Some low quality equalizers may be bad, but high quality parametric equalizers provide the only means to attain an accurate frequency response. (Or at least as accurate as is realistically possible.) But you have to use them the right way instead of casually experimenting. My links above show the way.
If there is indeed no defect in the OP's HD 700, he may just not like the sound signature, which is a fair ways away from neutral...but that can be fixed by...you know what. hehe. Personally, I don't care what a headphone designer intended. I am an audiophile (someone interested in high fidelity audio reproduction) and want to get as close as possible to what is actually on the recording, instead of further away, which is what happens when you don't use EQ. It's interesting how serious loudspeaker enthusiasts practically always use EQ, yet so many headphone enthusiasts are averse to it for mythical reasons.
Don't get me wrong, I suggested avoiding EQ to make the chain as simple as possible in order to judge if the headphone seems fine or not.
When properly applied quality equalizers can be very useful indeed. I've used DMG Equilibrium and Equality in the past with good results from both.
In my view, serious loudspeaker enthusiasts tend to use EQ because no matter how good the speakers are, the room plays a huge role and thus some equalization is most of the times a must in order to get a good frequency response. With headphones, the room doesn't exist and there's no consensus on a target response and thus people are less keen to use EQ.
Among the ones who use EQ for headphones you'll find those approaching Harman's curve, those approaching Orpheus FR, those approaching a flat line on an arbitrary measurement rig, those guided by ear, you know.
In my view, there's no possible target because:
1- Recording methods vary wildly, and music varies wildly. You'll find recordings all over the place in terms of tonal balance.
2- Different people has different hearing, some are sensitive to certain frequencies and some others don't.
3- We normally listen to music at different levels, when we raise the volume the headphone's FR remains the same but our hearing perceive it differently, so what's spot on at 85dB might be less than perfect at 75dB and viceversa.
4- Personal preferences (variable in time)
More so, the idea of a target is even more distant when you think about different placements on a live venue. They are listening to the real thing, but they are all getting a different tonal balance.
I don't use much EQ because if I go that route I would have to make a curve for each headphone and for each album, and that's a bloody matrix of equalization curves.
Normally, I simply try to pick the right headphone for the right moment, for the right album, and do my best to set the volume at an enjoyable level.
None the less, I use a bit of EQ from time to time when I'm on an EQ mood.
