a power amplifier and loudspeakers
an audio mixer and a tone control
microphones and pre-amplifiers
all the above stated systems
for large voltage amplification
for current amplification
to avoid loading effect of the signal source
for all the purposes stated above
wireless internal communication system
wired internal communication system
mobile communication system
video communication system
two separate microphones
two separate amplifiers
two separate speakers
all the above stated items
current amplifier
voltage amplifier
power amplifier
video amplifier