Just got the QP400 in.
I think this headphone will suit your needs much better.
Given you love the GMP 450 PRO except for the fact that it is indeed closed, the QP400 sounds perfect - the driver is identical, the clamping force is slightly greater, and the soundstage is quite large.
To be honest, it lost a little resolution and speed, but the open design really livens up the vocal ranges.
More on this as I A/B with more tracks.
My roomate and I plan on posting something, as mentioned before.
OK now, I believe to have started to understant the sound of the GMP better.
As I've said before, this is my first full sized headphone so they are "educating" my ears in a different way of IEMs... and in a better way I believe.
Recessed bass, brightness and other aspects that confused me at first are now a non issue because my ears were definitely biased.
The seal and the proximity of the driver to the ear canal of IEMs has to do with this, since that gives one a different perception of sound.
Stronger and more direct sound pressure level at the ear canal of IEMs provide smaller soundstage, stronger bass... a "closer" sound than the GMP.
I perceive the GMPs sound as naturally bigger and actually more well balanced and spacially realistic. Not only bass, but all the frequency spectrum is perceived as less upfront, more "laid back", distant. There's more air, breath and space on which the sound can develop. It's, in a way, a more "open" sound.
I say "in a way" because, despite the spacial perception improvement, I can still sense that the GMP is a closed headphone when comparing the "purity" of sound with IEMs.
Listening to a voice on IEMs for example gives me the feeling that the voice Is on a open space, with no phisical limits and with the GMP it's like the voice Is within a ressonant room. I think it irks slightly the excelent tonal accuracy of the GMP.
At first I confused the bigger, spacier and less "pure" sound/tone of the GMP with brightness but now I understand and like quite a lot what I'm hearing through this GMP 450 Pro.
It's, also, not a basslight headphone by any means, it has a much more realistic bass output than IEMs, just that. When the music demands the bass shows very appreciable weight and punch.
Don't get me wrong, it is a bright sounding headphone but not overly so as I thought.
I'm loving it with classical music, jazz, folk... actually any kind of acoustical music. This headphone is really marvelous with voices and instruments.
Now I'm fiinding that I, almost, can't go back to IEMs with this kind of music, but with some synthesized or electronic music I still prefer the presentation given by IEMs.(Let me note here that I'm refering mostly to my slighly modded Head Direct RE0 IEM, since it's the only one able to somehow keep up with the level of sound resolution of the GMP 450 Pro)
What has come up from my better understanding of this headphone sound, is that it is a very balanced and neutral sounding headphone. It's a fairly relaxing sounding headphone yet very engaging and athletic. Not as smooth as my Head Direct RE0, but more textured and slightly more detailed I believe. Great spacial resolution.
Very confortable headphone on the head indeed. A bit loose could use some more clamping force.
More listening still required though.
Will keep my eyes open for that thread R-Audiohead.
And looking forward on impressions of the QP 400 vs SP-1.