PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Variability in the ISO 3382-3 metrics based on repeated acoustic
measurements in open-plan offices 1
Manuj YADAV2,3,4; Densil CABRERA2; James LOVE2; Jungsoo KIM2, Jonothan HOLMES2, Hugo
CALDWELL2 and Richard DE DEAR22
34The University of Sydney, Australia

HörTech gGmbH, Oldenburg, Germany

Carl von Ossietzky University, Oldenburg, Germany

ABSTRACTThis paper investigates variability in the key ISO 3382-3:2012 metrics based on two types of repeatedmeasurements in open-plan offices – Type1, where the same path over workstations was measured from
opposite ends, and Type2, where two different measurement paths were measured. Per metric, analyses
performed used (i) the range of observed values; and (ii) the observed values. Results from category (i)¨Type1, and 95% confidence intervals were 1.2 m(0.9,1.5) for rD; 0.8 dB(0.6,1.0) for D2,S; 1.2
analysis: തതതതതതതതതത
തതതതതതതതതത were between twice and thrice the respectivedB(0.8,1.5) for Lp,A,S,4 m; and 1.2 dB(0.7,1.7) for Lp,A,B. ¨Type2തതതതതതതതതത
values of ¨Type1. Results from category (ii) analysis: the reliability, based on intra-measurement correlation
coefficient, was fairly high for all metrics, except for Lp,A,S,4 m for Type2 repeats. The repeatability
limit/coefficient (r) was 2.5 m for rD; 1.7 dB for D2,S; 2.9 dB for Lp,A,S,4 m; and 3.0 dB for Lp,B, for Type1
repeats. The r values for Type2 repeats were substantially higher except for D2,S. Overall, most of the Type1
results seem reasonable considering repeats were conducted in complicated room acoustic environments,
while Type2 repeats needs larger sample sizes in future studies. Some recommendations are outlined for ISO
3382-3 vis-à-vis Type1 and Type2 repeats.
Keywords: Office acoustics, Measurement uncertainty

1. INTRODUCTION
ISO 3382-3:2012 (2) is the main international standard for measuring the room acoustics foropen-plan offices. The metrics within the standard include those that are based on speech soundpressure level (SPL Speech ) – the spatial decay rate of speech per distance doubling (D2,S), A-weighted
SPL of speech at a distance of 4 m (Lp,A,S,4,m); those based on spatial decay of the speech transmission
index (STI) – distraction distance (rD), privacy distance (rP), and STI at the nearest workstation; alongwith the A-weighted background noise level (Lp,A,B). Apart from Lp,A,B, the salient feature of these
metrics is that they characterize aspects of the spatial decay of speech over workstations within an
office. These metrics are calculated from room acoustic measurements over a more-or-less linear pathcomprising a set of measurement positions near workstations. ISO 3382-3 requires at least two
measurement paths per office. If only one measurement path is possible, then two measurements perpath are to be conducted with the source loudspeaker positioned on the opposite ends of the path (2).
This study considers the variability of the key ISO 3382-3 metrics – Lp,A,B, D2,S, Lp,A,S,4,m and rD – dueto repeated measurements in the same office (i) with two paths that traverse the same set ofworkstations, but using the source loudspeaker on the opposite ends of the path per measurement, and(ii) with different measurement paths (see section 2.3 for details).

2. METHODS
2.1 Room acoustic measurements
Acoustic measurements were made according to ISO 3382-3 (2) in 27 furnished, unoccupied
1

This research has previously been published in more detail as (1). Reprint of the copyrighted material forthis conference has been cleared by Elsevier under the license number 4596981407529 on May 27, 2019.

