🔊 Attenuation of sound during propagation outdoors — CALCULATION method according to PN-ISO 9613-2

Environment PN-ISO 9613-2

Overview

STATUS (state of the PKN card on 22.09.2026). PN-ISO 9613-2:2002 is CURRENT — the card contains no withdrawal note and no "Replaced by" row. Publication 02-09-2002, technical body KT 115 (Environmental Noise), ICS 17.140.01. "Implements" field: ISO 9613-2:1996 [IDT]. A search of the PKN catalogue for the string "9613-2" returns this single edition — there is no newer Polish one.

A CURRENT NATIONAL STANDARD WHOSE INTERNATIONAL SOURCE HAS BEEN REPLACED. This is a situation that the PKN card does not show and has no obligation to show. In 2024 ISO issued a new part 2 — and changed its title: it was "General method of calculation", it is now "Engineering method for the prediction of sound pressure levels outdoors". The Polish standard implements the 1996 edition, i.e. a document twenty-eight years older than the international edition in force. For a laboratory this has a practical consequence: citing PN-ISO 9613-2:2002 is citing a CURRENT standard in the PN collection, but a result calculated according to it corresponds to the 1996 ISO edition. Checking the PKN card alone does not reveal this — the discrepancy can only be seen on the ISO side. WE HAVE NOT ESTABLISHED whether and when PKN intends to introduce the 2024 edition or what the substantive differences between the editions are; we did not have the text of the 2024 edition apart from a sample extract covering the clauses up to 7.1.

THIS IS A CALCULATION STANDARD, NOT A MEASUREMENT STANDARD — AND THIS DECIDES WHAT THE READER SHOULD LOOK FOR IN IT. The title says "method of calculation", and this is also how the scope in the text of the standard reads: an ENGINEERING method is given for calculating the attenuation of sound during propagation outdoors in order to PREDICT the levels of environmental noise at a distance from a variety of sources. The standard does not describe how to carry out a measurement — it describes how to calculate, from data on the source and the terrain, the level at a point where no measurement was made. Consequence for the accreditation scope: the methodologies standing next to this standard in the scopes are "Równoważny poziom dźwięku A" [equivalent continuous A-weighted sound level] and "Równoważny poziom dźwięku A dla czasu odniesienia T wyrażony wskaźnikami LAeqD i LAeqN (Z OBLICZEŃ)" [equivalent continuous A-weighted sound level for reference time T expressed by the indicators LAeqD and LAeqN (CALCULATED)]. Some laboratories mark this explicitly, some do not — and the difference is fundamental, because a calculated result and a measured result answer different questions.

WHAT ONE NEEDS TO KNOW TO CALCULATE AT ALL (from the text of the standard, clauses 4–6). The method requires knowledge of: the sound power of the source given in OCTAVE BANDS for the directions relevant to propagation, the geometry of the source and its surroundings, and the characteristics of the ground surface. If only the A-weighted sound power is known, the standard permits an estimate: the attenuation terms for the 500 Hz band may be used. This concession is given in the text as a NOTE, not as an equivalent procedure — and an entry on the method should not present it as a short cut.

FIVE ATTENUATION TERMS (equation 4 of the standard): A = A_div + A_atm + A_gr + A_bar + A_misc, where: • A_div — geometrical divergence, i.e. spherical spreading in the free field; the standard gives the formula A_div = [20 lg(d/d₀) + 11] dB, where d is the distance from the source in metres and d₀ = 1 m; • A_atm — atmospheric absorption; • A_gr — ground effect; • A_bar — barrier effect; • A_misc — miscellaneous effects: propagation through foliage, industrial sites and housing; described in Annex A. The standard describes the first four terms in the main part, the fifth in the annex.

THE CONDITIONS TO WHICH THE RESULT REFERS — AND WHY IT IS NOT AN "AVERAGE". The method predicts the equivalent continuous A-weighted sound pressure level UNDER CONDITIONS FAVOURABLE TO PROPAGATION from the source to the receiver: with wind blowing from the source to the receiver or — equivalently — with a well-developed moderate ground-based temperature inversion, such as commonly occurs at night. The standard also provides for a long-term average A-weighted level, but this is a separate quantity, calculated with the meteorological correction C_met. The result is therefore neither a "typical level" nor an "average" — it is the level under the conditions in which sound carries best. Giving the result without this reservation changes its meaning.

