Sound quality is a subjective matter. However, I think we can all generally agree on the frequency response, muddiness, detail, sound stage, etc.
Please note that when I say 'Sound Quality', I'm not taking into account the sound signature - some headphones have a warmer sound whereas others are more analytical but that doesn't mean any of the two are superior.
I made this little thing based on my opinion of what the sound quality to price ratio would generally look like.
I say generally because there are a number of exceptions such as cheap headphones that have superior sound and vice versa.
I find that the sound of headphones in the lower end of the price scale improve greatly the more you spend, up to about $300~$350 - hence the steep incline.
After about $350, the the ratio between the clearly audible improvements and price is not as great but nonetheless evident until we come to the ~$1000 price range.
Past ~$1000 the improvement to sound quality is relatively minuscule (please don't eat me, audiophiles ). At this stage, we're looking at very minor differences - hence the plateau.
The scaling is also purposely inconsistent as I think that the number of headphones is not evenly distributed across the price range, but rather generally massed below ~$350.
NOTE: Although the curve doesn't show it, the sound to price ratio isn't such as smooth ascent, but rather quite erratic due to the wild variations. (thanks billybob_jcv)
So, what are your opinions?
EDIT: Updated the graph and shifted scale/explanation. (thanks Brooko)
Edited by gamerich - 5/8/13 at 12:57am