ISO/TS 9241-620:2023

TECHNICAL ISO/TS
SPECIFICATION 9241-620
First edition
2023-07
Ergonomics of human-system
interaction —
Part 620:
The role of sound for users of
interactive systems
Ergonomie de l'interaction homme-système —
Partie 620: Rôle du son pour les utilisateurs de systèmes interactifs
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sound and noise . 3
4.1 How sound and noise impact users . 3
4.2 Types of sound events . 4
4.3 Interference with the task . 5
4.4 Lombard effect . 8
4.5 Irrelevant speech effect (ISE) . 9
4.6 The importance of the concept of T-O-P. 9
5 Measures to control the impact of sound events .10
5.1 Overview . 10
5.2 Controlling sound and noise . 10
5.2.1 General . 10
5.2.2 Reducing the rating level . 11
5.2.3 Reverberation time . 15
5.3 Optimizing signal-to-noise ratio . 15
5.3.1 General .15
5.3.2 Transmission paths for the voice in use environments . 17
5.3.3 How the communication is affected by unwanted sound . 18
5.3.4 How to improve the intelligibility of speech . 20
5.4 Sound reduction within use environments or immediate environments of
workstations. 22
5.5 User involvement . 23
Annex A (informative) Example of a user survey questionnaire .24
Bibliography .25
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium
such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves
and their perception by the brain. Unwanted sound is referred to as noise and is often perceived as the
most serious disturbance factor at office workstations. In many industrial environments, sound can be
a serious threat to health in general, not limited to auditory effects alone.
While sound is a measurable physical reality, acoustic noise is a psychoacoustical concept. The main
goal of this document is minimizing the impact of noise while operating interactive systems, for example
on the behaviour of users, their well-being and/or performance. This can be accomplished by technical
measures, organizational means, interventions at the personal level and any combinations thereof.
The overall concept T-O-P (technical – organizational – personal) indicates the reasonable order
of measures that can be taken to control the impact of the acoustic environment on human work. In
this context, technical solutions have priority over organizational measures and personal protective
equipment (PPE).
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and
audiology – how humans perceive various sounds. More specifically, it is the branch of science studying
the psychological responses associated with sound (including noise, speech and music). This document
deals with the undesired effects of sound, which can be classified as follows:
— impaired hearing;
— undesired responses of the central and autonomic nervous system;
— hindrance of verbal and other communication;
— reduced performance and cognitive functioning;
— annoyance.
Acoustic satisfaction of a space cannot be guaranteed without consideration of each of the three
principle parameters of architectural acoustic design, formalized and established in the early 1900s
[28]
by Sabine. The three principle parameters are known as the ‘ABCs’ of architectural acoustics: A for
absorption – Sufficient absorption in the built environment; B for blocking – Sufficient isolation of the
built environment; and C for control – Control of sound levels in the built environment. For a given
space, various measures in combinations can be taken to control the acoustic environment to achieve
satisfaction. In ISO 9241-6 such measures are briefly listed and partly explained. Experience now
suggests that a more thorough consideration of the acoustic environment is required because of the
changes to work organization and tasks.
Controlling the acoustic environment is considered part of the T-O-P concept. It can comprise, for
example:
— reducing the rating level
— insulation in structural components;
— reducing noise emission from equipment;
— increasing sound absorption;
v
— reducing the ambient noise level;
— optimizing the signal-to-noise ratio
— reducing the sound level in speech frequencies;
— sound reduction within use environments
— sound-absorbing ceilings;
— partitions;
— adequate distances between workstations;
— reducing reverberation.
While all these measures are of a technical nature (T of the T-O-P principle, Figure 1), the impact of
sound events on persons and work can require organizational measures, such as holding small meetings
dedicated to certain tasks outside the workspace. The final argument comprises measures at a personal
level, including training to cope with adverse environments.
