headphone specs which are good ratings?

[holden j caufield]

Frequency response - what's a good range? 20 - 20,000hz?
Impedance - ohms (higher or lower)?
Sensitivity - db SPL/1mW (higher or lower) 104?
Distortion - < .x ?

I'm only looking at <$30 headphones

 

[MikeMike]

as long as THD is <1% you should be fine.
impedence, lower the better, but a lot of the nicer headphones are higher which makes them harder to drive efficiently
Sensitivity, is basically how loud they will be compared to power put out.

20-20K sounds good.

MIKE