2445

offices in 8 buildings with fully operational heating, ventilation, and air conditioning. These offices
are either non-contiguous units within a larger floor plate, or single units that cover the entire floor.
The software used to generate, play, record, and analyze the signals was AARAE, which is a
MATLAB-hosted GUI-driven environment (3). The measurement signal used was an exponentiallyswept sinusoid (50 Hz - 20 kHz) of 30 s duration. The signal chain for the measurements included a
computer running AARAE, an audio interface (RME Fireface UFX, Haimhausen, Germany), an
amplifier (Brüel & Kjær Power Amplifier Type 2716-C, Nærum, Denmark), an omnidirectional
loudspeaker (Brüel & Kjær OmniSource Type 4295) with a known sound power output that wascalculated using ISO 3745 (4), omnidirectional microphones (Earthworks M30, Milford, USA), and a
preamplifier unit (RME OctaMic XTC). For each path, the measurement signal from the source
loudspeaker was recorded using between 5-8 microphones simultaneously, where the microphones
were located at receiver positions near workstations, as described in ISO 3382-3 (2). The number ofmicrophones used within a given office was always the same – determined by the floor plate of theoffice measured – whereas the number of microphones used between offices varied. Background noise
measurements were made at each microphone position for at least 60 s.
Overall, the measured offices included a reasonably wide variation in several relevant aspects, suchas the floor plate geometries (rectangular to curved on one or more sides), absorption profile (carpeted,timber, concrete) and areas (53-719 m2 ); the partitions between workstations (cubicle designs, single,
double, or no partitions); ceiling heights and shapes (most being flat and measuring 2.7-2.8 m, and 5
vaulted ceilings of heights between 4.1-7.6 m to their apex), and absorption profile (absorptive, hardceiling, or a combination of the two), density of workstations on the floor (4-24 workstations per 100
m2 ), etc. More details are presented in Table 1 in (1)2.2 Calculation of the ISO 3382-3 metrics
The sinusoidal sweep recordings from microphones per measurement path were used to derive the
SPLSpeech metrics, i.e., D2,S and Lp,A,S,4,m. Modulation transfer functions (MTFs) used for calculating
STI, and subsequently rD, used the male octave-band weights and redundancy factors [8]. Lp,A,B was
calculated as described in ISO 3382-3, from octave-band SPLs that represented spatially averaged
values for the microphones along a measurement path (2). In order to avoid potential problems withextrapolation, rD values were considered acceptable if they were within the range of the measured
physical distances extended by 10% on either end (5). Otherwise, in order to use the remaining offices,
the background noise was adjusted, with the same gain applied in all bands to all measurement lines ina given office, as described in (5). While not an ISO 3382-3 metric, in order to further characterize theoffices, spatially averaged and mid-frequency (average of 500 Hz and 1kHz octave-band values)
reverberation times (T30 ) were calculated from the impulse responses (12th order filters).
2.3 Repeated measurements in offices
Variability within the ISO 3382-3 metrics was considered for two types of repeated measurements:(i) Type1, where two measurements per path were conducted. Here, after conducting one
measurement with the loudspeaker on one end of the path, the other measurement was conducted either
by placing the loudspeaker on the opposite end, or by swapping the positions of the last microphone
and the loudspeaker from the previous measurement. All the paths in the 27 offices were measured
using Type1 repeated measurements, with 36 paths measured in total (Table 1).
(ii) Type2, where two measurement paths were measured within the same office (i.e., the sameacoustic zone). Type2 repeated measurements were only possible in a small subset of all offices
measured (7 in total; Table 1): these being the offices for which the allocated access times permitted
several repeated measurements. The idea here was to determine the variation in the ISO 3382-3
metrics (2) over two paths that can be considered as likely options to characterize the office overall.
These measurement paths included those that were on an adjacent row of workstations relative to thefirst path, or more-or-less linear paths that were at a small angle to the length of the office, or the main
measurement axis.
2.4 Measurement conditions
All the measurements were supervised and conducted by the first author, with assistance fromothers. Per office, the repeatability conditions included measurements conducted by the same operator
over a short time period, using the same method, and the same apparatus. Hence, given the constraintsof the definition of an ‘office’ (see sections 1, 2.1), the guidelines in ISO 5725 1-6 (6), especiallyregarding repeatability conditions, were followed as closely as possible.

