Sound system could have weird acoustics using leads (5)

I believe the answer is:

schwa

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'sound' is the definition.
(I know that schwa is a type of vowel)

I don't understand how the rest of the clue works.

(Other definitions for schwa that I've seen before include "sound unstressed" , "Uh' sound" , "Indistinct sound" , "Stress-free sound" , "Unstressed vowel (phonetics)" .)

I've seen this clue in The Independent.

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