OK, there seems to be a set of flats lovers here. I have two basses with flats on them (TI and some second hand ones with blue silks on them). The thud totally does it for me for when it is the right time, but there is something about the upper mids that really gets under my skin. I can wind that off with the tone control but even though that makes things warm and creamy by the speaker the sound can get a bit boomy or dark in the audience. Is there a flat that does not have that kind of grating top end or am I just being too fussy?