Headphone Impedance

Hi There

I was about to purchase a pair of Beyerdynamic DT100s when I noticed they come with two different impedance ratings. One is 16 Ohms whereas the others are 400 Ohms.

Which should I get? I'd be wearing them for tracking vocals and guitar/bass and general monitoring duties etc. I'll be feeding them via my Samson S-Phone Headphone Amp or via my RME MultifaceII's headphone out.

Just for the sake of my own knowledge, which ones are best for which types of applications?



Regards

Stewart

In addition to what GuitarHacker said the higher impedance units are usually designed to have better low frequency dampening which results in a crisper and more controlled bass response.

That makes them a very good match for a hi-fi headphone amp that has adequate power and a poor choice for a small device with a low powered amp that may even be running on batteries.

The lower impedance headphones are usually designed to be a good match for battery powered gear.

There are probably many exceptions to what I just said.


best regards,
mike

Thanks for that Herb, Mike and Drew.

Your information is greatly appreciated. I was in two minds what to get.

I know for a start that my RME MultifaceII is a little short on output volume even with a pair of 16 Ohm Panasonic Cheapos I have. My Sennheiser HD-280 Pros are 64 Ohms and not much better on my MultifaceII. Don't get me wrong, they both do their job but the unit could do with delivering more ooomph to them.

Like Drew said, for larger projects with more folks playing and monitoring, the higher 400 Ohm ones may be a better camp to join now for the long run with subsequent purchases of these as time goes on (should need require). My Samson S-Phone Headphone Amp has 12 Outputs and ain't exactly a walkman but I guess a load of low impedance headphones may draw heaps of current.

Looks like it's a pair of DT-100 400 Ohms then. 

Also, I'm off to read an "Understanding Impedance" article on SOS. Understanding impedance has been one of my weaker points.


Cheers guys

Stewart

For a high impedance load (headphone), you need a higher output voltage and less current. This is good, if you want to use long calbes. It is bad if your voltage is limited (battery powered devices). The volume may be too low.
If you connect several headphones to one output (using passive Y-type splitters), all headphones should have the same impedance. Ideally, they should be the same. Otherwise, the low impedance ones will be loud and the other silent. If you plug too many low impedance headphones into one output, you may end up with an distorted signal. Up to 4 may work.
If you have a dedicated headphones amplifier with multiple outputs (and seperate volume pots), you won't have to worry. Every output will have its own amplifier, and they will work with any impedance just fine.

Wilko

Guitarhacker


I know for a start that my RME MultifaceII is a little short on output volume even with a pair of 16 Ohm Panasonic Cheapos I have


YEAH... so is my Saffire and from what I hear, so many other interface as well. You would think they would install a better headphone output amp in those things. That is why I route two (out of 8) of my outputs on the saffire to my stereo receiver/amp and use it as the headphone amp.

Yeh...totally. I wonder why interface manufacturers do this? Perhaps they feel that most folks might use external amp for this. Who knows.

Stewart,

If the minimum impdance is 8 Ohm, then you can plug in 2 headphones with 16 Ohms into one output or 4 headphones with 32 Ohms.

For an amplifier with a low source impedance, i.e. the voltage does not depend on how much current you draw, you would expect a higher output power for a lower load impedance. Audio amplifiers for speakers have an extremely low source impedance.

This is not true if there is a resistor in series with the output (for safety), i.e. a relatively high soure impedance. In this case, you will see the highest power output if the load impedance matches the source impedance (impedance matching). If your load impedance is low, you will get more current. But most of the available voltage will drop across the source impedance, not across the load. So, you are wasting voltage. If your load impedance is higher than the source impedance, you see a higher output voltage, yet the current going through the load will be low. It turns out that the product of voltage across the load and current through the load reaches its maximum if the load impedance equals the source impedance.
The headphones outputs of audio amplifiers often have a series resistor (with quite a high resistance). Otherwise, you could put the full output power into the phones. Dedicated amplifiers for headphones may still have a series resistor. But I would expect a much smaller value which should be better. (Note that a low source impedance (compared to the load impedance) dampens ringing. Mike mentioned this effect above.)

Wilko