Dont want to sound like an arse but there are alot of threads where people say BKP are a tad on the bright side. I've always thought the same thing, having owned 3 different sets of BKP - they sound great but they are fairly bright, but defined.
Is the brightness an achiles heel in BKP?
Only if you dont like bright pickups!
Its not a flaw, its a feature!
It kind of stands out because most humuckers are perfect humbuckers: equal number of winds on both coils, and most are machine wound so the sound lacks depth and comlexity, which includes the highs, of course.
I think all BKs have an offset, as philly says. This is where one coil is overwound. Its the number of turns that matters for hum cancelling, so if they arent equal then any turns left over on one coil will act as single coil turns. It takes rather a lot of offset to allow hum to set in, and somewhere in between there and no offset you get a more open, brighter tone by adding a tinge of SC to a HB.
Being a primarily metal player I want a heavy low end with a clear high end. BKP design allows a buttload of lows to exist in the same pickup as a clear and articulate high. Perhaps one mans clear is anothers bright, but I love it: they have a tremendous breadth of frequency response, lows and highs. I think people just arent used to that, from hearing stock, dumbcans and dumbarseios all the time.