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Effects of sound masking on workers - a case study in a land- scaped office

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Effects of sound masking on workers - a case study in a land- scaped office

Template 9th International Congress on Noise as a Public Health Problem (ICBEN) 2008, Foxwoods, CT
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Effects of sound masking on workers - a case study in a
landscaped office
Valtteri Hongisto
Finnish Institute of Occupational Health, Indoor Environment Laboratory, Turku, Finland,
valtteri.hongisto@ttl.fi
INTRODUCTION
Noise is the most disturbing factor of indoor environment in open offices
(Haapakangas et al. 2008a). Several independent laboratory experiments have
shown that noise, especially speech, reduces task performance of cognitively
demanding tasks. According to the model of Hongisto et al. (2008), task performance
reduces with increasing speech intelligibility. The room acoustic design of open
offices should, therefore, aim at the reduction of speech intelligibility between
workstations. This can be achieved by mainly by three factors: increasing room
absorption, increasing screen height and increasing masking sound level.
Appropriate masking is necessary to reach acceptable speech privacy between two
neighbouring workstations. Masking means that the stable background noise of the
office is raised controllably to minimize the intelligibility of nearby speech without
creating a new source of distraction. In Finland, the recommended level of masking is
40 to 45 dBA (SFS 5907). Optimum masking sound is smooth and unnoticeable, e.g.
ventilation noise. Sound pressure level and spectrum need to be considered to obtain
a balance between acoustic comfort and efficient masking performance. In many
cases, ventilation creates an appropriate masking. In large and high open offices,
constant occupant activities and babble can create an appropriate masking. But in
many cases, the creation of optimum masking requires an electronic audio system.
Masking was mentioned already in the early open office design guidelines (Hardy
1957). Masking was the presupposition of speech privacy also in the original
concepts of landscaped and open-plan offices in 1960's (Boje 1971). However, the
use of electronic masking has not become a common practice although the
importance of masking is emphasized in the acoustic design guidelines worldwide.
One reason may be that very few scientific experiments have been published in this
area and the results have been contradictory. Some studies are reviewed below.
Warnock (1973) conducted experiments with electronic masking sound levels 45 to
51 dBA. Occupants responded to simple feedback forms. The sample size was not
reported. They rejected each masking condition and preferred the situation without
electronic masking. Interviews revealed that their work was not distracted by intruding
speech sounds indicating no need to improve speech privacy. In addition, the original
sound level of ventilation was already at a recommended masking level, 40 to 45
dBA, producing nearly sufficient speech privacy and additional need for masking was
questionable on the whole. Although the setup of the study was interesting, the
methodological weaknesses of the experiment are obvious.
Keighley and Parkin (1979) tested different masking sounds, sound levels and
spectra. The experiment was carried out in a landscaped office of 40 workers.
Altogether 15 different masking conditions, with sound levels from 37 to 46 dBA,
were tested, 3 weeks each. Questions about of conversation difficulties, overall
acoustic satisfaction and acceptability were presented. None of the conditions were
found successful. Unfortunately, no masking sound was produced at and above 4
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kHz and very little also at 2 kHz. Therefore, the efficiency of masking in the
consonants area did not occur. Acoustic attenuation performance of the room was
not described so that the objective speech privacy remained unknown. The
measurement of perceived concentration difficulties, acoustic distraction and speech
privacy could have been very informative as well. The study has antiquated because
typewriters, which produced natural masking itself, are no longer used.
Lewis (2003) investigated the effect of masking system on 136 office workers.
Masking system reduced significantly subject's self-reported level of distraction and
their awareness of sounds. Suggestive evidence was found that performance was
improved after the change. Unfortunately, technical information of the masking
system, room acoustics and sound levels was not reported.
Helenius and Hongisto (2004) studied the effect of noise control on workers in an
open office. Noise control included the installation of masking system, added ceiling
absorption and some phone conversation rooms. Noise control improved the
perceived acoustic conditions. However, the influence of masking cannot be
separated.
