If we could have it all, we would.

Well said. On that note, LCD-4.3 for the win!

It's also FR though.  Headphones are all over the place.  There is no way our HRTF's are that wildly varied.  Unless for some reason HRTF applies to full size headphones, but not IEM's, speakers, or the real world?  This is the other problem I have with the HRTF theory:  if someone hears a dip at 6khz relative to other people with headphones, they hear the same dip in real life.  So guitars will have that same dip whether it be real life, headphones, or speakers, so it's irrelevant.  A headphone that has the same general characteristics of real life (isn't adding or subtracting in a huge way) won't sound more "off" to them than to someone without that 6khz dip. 

My point is that everyone's reference is real life.  If your ears have a dip or peak somewhere, it's already compensated for and isn't part of the picture. 

My Mackies sound better than almost every headphone ever made regardless of the room they're in.  I don't think you could change that with any room.  Even a frickin cement hole woudn't make them sound as bad as even the better headphones out there not to mention a Grado.  Right now there is a huge glass door right behind one of my speakers (it's a really difficult room to arrange things in...) and they sound great.  They're a bit warm and bassy right now, but it doesn't bother me hardly at all.  Because they're still more accurate than nearly any headphone out there. 

The reason the opinions very so wildly on the neutrality of the LCD-2 and SR-507 is because neither one is neutral.  People who say they are neutral are deluding themselves.  If a headphone was in fact neutral, it would be regarded as such by the majority of people out there (the experienced ones at least) just like the UERM and JH13 are highly regarded. 

That's why the LCD-2 vs HD800 thread was so crazy.  Both parties were wrong.  Neutral is right in between both headphones. 

It's also FR though.  Headphones are all over the place.  There is no way our HRTF's are that wildly varied.  Unless for some reason HRTF applies to full size headphones, but not IEM's, speakers, or the real world?  This is the other problem I have with the HRTF theory:  if someone hears a dip at 6khz relative to other people with headphones, they hear the same dip in real life.  So guitars will have that same dip whether it be real life, headphones, or speakers, so it's irrelevant.  A headphone that has the same general characteristics of real life (isn't adding or subtracting in a huge way) won't sound more "off" to them than to someone without that 6khz dip. 

My point is that everyone's reference is real life.  If your ears have a dip or peak somewhere, it's already compensated for and isn't part of the picture. 

My Mackies sound better than almost every headphone ever made regardless of the room they're in.  I don't think you could change that with any room.  Even a frickin cement hole woudn't make them sound as bad as even the better headphones out there not to mention a Grado.  Right now there is a huge glass door right behind one of my speakers (it's a really difficult room to arrange things in...) and they sound great.  They're a bit warm and bassy right now, but it doesn't bother me hardly at all.  Because they're still more accurate than nearly any headphone out there. 

The reason the opinions very so wildly on the neutrality of the LCD-2 and SR-507 is because neither one is neutral.  People who say they are neutral are deluding themselves.  If a headphone was in fact neutral, it would be regarded as such by the majority of people out there (the experienced ones at least) just like the UERM and JH13 are highly regarded. 

That's why the LCD-2 vs HD800 thread was so crazy.  Both parties were wrong.  Neutral is right in between both headphones.

Except for a little extra energy around 9-10kHz all the Lambdas are really close to an ideal free field FR which is basically how stuff would sound in a wide open space with no walls for stuff to reflect off of.  If the 507's FR doesn't sound pretty close to your Mackies being set up in an empty field then apparently your HRTF is pretty different from average.  :p

Full size headphones do in fact have different HRTFs than IEMs because the IEMs bypass more of your anatomy.  Speakers don't have HRTFs and don't need them.  An HRTF isn't about the sensitivity of your own hearing at any given frequency.  That would indeed effect your perception equally no matter what you were listing to.  An HRTF is about how your torso, head, and outer ears reflect and amplify sound waves at different frequencies.

With a speaker flat is flat because each person's body interacting with the sound waves changes the FR that makes it to their eardrums regardless of whether those sound waves come from a speaker or an actual instrument.  The sound waves from headphones come at different angles and bypass parts of your anatomy so they need a different FR to compensate.  This is calculated by putting tiny microphones deep in someone's ear, playing some tones at them, and seeing what FR the microphones record.

Keep in mind this all talking about only the FR.  The rest of a full HRTF involves delay and attenuation or sounds at different angles from your head.  That's how your brain can tell what directio n something is coming from in RL and it's not something a headphone can do on its own.

The free field I mentioned before is without any extra reflections.  They're measured in anechoic chambers.  The room reflections from a diffuse field measurement don't actually add whole lot of extra energy compared to the rest of it. but -3dB at 3kHz is pretty damn close to the to the averages.

Here's a picture out of the brochure for the HATS that Tyll uses.  It shows the correction you apply to its measurements for different HRTFs but I flipped it upside down so you can compare it to the raw curves on Innerfidelity and see how a 'phone matches to different HRTFs.

http://www.head-fi.org/gallery/image/view/album/131808/id/501495/sort/display_order

The labels are upside down but the blue is the independent of direction curve that Tyll uses on his Innerfidelity graphs.  I don't really know what its supposed to actually represent though.  Headroom uses the yellow diffuse field curve which is supposed to be equal sound intensity from every direction.  The red is free field which assumes no reflections.

I agree that these simple curves do over simplify things but that's mostly because of the content they play since stereo =/= binaural.  I think the ID curve Tyll uses now is supposed to be a compromise between DF and FF since neither are all that close to listening to stereo music over speakers in any realistic environment.

I'd like to study this a little more in depth but almost all of the relevant papers are behind the AES paywall and the documentation for the official standards are quite expensive too.