TNAG-1613-FCO40-2221-Executive-Council-of-Hong-Kong-memoranda-and-minutes-of-meet-1987 — Page 226

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2.9 Step 9

2.9.1

Distance Attenuation and Summation of Noise Levels

General

In determining the distance from the source position to the NSR

(the plan distance or, where appropriate, the slant distance), blank

facades shall not be considered and the distance shall be determined to

the nearest NSR facade with windows, doors or other openings.

2.9.2

Procedure for Use with a Single Notional Source Position

If all items of PME are assumed to be located at a single

notional source position, the sound power levels obtained in Step 8 shall

be summed logarithmically in accordance with Table 4 to obtain a total

sound power level.

•

The distance between the notional source position and the NSR

shall be determined and the appropriate correction factor shall be

obtained from Table 5. This correction factor shall be subtracted from

the total sound power level to give the Predicted Noise Level (PNL) at

the NSR.

2.9.3

Procedure for Use with Actual Source Positions or a Combination

of Actual and Notional Source Positions

If in addition to a notional source position a number of actual

source positions are being used, or if only actual source positions are

being used, the distances between the actual source positions and the NSR

shall be dete. mined and the appropriate correction factors shall be

obtained from Table 5. These factors shall be subtracted from the

individual sound power levels for each item of PME to give the individual

sound pressure levels for each item of PME at the NSR.

Any combined sound pressure level from items of PME assumed to

be located at a notional source position shall be determined in

accordance with Section 2.9.1 and shall be added logarithmically to the

individual sound pressure levels from items of PME assumed to be at

actual source positions, in accordance with Table 4, to give the PNL at

the NSR.