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2.5 Statistical analyses
All the analyses were done within the software R [11], using the packages tidyverse (datamanagement and plots) [12], boot [13], robustbase [14], and robustlmm [15]. Robust statisticalmethods were used throughout to reduce the influence of outliers, which included robust linear
regression, and mixed-effects models; and using bootstrapping for calculating confidence intervals(CIs). In the following, wherever the use of bootstrapping is indicated, 10 5 bootstrap resamples (eachresample the size of the original data, and resampling with replacement) were generated, using thefunction boot, and the percentile CIs [18] calculated using the function boot.ci are reported; both
functions are from the package boot [13]. Broadly speaking, analyses were performed on the
difference between the largest and smallest observed values – the range – per metric, per Type1 andType2 repeated measurement, which are referred to as ¨Type1 and ¨Type2, respectively (section
2.5.1); and on the observed values of the metrics (section 2.5.2).
2.5.1 Analysis using ¨Type1 and ¨Type2
The summary statistics included the mean and bootstrapped CIs (68% and 95%) of ¨Type1 and¨Type2, where the mean values were calculated as,ଷ଺

1തതതതതതതതതത =¨Type1෍ οType1௜
36

(1)

௜ୀଵ
଻

1
തതതതതതതതതത
¨Type2 = ෍ οType2௝
7

(2)

௝ୀଵ

where i and j are the path, and office indices, respectively. Furthermore, for each metric, eachതതതതതതതത , Type2തതതതതതതത ) of their respective
οType1௜ and οType2௝ values were compared against the means (Type1௜௝
underlying observed values; the latter being indicative of the magnitude of the metric for the i-th, andj-th index, respectively. These comparisons were made using the corresponding effect sizes for robustଶlinear regression, i.e. R 2 values (referred to as ܴ¨amean
in the following) and its 95% CI; and thesignificance (using 95% CIs) of the regression slopes, calculated using the lmrob function in therobustbase package (7). Also, to determine the mutual relationship between the metrics for theirrespective ¨Type1 and ¨Type2 values, Kendall’s ߬ correlation coefficients, along with bootstrapped
95% CIs were used.
2.5.2 Analysis using observed values of metrics
An important consideration for repeated measurements is reliability, which can be quantified using
the intra-measurement correlation coefficient (ICC; generally known as intra-class correlation
coefficient) (8) for both Type1 and Type2 repeated measurements, using the following equation:
ICC =(ߪ஻ଶ )
ଶ
ሺɐଶB ) + (ߪௐ)(3)

The ICC (value between 0 and 1, presented alongside its 95% CI in the current study) in equation 3
quantifies reliability as the relationship between the magnitude of the measurement error in theଶ
observed values per metric (i.e., within-measurement variance, ߪௐ), and the inherent variability in the‘error-free’, or ‘true’ observed values of the repeated measurements per metric (i.e.,
between-measurement variance, ߪ஻ଶ ). The idea is that if the reliability is high (i.e., high ICC), then themeasurement errors are small in comparison to the true underlying variability between repeatedmeasurements. Conversely, if the reliability is low (i.e., low ICC), measurements are error-prone, andthe variability between repeated measurements could be predominantly due to the large underlying
measurement errors, rather than due to actual variability between observed values. The measurement
reliability was classified according to common criteria (9) as excellent (ICC > 0.75), fair to goodଶwere calculated by fitting a(ICC = 0.40–0.75) and poor (ICC    In equation 3, ߪ஻ଶ and ߪௐ
robust mixed-effects model per metric, using the rlmer function from the robustlmm package (10).
Each robust mixed-effects model, where the robustness corresponds to minimizing the contribution of
outlying values (10), comprised of the fixed-effect of the respective metric (e.g., rD), and therandom-effects due to the repeated measurements in the offices.
To express the repeatability, several values could be provided, which are nevertheless dependent on
the measurement error, i.e., within-measurement variability (8). These values include ߪௐ , ξ݇ × ߪௐ ,2447

where k is the number of repeated measurements made per path/office ((6), part 6) , and therepeatability coefficient (or, limit) r. The repeatability coefficient is calculated as:(4)‫ × ݂ = ݎ‬ξ݇ × ߪௐ
The term f in equation 4 depends on the probability level to be associated, and on the underlying
probability distribution (6). For an assumed normal distribution, and a probability level of 95%, thevalue of f is 1.96. Hence, for k = 2, the repeatability coefficient becomes ‫ = ݎ‬2.8ߪௐ , and the calculated
value represents the upper limit within which 95% of the future differences between the Type1
repeated measurements are expected to occur. Similarly, for Type2 measurements, k = 4, and ‫= ݎ‬
3.6ߪௐ ((6), part 6).
Table 1: Calculated ISO 3382-3 metrics and reverberation times for the all paths, where Type2
repeated measurements are highlighted in bold. The subscripts for the ISO 3382-3 metrics denote theindex of the repeated measurement. The symbols ‘*’ and ‘#’ identify ‘poor (or insufficient’) and ‘good’values respectively based on the criteria in Annex A (informative) of ISO 3382-3 (2).
Building (Office.Path)

