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Dose is a measure of noise exposure similar to Lex. It is dependant on exchange and criterion levels. In the UK, where the criterion level is 90dBA, dose can best be described with the following statement:
100% Dose = 90dBA for 8 hours
Dose is related to exposure time and Lex. The following tables give examples of dose levels using different changing factors, a criterion level of 90dBA is used throughout.
Effects of Changing Lp
|
Lp (dBA) |
Exposure Time (Hours) |
DOSE (%) |
Lex (dBA) |
|
99 |
8 |
800 |
99 |
|
96 |
8 |
400 |
96 |
|
93 |
8 |
200 |
93 |
|
90 |
8 |
100 |
90 |
|
87 |
8 |
50 |
87 |
|
84 |
8 |
25 |
84 |
Effects of Changing Exposure Time
|
Lp (dBA) |
Exposure Time (Hours) |
DOSE (%) |
Lex (dBA) |
|
90 |
16 |
200 |
93 |
|
90 |
12 |
150 |
91.76 |
|
90 |
8 |
100 |
90 |
|
90 |
4 |
50 |
87 |
|
90 |
2 |
25 |
84 |
|
90 |
1 |
12.5 |
81 |
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, the dose will halve for the same exposure time.
Doubling the exposure time doubles the dose and halving the exposure time halves the dose, given the same sound level.
The operation of dose can be mathematically described by the following equation which relates the percentage exposure, D, to the integrated sound power.
Where
- † represents the anti-log
- 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)
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