Soulful singer King, American tenor, first part of harmony set lower (7)
I believe the answer is:
beneath
'set lower' is the definition.
'soulful singer king american tenor first part of harmony' is the wordplay.
'soulful singer king' becomes 'Ben E' (singer Ben E King).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'tenor first' becomes 't' (1st letter of 'tenor').
'part of' indicates taking the first letters (I've seen 'part' mean this).
The initial letter of 'harmony' is 'h'.
'bene'+'a'+'t'+'h'='BENEATH'
(Other definitions for beneath that I've seen before include "Unbefitting" , "Directly under" , "Inferior to" , "At a lower place" , "in a lower position" .)