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A guide to sound insulation

A guide to sound insulation

Things to think about before you decide to sound proof your home

The noise starts slowly and then screams at you as high-powered motorcycles jet past your front door in their own version of the Isle of Man TT – only this time it’s at the end of your road. Road raging motorists hold down their horns to rebuke the old lady who has just pulled out in front of them on the mini-roundabout; and your existing windows shake and rattle with every passing lorry and bus.

No wonder then, that after air pollution, traffic noise is the single largest environmental problem facing Europe, causing more than 60,000 premature deaths each year, leading to high blood pressure, heart problems and the increased risk of a stroke or even diabetes.

So how do you sound proof your home to stop road and other nuisance noise including barking dogs and noisy neighbours from ruining your precious R&R time?

Well the first and most critical point, is that sound insulation is only ever as good as its weakest point. You can build thicker walls or stuff them with as much insulation as you want or invest in the latest sound insulating windows but in isolation they won’t deliver the results you’re looking for – they need to work together.

How does sound enter the home?

Sound is a form of energy that's produced when things vibrate. Imagine the banging of a drum. The energy radiates outward, away from the sound source, in this case the drum, making objects and the air vibrate until the energy reaches our ears.

Sound starts life at a source, travels through the air or objects and enters our ears, which in turn vibrate, turning that initial energy source into something that we hear. To insulate your home and stop noise you need to interrupt this sequence.

The challenge is that sound has a long-wave length and ‘bends’ (diffracts) around objects. This means two things: it will find its way through any gaps; and it will pass through solid objects retaining much of its original energy.

It also passes through different materials at different rates dependent on sound frequency. This complicates the process of sound proofing because a material that may be highly effective at eliminating a particular sound or frequency, for example a conversation, will not necessarily be effective at eliminating sound generated at a different frequency, for example the bass from a speaker.

How does sound insulation work?

Soundproofing works in three ways – or combination of them. The first is to stop the noise by adding mass to the structure to reflect sound. You’re effectively creating a very dense acoustically ‘dead’ surface, which doesn’t vibrate or does so less than other materials. This is called dampening.

The second is through absorption, where the sound is absorbed by a material preventing it passing through to the other side, for example wall insulation.

The third is to create a barrier between one structure and another, which stops the sound passing between them in the form of vibration, effectively creating a gap which the vibrations can’t ‘jump’.  This is called decoupling.

How is the performance of sound insulation measured?

The Sound Reduction Index (SRI) is the standard measurement for how effective a particular material is at reducing noise measured in decibels.

As an illustration, this would give two brick walls separated by a large air cavity an SRI of 60-75 dB. This compares to just 20-25db for a standard pane of glass. 

This is why standard double-glazed and triple-glazed windows may help a little, as long as seals and gaskets are tight, but they won’t reduce noise by much and which is why if you want to sound insulate your home, you need to choose windows and doors which feature specially designed acoustic glass.

Without getting too technical, it’s worth noting that the decibel is not a linear measurement but instead uses a logarithmic scale. This means that a 10dBsound pressure increase represents a perceived doubling of loudness. Another way to look at it is if you improve the sound insulation of your home by fitting acoustic glazing, you’re effectively halving the perceived loudness of nuisance noise.

How do soundproof windows and acoustic glass work?

Acoustic glass limits noise pollution through the deflection and dissipation of soundwaves. It does this through a combination of glass thickness, the use of acoustic interlayers and the space between the glass, the variables of which disrupt the soundwave.

In general, the rule is that denser materials are better at doing this so the thicker the glass the better but this also needs to be set at different thicknesses.

It’s why simply adding a third pane to a unit in a triple-glazed window will only have a limited impact in reducing noise – something which nor all window and door salespeople necessarily understand or always communicate effectively to the homeowner.

Sound passes through objects in a linear direction. Using different thickness of glass in combination means that units are more effective in disrupting and dissipating sound.

Acoustic glazing maximizes the effectiveness of this by combining not only different glass thickness but also specially developed PVB interlayers, which are applied to the glass during manufacture. These provide another layer at another thickness, dampening and absorbing sound, stopping it from passing from one side of the glass to the other.

The other advantage is that because these polyvinyl butyral layers are bonded to the glass they also provide an additional layer of security because even if glass is smashed, the PVB interlayer holds it together.

If thicker and more layers to disrupt soundwaves form the basic principle of sound proof glass window design, there are lots of different variables within it to address different types of noise.

As we’ve seen, sound travels at lots of different frequencies. This means that certain combinations of glass thickness and PVB interlayers will be more effective at soundproofing against some noises, than others. This means that if you want to insulate your home against road noise, you might select one combination of glass and PVB interlayer as opposed to another combination to block out a barking dog.

Soundproofing secondary glazing

If you can’t simply replace your existing windows with soundproof windows because you’re the owner of period property or live in a conservation area, you can still significantly improve the energy efficiency of your home and sound insulation, by installing secondary glazing.

Again, the same principles apply. Installing energy efficient secondary glazing won’t by default improve the soundproofing of your property, although in common with new energy efficient replacement double and triple glazed windows, better sealing may contribute to a small reduction in noise.

As we have seen, that requires specialist acoustic double and triple-glazing which can go a long way to reducing nuisance noise, delivering high level of sound insulation – but secondary glazing goes one better, cutting noise by up to 70 per cent.

It does this through absorption and dampening in the same way as acoustic double or triple glazed windows but also decoupling. This is because secondary glazing is, by definition, separate to, the external facing window.

Again, establishing right gap between primary and secondary glazing is important if you’re going to achieve optimum performance.

Most panes of glass used in single glazed windows, are around 4mm thick. If it’s pre-20th century, say an original sliding sash window, it might be as little as 3mm.  In this case, to maximize sound insulation, you need a space between secondary glazing and the original window of 150mm. If the original glass is 6mm thick, this can drop to 100mm.

The same principles that apply to sound proof windows, then also apply to secondary glazing; namely combination of different glass thickness and the use of special dampening PVB interlayers. 

Soundproof windows from KJM Group

We work with the UK’s leading glass suppliers and energy efficient IGU manufacturers to offer a range of high-performance energy saving windows and doors, including soundproof windows and noise reducing secondary glazing.

This includes Saint Gobain Planitherm, which combines high levels of acoustic performance with exceptional levels of energy efficiency in the Saint Gobain Planitherm Comfort and Comfort+ ranges.

These feature Saint Gobain Stadip Silence, a specially developed acoustic glass.  This uses a specially developed laminate interlayer, designed to suppress noise at the specific resonant frequency of glass, achieving an airborne sound insulation index value of 54dB

We can also supply a range of noise reducing acoustic energy efficient window units from Pilkington.

If you’re looking for help in planning your next home improvement, or simply want to talk about any of the points raised in this discussion, please don’t hesitate to contact me or a member of the team for more by calling 01264 359355 or emailing email sales@kjmgroup.co.uk



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