Horses for courses

Posted on: Wednesday, September 5th, 2018

Once upon a time, in a far away land … wait, this is not a fairy tale, so let’s restart.

The encounter and exchange below did take place some years ago, when I was still reading engineering quite close to home (you see, whilst this anecdote qualifies for ‘once upon a time’, it is not about ‘a far away land’ …). During our sophomore year, we shared our electronics engineering classes with physics and engineering students from streams other than electrical. Some students were bored stiff, others lost and disinterested, and a few lapped up all that could be slurped from the lecture.

I recall an interesting exchange between a physics student (let’s call the student PT) and the lecturer, a seasoned electronics engineer who must surely have burnt his finger with a soldering iron once too many whilst inhaling the toxic rosin flavored lead-laden fumes from the melting solder. The subject was on audio amplifiers, the topic on which amplitude of the input signal would we need to get an output through a loudspeaker at a comfortable listening level of 5W in a typical sitting room of about 5 x 4 meters.

This is not a terribly complex computation, which, in any case, I will not bore you with. So, let’s say that the result we got was 0.7753421V which the lecturer rounded to 0.775V. The physics student, our PT, promptly questioned the rationale behind the rounding up.

The lecturer explained that whilst it’s true that shaving off numbers does introduce rounding errors, in practical terms, these will give rise to a marginal error which is insignificant. The amplifier will not sound any less loud.

Whilst physics does provide the ‘full’ answer which may carry many digits after the decimal point, engineering is all about the application of physics, which puts the real world aspect to the workings.

Having an input signal with an amplitude of 0.7753421V instead of 0.775V will not make the sound emanating from the loudspeaker any less than the 5W loudness aspired to.

‘It’s all about perspective. It’s horses for courses’, the lecturer conceded with a knowing smile, before exiting the lecture room.

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