Headphones: high versus low impedance?

Question

So I have a Sennheiser HD 280 PRO headphones. These headphones have an impedance of 64 ohms. They sound great.

http://en-us.sennheiser.com/professional-dj-headphones-noise-cancelling-hd-280-pro

I also have a Sennheiser HMD 280 PRO headset (notice the M, means with a microphone). They look and feel almost exactly the same as the HD 280s, except they have a microphone. These however, have an impedance of 300 ohms.

http://en-us.sennheiser.com/stage-monitoring-headphones-headset-broadcast-hmd-280-pro

Both of these get plugged into a headphone distribution amp to get sound from a single source. What I've noticed is that I have to turn the amp up to 100% on the 300 ohm headset in order to hear the same level of sound that only requires the amp turned up to 60% on the 64 ohm headphones.

My question... why would I ever want a 300 ohm headset, over something with lower ohms?

I'm looking to get some Sennheiser HMD 26-II headsets, and they come in both a 600 ohm and 100 ohm variant. Why would I ever want the 600 ohm variant if it requires me to jack my amps up so high? Jacking my amps up also jacks up any sort of electrical noise and interference in my lines.

Answer 1

There are some characteristics for low and high impedance headphones - but these are not to be taken as universal truths (you'll find excellent sounding low impedance headphones and horrible sounding high impedance headphones and visa versa).

However let us generalize a few characteristics:

High Impedance (above 100 ohms)

• Typically has more windings in the coil and following hereof a more precise replications of dynamics ("they're more dynamic")
• Requires lower current, but higher voltage compared to low impedance
• Dissipates more power in the coil (typically better for the amplifier)
• Requires thinner wires to achieve the high impedance without the coil getting too big and heavy. Many high end head phones are only produced as high impedance

Low Impedance (below 100 ohms)

• Typically has fewer windings with thicker wire (compared to high impedance). Dynamics may suffer from this, but the coil it self may handle overload better in a longer period.
• Requires higher current, but lower voltage compared to high impedance (good for low voltage devices - phones, ipods, some computer sound adapters etc)
• Easier to produce coilwise, thereby also cheaper

So concluding from this alone: go for high impedance for studio/stationary hi-fi use and low impedance for mobile and computer use (I know 'computer use' is pretty broad - here I have in mind on board adapters and purely USB powered devices in mind).

BUT (and thats a very big BUT!) - there is so much else to it, like the membrane construction, chambers, fitting and rejection of ambient noise.

Finally if you intend to use them for many different purposes - why not go for "medium" impedance head phones in the range from 50-200 Ohm..

One other thing that may be concluded: cheap high impedance headphones are likely to be wound using thicker wire with higher resistance which means less dynamic and less output..

Sources:

• Headphone buyers: Here's what you need to know about low- vs. high-impedance models
• Low Impedance vs. High Impedance? Huge Difference?
• Headphones @ wikipedia

Answer 2

Your question is referring to professional headphones so I'll try to answer in that context.

High impedance headphones typically have lower distortion due to the high ratio of the input impedance vs output impedance, otherwise known as the damping factor. Here is a link on that topic.

http://benchmarkmedia.com/blogs/news/11653109-the-0-ohm-headphone-amplifier

In a typical home hifi setup, this isn't something you need to worry about too much. However in a studio/broadcast/DJ setting you could easily have really long cable runs which can add a significant amount of impedance to the output. Let's say the original output impedance is 1 ohm and the long cables add 30 ohms. For a 600 ohm headphone the damping factor would be ~19 which is really good. However for a set of 32 ohm headphones the damping factor would be 1.03, which is terrible and would lead to a lot of distortion.

Another factor is that a lot of professional headphone amps have multiple outputs wired in parallel. The following amp by Lake People is one example:

http://www.lake-people.de/produktdetails/G103-S.html

Plugging in two headphones effectively drops the headphone impedance by half. To power two headphones means you need to draw twice as much current. For low impedance headphones the amp could easily start clipping with multiple headphones plugged in and cause distortion. However high impedance headphones require far less current and plugging several in would not overload the amp. Typically amps that can power 600 ohms headphones can also do 150 ohms without a problem. This means if you are monitoring a recording with a band, you can split the output 4 ways and they would all hear undistorted sound. However with low impedance headphones you would basically need 4 separate headphone amps.

Answer 3

There was a good answer on headphone impedances on this topic: https://sound.stackexchange.com/a/22545/16344
I digged it up for you, but I still think there was another enligthening answer by the same user on a different question.
Search his answers and also search for headphone impedance in general on the site (I found the best answers here some years ago, and now I am a happy owner of a Beyerdynamic 880): https://sound.stackexchange.com/users/7200/leftaroundabout?tab=answers
Regarding your question, I guess you should pick the 100 Ohms version, if you have to use full power in your system already with the 300 Ohms version.