How Is Soundproofing Measured?

‘Soundproofing’ is the term given to the process by which an area, space or room is made less receptive to sound: it insulates the place against sound and is usually used to reduce unwanted noise.

To what extent a room or space has been made ‘soundproof’ depends on how much sound is able to get through the soundproofing materials used. As sound is measured in decibels, this is how the efficacy of soundproofing is also measured. ‘Decibel’ is a contraction of two words being ‘deci’ (one-tenth) and ‘bel’ being short for Alexander Graham Bell, who invented the telephone.

Decibels (dBs) are not actually units of sound: rather, they are a way of expressing the ratio between two levels of sound. Our ears perceive a vast range of decibels (about 120dB to be exact), which is roughly the difference between the quietest perceivable sound at about 0.000000000001 watts per meter square and the loudest sound we can hear without unbearable pain at about 1 watt per meter square.

Increasing the power (wattage) of a sound does not increase our perception of the sound in the same proportion: if one sound has double the number of decibels of a second sound, we would not hear that first sound as if it were twice as loud; in fact, we’d barely notice the difference. We would only usually perceive that a sound had become ‘twice as loud’ when the number of decibels had increased by 10.

It is probably easiest to understand how we perceive different levels of decibels by giving some common examples of noise and how many decibels of sound those examples typically make. So:


  • 0dB – the lowest threshold of hearing;
  • 20dB – a whisper;
  • 50 – 65dB – loud conversation;
  • 90 – 100dB – a train; thunder;
  • 115dB – rock concert;
  • 140dB – a plane taking off;
  • 180dB – a shuttle launch.


These are approximations of the level of dB perceived as different factors geluidsoverlast buren including how far away from the noise source a person is situated.

Long-term exposure to quite high levels of dB (upwards of around 65-75dB, such as living near a busy road or airport) can cause hearing loss. Even short-term exposure to high levels of noise (upwards of 85dB, such as through listening to loud music) can cause hearing loss. How much risk of hearing loss there is depends on the number of decibels perceived and the length of exposure.

In the UK, Codes of Practice affecting building works defines ‘reasonable’ internal noise as being up to 35dB-40dB and so noise insulation and other measures must be taken when building new properties to protect inhabitants against greater noise levels.

The effectiveness of soundproofing is measured by determining by how many decibels noise within the protected area has decreased: to what extent has the level of noise been reduced since an area was soundproofed? In some areas it is vital that all external noise is excluded: such as in an audiology suite at a hospital where hearing tests are undertaken. But for most people, soundproofing is used to reduce the level of noise to an acceptable level, where hearing is not damaged and noise is not perceived as a nuisance.