I do like the tone of the mids on B&W speakers. They have a very sweat sound that is very special on female vocals. I do how ever find the mids a little unnatural.
I have had a hard time putting my finger on what the unnaturalness is but the problem seems to be in the upper most part of the mids.
B&W's use their 6 inch Kevlar midrange up to around 4 Khz. A driver this size starts to beam at 1 Khz. This means there is a roll off in the off axis sound field from 1 Khz to the point where the tweeter kicks in. B&W do not appear to use a waveguide on the tweeter so the tweeter dispersion is very wide and even when it kicks in.
So what doses this design choice mean?
In an anechoic space you hear only primary sound so it won't matter but in an average room you hear a combination of primary and reflected/reverberant sound (70% to 30% or as much as 30% to 70% depending on your setup/room size) - so it will matter. The discontinuity between the midrange and tweeter will place undue emphasis on the tweeter and a "scoop" in the midrange (lack of emphasis). There is also a school of thought that says the ears/brain are somehow able to tell when off axis reflected engery does not match on axis response...the effect is that the sound loses some of its "naturalness" but in return you get a "hi-fi" sound that is more detailed/precise with super tight imaging - you can observe this especially on acoustic guitar where string plucks which can seem over emphasized... and on male vocals which may seem too recessed compared to the bass and treble (whilst female vocalists may jump out at you).
Clearly, the benefits well outweigh the drawbacks for the many B&W fans around the world. The design is clealry a success and it certainly differentiates B&W sound from others.
I hope this helps...
