What is the sound reduction index?

There are two forms of sound insulation for domestic and commercial properties: airborne and impact. The former is used when sound emitted directly into the air is immediately insulated and is determined by using the sound reduction index. Impact sound insulation is used for floating floors and is determined by the sound pressure levels in the adjacent room beneath.

In this article, we’re going to focus more closely on the sound reduction index and why it is an accurate measure of the levels of sound insulation provided by a structure such as a window or door system.

The sound reduction index is expressed in decibels (dB) and is used only to describe the index for a single component or partition. Put simply, the index expresses the difference between the sound intensity hitting one side of a component or partition and the resulting sound measured on its other side.

The formula for deriving the sound reduction index of a single component or partition is as follows:

Sound reduction Index (R) = L1 – L2 + 10lg (S/A) dB

L1: average sound pressure level in the source room
L2: average sound pressure level in the receiving room
S: area of the test space (m²)
A: the equivalent sound absorption area of the receiving space

Another simple way to consider this formula is this example:

A high-performance window with a sound reduction index of 20dB should reduce a 60dB outside traffic noise level to 40dB within the next room.

Double glazed lift and slide doors, Essex

For single leaf structures, like a standard concrete wall, the transmission of sound generally follows the rule that, the bigger the structure, the less sound that’s transmitted. For structures with more than one layer, like a gypsum drywall for instance, the spring-mass law applies. If highly absorbent material is utilised as the spring in a double leaf wall, the levels of sound insulation will almost certainly improve. The larger the cavity between the layers, the more beneficial absorbent material such as stone wool can be.

It is very much the same with our high-performance aluminium window and door systems whose cavities tend to be filled with low conductivity gas (usually argon or krypton) to minimise both acoustic and heat transmission.
However, before deciding on the type of product to use to minimise sound absorption, it is a good idea to understand the difference sound reductions will actually make to your living areas. Privacy levels for each room in your home must be weighed up to reach an agreeable level of sound reduction through your walls, windows and doors.

Typical sound levels (dB) of human speech are:

• Normal, relaxed conversation – 60-65dB
• Loud speech – 65-75dB
• Persistent shouting – 80-85dB

At Livingwood, we manufacture all our Aluminium contemporary windows and doors from our own manufacturing centre in Bury St Edmunds, Suffolk. We can provide bespoke glazing specifications for projects at risk of noise pollution; whether it’s air traffic or proximity to busy roads. Acoustic glazing can protect homes and workplaces from this type of disturbance by minimising noise pollution and improving sound reduction indexes as a result.

This specification gets straight to work by minimising the energy of any given sound wave. It is important that the specification for your glazing features the right acoustic insulation properties according to the frequency or pitch of the external noise that must be blocked. Higher-pitched frequencies are easier to absorb, but reducing lower frequency noises such as traffic can be a little trickier.

Acoustic glazing specifications are essentially a sandwich of two or more sheets of glass which are bonded together using heat or pressure methods with polyvinyl butyral (PVB) interlayers. These are used to act as an additional barrier to dampen down the levels of noise transmitted through the glass into living and work spaces by weakening the energy of the sound waves.

The specification can be applied to window and door systems for use in both domestic and commercial buildings. Acoustic glazing not only offers sufficient insulation for impact and airborne noise, the laminated glass panes also provide heightened security and safety for your property.

Part E Building Regulations

It’s important to understand the Part E Building Regulations (2003) regarding minimum levels of acceptable sound performance in commercial buildings, as well as schools. Below is a list of the recommended maximum noise levels acceptable in various commercial environments:

• Offices – 40-45dB
• Larger offices – 45-50dB
• Classrooms – 40dB
• Music rooms – 30dB
• Large lecture rooms – 35dB

For bespoke aluminium window and door systems that not only meet your aesthetic needs but your sound absorption and reduction needs too, at Livingwood we offer double and triple-glazed window and door systems with acoustic glazing specifications to transform your unique project; giving you an abundance of natural daylight and a comfortable environment to savour.

For more information regarding our product range and to discuss your bespoke glazing requirements, please don’t hesitate to contact our friendly and experienced team today on 01284 764045 or drop us a line using our online contact form.