Laboratory experiments have shown the benefits of masking for both acoustic
comfort and task performance, e.g. Venetjoki et al. (2006) and Haapakangas et al.
(2008b).
None of previous field studies have been able to combine room acoustic and
environmental psychological expertise to a robust longitudinal workplace experiment.
The aim of this pilot study was to investigate the effects of artificial masking sound at
44 dBA on workers in a small department of 15 workers. Room acoustic
measurements and occupant questionnaires were conducted before and after
launching the system.
MATERIALS AND METHODS
The experiment was carried out in the telephone exchange of an international Finnish
bank in Helsinki. More than 60 % of working time consisted of connecting the calls of
clients to correct person in the company. The workers had complained about acoustic
distractions from nearby speech and lack of confidential privacy during phone
conversations. The company was aware of the expected benefits of masking and
wanted to test the technology in this small department.
A total of 15 workers took part in the survey before and 13 after the installation of
masking. All subjects were female. 13 workers responded both before and after the
masking and the statistical analysis was made with these respondents. The response
rate was above 80 % both before and after the survey. Subjects were informed that
the masking system will be installed to reduce acoustic distractions. No
organizational changes took place during the test period.
The acoustic measurements were made to evaluate the objective speech privacy.
The measurements included the spatial attenuation of sound pressure level, SPL, of
normal effort speech and spatial decay of Speech Transmission Index, STI, which
decribes well the speech intelligibility, or inversely, speech privacy. Measurement
method is described by Hongisto et al. (2007).
The questionnaire method is described by Haapakangas et al. (2008a). Here, only
the most important findings were reported. The analysis was made using SPSS
software and Wilcoxon signed rank test.
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The floor area of the office was approximately 250 m
2
(Fig. 1a) including 20
permanent workstations. The room height was 3.3 m. The height of the screens was
1.4 m. Workstations were enclosed from 2 to 4 sides. Screens were weakly sound
absorbing (EN 11654 class E). The whole ceiling was covered with sound absorbing
material (class A). Three walls out of six were covered with the same material by 40
% of area. The floor was not sound-absorbing. Because room absorption was initially
exceptionally high and higher screens were not permitted, the remaining room
acoustic means was the installation of a masking system. It was recommended by
the research group because of low background noise level of ventilation, L
A,eq
=35 dB.
The sound masking system consisted of a central unit (sound generator, filter,
amplifier) and 21 loudspeakers, Fig. 2. The spectrum of noises is presented in Fig.
1b. The spectrum was a compromize between the suggestions of Veitch et al. (2002)
and the original spectrum of ventilation noise. The masking level was raised from 35
dB to 44 dB slowly to avoid complaints about sudden change, Fig. 3.
Sound pressure level [dB]
10
15
20
25
30
35
40
45
50
125 250 500 1000 2000 4000 8000
Octave band [Hz]
Average, before (35 dB)
Average, after (44 dB)
(a) (b)
Figure 1: (a) The layout of the office. The average distance between loudspeakers (balls) was 3
meters. (b) Spectrum of the background noise of ventilation (before) and masking system (after). The
average A-weighted sound pressure levels were 35 and 44 dB, respectively.
(a) (b)
Figure 2: (a) Central unit of masking system consisting of rack mounted signal generator and
amplifier. The filters of the signal generator were configured with PC. (b) One of the masking
loudspeakers installed above electric ceiling shelf. The cone is directed towards the ceiling to have
smoother spatial distribution of sound and to make aural localization of the loudspeaker more difficult.
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A-weighted sound pressure level [dB]
0
10
20
30
40
50
60
16 20 24 28 32 36 40 44 48 52 4 8 12
Week
2005
questionnaire
phase I
questionnaire
phase II
planning (16-22)
cable installation (23)
loudspeaker installation (23)
central unit finishing (26)
launching (26)
gradual increase of masking
2006
36 dBA
43 dBA
Figure 3: Time schedule of the experiment.
RESULTS
The results of room acoustic measurements are summarized in Table 1. The spatial
attenuation of the SPL of speech and spatial attenuation of STI are presented in Fig.
