I will start a thread comparing all four as soon as they have a decent burn-in and my homework loads lightens up.
The HFI-580s are not my cup of tea... Just too exaggerated.. I guess I like a flatter/studio sound. These have quite an erratic/unpredictable response to different genres and frequencies. Amazing bass, excellent build quality, but the agonizing spikes all over the frequency spectrum killed it for me.
The Q-40s had just as much bass as the 580s. The Q40 bass was more "thunderous" and the 580 bass was much cleaner/tighter. However the Q40s had far less fatiguing (although still not that great) mids and treble. 90% of the "bassfactor" of the HFIs with way less fatigue.
The K 240s have extremely lo-fi, muddy bass response straight out of the '70s and were a real let down in that area but they have very nice mid range and laid back treble and I like the overall design. Plus they were the cheapest phones in the test.
The SRH840s sounded and felt the most expensive and "won" the comparison. They are the only headphones out of this bunch I would want to use for mixing/recording. Occasionally harsh treble and boring looks, but really the only headphone that felt and sounded like its price tag and stayed consistent across every genre.
None of these are quite perfect for me and my search for the "ultimate" headphone continues.
2. Q 40
3. K 240
4. hfi 580
Rankings (relative to price/value):
2. Tie: K 240 and Q 40
4. hfi 580
Edited by machoboy - 9/3/12 at 3:49pm