How Do We Measure Noise

July 11th, 2018

It’s that old question, ‘when a tree falls in the forest, and there’s no one around to hear it, does it still make a sound?’ Baffler of generations, the simple answer is yes. Yes it does. The more complicated answer is no. No it does not.

Noise is the reception of pressure waves by a recording device or an instrument like your ears. If nothing is there to hear it, then there’s no sound being produced, just a pressure wave. Ok, so perhaps we’re becoming a little too esoteric here, but in our line of work it is interesting to consider how is created, received and processed, so that we can ensure the best noise reduction through our products.

One thing to consider is the power of the sound wave and how we quantify it. Our ears can hear the tinny whine of a mosquito passing by our ears at the same time as we can register a jet plane 30,000 feet over head.

This is because the pressure wave created by the plane’s engines is around 1 billion times more powerful than the former. Now, in order to make this an understandable figure, the decibel scale was created to simplify these huge figures into chunks we can understand.

Using the decibel system, the smallest audible sound is measured at 0 dB. Following this, a sound that registers at 10 dB is ten times more powerful. Consider this to be the sound of your breathing. Then a sound of 20 dB is 100 times more powerful than one of 0 dB.

The decibel scale is a logarithmic system. For every incremental factor of 10 dB, the power of the sound wave increases exponentially, by a multiple of ten. So it follows that at 30 dB, you are experiencing a noise that is 1,000 times more powerful than the smallest audible sound.

A simple way of understanding this is to look at examples of common noises and their place on the decibel scale.

  • 0 dB threshold of hearing
  • 10 dB barely audible breathing
  • 30 dB a whisper in a quiet space at 6”
  • 60 dB a normal conversation
  • 80 dB average city traffic
  • 88 dB trains at 25 ft
  • 105 dB a jet plane 100 ft overhead

What’s important to understand is that the leap between each of these examples is far greater than the previous. The difference between a whisper and a normal conversation is far smaller than the difference between a normal conversation and city traffic.

This becomes interesting to us when we consider how to implement noise reduction through our windows’ designs. Using a system that effectively dampens the pressure wave of the noise, we can create a 30 dB differential.

Think about it like this. If average city traffic noise when you’re on the street is around 80 dB, when stood behind one of our windows this is reduced down to around 55 dB – quieter than an average conversation.

So the answer to the question is, ‘if a tree falls in the forest and no one is around to hear it, does it still make a sound?’

Well the answer is no, not if you’re stood behind one of our noise reduction windows.

Photo by thewolf

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