BS EN ISO 3382-3:2022 pdf free download – Acoustics – Measurement of room acoustic parameters Part 3: Open plan offices.
5.4 Background noise level
The background noise level is measured at each measurement position in octave bands rrom 1Z5 to 8 000 Hz. The average SPL of background noise at the measurement positions of the path is determined in octave bands. The average SPL is used in the determination of STI. The average A-weighted SPL of background noise at the measurement positions, LPAB and the related standard deviation are reported.
5.5 Speech transmission index
The STI shall be determined according to JEC 60268-16 for each measurement position. The OSS shall be used to produce the test sound. The indirect method shall be used where the modulation transfer functions between source and receiver are measured. The octave band weighting factors a (STI weighting factor) and (redundancy factor) for male gender shall be used. The reason of using male gender is that SPL for 125 Hz octave band is not available for female voice but both genders can be present in offices.
The STI values shall be adjusted for the influence of the background noise level in each position. The background noise level averaged over every measurement position of the measurement path shall be used instead of position-dependent background noise levels. Spatial variation of background noise level along the measurement path can increase direction-dependent differences of rD and this situation is avoided by taking the average over the measurement positions.
STIPA (speech transmission index for public address systems) shall not be used to replace STI measurements.
5.6 Comfort distance and distraction distance
This document defines two single-number quantities which both have a unit of meter: comfort distance and distraction distance.
Comfort distance describes the effect of spatial attenuation in the office without paying attention to speech privacy, background noise level, or sound masking. Comfort distance, r [m], is determined using Formula:
If Lp,A,s is below 45 dB at the first measurement position (the nearest workstation to the OSS), rc iS determined by extrapolation and it shall be stated to he smaller than the distance from the OSS to the first measurement position. This situation is possible in an open-plan office having very high ceiling, large sound absorption, and high screens between workstations. If LPAS is above 45 dB even in the remotest measurement position, rc is determined by extrapolation and it shall be stated to be larger than the distance from the OSS to the remotest measurement position. This situation is possible in a very reverberant open-plan office.
Distraction distance, rD [m], is a predictor of the objective speech privacy of the open-plan office. It considers both spatial attenuation and background noise level. The justification of rD is explained in Annex A. Distraction distance is determined by plotting the STI as a function of the linear distance to the OSS as shown in Figure 3b. All measurement positions are used for the regression line except the reference position at 1,0 m distance. According to Reference [12] rD is usually shorter than 16 m and it can be determined using interpolation.
If STI < 0,50 at the first measurement position (the nearest workstation to the OSS), rD is stated to be smaller than the distance from the OSS to the nearest measurement position. If STI > 0,50 even in the remotest measurement position, rD is reported to be larger than the distance from the OSS to the remotest measurement position. In both cases, the exact value of rD shall be determined using extrapolation.
5.7 Typical single-number values
Examples of typical single-number values are shown in Annex C.
6 Precision
Precision of the single-number values is described in Annex D.
7 Test report
The test report shall include the following information:
a) A statement that the measurements were made in conformity with this document, i.e.
ISO 3382-3:2022;
b) Address of the building and the location of the open-plan office in the building;
c) A sketch of the plan and furniture layout, with an indication of the acoustic zones, and their horizontal and vertical dimensions.