# 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) 94 8 800 94 91 8 400 91 88 8 200 88 85 8 100 85 82 8 50 82 79 8 25 79

### Effects of Changing Exposure Time

 SPL Sound Pressure Level (dBA) Exposure Time (Hours) Noise Dose (%) Lep’d (dBA) 85 16 200 88 85 12 150 86.8 85 8 100 85 85 4 50 82 85 2 25 79 85 1 12.5 76

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. 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: Where

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