## Calculation of average number of noise-induced awakenings

In this form you can fill in the average number of noise occurences during the night and
the noise levels (either Lmax or SEL; if you don't know the difference: if nothing is
specified you can assume Lmax is measured or calculated). If the noise is impuls like (shooting, hammering or the like), an impuls correction of 12 dB is applied. If a SEL-value is supplied, you have to add 12 dB to this value yourself.

Together with the number of awakenings the nighttime LAeq is calculated. The number may seem surprisingly low; it should be noted that only behavioural awakenings (button pressed) are taken into consideration. Sleep is extremely important for the organism, and is well protected. So awakenings are avoided at all cost. Other effects however (arousals, hearth beat increases, movements) occur in much greater numbers - and at lower levels. Look here for details on awakenings.
You could do this the other way around: specify the LAeq for an 8 hour night, and either
the Lmax OR the number of events to get the missing one. (Puzzled? Here is an example).

The same approach can be found at this
TNO-site. In addition a graphical representation of the relations is given.

**Example**
Suppose that during the night 10 trains are passing at a distance of 50 meter. The average
Lmax of trains at such distance could well reach 87 dB(A) (but this depends much on
speed and train type). As the normal insulation value is around 20 dB(A), this gives a
level of 87-20=67 dB(A) inside. So fill in:

"10" for the number of events;

"67" for the Lmax;

"click" on the rail-radio-button;

"click" on the Compute button!
The result is :

- a "SEL" (Sound Exposure level) of 71 dB(A)

- an LAeq (night) of 36 dB(A) inside

- an estimated 15 additional awakenings per year.

If you would like to know what it takes to go down to the limit of 25 dB(A), just push
"reset" and fill in 25 in the LAeq-box, push the rail button, and the result is a "worst
case" approximation, which gives the maximum number of awakenings possible within 25
dB(A); and that happens at 10 events (train passbys) per night. You can easily check that
all other combinations giving 25 dB(A) give lower number of awakenings.
*Page update 31 Dec 2004*