Possible Clues:

• Where to find the ends of 17-, 25-, 36- and 49-Across
• US composer’s endless ambition to produce close harmony
• Suitable music for the hairdressers' ball?
• With 65-Across, a cappella group, and what the starts of the answers to starred clues comprise
• Close harmony singing
• Fleet Street source of legendary piemeat, herbs or nuts filling roll
• Composer introduces brief entertainment: piano quartet music?
• Where people subject to cuts might be singing
• Establishment where the ends of 16-, 22-, 37- and 49-Across take place
• Sort of singing composer's bound to produce