Loud group, on reflection, needed gripping finale for concert (9)

I believe the answer is:

bombastic

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'loud' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for bombastic that I've seen before include "affected" , "Extravagant" , "Pompous -- inflated" , "High-flown" , "Pretentious" .)

I've seen this clue in The Daily Express.

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