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The Making of a Sound Meter

Do you remember the first time you were asked to measure how noisy something was? If you do, you’ll more likely to remember pulling a sound level meter out of the tool crib. You may have skimmed through the manual, and twiddled a few knobs. You probably stared at an analog meter needle bouncing up and down, and I bet you whistled ... My first experience was just like this, as a young avionics engineer at the Learjet Company, I was asked to evaluate some cockpit noise levels. My visit to the tool crib brought me face-to-face with a pale green instrument that was a bit intimidating, if only by its size. It barely fit in my large hands, and definitely two hands were required. The sturdy instrument offered a tapered “top” to minimise reflections that may disturb the accuracy, and had only two knobs, making it easy to figure out. The top “range” knob was a clever double attenuator that allowed me to set the measured level to easily fall in the instruments massive 20 dB display range. It wasn’t long before the measurement was complete, with the stepped octave filter determining that the highest noise level was in the 500Hz octave frequency band, and loud enough, according to Beranek, to interfere easily with speech communication in the cockpit.