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AudioGLOSSARY

SPL — Sound Pressure Level

Definition

Sound pressure level (SPL) is the level of the acoustic pressure of a sound, expressed in dB relative to 20 µPa, the value taken as 0 dB SPL and as the nominal threshold of hearing. Doubling the pressure adds 6 dB. For a point source in free field, the level falls by 6 dB for each doubling of distance (inverse-square law). A level of 94 dB SPL corresponds to 1 Pa and is the reference used for microphone sensitivity. The threshold of discomfort is usually placed around 120 dB SPL and the threshold of pain around 140 dB SPL. Time-averaged exposure is measured with A weighting, in dB(A), and peaks or low-frequency content with C weighting, in dB(C).

In the field

Exposure limits differ by region. In the United States, OSHA sets a permissible exposure limit of 90 dBA over 8 hours with a 5 dB exchange rate, while NIOSH recommends 85 dBA over 8 hours with a 3 dB exchange rate. In the European Union, Directive 2003/10/EC sets action values of 80 and 85 dB(A) over 8 hours, with peaks of 135 and 137 dB(C), and a limit value of 87 dB(A) and 140 dB(C) that takes hearing protection into account; the United Kingdom applies the same values through the Control of Noise at Work Regulations 2005. These texts protect workers. For audiences, the French Decree 2017-1244 limits venues diffusing amplified sound to 102 dB(A) and 118 dB(C) over 15 minutes, or 94 dB(A) and 104 dB(C) for events aimed at children up to 6 years old. The WHO global standard for safe listening venues and events (2022) recommends no more than 100 dB LAeq over any 15 minutes. Technicians working close to the loudspeakers usually receive a higher dose than the audience.

Related lessons

Decibels and Distance Loss→Microphone Transducers→Amplification and Speakers→

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
  • OSHA, Occupational Noise Exposure (29 CFR 1910.95) : PEL 90 dBA sur 8 h, facteur d'échange 5 dB · osha.gov
  • NIOSH, Criteria for a Recommended Standard: Occupational Noise Exposure (1998) : REL 85 dBA sur 8 h, facteur d'échange 3 dB · nonoise.org
  • Directive 2003/10/CE, art. 3 : valeurs d'action 80/85 dB(A) et 135/137 dB(C), valeurs limites 87 dB(A) et 140 dB(C) avec protections · eur-lex.europa.eu
  • Décret n° 2017-1244 du 7 août 2017 : 102 dB(A) et 118 dB(C) sur 15 min ; 94 dB(A) et 104 dB(C) pour les enfants jusqu'à 6 ans · legifrance.gouv.fr
  • OMS, Global standard for safe listening venues and events (2022) : 100 dB LAeq sur 15 min · who.int
  • The Control of Noise at Work Regulations 2005 (SI 2005/1643), Royaume-Uni : transposition de la directive 2003/10/CE · legislation.gov.uk