Audio
SPL — Sound Pressure Level
01 — Definition
The measurement of acoustic pressure, referenced to the threshold of hearing (20 μPa = 0 dB SPL). It doubles every +6 dB and halves with every doubling of distance. A few markers: 85 dBA over 8 h, the NIOSH recommended limit — recommended, not harmless; 94 dB SPL = 1 Pa = the standard microphone sensitivity reference; 120 dB = threshold of discomfort; 140 dB = threshold of pain.
02 — In the field
OSHA caps at 90 dBA over 8 hours; NIOSH recommends 85 dBA, much stricter, and most EU countries follow that model. Remember that your crew near the PA stacks always takes more dose than the audience.
04 — Sources
- Handbook for Sound Engineers, Ballou, 4e éd. 2008, p. 545 — 0 dB SPL = 20 µPa ; 94 dB SPL = 1 Pa, référence de sensibilité micro
- Ballou §47 — OSHA 90 dBA sur 8 h, NIOSH recommande 85 dBA