Studio headphones - impedance

Haych

Looking at acquiring some decent closed back headphones next for recording purposes.

I notice most sale listings state the impedance of the headphones.  Is this important to get right?

Research I've done so far - well, a quick google search - suggests headphones with higher impedance reproduce lower frequencies better but aren't as useful/kind to portable devices (not that this would be a consideration anyway).

Is there a rule of thumb as to which impedance to choose, or does it make not much difference?

TIA

octatonic

Higher impedance headphones tend to suit studio use, where the headphone amp can drive them properly, while lower impedance models are better for phones and portable devices. Low impedance is easier to drive and high impedance needs more power, although sensitivity plays a big role too. If your interface has a weaker headphone amp, something around 80 ohms is usually a good compromise.

Danny1969

High impedance cans don't need more power but do need a higher voltage swing than low impedance cans .. their high impedance though means they will draw less current. 

Low impedance cans need a higher current but at a lower voltage 

P = VI where I is the current so 100 miliWatts would need around a 4V swing through a 160 Ohms set of cans .. that's 8V peak to peak so not directly possible from a traditional 5V portable source. For these cases a lower impedance set of cans makes more sense. Modern devices tend to use class D headphone amps though which can also have DC to DC voltage step up so might be able to manage better. 

Haych

Thanks both.  I will try to digest all of that.

Currently trying to get through a video of Julian Krause where he goes quite in depth into a bunch of different audio devices and headphone impedances.

Whodda thunk headphones could be such a complicated decision!

octatonic

Danny1969 said:

High impedance cans don't need more power but do need a higher voltage swing than low impedance cans .. their high impedance though means they will draw less current. 

Low impedance cans need a higher current but at a lower voltage 

P = VI where I is the current so 100 miliWatts would need around a 4V swing through a 160 Ohms set of cans .. that's 8V peak to peak so not directly possible from a traditional 5V portable source. For these cases a lower impedance set of cans makes more sense. Modern devices tend to use class D headphone amps though which can also have DC to DC voltage step up so might be able to manage better. 

Good point, thank you. High impedance headphones need more voltage and low impedance ones need more current. I was mainly talking about practical pairing, since studio amps usually have enough voltage while phones do not. Sensitivity still matters as well.

octatonic

Haych said:

Thanks both.  I will try to digest all of that.

Currently trying to get through a video of Julian Krause where he goes quite in depth into a bunch of different audio devices and headphone impedances.

Whodda thunk headphones could be such a complicated decision!

In most cases you won't have too much trouble mixing and matching.
Are you mixing for release?
If so then it can start to matter.

I don't mix on headphones, other than a bit of reference checking and for some minor fine editing.

Haych

Mixing for release? Me? I'm flattered that you even asked the question, but no.

I am mostly interested in them for tracking rather than mixing, hence why I am looking specifically at closed back 'phones.

Stuckfast

Most of the reasons why high-impedance headphones exist are historic as far as I'm aware. The only real reasons for using them these days are (a) because you have a weird old headphone amp that expects to see a high impedance, or (b) you are recording an orchestra and you want to run lots of pairs of headphones paralleled off the same amp.

In practice any current model that's not specifically described as a high-impedance model will be fine. 

Danny1969

The really old cans were 600 Ohms ish ... this may have been due to the power amplifiers in the telephone industry being valve based .. so high voltage but not capable of driving low impedance's directly without an output transformer. 

In reality nowadays, even headphone outputs that expect to drive a low impedance set of cans will have a resistor in series with the output. This stops low Z cans drawing too much current and prevents the capacitance of the headphone cable causing problems. This is also acting in series with the headphones own impedance as part of a voltage divider, so can even things out a bit volume wise between cans of different impedances.