Possible Clues:

• Instrument found in small room by orchestra's leader
• It takes a bow at a musical performance
• Unlikely marching-band member
• Music-maker's old room at the front
• Small room at back of No 10
• Ma's forte
• Instrument's fifteenth compartment?
• Head of company introduces pound line — one takes a bow
• Pablo Casals's instrument
• Group ring music-maker