Figure 1 — T-O-P principle for controlling the impact of the acoustic environment on human
work
vi
TECHNICAL SPECIFICATION ISO/TS 9241-620:2023(E)
Ergonomics of human-system interaction —
Part 620:
The role of sound for users of interactive systems
1 Scope
This document provides users with a summary of the existing knowledge about ergonomics
considerations for the influence of sound in use environments on humans. It describes how unwanted
effects of sound (noise) can be controlled. The main goals for controlling the acoustic use environment
are reducing the rating level of sound in general, optimizing signal-to-noise ratio and sound reduction
within the workspace.
This document also provides users with organizational measures that can be taken if and when
technical measures do not help sufficiently. Also included are measures on a personal level.
This document deals with sound events that can cause extra-aural effects. Noise-induced hearing loss
prevention and the ways to eliminate or reduce hazardous noise exposure are not covered by this
document.
The intended users of this document include:
— developers of systems, products and services;
— public and corporate purchasers;
— occupational health and safety professionals;
— architects and interior designers;
— human resource professionals;
— usability, ergonomics or human factors professionals;
— users of interactive systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
irrelevant speech effect
ISE
negative effect of verbal sound level
3.2
rating level
L
AR
equivalent continuous A-weighted sound pressure level during a specified time interval plus adjustment
for tonal character and impulsiveness
Note 1 to entry: ΔLT = 0 dB or 5 dB according to subjective assessments
where
Δ is difference;
L is level;
T is tonal.
Note 2 to entry: Impulsiveness is specified only if the difference of the measured sound level with and without
impulses exceeds 2 dB.
[SOURCE: ISO 9241-6:1999, 3.19, modified — Notes to entry replaced.]
3.3
background noise level
L
p,B
A-weighted sound pressure level present at the workstation during working hours with people absent
Note 1 to entry: The A-weighted background noise level L is expressed in dB.
p,B
3.4
total noise sound pressure level
L
NA
sound pressure level that contains all noise components affecting the listener during use, such as noise
generated by building systems, operating equipment or the audience, and which is determined at ear
height for the area in which people are normally located
Note 1 to entry: The A-weighted total noise sound pressure level L is expressed in decibels.
NA
Note 2 to entry: If not otherwise specified, noise is determined according to DIN 45641 as the A-weighted
equivalent continuous sound pressure level averaged over the time that is representative for the disturbance.
3.5
impulsive sound
sound with a rapid rise and decay of sound pressure level, lasting less than one second and causing an
increase in the sound level of at least 6 dB(A)
3.6
reverberation time
T
time required for the sound pressure level in a room to decay by 60 dB once sound excitation has
stopped
Note 1 to entry: The reverberation time is expressed in seconds.
3.7
speech transmission index
STI
metric ranging between 0 and 1 representing the transmission quality of speech with respect to
intelligibility by a speech transmission channel
[SOURCE: IEC 60268-16:2020, 3.3]
Note 1 to entry: Speech transmission channel can also be the use environment.
3.8
sound pressure level
SPL
logarithmic measure of the effective pressure of a sound relative to a reference value
4 Sound and noise
4.1 How sound and noise impact users
Hearing (audition, auditory sense) is one of the five basic senses used by humans to perceive the physical
environment, alongside sight (vision, visual sense), taste (gustation, gustatory sense), smell (olfaction,
olfactory sense) and touch (somatosensation, somatosensory sense). Even if its sensor, the ear, seems to
function independently from those of the other senses, they all function in concert. Sight and hearing,
or those sensory aptitudes that can collect information from a distance (relatively speaking), are called
far senses. Hearing is the only sense that can detect objects or events beyond the (optical) horizon.
Evolution has programmed human beings to be aware of sounds as possible sources of danger. The
hearing as the far sense gives notice of things that cannot be seen but that could be important. It plays
an alerting function. Even if this function is not needed in most use environments, it cannot be switched
off or ignored. While the sense of sight is relatively inactive during sleep, hearing remains on. The alert
function requires that hearing is almost non-directional compared with sight. It is possible to look
away or even close the eyelids, watch certain objects while ignoring others, but there is no mechanism
to ignore acoustic events.
