Headphone Ohms Question.

[Uppercut]

This may sound like a dumb question but i'm a tad confused as to why the Beyerdynamic DT 770 @250ohms would be prefered over the Beyerdynamic DT 770 @80ohms. My understanding of ohms law is the higher the impedence/resistance, the more power that is required to drive it. And driving 4 ohms speakers with say an 8 ohms amplifier is wasted power/current that causes the amplifier to overheat. I've always assumed that having a lower impedence would be prefered over a higher impedence. What advantages are there in having a higher impedence with regards to audio cause i seem to be missing something here.

 

[ashmedai]

80Ω is easier to drive if you don't have a good amp. 250Ω needs an amp more, but benefits from it more. If you have the gear to support it, 250Ω will give better results. If you don't have the gear, 80Ω will do a better job of playing nice (as you said, doesn't require as much power).

Consider a limiting case as R --> 0Ω. Any little thing will affect the coil. For R increasing, the vibration and thus the sound becomes more and more controlled by deliberate excitation.

 

[keenan]

Higher impedance usually means you need a higher drive voltage to get to a similar volume level, but not necessarily more power - that is related to the efficiency of the cans which doesn't have much to do with their impedance. There isn't really any direct advantage to 250Ω over 80Ω, but the designs are different and will have different characteristics, even though they have the same model number in this case.

Generally anything over 100Ω will be difficult to drive with an 'average' source and you'll need a proper amp, though some very efficient designs can still work well.

 

[450]

but the designs are different and will have different characteristics

So are there more differences between the 80 ohm and 250 ohm versions than just the impedance? Could you have the benefits of both versions by merely using the 80 ohm DT770 coupled with a DIY 170 ohm adapter? I know some people did this with Etymotic ER4P's so they'd be like a ER4S. I'm wondering if the same concept will apply to the DT770's.

 

[ashmedai]

Higher impedance usually means you need a higher drive voltage to get to a similar volume level, but not necessarily more power

Well yeah, if you want to be all p = v^2 / R about it.

Better term, oomph. You need an amp with more oomph to handle the higher impedance phones. More powerful is correct or at the least close enough in the nontechnical usage, but has connotations for circuit analysis which aren't always valid.

Generally anything over 100Ω will be difficult to drive with an 'average' source and you'll need a proper amp, though some very efficient designs can still work well.

Too low, and we start talking about extraordinary current instead of extraordinary voltage. 60-80Ω is fairly normal for relatively undemanding headphones, but it can go a bit higher or lower depending on efficiency etc.

So are there more differences between the 80 ohm and 250 ohm versions than just the impedance?

Not really, although note that there are a number of related versions which do have other differences. For the same version at different impedances - the impedance should be the only difference.

Could you have the benefits of both versions by merely using the 80 ohm DT770 coupled with a DIY 170 ohm adapter? I know some people did this with Etymotic ER4P's so they'd be like a ER4S. I'm wondering if the same concept will apply to the DT770's.

No. If anything, this could make matters worse. The problem is that you create a voltage divider; the adapter and the headphone itself get voltage in proportion to their respective impedance values.

The reason this is sometimes useful is that it lets you alter how much voltage goes to the headphone. If you have insufficient control over amplifier gain, this can put the headphone into the regime where the volume knob on the amp does something useful.

 

[keenan]

So are there more differences between the 80 ohm and 250 ohm versions than just the impedance?

Well there are ancillary things, like a 250ohm driver is going to be wound with finer wire, and possibly wound differently as well, and that will affect its physical design too. Then this differently wound coil is going to have different electrical and magnetic properties, so maybe the magnet and spider configuration is changed as well. It's a system, changing one thing changes others as well, though I don't really know about the DT770 in particular. I've got the Pro 80 ohm version and I haven't heard the 250 ohm or the non-Pro 80 ohm. Most folks I've talked to think the 80 ohm and 250 ohm pro versions sound very similar, so you should probably just buy the one that's more convenient, I don't think you'll notice much difference assuming you have the equipment necessary to drive the 250 ohm properly.

Could you have the benefits of both versions by merely using the 80 ohm DT770 coupled with a DIY 170 ohm adapter?

It shouldn't do anything, all that resistor is doing is burning power and hurting the damping factor of your headphones. You'll get the disadvantages of the 250 ohm model (you need an amp), but it's still the 80 ohm headphone you're driving.

 

[obobski]

beyerdynamic doesn't seem to acknowledge any intended sonic/performance variations between the two models

they list the DT770 with a single freq response, sensitivity, etc, and four order codes (250 or 80 ohm, with or without in-line volume control)

I'm wondering if the 250ohm version isn't the same driver with a resistor or similar in-line, or something equally simplistic like that, as they aren't advertising any specific differences between the two (or if they are different drivers/designs, but are intended to be "the same", could be either way)

either way, to the OP, any difference you're likely to read about is purely subjective (not a bad thing, mind you), yes there are going to be variations in the system's relationship to the amplifier (as keenan has explained), but an IEC standard amp will (should) be designed to hit 5V into 120ohms, the 250ohm model will get a bit less power and the 80ohm model will get a bit more power, shouldn't make a huge difference either way (one of them will just make you deaf faster at max volume), now as far as connecting these to something craptastic, yeah I'd probably get the 80ohm version, otherwise, shouldn't matter either way (if you're using an ipod or something that doesn't have very much output power, the 80ohm version should have some advantage, if you're connecting them to a receiver, headphone amp, or headphone amp soundcard, etc, should not matter either way)

tl;dr:
if people would design their stuff the way the IEC/logic dictates they should, there isn't a problem