Is it correct to use speakers were amplifying their laughter? For example:
At the beginning Jack and Jill were just laughing between themselves. But five minutes later they came up to the counter and began to laugh into the cashier's microphone. Now all the speakers in that eatery were amplifying their laughter.
Given the normal relationship between "amplifiers" and "speakers", and the fact that people chatting and laughing may also be referred to as "speakers", I would avoid OP's particular combination.
Perhaps something more like Now all the loudspeakers in that eatery were broadcasting their laughter would be better.