The directionality of the human auditory system is limited to sound localization. The brain utilizes
subtle differences in intensity, spectral and timing cues to allow sound sources to be localized. Thus,
even if someone tries to ignore a certain acoustic event there will be a response. Although people tend
to get used to noise exposure, the degree of habituation differs for individuals and is rarely complete.
Adverse effects of sound events can be of a different nature. The simplest effect is characterized as
annoyance without further consideration of the genesis and aftermaths. Other effects can be of a
physiological and/or psychological nature (see Table 1).
[15]
Table 1 — Classification of factors that affect individual annoyance with noise
Factors that affect individual annoyance with noise
Sound level
Primary acoustic factors Frequency
Duration
Spectral complexity
Fluctuations in sound level
Fluctuations in frequency
Secondary acoustic factors
Rise-time of the noise
Localization of noise source
Physiology
Adaptation and past experience
How the listener’s activity affects annoyance
Non-acoustic factors Predictability of when a noise will occur
Is the noise necessary?
Individual differences and personality
SOURCE: Canadian Centre for Occupational Health and Safety (CCOHS). Noise – Non-Auditory Effects. Available
from: https:// www .ccohs .ca/ oshanswers/ phys _agents/ non _auditory .html. Reproduced with the permission of
CCOHS.
Recent research supports earlier results regarding the association of ambient sound and heart rate with
longitudinal data that demonstrate that the real-world ambient signal-to-noise ratios are associated
with lowered heart rates, suggesting that sound conditions which reduce the auditory perceptual load
[16],[27]
and listening effort de-stress the human cardiovascular system.
If many people work together in close proximity, as is the case in multi-person offices, disturbances to
activities and annoyance reactions from staff due to various environmental factors become particularly
evident, in particular since working practices often require switching between communicative
exchange and focused work.
The resulting annoyance reactions can occur in the following forms:
— disturbance component “annoyance”;
— impairments of well-being, irritation, tension, exhaustion;
— changed communication behaviour (withdrawal, avoiding interactions).
The most disturbing characteristics of speech-specific noise are the information content and the
uncontrollability, whereas uncontrollability and unpredictability of the noise play a big role in the
case of noises from office environments. Only approximately 30 % to 40 % of the annoyance effects
resulting from noise can be explained by technical-acoustic factors. The predominant part originates
from moderators of annoyance (see VDI 2569).
4.2 Types of sound events
The type of sound has a bearing on how it is to be measured, what type of sound-level meter setting
should be used and what descriptors and other data should be presented.
Sound events are generally classified into the following categories (Figure 2):
a) steady sound levels (e.g. air conditioning);
b) steady but intermittent sound levels (e.g. printers that print in bursts);
c) time-varying sound (e.g. traffic sound over a specific time period);
d) impulsive sound signals that can include one or more impulses (e.g. ringing telephones, high-impact
printers).
a) Steady sound b) Intermittent sound
c) Time-varying sound d) Impulsive sound
Key
X time
Y sound pressure level, dB(A)
Figure 2 — Types of sound events
Sound level descriptors or metrics differ according to the type of sound events. Most metrics, for
example A-weighted sound pressure level, have been developed for non-impulsive sound events. For
characterizing impulsive sound levels, different methods are used.
4.3 Interference with the task
The impact of sound from sources other than speech is normally considered by its sound pressure level
(L ) or the equivalent continuous A-weighted sound pressure level (L ). If the sound includes impulse
pA Aeq
noise, a certain margin is added to the level [e.g. +2 dB(A)].
