This is an example of calculations with a PA voice alarm system for an off-shore oil platform. The background noise is assumed to be 85 dB(A) with a pink noise spectrum, i.e. the same SPL in all octave bands. Even though speech is played back from the loudspeakers of the PA system, pink noise spectrum has to be assumed instead of the male speech spectrum. The reason is that this kind of loudspeaker has a very limited frequency range, and sound is mainly emitted in the three octave bands 500 – 2000 Hz. As a result the the frequency response of the speaker dominates over the frequency response of the speech. For security reasons there are two independent loudspeaker installations, and calculations has to be made for each of them and for both together. Only one of them is active in this example.
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