Noise – What is Dose and how is it calculated?

In acoustics, what is noise Dose, how is it calculatedĀ and what is it used for?

Noise Dose is a measure of noise exposure similar to Lep’d, and is shown as a percentage (sometimes named Percentage Dose). It is dependant on exchange and criterion levels. In the UK, where the criterion level is the Upper Action Level of 85dBA, dose can best be described with the following statement:

100% Noise Dose = 85dBA for 8 hours

It is related to exposure time and Lep’d. The following tables give examples of dose levels using different changing factors, a criterion level of 90dBA is used throughout.

Effects of Changing SPL

SPL Sound Pressure Level (dBA)Exposure Time (Hours)Noise Dose (%)Lep’d (dBA)
94880094
91840091
88820088
85810085
8285082
7982579

 

Effects of Changing Exposure Time

SPL Sound Pressure Level (dBA)Exposure Time (Hours)Noise Dose (%)Lep’d (dBA)
851620088
851215086.8
85810085
8545082
8522579
85112.576

Each time the sound level increases by 3dB (the exchange rate), the dose doubles given the same exposure time. Similarly, if the sound level decreases by 3dB, it will halve for the same exposure time.

Doubling the exposure time doubles the dose and halving the exposure time halves the it, given the same sound level.

The operation can be mathematically described by the following equation which relates the percentage exposure, D, to the integrated sound power.
Noise Dose Equation 2
Where

  • D = percentage exposure
  • Tc = criterion sound duration
  • T = measurement duration (in hours)
  • L = weighted sound level
  • Lc = criterion sound level

With respect to Lc, criterion levels of 90dBA and 85dBA are most often used. For discrete time intervals at a constant sound level the equation can be written as:
Noise Dose Equation
Where

  • time = exposure time, in hours
  • Q = exchange rate (typically 3dB)

Here are some Sound Meters which measure in Noise Dose:


Find out more about Noise Dose and measuring sound on our Noise at Work Regulations Competent Persons Course

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