T30,mid (s)Lp,A,B (dB)

rD(1) (m)rD(2) (m)A (1.1)

0.7

40.0

12.9*

A (2.2)

0.7

37.0

16.5*

B (3.3)0.4

45.0

B (4.4)0.4

B (5.5)C (6.6)D (7.7)D (8.8)

D2,S(2)

Lp,A,S,4 m(1) (dB)

Lp,A,S,4 m(2) (dB)

13.9*

5.1

4.4*

53.4*

54.0*

17.6*

4.8*

2.6*

51.3*

51.4*

9.4

9.7

6.2

5.0

48.3

46.5

45.0

9.9

6.9

5.0

5.8

49.1

46.4#

0.4

45.0

12.2*

8.9

4.3*

5.8

48.8

46.7#

1.2

41.0

9.2

7.0

3.7*

3.7*

51.7*

50.9*

0.7

41.0

8.3

9.2

4.8*

5.4

47.5#

48.0#

5.5

46.0#

46.2#

0.6

38.0

11.9*

11.0*

5.1

E (9.8)

0.5

46.0

7.0

7.7

4.0*

4.8*

53.8*

54.2*

E (10.10)

0.7

40.0

12.1*

9.7

5.0

4.1*

54.4*

51.6*

E (11.11)

0.6

43.0

10.3*

11.6*

4.2*

4.0*

53.2*

54.8*

F (12.12)

0.5

38.0

11.5*

11.0*

5.8

5.2

51.8*

50.3*

F (13.13)

0.5

44.0

8.7

7.9

5.0

5.4

49.0

49.2

F (14.14)

0.5

47.0

9.3

8.5

3.7*

3.0*

53.3*

53.0*

F (15.15)

0.4

54.0

8.7

9.4

3.6*

2.7*

56.0*

55.2*

F (16.16)

0.5

46.0

10.7*

9.1

5.5

3.8*

52.4*

49.0

F (17.17)

0.4

46.0

9.0

9.0

6.2

7.0#

50.7*

51.7*

G (18.18)

0.4

42.0

8.4

8.5

4.6*

4.6*

52.0*

52.4*

G (18.19)

0.4

42.0

8.5

7.6

4.0*

4.5*

52.2*

51.8*

G (18.20)

0.4

42.0

8.7

10.5*

4.7*

5.8

52.3*

54.3*

G (19.21)

0.4

48.0

6.8

6.4

4.8*

3.8*

52.7*

52.8*

G (20.22)

0.4

45.0

8.0

8.0

6.2

5.6

55.1*

53.3*

G (21.23)

0.4

44.0

7.1

6.9

4.9*

5.0

53.7*

53.6*

G (21.24)

0.4

44.0

5.1

7.3

4.3*

4.1*

52.6*

53.9*

G (21.25)

0.4

44.0

7.6

8.2

4.0*

3.1*

52.4*

53.4*

G (22.26)

0.4

44.0

11.8*

10.2*

5.7

5.4

53.8*

53.4*

G (22.27)

0.4

44.0

9.6

10.1*

4.8*

7.1#

51.4*

55.6*

G (23.28)

0.3

40.0

12.2*

11.5*

6.6

6.3

52.7*

52.3*

G (23.29)

0.3

40.0

13.1*

14.2*

5.3

5.8

51.1*

52.4*

G (24.30)

0.4

38.0

10.6*

10.3*

6.6

6.0

52.9*

52.8*

G (24.31)

0.4

38.0

11.4*

12.3*

6.4

5.4

52.9*

52.3*

H (25.32)

0.4

45.0

7.7

8.7

5.4

6.5

50.5*

52.4*

H (26.33)

0.4

40.0

11.5*

12.0*

8.7#

8.3

52.8*

52.3*

H (26.34)

0.4

40.0

8.8

9.7

6.9

6.9

47.3#

47.9#

H (27.35)

