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Originally Posted by P.F. Jo /img/forum/go_quote.gif
erm.. I have.. no amp. im just trying to figure out what the impedence means.
one friend tells me the higher it is, the more volume - it makes no sense however..
in some places I read that the higher impedence headphones got, they will be 'harder to drive' and require Amps more than lower impedence ones..
So im just trying to make some logic out of this mess.
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It sure is a mess.
Historically, 600 ohms was a good standard for recording studios because recording studios were already lousy with 600-ohm line drivers and 600-ohm loads. So you could just wire your headphones to a couple of 600-ohm line stages.
Impedance is not the only factor controlling how hard a headphone is to drive, and in fact hardness in driving can be any of at least three and probably four or more factors.
In general, all other things being essentially the same, such as between beyerdynamic drivers that are 32, 80, 250, or 600 ohms for the same dt770, they all use the same amount of "power" but the 32-ohm version gets loud lower in the dial than the 600-ohm version.
But what the volume knob controls is voltage. Ohm's Law says that the lower impedance load will sink more current.
So, if you assume that the only difference is the impedance of the coil in the driver - if the coil weight and shape is consistent, along with the magnets, diaphragm, etc, for the same sound pressure, each version of the driver will sink the same amount of "power", but the low impedance version will need more current and less voltage while the higher impedance version needs more voltage and not as much current.
The Ohm's Law factor affects the sound in a couple ways that have everything to do with what you plug the headphones into.
Since portable devices are generally low voltage devices, to get a high impedance headphone to a comfortable listening level with a portable device may require that you turn up the volume to the point where the output is clipping. This isn't an issue if you have an amp with enough gain and a reasonable power supply (9v on up).
If your headphones are really low impedance, like 16 or 32 ohms, they may require more current for things like big bass notes than the source can supply. In these situations the bass can seem lean because what should slam is just kinda going *splat* instead.
If you push a 60hz square wave through a not-enough-current amp with a low impedance load and watch the output on a scope, what you see is the left hand side of the wave going all the way to the top, and then just dropping off to ground again instead of making a straight line to the right-hand side of the wave.
But I'll say it again: these are not the only factors.
My 60-ohm RFT HOK80-2 needs a higher setting on the volume knob than my 600-ohm K240 Sextett. It also needs at least 10 times as much current thanks to 1/10th the impedance. The mighty HOK is truly hard to drive - y'all don't know from hard to drive.
The difference? efficiency. Mechanically speaking, it just takes more current to move air with the HOK's PMB-knockoff orthodymamic driver than it does with AKG's relatively efficient DKK32 dynamic driver.
My 30-plus-years-old DT302 has a 600 ohm impedance and i can drive it to a comfortable listening level without clipping from the line-out jack on my iRiver H120. Why? It's yet more efficient than AKG's driver.
Another factor - sensitivity. It may well be that the higher impedance coil can react to smaller nuances in the signal than the lower impedance coil, but I don't really know if this is a practical truth in the reality of headphones or not.
But generally it's true that, given enough voltage in the power supply, the higher impedance load is actually easier for the amplifier to drive, thus the amp will be more accurate and run faster.
The flipside of that - really low impedance loads like 16-ohm IEMs can make the amp in the source misbehave a bit, resulting in audible hissing.