Speech sounds and speech-like sounds lead to losses of performance of the working memory. This effect
does not necessitate the understanding of speech; an unknown foreign language or a musical piece can
also have adverse effects. In this context, it is essential that the sounds are not mandatorily perceived
as noise and that, despite focusing the attention on the material to be memorized, the irrelevant speech
effect (ISE) can occur. This disturbing effect can already occur at A-weighted speech levels from 35 dB
[30]
if they are clear speech signals. The disturbing effect is due to the spectro-temporal structure of
the speech or music sound, which results in this sound gaining access to the cognitive system (see
VDI 2569)
The interference of speech with the user performance can be a result of the disturbing effect on
the “inner speech”. Ambient noise can affect both reading and typing, because most users “speak to
themselves” during these tasks. As for the mechanism for such effects, some research indicates that
[28]
masking the relevant information with ambient sound is responsible. The role of inner speech in
human communication has been investigated (see Reference [20]). Inner speech, also called self-talk
or internal monologue, is a person’s inner voice that provides a running verbal monologue of thoughts
[18],[31]
while they are conscious. Inner speech plays several crucial roles in reading. Reading is a complex
process that involves the interaction of two levels of processing: decoding individual units and using
text as a whole to establish broader meaning. Both can be affected by ambient sound, but the effect
seems to be much stronger if the ambient sound is speech or speech-like.
The characteristics of sound events are very different for environments with “normal” noise sources,
such as street noise or machine noise, than for those environments dominated by speech sound. While
for the first the concept of a sound “level” can hold true (Figure 3), in the latter each sound event is
separated from the others (Figure 4). In these studies, the base level without any work activity was
33 dB(A); single events were up to 65 dB(A) in the recorded session. The highest recorded level was
75 dB(A) with a speaker at a distance of 11 m. Whereas in acoustics, mostly a level of 65 dB(A) for
normal speech in one meter from the speaker’s mouth is assumed.
In real work environments, speakers can emit sound levels between 45 dB(A) and 75 dB(A) while
telephoning, depending on the task and the quality of the sound transmission from the opposite side. In
contrast to earlier landline phones, mobile networks do not guarantee a certain transmission quality.
In addition, users do not speak in rooms with controlled acoustic conditions.
A “silent” train compartment in modern trains has noise levels beyond any recommended environments
for acceptable telephone communication. However, those levels are still lower than those in cars or
aeroplanes. While communicating with people in such environments, the speaker adjusts her or his
speech level to a certain degree to the level of that noisy environment.
Key
X time
Y sound pressure level, dB(A)
NOTE The red line approximates the sound “level”.
Figure 3 — Typical sound event with slow changes in the level
Key
Y sound pressure level, dB(A)
a
Base level = 33 dB(A).
NOTE The base level is the sound pressure level (SPL) with all users if they are inactive.
Figure 4 — Sound events in an office room within 90 seconds
In a given room with good acoustic conditions, the sound level can be 15 dB(A) higher if many people
use a telephone (Figure 5).
Key
Y sound pressure level, dB(A)
1 regular office work with computers
2 office work with intensive telephone conversations
a
Base level = 37 dB(A).
NOTE The base level is the SPL with all users if they are inactive. The events do not include ringing
telephones.
Figure 5 — Acoustic events in a multi-person room according to type of work
Uncontrolled phoning can heavily interfere with the work of others. One of the mechanisms leading to
this level of interference is the Lombard effect.
4.4 Lombard effect
The Lombard effect or Lombard reflex is the involuntary tendency of speakers to increase their vocal
effort when speaking in loud noise (total noise sound pressure level) to enhance the audibility of their
[24]
voice. This change includes not only loudness but also other acoustic features such as pitch and rate
and duration of sound syllables. This compensation effect results in an increase in the auditory signal-
[33]
to-noise ratio of the speaker’s spoken words.
[24]
It is suggested that the magnitude of the speakers’ response to noise is likely to be governed by the
desire to achieve intelligible communication, as in noisy conditions speakers would not change their
voice level if talking to themselves.
Speech is often considered the primary communicative signal, but it is heavily integrated with signals
from the face and body. Visual signals, including hand gestures, are integral to human communication
[19]
and can play a particularly important role in noisy situations when verbal communication fails.
In noisy environments, noise is not only associated with increased speech intensity but also with
enhanced gesture kinematics. Acoustic modulation of the speech signal only occurs when gestures
are not present, while gesture kinematic modulation occurs regardless of co-occurring speech.