WHAT THE STANDARD DOES NOT COVER (from the scope, explicitly): it does not apply to sound from aircraft in flight or to blast waves from mining, military or similar operations. Nor does it cover inversion conditions over water surfaces, which may give levels HIGHER than those predicted by this method — this is a reservation about the direction of the error, and therefore important when assessing complaints.

HOW FAR THE AVAILABLE TEXT REACHES. We have a sample extract of the national edition of another country (SIST ISO 9613-2:1997, the counterpart of the same ISO 9613-2:1996) covering clauses 1–7.3.1: scope, normative references, definitions, source description, meteorological conditions, basic equations and the terms A_div, A_atm and the beginning of A_gr. We DO NOT HAVE clause 7.4 (barriers), clause 8 (meteorological correction C_met), CLAUSE 9 (accuracy of the method and limitations of its use in practice) or Annexes A and B. Everything this entry says about accuracy, barriers and the meteorological correction therefore comes from the scope and from the cross-references in the part we have — not from those clauses.

Method principle

For each source and each octave band, the sound pressure level at a distant point is calculated: the sum of five attenuation terms — geometrical divergence A_div, atmospheric absorption A_atm, ground effect A_gr, barrier A_bar and miscellaneous effects A_misc (foliage, industrial sites, housing) — is subtracted from the sound power level of the source. The results for the individual sources and bands are summed energetically, giving the equivalent continuous A-weighted sound level under conditions favourable to propagation. The long-term average level additionally requires the meteorological correction C_met.

Applications

• Prediction of industrial noise in the environment — calculations for permits and environmental impact assessments
• Noise maps and noise forecasts before an installation is built, when no measurement can be made
• Determination of the indicators LAeqD and LAeqN "calculated" listed in accreditation scopes
• Assessment of the effectiveness of noise barriers and other noise reduction measures
• Reading an accreditation scope in which a calculated value stands next to a noise measurement

Key parameters

Standard

Standard number

PN-ISO 9613-2:2002 (wersja polska; wprowadza ISO 9613-2:1996 [IDT])

Title (PL)

Akustyka — Tłumienie dźwięku podczas propagacji w przestrzeni otwartej — Ogólna metoda obliczania

Title (EN)

Acoustics — Attenuation of sound during propagation outdoors — Part 2: General method of calculation

Step-by-step procedure

1. Checking whether the method applies

   Establish whether the source and the situation fall within the scope: the method does not apply to aircraft in flight or to blast waves from mining and military activity. With propagation over water under inversion conditions, the actual levels may be HIGHER than those calculated.

2. Collecting data on the sources

   Collect the sound power levels in OCTAVE BANDS for the directions relevant to propagation. If only the A-weighted power is available, the standard permits an estimate using the attenuation terms for 500 Hz — state this in the report, because it is a concession, not an equivalent procedure.

3. Describing the terrain

   Describe the geometry of the source and its surroundings and the characteristics of the ground surface along the propagation path. The ground effect is a separate attenuation term and depends on the type of surface, not only on the distance.

4. Calculating the attenuation terms

   For each band, calculate A_div = [20 lg(d/d₀) + 11] dB and the other terms: A_atm, A_gr, A_bar and A_misc. NOTE: we did not have the clauses on barriers (7.4) and on the meteorological correction (8) — check the formulas in the standard itself.

5. Summing and expressing the result

   Sum the contributions of the individual sources and bands energetically. State that the result refers to CONDITIONS FAVOURABLE TO PROPAGATION (wind from the source to the receiver or a night-time inversion), not to typical conditions.

6. Marking the result as calculated

   In the report and in the accreditation scope, mark the calculated indicators with the annotation "(z obliczeń)" [calculated]. A calculated result and a measured one answer different questions and are not interchangeable — in a noise complaint it is usually the measurement that decides, in a forecast before construction the calculation.

7. Checking accuracy and limitations

   The standard describes the accuracy of the method and the limitations of its use in clause 9. We did not have this clause — check it in the standard before giving the uncertainty of a calculated result.

Required equipment and apparatus

Health and safety (OHS)

• A calculated result given without stating the propagation conditions is often read as a typical level — yet it is the level under the conditions most favourable to the spreading of sound
• The method does not cover propagation over water under inversion conditions, where the actual levels are sometimes HIGHER than those calculated; using it there underestimates the forecast
• A calculation made on the A-weighted power instead of octave bands is a concession in the standard, not an equivalent — without an annotation in the report the reader will not tell one from the other
• A calculated indicator must not be presented as a measurement result; in accreditation scopes the annotation "(z obliczeń)" [calculated] is used for this

Frequently asked questions