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Sound Reduction

What is sound?

‘Sound’ is vibration that travels in waves. These sound waves will ripple out in all directions from the source of the sound, much like water will ripple in all directions from the source of a splash. These waves of sound cause our eardrums to vibrate, and it is this vibration that is interpreted by our brain as ‘sound’.

Amplitude

The intensity of a sound wave is called its Amplitude and is measured in decibels (dB). It is this amplitude that determines the loudness of the sound. As a sound wave moves further from the source, its Amplitude diminishes and therefore so does its loudness.

Frequency

Frequency is the number of waves per second.
Higher frequency = more waves per second = shorter wavelengths.

We perceive frequency as pitch, with a higher frequency sound resulting in a higher-pitched noise, and a lower frequency sound resulting in a lower-pitched noise.

Why does it bother me so much?

Interestingly, the actual change in amplitude is not always equal to the perceived change in loudness. This is because sound perception varies from person to person, and relies on many factors such as the pitch of the noise, the source of the noise and how desensitised to a certain type of noise someone is.

FENSA has provided us with the following information, showing the relationship between actual amplitude change and perceived loudness change.

+ / – 3 dB = Just about noticeable
+ / – 5 dB = Clearly noticeable
+ / – 10 dB = Double / half the original volume.

For example, a ‘noisy street’ usually has an amplitude of around 75dB – 95dB, but let us assume that the street measures at an amplitude of 85dB. If the amplitude is actually reduced by 10 dB, so that the amplitude of sound is now 75 dB (the lower end of a ‘noisy street’), the loudness will be perceived as around 42.5 dB (less than standard conversation volume).

How can I reduce it?

Choosing double glazing in place of existing single glazing, or additionally upgrading to Acoustic Glass, can help to reduce the level of sound that enters your home. However, please bear in mind that replacement glazing will not reduce sound that is transmitted through walls, floors or ceilings.

How can Double Glazing help?

Whilst sound waves are capable of travelling through all states of matter (solid, liquid and gas), they travel far less efficiently through thicker solids. For this reason, increasing the amount of glass thickness that the sound waves have to pass through will reduce the level of sound that is able to enter your home through the windows.

Most single-glazed glass panes are 4mm in thickness, whilst a Double Glazed Unit (DGU) will have 2 panes of 4mm glass, thereby resulting in a total of 8mm of glass thickness. To this end, a DGU will have double (surprised?!) the amount of sound reduction capability from the glass alone vs. a single glazed pane.

Additionally, as mentioned earlier, as sound waves travel further from their source they lose Amplitude and therefore suffer a reduction in loudness. With regards to a DGU, there is an additional 12-16mm of Argon gas between the 2 panes. This ‘dead space’ serves to improve the thermal efficiency of a Double Glazed Unit (a full article on Thermal Efficiency can be found here) but larger gaps also serve to improve sound insulation; another advantage over single glazing.

What is ‘Acoustic Glass’?

‘Acoustic glass’ is effectively a standard DGU, but instead of having 2 glass panes, each at 4mm thickness, you have 1 glass pane of 6mm thickness, and 1 of 4mm thickness. The most obvious advantage of this is that you gain an additional 2mm of glass thickness to aid in sound reduction. However, the true benefit is much less obvious.

Different thicknesses of glass are more effective at reducing certain frequencies of sound. Simply put, this is to do with the wavelengths of different frequencies, and the distance the wave must travel in order to complete a full ‘wave’ (although the true science here is far too complicated for a window blog!).

Therefore, by including different glass panes of different thicknesses within the DGU, you are increasing the range of frequencies at which the unit can effectively reduce sound. This makes an Acoustic Glass DGU more effective at sound reduction than a standard DGU, which in turn is more effective at reducing sound than a single glazed window.

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