0.3

35.0

13.7*

12.0*

8.4#

7.3#

52.4*

48.7

9.7

7.0#

7.0#

54.1*

53.9*

H (27.36)

2448

D2,S(1)

0.3

35.0

8.9

3. RESULTS AND DISCUSSION
3.1 Acoustic summary of the repeated measurements in offices
The calculated acoustic metrics are presented in Table 1, where each row contains a path with a
Type1 repeated measurement, with Type2 repeated measurements in seven offices (18, 21, 22, 23, 24,
26, 27; Table 1). The current research (also published as (1)) presents the largest collection ofpaths/offices measured using the ISO 3382-3 method (Cabrera et al. (5) reported a subset of the current
results), and is the first one that reports on more than one Type2 repeated measurements (Haapakangas
et al. (11) reported results from repeated measurements in a single office described in Hongisto et al.
(12)). The R2 values for the linear regressions used to derive rD and D2,S (2) were fairly high: 0.94±0.05,
range: 0.75-1.00 ; and 0.95±0.04, range: 0.85-1.00, respectively. As seen in Table 1, not many
paths/offices measured are indicated to have ‘good’ acoustic conditions as per the calculated values ofthe metrics, including none for rD, whereas plenty had ‘poor’ or ‘insufficient’ acoustic conditions (2).
3.2

Variability in ¨Type1 and ¨Type2
Table 2: Results for analyses on ¨Type1 and ¨Type2 values, as described in section 2.5.1.
തതതതതതതതതതതതതതത
¨Type1or 2, bootstrapped 95%, andଶ, associated slope, and respective 95%
ܴο~mean

68% Cisbootstrapped CIs

rD (m)

1.17 (0.88,1.51), (1.02,1.33)<10-2 (10-5,0.15), 0.15 (-0.35,0.83)

D2,S (dB)

0.78 (0.59,0.98), (0.68,0.88)

0.11 (10-2,0.35), -0.38 (-0.70,0.01)

Lp,A,S,4 m (dB)

1.16 (0.82,1.53), (0.98,1.34)

0.15 (10-2,0.40), -0.40 (-0.89,0.03)

Lp,A,B (dB)

1.20 (0.72,1.73), (0.92,1.44)

0.21 (10-3,0.72), -2.13 (-3.97,1.05)

rD (m)

2.57 (1.79,3.42), (2.15,2.99)

0.21 (10-3,0.72), 0.83 (-0.12,2.69)

D2,S (dB)

1.36 (0.98,1.77), (1.16, 1.57)

0.50 (10-4,0.95), 1.60 (-0.95,3.48)

Lp,A,S,4 m (dB)

2.74 (1.33,4.27), (1.97, 3.49)

0.28 (10-4,0.71), -0.24 (-0.69,0.29)

Type of repeatedMetricmeasurement
Type1 (n = 36, except
for Lp,A,B , where n =13)Type2 (n = 7)

3.2.1 ¨Type1 results

Figure 1: οType1 for each path in Table 1, plotted against the office floor area, where the offices
are grouped according to their workstation densities.
ଶvalues in Table 2, except for rD, indicate some correlation between the οType1௜
All the ܴο~meanതതതതതതതതത values
values (i.e., difference per i-th path, per metric, in Table 2), and the corresponding οType1
௜(i.e., mean per i-th path, per metric in Table 1). However, the 95% CIs of their respective slopes
crossed zero, i.e., are non-significant. In other words, overall, οType1 values did not vary significantlyതതതതതതതതതത values (equation 1), which are basedwith the magnitude of the metric. With that in mind, the ¨Type1
on measurements conducted with the loudspeaker on either end of the same path are fairly large,
especially for both the SPLSpeech metrics (D2,S and Lp,A,S,4 m), and Lp,A,B (Table 2). However, the largeതതതതതതതതതത
¨Type1 value for Lp,A,B is perhaps less reliable due to the small sample size (n = 13). Hence, the effect¨Type1 for rD is arguably not that large (~1.2 m, Tableof Lp,A,B on rD is not attempted here; moreover, തതതതതതതതതത
2).
Furthermore, while there are no obvious global trends as seen in Figure 1, several paths had a large

