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Measuring & Human Perception of Noise - for Sound Proof Windows London

Secondary Glazing for Noise Reduction Windows

Measuring Noise & the Benefits of Sound Proof Windows

Central London Typical Not Rush Hour Daytime Traffic Noise Seventy Four Decibels Secondary Glazing London

Here we explain how sound is measured and how we experience an increase in noise, which is important because a 40 dB increase may not sound like very much - but it is actually 16 times louder!

We also demonstrate how to achieve 80% noise reduction windows in a very typical situation, using patented soundproof glass in the secondary glazing.

For the purposes of measuring the noise pollution entering through a window or door - and the subsequent noise reduction after installing secondary glazing with soundproof glass - the decibel (dB) scale is used.

Decibels are used in different formats, the main being below:

  • Decibels - the scale used for all general noise - uses electronic filtering to represent what the average human ear will hear in response to different types, frequencies and volumes of noise
  • dB Rw - the sound insulation test result from a tested sample - Rw is the weighting of 16 separate frequencies against a reference curve to give the result as a single number.
  • Rw + Ctr - the scale used specifically for Road Traffic Noise - it is based upon the Rw testing with a pre-set scale added representing average traffic noise.

The decibel scales and the response of the human ear to noise are both logarithmic (curving lines) - rather than linear (straight lines).

The importance of this is:

  • A halving or doubling of the measured noise level - is not the same as - a halving or doubling of - the noise level that we actually perceive.

For this reason:

  • All measurements must be made against a Predetermined Starting Point.

Here are some simple “rule of thumb” formulae to guide us on what different measurements actually mean in practice to what we hear:

Human Perception of an Increased or Decreased Noise Level from a Predetermined Starting Point or Measurement

a 10 dB increase / decrease in the
measured level of noise
a doubling or halving of noise
a 20 dB increase / decrease in the
measured level of noise
the noise is 4 x louder / quieter
a 25 dB increase / decrease in the
measured level of noise
the noise is 6 x louder / quieter
a 30 dB increase / decrease in the
measured level of noise
the noise is 8 x louder / quieter
a 40 dB increase / decrease in the
measured level of noise
the noise is 16 x louder / quieter

Measuring the Noise Entering Through a Window

Working Example - With & Without Sound Proof Windows (London - Central)

You are overlooking a very busy road - the measured or estimated noise level is 75 dB

The primary window is made of wood with putty glazed 4mm float glass

The primary window when closed provides a 25 dB reduction in the noise - you still hear 50 dB of noise

So, with the window closed, our Predetermined Starting Point = 50 dB

You install our secondary glazing noise reduction windows, with 6.4mm laminated acoustic soundproof glass and a 100mm cavity

The primary window plus the secondary glazing now provide a combined 50 dB reduction in the noise as compared to the “open window” situation

You are now hearing a noise level of 25 dB

We have therefore achieved a Decrease in the Level of Noise of 25 dB from our Predetermined Starting Point of 50 dB

There are several ways that we can express this result:

In Acoustics, there is no absolute minimum and no absolute maximum. So, (and this is strange but true!) it would be correct to say that,
from our Predetermined Starting Point of 50 dB:

  • the level of noise that you experience has decreased by 600% - or - it is 6 times quieter

Or - to put it another way:

  • without the secondary glazing, the noise that you hear is 600% greater - or - it is 6 times louder

To express this in more straightforward terms, we need to refer back to our Predetermined Starting Point of 50 dB - from that starting point:

  • the level of noise that you hear has decreased by 25 dB - so it has been halved (10dB) and then halved again (another 10 dB) and then reduced by a further quarter (another 5 dB) - so that the level of noise that you experience has:
  • decreased by 81.25%

To see what this actually means in practise, please refer to What our Customers Say about the secondary glazing noise reduction windows that we have installed for them.

Noise Reduction Windows & Sound Proof Windows

As experts in Sound and Noise Insulation for over thirty years we know that this subject takes some time and concentration to get a full understanding!

If you do not have time for that right now - or would like a condensed version, then we invite you to download the following Shortcuts:

Noise & Sound Insulation Shortcuts:

Further information:

pdf Download our Secondary Glazing Brochure

Thank you for visiting - please Contact Us if we can be of any further help.