When A Premier League Ref Blows His Whistle............

[10ClarionSt]

..........right next to his mouthpiece, how does it not blast the ears off the other officials with headsets? Is there some kind of muffling or subduing device built in?

[-Talbot-]

I assume the 'mouthpiece' has to be manually turned on by the ref to speak to the other officials.

[Buenchico]

A simple AGC circuit in either the transmitter or the receiver (or both) would be all that's required to limit the maximum output volume to a safe level:
https://en.wikipedia.org/wiki/Automatic_gain_control

[-Talbot-]

They wouldn't want it on all the time, imagine listening to a bloke heavy breathing for 90 minutes :0/

[Hopkirk]

Ugh, no thanks.

A lady ref perhaps.

[Buenchico]

>>> I've often wondered if it would be possible to hack into the communications between the officials

Get yourself a scanner which can handle WFM (wideband frequency modulation) signals on 61.2, 61.7, 62.3 and 62.7MHz. Those are the frequencies made available to Premier League referees under PMSE (programme-making and special events) licences by OfCom.