Think of a "U" as a graph, which is not an unreasonable analogy. Can you see the shape of the "U"? Are you sure? OK, .
Arguing for the sake of arguing, is not really proving your point, Beagle.
So, just as you stated that there is no such thing as a "V" shape, sonic Sig, you are also apparently unfamiliar with a "U" shape, as your description has indicated.
Lets then, inform you for the sake of future reference.
First, when describing a "V" shape, this does not mean that the mids are missing, it simply means that in the context of an overall freq balance, they are reduced. This manifests in many ways... including , "laid back mids", "recessed mids", ect.
Often this type of sound is reviewed as having more bass and treble, but the reality is, the mids are less balanced regarding the bass and treble,...
Now, to understand the essence of a "U" shape, is not to comprehend that the mids are there and the bass and treble are missing. But rather, the mids are the widest part of the sound, yet, not necessarily forward.
Audiophile headphones should have more of a "U" shape, then a "V", because Audiophile sound is foremost about the midrange.
Many audiophile headphones try to impress with treble, and many reviewers who are not really capable of reviewing on a professional level, will get all hot and excited about "treble response"....."treble detail"... But, that is not where audiophile sound is located. Audiophile sound is in the MIDRANGE, and if the mids are stellar, then you dont need to try to "fake audiophile" sound by blowing up the treble to give the impression that you are getting great detail.
If the midrange is great, then all the detail you can ever want, all the clarity you can ever hope to hear, is RIGHT THERE.