Reasonable Noise Levels and how to measure them

Measuring Sound

Sound is measured as a pressure and is expressed in decibels (dB). 0dB is defined as the pressure level at the threshold of hearing and 120dB marks the onset of pain. The scale is logarithmic and an increase in Sound Pressure Level (SPL) of 10dBA approximates to a doubling in the loudness of the sound whereas a change of 3dBA is just about noticeable.

Our ear responds to loudness which is dependent both on the sound pressure level and the frequency of the sound. The ear is more responsive to higher frequencies and so these appear louder than a sound of lower frequency having the same sound pressure level. Measuring equipment can be weighted to mimic the ear's reaction and measurements are then defined as 'A' weighted or dBA.

Laboratory measurements can test the sound insulation capability of a material or building element over a range of frequencies from 100Hz to 3150Hz.  The average of these measurements is the Mean Sound Reduction Index (or Rm) and, when adjusted for the human ear’s response, it is termed Rw or the Weighted Sound Reduction index.

The ability of a material to absorb sound is assessed in the laboratory by taking measurements over a recognised range of frequencies between 100Hz and 3150Hz. The average of these measurements is expressed as Rm or the Mean Sound Reduction Index. When adjusted for the ear’s response to loudness it is termed Rw or Weighted Reduction Index and is expressed in dB.