Accountant and diva regularly seen at concert halls (9)
I believe the answer is:
auditoria
'concert halls' is the definition.
(I've seen this before)
'accountant and diva regularly seen' is the wordplay.
'accountant' becomes 'auditor' (auditor is a kind of accountant).
'and' means one lot of letters go next to another.
'regularly seen' indicates alternate letters.
The alternate letters of 'diva' are 'ia'.
'auditor'+'ia'='AUDITORIA'
'at' is the link.
(Other definitions for auditoria that I've seen before include "Locations for houses" , "Theatres, concert halls" , "music halls" , "lecture theatres" , "Spaces for audiences" .)