2449

οType1 value for Lp,A,S,4 m, and to an extent D2,S, which implies that the direction of the measurement
along a path is likely to be important in some cases, and needs to be judiciously considered during ameasurement. In terms of mutual correlations between metrics for their respective οType1௜ values: οr D
was not significantly correlated to either ο D2,S ( ߬ = 0.07; (െ0.19, 0.30)), or to ο Lp,A,S,4 m ( ߬ =0.2; (െ0.02, 0.46)); however, οD2,S was significantly correlated to οLp,A,S,4 m (߬ = 0.32; (0.03, 0.54)).
The latter, although not surprising given the underlying overlap in the calculation of the SPLSpeech
metrics, is nonetheless noteworthy, and can be expressed as the following robust linear model:ο‫ܦ‬ଶ,S(οType1) = 0.33 + 0.31 × ο‫ܮ‬p,A,S,4 m(οType1)(5)
2
The R = 0.46, 95% CI: (0.16,0.79) for equation 5, and the 95% CIs for the intercept and slope are(0.12,0.50) and (0.16,0.47), respectively. Overall, it can be surmised that the SPLSpeech based
parameters seem more susceptible to a wide variation per Type1 repeats, and any averaging of thesevalues must be done with caution.
3.2.2 ¨Type2 results

Figure 2: The relationship between the οType1 and οType2 for the offices where both these typesof measurements were performed (see Table 1 and 2 for details about office and path numbers). The
points plotted depict the path numbers, with the dashed line depicting the line with slope of 1 andintercept of 0.
Due to the small sample size for οType2 (n = 7), the corresponding results in Table 2 are at best
considered preliminary/exploratory at this stage, and are not discussed here (although they are
discussed briefly in (1)). Nevertheless, as surmised in (1) and seen in Figure 2, there are several highvalues of οType1 and οType2 in the current dataset. Given the plethora of variations in office
topologies and the associated room acoustics variations, ISO 3382-3 perhaps needs to be very specificin what would constitute a repeated measurement that is not a Type1 repeat. Furthermore, there mightneed to be a threshold for tolerance of οType2 and perhaps also οType1, beyond which measurements
cannot be used to characterize an office. Determining just-noticeable differences, especially for rD,
might also be beneficial.
As an aside, a comment can be made about the ISO 3382-3 requirement of keeping the loudspeakerand measurement positions at least 2 m away from large reflective surfaces (2). This requirement,
which is of course important from a wave theoretical perspective, limits the use of ISO 3382-3 method
to mostly medium- to large-sized offices. The current finding of large οType2 (and the underlying
οType1) values provides a practice-based evidence in favour of ‘2 m rule’, which would otherwise bea confounding factor in critically assessing results related to the ISO 3382-3 method in the current, andin future studies.
3.3 Variability in the observed Type1 and Type2 values
Based on the discussion in section 3.2, where it was shown that the findings about Type2 repeatedmeasurements are at best exploratory, and require future studies, the focus in this section will be on
Type1 repeated measurements that have larger sample size.
3.3.1 Reliability
ICC values above 0.8 are generally considered between excellent (9) in terms of reliability, which
is applicable to all the metrics and both Types 1 and 2, as seen in Table 3, except for Lp,A,S,4 m for
Type2 repeats, which had low ICC, and hence, poor reliability (also non-significant). The latter2450

provides another perspective on the large οType2 values, as discussed in section 3.2.2, and reinforces
the need to further investigate, and define the scope of Type2 repeated measurements. Also note that
the Lp,A,B ICC results are based on thirteen samples, which can be considered a small sample from astatistical perspective. Overall, the high reliability of the ISO 3382-3 metrics implies that the current
findings are primarily addressing the true variability between the underlying values, with acceptablemeasurement errors – providing support for the critical assessment of the ISO 3382-3 measurement
method in the current, and similar studies in the future.
Table 3: Some reliability (intra-measurement correlation coefficient: ICC) and repeatability
metrics (within-measurement standard deviation: ࣌ࢃ ; and repeatability limit/coefficient: r) for both
Type1 and Type2 repeated measurements.
Type1 (n = 36, except for Lp,A,B , where n = 13)
MetricICC (95% CI)࣌ࢃrrD (m)

0.87 (0.77,0.93)

0.90

2.5

D2,S (dB)0.85 (0.73,0.92)

