Let’s go back to the unit of measurement – the Decibel

In the second of our new series of articles on soundproof doors we’re going to take another look at the unit that measures the loudness of a sound, namely the Decibel. We need to understand how this unit operates so that we can understand relative noise reduction.

The Decibel scale

The Decibel is a logarithmic unit, which expresses the ratio between two values of a physical quantity (commonly being power and intensity). The unit was originally named in honour of Alexander Graham Bell. Sound intensity follows an inverse square law from the source i.e. doubling the distance from a noise source reduced its intensity by a factor of four. On the scale, the smallest audible sound (near total silence) is set at 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence, however, is 20 dB, and a sound 1,000 times more powerful than near total silence is 30 dB.

Here are some common sounds and their decibel ratings:

Near total silence (threshold of normal hearing) – 0 dB
A whisper at 2 meters – 15 dB
A normal conversation at 1 meter – 60 dB
City traffic, from inside the vehicle – 85 dB
A lawnmower – 90 dB
A jack-hammer at 20 meters – 95 dB
A car horn – 110 dB
A rock concert or a jet engine – 120 dB
A gunshot or firecracker – 140 dB
Death of hearing tissue – 180 dB

Recommended noise levels

Below are recommended maximum noise levels for a variety of workspaces:

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Here are some sound reduction guidelines:

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So how do we measure the noise reduction?

Since the Decibel is a logarithmic unit, and the percentage scale is linear, a statement like “the soundproof door would reduce noise by N %” is meaningless. And to emphasise the point, the Decibel scale has no maximum value, so it’s impossible to calculate a percentage reduction anyway!

We use instead a ‘Weighted Sound Reduction Index’, Rw, which expresses the difference between the sound intensity hitting one side of a structure and the resulting sound measured on the other side, i.e. it rates the effectiveness of a soundproofing system or material. Increasing the Rw by 1 translates to a reduction of approximately 1db in noise level. Therefore, the higher the Rw the better the insulation provided by the soundproof door will be.

Follow this link for ratings for acoustic doors provided by Enfield Doors: Acoustic ratings

Contact the experts

There’s a lot to think about, and of course you want to get it right, so you’ll need to speak to the experts. Here at Enfield Doors we have been manufacturing soundproof doors for many years for numerous satisfied customers, and we’ll be able to give you pragmatic advice and answer any questions you may have.

Click here to visit our home page, here to go directly to our page on soundproof doors, or here to go straight to our contact page.

Alternatively, call us any time on 020 3199 5860 and we’ll be delighted to help you.