Notes singers in the auditorium (7)
I believe the answer is:
tenners
'notes' is the definition.
(ten pound notes)
'singers in the auditorium' is the wordplay.
'singers' becomes 'tenors' (tenor is a singing voice).
'in the auditorium' shows a homophone (sound like) (ie as heard on a stage).
'tenors' sounds like 'TENNERS'.
(Other definitions for tenners that I've seen before include "Monetary notes" , "PS10 notes" .)