4. DL
2
expresses the reduction of SPL of speech per distance doubling. It did not
change because attenuation was not changed. Radius of distraction, r
d
, is the
distance where STI falls below 0.50. A significant improvement in objective speech
privacy occurred after the installation of masking system. The radius of distraction
reduced from 13 to 6 meters.
Noise and thermal conditions were the most disturbing indoor environment factors in
the office, Fig. 5. After the installation of masking system, noise disturbance declined
but the change was not statistically significant. Other indoor environmental factors
were also rated better. The change in thermal conditions and draught could be
explained by seasonal changes. Disturbance caused by lighting was reduced
significantly (p<.05). The reason for the unexpected change is unknown but it may
reflect general satisfaction to the improvement. However, satisfaction with work
environment as a whole and satisfaction with acoustic environment did not change
significantly.
Speech and human-borne sounds were the most disturbing sound sources, Fig. 6.
The distraction of most sound sources reduced but only the distraction of speech and
laughter was reduced significantly (p<.05). Disturbance caused by ventilation and
background hum, including masking, increased slightly but not significantly. It seems
that masking sound was noticed by some people but the loudness was not too high
to create a new source of distraction for most workers.
Before the masking, noises disturbed phone conversations, the primary task, the
most, Fig. 7. After the change, all types of work were less distracted by noise. The
change in the task "email, internet" was statistically significant (p<.05).
The use of coping methods altogether reduced significantly (p<.05, Table 2). After
the masking, these negative behavioural effects of noise were on a very low level.
The self-rated waste of working time due to noise halved after the installation of
masking. The change was not statistically significant, Table 3.
Noise-related symptoms were also inquired. Concentration difficulties did not change.
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Table 1: Summary of the room acoustic measurements. A-weighted SPL of speech at 4 m from the
speaker, L
p,S,4m
, spatial attenuation rate of A-weighted SPL of speech per distance doubling, DL
2
,
radius of distraction, r
D
, A-weighted background noise level, L
p,B
, and average reverberation time, T
20
,
in the range 125-8000 Hz.
L
p,S,4m
DL
2
r
D
L
p,B
T
20
[dBA] [dB] [m) [dBA] [s]
Before 51 6.0 13.2 35 0.3
After 51 6.0 6.2 44 0.3
A-weighted SPL [dB]
15
20
25
30
35
40
45
50
55
1 10 100
Distance from speaker [m]
speech, before & after
background, before
background, after
speech, desirable
DL
2
=6 dB
DL
2
=11 dB
Speech Transmission Index, STI
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 10 100
Distance from speaker [m]
before
after
r
D
=13 m
r
D
=6 m
Figure 4: (a) Spatial attenuation of the A-weighted SPL of speech. (b) Spatial reduction of STI.
1
2
3
4
5
draught
thermal conditions
dry or humid air
smellsnoise
lighting, glare
dust or dirt
Before
After
1 not at all
5 very much
(p<.05)
Figure 5: "How much have the following indoor environmental factors disturbed you at your work
station during the last month?" Mean values.
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1 2 3 4 5
Speech and laughted from neighboring
workstations
Ventilation, background hum
Telephone ringing tones
Movement in corridors, footsteps, doors, lift, clatter
Construction sounds
Computer noise
Road traffic noise
Sounds caused by work, e.g. keyboard strikes,
paper rustle
Common office equipment
Before
After
1 not at all
5 very much
p<.05
Figure 6: "How much do the following sounds disturb your concentration on your work at your work
station?" Mean values.
1 2 3 4 5
reading, studying
phone conversations
work-related conversations
email, internet
planning, creative work
counting
text processing, writing
practical organization, e.g. copying
Before
After
1 not at all
5 very much
p<.05
Figure 7. "How much do the sounds disturb the following types of work?" Mean values.
Table 2: "How often do you act in the following way to cope with your work because of the sounds in
your work environment?" Mean values. Scale: 1=never 5: very often.
