this to Audio Technica, we’ll see what they say…

“Hello,
So I own the ath-m50’s, the older ones, not the x model.
I am wondering about impedances.
From what I understand you want your headphones to be a higher impedance that the output of what they are plugged into.
The m50’s are 38ohms and my mixer has output 120 ohms, my drum machine 55 ohms.
What are the implications of using the m50’s with devices that have a higher output impedance than the phones?
Will they not sound ideal? More importantly, can they be damaged or damage the output device?
Thanks for your time,
Mike”

#10

Post their reply please.

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#11

Nice! I def. understand wanting to learn, i often do the same - it just seems I’ve lately been on a “focus on the big things” kick :slight_smile: really would like to see At’s response

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#12

Well, here’s the response:

“Depending on the device you are plugging the headphones into, the impedance may differ and impedance matching should be observed when using different devices. The “ideal” setup is to have the headphones impedance be 8 times that of the source. The ATH-M50x headphones have an impedance of 38 ohms which would make the ideal source be 4.75 ohms. As you move up/down from there, the performance will change. Too much impedance is not really an issue but lack of is where you run into noticeable issues. You should be fine with either of your listed devices.”

I guess I like the “you should be fine” part, the rest is a bit confusing as it says impedance matching should be observed, ideally 8 times higher, and then says too high of impedance is not an issue but too low is. ??

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#13

Too low impedance - puzzled by this… AFAIK there are even headphone amps that proudly boast “0 impedance”, meaning they can bridge to any ohmage headphones??

This topic is interesting to me as well, as topics such as impedance, resistance and capacitance regularly pop up in my bedtime reading material… And it seems like they are very important things in audio engineering (ciruit design etc) yet I have a difficulty in grasping the implications fully :pl:

But maybe what AT meant by their reply was that the freq response changes by improper impedance bridging are not a big deal “in the real world”…?

#14

It’s funny, every time I try to learn more about this area something happens and I don’t get anywhere then give up. The response almost confuses me more. Do they mean don’t plug in to a .5ohm output because that would be too low? Did they mispeak?
why wouldn’t they say the output should be “at least” 1/8 of the phones?

#15

Well that 8-times impedance rule of thumb was already well known by us … The reply seems to be sloppy with the term impedance and sometimes it’s not clear, is the guy talking about source-output-impedance or headphone-input-impedance. But maybe that I missed something here.

#16

I was gonna give up again but instead I may just email them again for some clarification and sanity purposes…

#17

I understood that any impedance not beeing zero at the headphone-input (which would equal to be a kind of short-circuit), does not destroy the equipment. But if the source-output-impedance is not much lower then the headphone-input-impedance, we lose audio quality and performance.