Originally Posted by jodgey4
Before we wrap this one up... I still don't understand this point. 600 ohm should always have the higher damping factor I thought, which is usually better? And I won't comment on things such as 'more bass control' until I hear both pairs... but nearly everyone agrees differences are minimal if any, so let's not rehash that.
Sorry, I seem to have gotten my terms mixed up. Damping factor will indeed work for the higher impedance cans, as they will draw less current from the amp but however, more voltage. I was thinking about voltage swing here, not damping. Lower impedance headphones will be easier to drive with amps that can't deliver high voltage (typically, tubes will be better at voltage, solid state at current, but a portable amp or a soundcard for example will do alot better with lower impedance headphones). I only bother with damping factor when headphone impedance is really low, like my Grados or SA5000s, considering the 8:1 ratio is rarely a problem except as you pointed out, with some OTL tube amps (although that can be remedied by using higher capacitance output caps).
Anyway, I'm no engineer so to simplify, you shouldn't pick a pair of headphones based on a high damping factor (high impedance, unless you have an OTL amp that will struggle with lower impedance headphones such as Grados), because the moment you want to use them with pretty much anything portable, you will lack power to turn the volume up. With the DT990 though, 250ohm is plenty enough for the damping factor to be inaudible even with an OTL amp with lower capacitance output caps. I'm no good at math but it should be pretty easy to calculate the output impedance of an output capacitor if you're interested, that should give you a rough idea of how well the dt990 250ohm can be driven even by an OTL amp with lower capacitance output caps. I'm sure you can easily find capacitors values for many of the OTL amps out there, if the output impedance value isn't outright available. Typically, OTL outputs caps don't go under 220uF.
Edit: actually I found some very nice graphs to give an example:
Here is one with 470uF caps:
As you can see, damping factor wouldn't really be much of a problem for DT990s 250ohm, even with an OTL amp with low (220uF) capacitance output caps. You would struggle to be down 0.1dB at 20Hz.
Edited by elmoe - 5/25/14 at 4:31pm