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# Measuring the Spatial Sound Level Decay

Let’s first consider a measurement in an empty room. Measurements are performed using an omnidirectional sound source located at least 3 m from the nearest wall according to ISO 14257. The measurement points are located at a distance from the sound source that is a multiple of 2 and 3 m; they are taken at a height of 1.2 to 1.5 m from the floor and must be located at least 3 m from the nearest wall.

Let’s first measure starting from the sound source: Write down the relevant sound level value for each point. When finished, turn the page and repeat those measurements going back to the sound source. If the same results are found at 2 and 3 m from the sound source, either you cheated or your luck is uncanny: Taking into account that the floor covering may not be reflective, that the sound source may not be as omnidirectional as advertised, and that the measurer is not that precise in his positioning, one should not be surprised to find discrepancies of up to 3 dB at those points.

Let’s now consider a measurement in a fully fitted room (e.g., an open-plan office). Measurements are performed using an omnidirectional sound source located at a workstation according to ISO 3382-3. The measurement points are located at a distance from the sound source that is a multiple of 2 and 3 m; they are taken at a height of 1.2 m from the floor. You will find out quite quickly that according to the positioning of the sound source with regards to its environment (e.g., screen, tablet, etc.), the results may differ.

Lesson Learned: Always note all the measurement conditions.

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