Before After
discussed the noise problem with colleagues
3.4
2.5
made an even greater effort
3.1 2.5
tried to be quieter in the hope that others would
do the same 2.9 2.2
used a sign so that your colleagues avoid
disturbing you temporarily
2.4 2.2
made a proposal to the management to improve
the acoustic conditions
3.3 2.1
slowed down the pace to maintain concentration
and quality of work
2.5 2.1
interrupted your work or left your desk
1.7 1.8
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Table 3: "When you think about the effects of the sounds in your work environment, how many
minutes are wasted per day? Mean values and the corresponding percentage of daily working time.
[min] [%]
Before 14 3.2
After 6 1.4
GENERAL DISCUSSION
The need for further acoustic improvements became negligible because major
acoustic problems no longer existed after the installation of masking.
However, it is expected that even higher acoustic satisfaction would have been
obtained if the spatial attenuation had been increased together with masking so
much that DL
2
=11 dB would be reached (see dotted line in Figure 4). Now, DL
2
was
very low because of low screen height. Therefore, the acoustic conditions after the
installation of masking did not represent the best possible room acoustic situation.
No adverse effects of masking were reported by the workers. This contradicts with
previous studies, e.g. Warnock (1973) and Keighley and Parkin (1979) but agrees
with Helenius and Hongisto (2004) and Lewis et al. (2003).
The results showed several positive trends. Some of them were statistically almost
significant (p<.05). With a larger sample, many of positive trends found in this study
would have reached the statistical significance.
The study was carried out in a small department doing a specific job. Different results
might have observed in different kind of work. Regarding the noise sensitivity of job
types, this study agrees with the cross-sectional survey of Haapakangas et al.
(2008a), according to which verbal tasks and conversations are most distracted by
speech while routine work is not.
The background noise level was initially quite low. Therefore, the change in acoustic
privacy was reasonably large. If the change in background noise level would have
been smaller, the subjective responses would have been weaker as well. In general,
masking can be suggested only when the initial level is low, much below 40 dBA.
This study gives suggestive evidence that masking could be recommended in open
offices when acoustic complaints exist and initial background noise levels are low. It
is still expected that masking technology can be easily rejected because of emotional
grounds: everybody knows that noise is detrimental to health and comfort. The
increase of noise level is against this basic assumption and investment on additional
noise is not reasonable.
However, it must be emphasized that the SPL of recommended office masking is
very low, 42 to 45 dBA. This does not increase the average noise level during the
working day because the average noise levels in open offices are above 50 to 55
dBA because of speech and activities. Negative health effects are not expected to
take place because noise energy does not increase. On the contrary, this study gives
evidence that distractions reduce which imply that noise-related stress would reduce,
indicating positive rather than negative changes in well-being.
The need of future research is evident both in field and laboratory conditions.
Experiments in offices should include both team and individual office work, larger
number of respondents, different office sizes and different masking technologies.
Large-scale experiments are very difficult to carry out because of several practical
Template 9th International Congress on Noise as a Public Health Problem (ICBEN) 2008, Foxwoods, CT
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reasons. However, they are necessary to achieve scientific evidence about the
benefits and restrictions of masking. The methodology presented in this study seems
to work well in such interventions.
CONCLUSIONS
The effect of masking was experimented in a small open office of 13 respondents.
This pilot study gives suggestive evidence that masking can be recommended in
open offices when workers are dissatisfied with acoustic environment and the initial
background noise level is low. The current study restricted because of specific office
work and small sample size. Future experiments should include different types of
offices, job types, masking technologies and larger number of respondents.
ACKNOWLEDGEMENTS
This study was a part of national research programme MAKSI (Perceived and
modelled indoor environment) funded by Tekes, National Technology Agency,
Finnish Institute of Occupational Health and several participating companies. Thanks
are due to the company who let their premise at our disposal. Thanks belong to my
colleague Annu Haapakangas for giving comments to this manuscript.
REFERENCES
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July 21-25, Mashantucket, Connecticut, USA.
