# The Lawnmowers (Harmonization of Noise Emission Standards) Regulations 1992, Paragraph 3.6: Directivity index (DI)


The directivity index (DI), expressed in dB, to be adopted in applying this method is defined by the formula:
DI=LpAmax-LpAm+3 where:
LpAmax is the highest of the sound pressure levels recorded at the measuring points (see 6.4.2), calculated in accordance with 8.1.1 and corrected in accordance with the general principles laid down in 8.6.1, 8.6.3 and 8.6.4,
LpAm is the surface sound pressure level determined in accordance with 8.4,
3 is a conventional additive term.
In determining the values LpAmax and LpAm only the measuring points prescribed need to be taken into account.

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Source: https://www.legislation.gov.uk/uksi/1992/168/schedule/3/paragraph/3.6 (the official version)
Page: https://openlegislation.uk/lawnmowers-harmonization-of-noise-emission-standards-regulations-1992/schedule-3/paragraph-3.6
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.