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Slaying Dragons #19 – The deciBel

Alexander Graham Bell was a multi-faceted individual with wide ranging interests. One of the earliest machines to fly in Canada was down to him, and he also pioneered the hydrofoil. In audio the level unit we use commemorates his name.

Bell’s wife, Mabel, was profoundly deaf and as a result could not hear herself speaking and had difficulty enunciating words the way a hearing person might. Bell tried to figure out ways of converting speech into some graphic form so that a deaf person could compare their own graphic with that of the speech of others and somehow alter what they said until it got closer.

To do that, Bell needed a microphone, and as he couldn’t buy one, he had to create his own. One day a pair of his transducers got connected together, and sound going in to one of them ended up coming out of the other. The telephone was born.

It was not long before telephone signals were being sent over longer and longer distances. Unsurprisingly the signals got weaker with distance and engineers sought to understand and quantify what was going on. If one considers a length of wire that happens to halve the received power, then connecting a further identical length would yield one quarter the power. In other words…

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© John Watkinson

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