Haapakangas A, Haka M, Keskinen E, Hongisto V (2008b), Effect of speech intelligibility on task performance - an
experimental laboratory study, abstract submitted, 9th International Congress on Noise as a Public Health Problem (ICBEN)
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performance, Ergonomics 49(11) 1068– 1091.
... These experiments involved nearly similar sound masking spectra, which had a slope of −5 dB per octave doubling within 125 and 8,000 Hz (curve REF inFigure 1A). There are also some field studies where the effects of room acoustic refurbishments, such as sound masking, on employees' perceptions were investigated before and after the refurbishment (Warnock, 1973;Keighley and Parkin, 1979;Lewis et al., 2003;Helenius and Hongisto, 2004;Hongisto, 2008;Hongisto et al., 2012;Vassie and Richardson, 2017). These studies give quite contradicting impression on the perception of sound masking. ...
... The problem with masking off condition is also that it is not well-defined in scientific terms. In the office of our study, masking off condition would mean a level of 40 dB L Aeq (ventilation ofFigure 1) which is much higher than the masking off conditions in prior field studies (Helenius and Hongisto, 2004;Hongisto, 2008;Hongisto et al., 2012), or the silent conditions of laboratory experiments (Venetjoki et al., 2006;Haka et al., 2009;Haapakangas et al., 2011Haapakangas et al., , 2014). Therefore, the inclusion of masking off condition with a level of 40 dB might have led to misleading results. ...
... Our study is unique because careful field studies in this research area have not been published very much. A couple of field studies have investigated the change from the office without sound masking to an office with pseudo-random masking sound, such as P1a, using before-after design (Helenius and Hongisto, 2004;Hongisto, 2008;Hongisto et al., 2012). These studies gave some support for the use of pseudo-random masking sound when the SPL was approximately 43 dB L Aeq and the spectrum was close to −5 dB per octave doubling (seeFigure 1). ...
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The workplace environment is the most critical factor in keeping an employee satisfied in today's business world. Today's workplace is different, diverse, and constantly changing. Therefore, physical environment affects how employees in an organization interact, perform tasks, and be lead. Physical environment as an aspect of the work environment has directly affected the human sense and subtly changed interpersonal interactions and thus productivity. Ambient features in office environments, such as lighting, temperature, existence of windows, free air movement suggest that these elements of the physical environment influence employees' attitude, behaviours, satisfaction, performance and productivity. Therefore, the main purpose of this research is to study the two constructs and study the effect of physical work environment on employees' satisfaction and productivity in five-star hotels in Egypt, Hilton Hotels and Resorts. The target respondents of this study include back-of-the-house departments in Hilton hotels in Egypt as less care is given to them and more attention is given to front-of-the-house departments. A structured survey was distributed among twelve Hilton hotels in five main tourist areas; Cairo, Alexandria, South Sinai, Red Sea and Upper Egypt. The results of this study provide important evidence of the impact of the physical work environment on employees' satisfaction and productivity. This study links the physical work environment such as sound, lighting, colour, temperature, workspace, design, layout of equipment and tools with employees' satisfaction and productivity. The findings also revealed that the most satisfied and most productive employees at Hilton Hotels in Egypt are those who have the highest level of convenient physical work environment.
... P=.001that makes the second hypothesis (H2) is accepted. This result is in line with other authors and they said that: noise is the most disturbing factor of indoor environment in open offices (Haapakan, 2008). According to the model of Hongisto (2008) task performance reduces with increasing speech intelligibility. ...
