Meanwhile firm quashed one speaker’s system (8)
I believe the answer is:
intercom
'system' is the definition.
(I know that intercom is a type of communication system)
'meanwhile firm quashed one speaker's' is the wordplay.
I cannot quite understand how this works, but
'firm' could be 'co' (a firm is a company) and 'co' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for intercom that I've seen before include "Two-way speaking device" , "Speaker system" , "short range phone" , "communications system" , "Short-range telephone system" .)