It happens all the time. One of the older members of the
household is getting a bit deaf and needs the TV sound turned well up. But then
it is too loud for everyone else. It’s worse at night when people go to bed but
one family member wants to watch the late-night movie – or whatever.
Fig.1(a): how the transmitter works. The left and right channel audio signals are converted to mono, amplified and fed to comparator stage IC5 where they are compared to a 90kHz triangle wave (the sampling signal). The resulting PWM signal then drives transistor Q1 to pulse a string of infrared (IR) LEDs.
Fig.1(b): at the receiver, the transmitted signal is picked up by an IR diode and the resulting current pulses converted to voltage pulses (and amplified) by IC1b & IC1a. This amplified pulse waveform is then fed through a limiter and filtered to recover the audio waveform. This is then fed via volume control VR1 to an audio output amplifier (IC4).
The problem can be even worse if you have a hearing aid because
it also tends to pick up extraneous noises – coughs, heater fans, a radio in
another room, toilets flushing, planes flying overhead, cars and trucks passing
in the street and people washing up the dishes, to list just a few
The real answer is to listen via headphones – preferably good
"surround your ears" muff-type headphones which not only deliver the wanted
sounds directly to your ears and hearing aid(s) but also cut back the competing
sounds at the same time. And if you pick the right kind of headphones with some
acoustic damping in the earmuffs, they don’t cause your hearing aid(s) to feed
back and whistle either.
The result is comfortable listening at a volume level that’s
right for you, where you can hear and understand everything that’s being