Article
Full-text available
The workplace environment is the most critical factor in keeping an employee satisfied in today’s business world. Today’s workplace is different, diverse, and constantly changing. Therefore, physical environment affects how employees in an organization interact, perform tasks, and be lead. Physical environment as an aspect of the work environment has directly affected the human sense and subtly changed interpersonal interactions and thus productivity. Ambient features in office environments, such as lighting, temperature, existence of windows, free air movement suggest that these elements of the physical environment influence employees’ attitude, behaviours, satisfaction, performance and productivity. Therefore, the main purpose of this research is to study the two constructs and study the effect of physical work environment on employees’ satisfaction and productivity in five-star hotels in Egypt, Hilton Hotels and Resorts. The target respondents of this study include back-of-the-house departments in Hilton hotels in Egypt as less care is given to them and more attention is given to front-of-the-house departments. A structured survey was distributed among twelve Hilton hotels in five main tourist areas; Cairo, Alexandria, South Sinai, Red Sea and Upper Egypt. The results of this study provide important evidence of the impact of the physical work environment on employees’ satisfaction and productivity. This study links the physical work environment such as sound, lighting, colour, temperature, workspace, design, layout of equipment and tools with employees’ satisfaction and productivity. The findings also revealed that the most satisfied and most productive employees at Hilton Hotels in Egypt are those who have the highest level of convenient physical work environment.
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An important goal of both management scientists and human factors researchers is practical, objective measurement and comparison of changes in knowledge-worker productivity that result from proposed workplace improvements. But the cost of disrupting employees to measure their performance is often prohibitive when longitudinal field studies are used. Drawing on work done in the early 1980's the research team developed and administered a brief, standardized, web-based test that measures cognitive operations typical of knowledge work instead of actual workday tasks. The test was administered to 136 experienced knowledge workers in the Boston area using an experimental design with speech privacy technology (SPS) as the independent variable. The team collected data on subjects' performance with respect to speed, accuracy, retention and several self-reporting measures. The results of this short, web-based test are consistent with earlier longitudinal studies on the impact of speech privacy technology and demonstrate that knowledge worker productivity can be accurately and precisely modeled and measured in a non-disruptive manner using web-based, surrogate tasks in a manner that is useful to decision makers.
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A sound conditioning system was installed in a landscaped office accomodating 44 staff, where speech privacy was poor. Twelve different conditions of artificial background noise ranging from 36 dB(A) to 46 dB(A) were tested, each for a period of three weeks. The occupant's reactions were monitored at the end of each three-week test period by means of self-completion questionnaires. Eight conditions based on random noise were, on balance, considered acceptable, but were judged to be ineffective and were not considered by the occupants to give any overall improvement. Four conditions based on ``natural'' recorded noise were also tested, but two of these (office noise and seashore noise) were rejected as unacceptable and ineffective. None of the conditions tested was particularly successful. Such parameters as frequency spectrum and overall level appeared to have little influence, although acceptability and ease of conversation tended to decline with increase in level of the introduced sound. Now at the Institute of Sound and Vibration Research, University of Southampton, Southampton SO9 5NH, England.
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The aim of this study was to find out what are the effects of three different sound environments on performance of cognitive tasks of varying complexity. These three sound environments were 'speech', 'masked speech' and 'continuous noise'. They corresponded to poor, acceptable and perfect acoustical privacy in an open-plan office, respectively. The speech transmission indices were 0.00, 0.30 and 0.80, respectively. Sounds environments were presented at 48 dBA. The laboratory experiment on 36 subjects lasted for 4 h for each subject. Proofreading performance deteriorated in the 'speech' (p < 0.05) compared to the other two sound environments. Reading comprehension and computer-based tasks (simple and complex reaction time, subtraction, proposition, Stroop and vigilance) remained unaffected. Subjects assessed the 'speech' as the most disturbing, most disadvantageous and least pleasant environment (p < 0.01). 'Continuous noise' annoyed the least. Subjective arousal was highest in 'masked speech' and lowest in 'continuous noise' (p < 0.05). Performance in real open-plan offices could be improved by reducing speech intelligibility, e.g. by attenuating speech level and using an appropriate masking environment.
Acoustic classification of spaces in buildings. Finnish Standards Association
SFS 5907:en (2004) Acoustic classification of spaces in buildings. Finnish Standards Association, Helsinki, Finland, (in English).
The effect of acoustical improvement of an open-plan office on workers
  • R Helenius
  • V Hongisto
Helenius R, Hongisto V (2004), The effect of acoustical improvement of an open-plan office on workers, Proceedings of Inter-Noise 2004, paper 674, Aug 21-25, Prague, Czech Republik.