Sound-boosting boxes (4)

I think it could be either:

Which length description are you looking for?:

amps

(Other definitions for amps that I've seen before include "concert gear" , "Units of electrical power" , "'Units of electric current, in short (4)'" , "Basic units of electric current" , "Current measures" .)

I've seen this clue in the Newsday, the Newsday.com and the USA Today.

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