since joe grado is not making phones any longer....is there a currently made headphone that would be considered neutral by the same group who determined the hp1000 is neutral?  I'm not suggesting it is the senn800 but there seem to be alot of folks who feel it is the essence of neutral.

btw, the graph of the hp1000 here on this site is not flat, and rhythmdevils says that flat = neutral and the hp1000 is it? I'm still not following....

Only way for a headphone to be completely neutral... measure his personal HRTF with a dead flat speaker inside a anechoic chamber, then compensate a given headphone's response accordingly...

I would disagree. My own experience has told me that our brain already does a great job of filtering out HTRF effects. I think that any headphone that could replicate the performance of the reference speaker would get close to perfection. The only advantage that the Realizer provides is being able to account for time delay and aural-localization (inherent to the shape and size of a user head) that headphones cannot attain by conventional design. To that end, what the Realizer guarantees is natural sound-stage, not neutral FR.

Please do take the time to correct me if I am missing something.

RD, you're mising missing the point of  HRTF in headphones. It's only relevant due to the proximity of the transducer to the ear and the chamber that forms between them, it has nothing to do with how our brains adapt early on on life or how we hear real life. It's just the way sound waves behave and how physics work.

Angle of the sound to the ears is why HRTF is important... not just proximity. A flat FR speaker doesn't measure flat if measured with a mic inside your ears for instance. Then the same flat FR speaker will also measure different using the same mic measured while in my ears.

Neutral in audio terms is too tricky for me to describe. I can't trust my brain on this so I just go with what I prefer. Therefore I stopped looking for the next best thing and stuck to my favourite headphones.

"I don't trust my brain to know flat so I trust my brain to have preferences."

For me there are two approaches to find out what neutral really is: science or exposing yourself to live performances and taking a walk through the park every now and then.

The tricky part about live performances is that they're venue and recording dependent though. (You need a recording to compare the reproduction to the original. Preferably on the spot, when the memory is fresh. It pays to make friends with a good sound engineer.