It was possible to connect the MIC or EAR connector (I don't remember exactly which one, as this was 40 years ago) to a cassette recorder and start recording, which caused the cassette recorder to amplify the Spectrum's sound.

And when I'm mentioning cassette recorder - I had a neighbour in my building who also had a Spectrum and whose window was some 12 meters away from my window and once we connected our computer with audio cables (MIC to EAR and vice versa) so one types some short program (or just REM message) and enters SAVE while the other one enters LOAD and gets the message. Our networking adventure started bad as it turned out that cable had large signal loss so it seemed that this brilliant idea failed but then we connected cassette recorders between computers that hugely amplified signal and thing actually worked.

Experiment ended when a party-line neighbor started complaining that his phone line was unusable for hours - we used phones as yelling through the window while trying to synchronize wasn't producing satisfactory results.

Fun times.