0.61

1.7

Lp,A,S,4 m (dB)0.82 (0.68,0.90)

1.04

2.9

Lp,A,B (dB)

0.97 (0.91, 0.99)

1.01

3.0

rD (m)

0.80 (0.55,0.95)

1.15

4.5

D2,S (dB)0.82 (0.56,0.96)

0.44

1.7

Lp,A,S,4 m (dB)

0.21 (-0.1, 0.71)

1.62

6.3

Type2 (n = 7)

3.3.2 Repeatability
Table 3, columns three and four, provide the relevant repeatability metrics. In general, the standard
deviations reported here do not seem unreasonably large, especially for r D. The only previous data inthis regard was provided by Haapakangas et al. (11), where the variability, expressed as the 68%
confidence interval in the ISO 3382-3 metrics, was estimated as ±1 dB for D2,S, ±1.5 dB for Lp,A,S,4,m,±1.5 m for rD, and ±1 dB Lp,A,B. These variability estimates were based on unpublished data about
repeated measurements within a single open-plan office (described in Hongisto et al. (12)), which issimilar in principle to the current Type2 repeats, although there is likely to be a difference in therespective methods (i.e., current and in Hongisto et. al. (12)), including the number of repeats. Besides
including two types of repeated measurements, the current research includes measurements withinseveral offices, which allows providing variability estimates that are generalizable to a wider range of
offices. Nevertheless, compared to Haapakangas et al. (11), the standard deviations in the current study(࣌ࢃ in Table 3) were smaller for D2,S (for both Type1 and Type2 repeats), for Lp,A,S,4,m (for Type1
repeats; Type2 unreliable), and for rD (for both Type1 and Type2 repeats); and was almost the same for
Lp,A,B (for Type1 repeats).
The repeatability coefficient/limit (r) per metric provides a more exhaustive, and moreover,standardized account of the variability within repeated measurements (section 2.5.2). As seen from r
values in Table 3, for 95% of the instances of Type1 repeats – for measurements by the same observerusing the current method, on the same path measured with loudspeakers on either end – the οType1 for
Lp,A,S,4 m is unlikely to be more than ~3 dB. Similar assessments can be made for the other metrics for
Type1 repeats, whereas the r values for Type2 repeats are fairly large, and are not recommended forany use other than informing future research in more offices, and with, moreover, a clearly-defined(perhaps standardized in ISO 3382-3) nature of Type2 repeated measurements.
Overall, the practical implications of the standard deviations, and repeatability limit/coefficients
reported here, and whether an appraisal from a theoretical/methodological perspective is required, areopen questions.

4. CONCLUSIONSThe current findings represent a substantial step towards quantifying the variability of the ISO
3382-3 metrics in open-plan offices under repeatability conditions. The summary statistics, andrepeatability values reported here may be considered reasonable for the most part, especially for rD;
the variability of the SPLSpeech metrics may need to be considered further from a practical perspective.
In this regard, the excellent reliability values reported here imply that future investigations with2451

repeated measurements are more likely to be studying the ‘true’ variability between ISO 3382-3
metrics in offices, with acceptable measurement error.
For the Type1 repeats, the results here provide reinforcement for the ISO 3382-3 requirement of atleast measuring a path from two opposite direction, if it is the only path being measured. Moreover, wehighly recommended that all paths be measured from both ends. For exceptionally large οType1
values, it would be apt to flag such cases while reporting/using the results, and ISO 3382-3 may benefit
from amendments to its reporting format (Figure 3/Table 2 in (2)) to highlight such cases, and perhaps
more crucially, include instructions/comments on the relevance and potential remedies to large
οType1 from a practitioner’s perspective. The practical applicability of Type2 results is currently
limited due to small sample size in this paper. However, the results here suggest potential updates tothe ISO 3382-3 methodology regarding latent issues in Type2, e.g., clarity in its specification, etc.
Ultimately, more work is needed to further strengthen ISO 3382-3 in relation to measurement
repeatability (from current and future findings based on (6)), other aspects of variability in repeatedmeasurements including reproducibility (based on (6)), and perhaps even uncertainty at various stages
in the methodology (based on (13), similar to (14)).

ACKNOWLEDGMENTS
This study was funded through the Australian Research Council’s Discovery Projects scheme(project DP160103978).

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