Constant of the people to accept sopranos in such music? (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

C (constant: the speed of light in a vacuum, or a generic label for a constant) + LAICAL (of the people, as distinct from the clergy), containing (to accept) SS (two S = abbreviation for soprano in musical notation). A genre of music, which may or may not include sopranos or indeed any singers.