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I planned to compose song with my Macbook Pro and I like Beyerdynamic so I choose DT 990 as I wanted to try open back headphone.

The problem is which impedance to choose?

I don't plan to buy an amp, directly connecting to MBP is my desired workflow.

However, as I searching around this is my problem :

I know that my MBP can drive the lower impedance version louder. But what if on the 250 ohm version, I'm totally satisfy with the lower volume it provides (I'll have to turn up the volume of my computer a bit) This means 250 is better for me? For the reason of "damp factor" I've read.

In other words, when driving high impedance headphones without an amp is the sound is just lower or some quality is loss? If no quality is loss I would go with higher impedance ones because I'mnot a loud listener.

This is a quote from Beyerdynamic website's FAQ

The impedance is determined by the voice coil (dynamic headphones), which is a winded copper wire (coated to avoid a short-circuit). This copper wire is available in nearly every length, but not in every gauge (thickness) and a thicker wire has less resistance than a thin wire ("less fits through"). The magnetic field of the voice coil depends on the number of windings of the coil, causing a low impedance system to use a thicker (also heavier) wire and since the membrane foil can't be infinitely light-weight, the moving mass (voice coil and diaphragm) is relatively high. It's pretty clear that a higher mass can't move as easily (following an audio signal) as a lower mass. This low mass can easily be accomplished with thinner (lower weight) wire, but the thinner wire has a higher impedance. This means that the DT 770 PRO with 250 ohms sound more natural, but plays (depending on the used headphone amplifier) not as loud as the 80 ohms version.

This suggests the higher impedance ones is better... (but lower volume)

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It depends on the system that is driving them. Some gear (particularly consumer gear) will start distorting more as it nears it's maximum power output. On the one hand, you are further away from the noise floor, which means cleaner quiet parts, but on the other hand, if you have to push it so hard that it starts to distort the signal itself, then any gain you achieved is lost.

If you want to use the higher impedance headphones I suggest that you use a small headphone amplifier or external DAC to power them.

  • Then if I planned to not buying any amp, I should get lower impedance and reduce the volume on the computer instead? (because at full volume I'll basically become deaf) – 5argon Sep 8 '13 at 4:42
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    It all depends on your sound card. It may do fine at high volume (and thus the higher impedance may not be an issue) or it may distort producing a lower quality sound. You won't know until you try it unfortunately, unless you can find a review of how your card does at high power. – AJ Henderson Sep 8 '13 at 5:51
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According to a review by Ken Rockwell on the DT 880, the only real difference between the 32, 250 and 600 ohm versions was how loud you are able to play them.

http://kenrockwell.com/audio/beyer/dt-880.htm

He even plugged in the 600 ohm version to an iPod and said it got plenty loud but it was practically at max volume.There is no reason to think that the DT 990 would behave that differently so you should be fine with the 32 ohm or 250 ohm version if driving straight from your macbook pro.

The macbook pro has a voltage output of 1Vrms which means at 32 ohms you have an output of 31mW and for 250 ohm you have 4mW. Using the spec of 96dB/mW we get max levels of 110dB and 102db for 32 and 250 ohm respectively. 102dB is already at the level of hearing damage so it should be sufficient for your purposes. If not then you might need to add an amp.

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