Thus, in face-to-face encounters, the Lombard effect is not constrained to speech but is a multimodal
[32]
phenomenon where gestures carry most of the meaning . This means that noise modifies the entire
behaviour of the users.
4.5 Irrelevant speech effect (ISE)
In work environments such as open-plan offices, users communicate and interact with co-workers
verbally, and an open-plan office layout is commonly assumed to facilitate communication and
interaction between co-workers, promoting workplace satisfaction and teamwork effectiveness. The
assumption reflects the main purpose for selecting such layouts. On the other hand, open-plan layouts
are also widely acknowledged to be more disruptive due to uncontrollable noise. As an overall result,
the benefits need to overweigh the negative effects.
While most sources of noise can be controlled effectively, human speech is not that easy to control
because it is part of communication, although irrelevant to most users by definition.
The irrelevant speech effect (ISE) is the finding that serial recall performance is impaired under
[17]
complex auditory backgrounds, such as speech, as compared to white noise or silence. The effect
refers to the degradation of serial recall when speech sounds are presented, even if the list items are
presented visually. The sounds need not be a language the participant understands, nor even a real
language; human speech sounds are sufficient to produce this effect. The ISE represents one of the best-
investigated disruptions of short-term memory by sound events. Speech and tone are equally capable of
[22]
disrupting short-term memory.
Analyses of the objective effects of noise on human performance with respect to distribution, temporal
stability and the precision of measurement to be attained demonstrate the importance of ISE. Irrelevant
words can be disruptive to performance and the frequency of usage of the irrelevant words can affect
[14]
the magnitude of such disruption.
Both meaningful and meaningless speech disrupts the comprehensive aspect of the task, but the effect
of the meaningful speech is significantly greater. Both rehearsal and semantic processing, which are
involved in reading comprehension, seem to be susceptible to disruption by irrelevant meaningful
[26]
speech. Proofreading is disrupted by ISE. The deleterious effects of irrelevant speech depends on
[21]
the speech being meaningful.
In contrast to intended listening, where familiarity with an attended speaker’s voice improves speech
comprehension, experiments show that familiarity with an ignored speaker disrupts working memory
[23]
for target speech. This means that, for work environments, disruption by colleagues’ (irrelevant)
speech is considered to be higher.
4.6 The importance of the concept of T-O-P
While in private environments the users can select any measures to reduce the annoyance through
noise arbitrarily, in organizational contexts other considerations apply. The rationale behind the
concept of T-O-P lies in the experience that avoiding sound events that can be considered noise at the
source causes fewer issues than fighting their impact. This rationale is in agreement with the principle
“freedom from interference between task and environment” of ISO 9241-500.
Where the task at hand of a user can cause impairments or unwanted effects for others and/or the
environment, avoiding its effects should begin with technical measures. Organizational measures
require a change of the behaviour of others and should therefore be introduced as the next step, because
any change in the behaviour of an organization can be the reason for further unwanted effects. Finally,
changing the personal behaviour of the user or equipping her or him with, for example, PPE, is the
final resort for different reasons but can be necessary under certain circumstances. Giving collective
protective measures priority over individual protective measures is a well-established principle in the
health and safety domain.
The organizational and personal contributions for noise reduction are indispensable but are not
dealt with in technical standards, mostly because organizational measures and changes of personal
behaviour are out of scope for them.
5 Measures to control the impact of sound events
5.1 Overview
In ISO 9241-6, space organization and workplace layout are described as the starting point for an
acceptable environment (Figure 6). All named aspects, including “artificial and natural light”, can
contribute to successfully control the acoustic environment.
Figure 6 — Space organization and workplace layout as important parameters
A direct contribution is given for “circulations and wayfinding”, for example by avoiding groups and
persons moving through work environments with verbal communication. (Type of measure: technical
and organizational.)
An appropriate organization of the work, for example the introduction of “silent hours” with no phone
use or similar, can help reduce annoyance from sound events. (Type of measure: organizational.)
“Psychosocial factors”, such as respect for the other colleagues’ requirements or learning appropriate
speech technologies, usually help more than most technical measures that are feasible. (Type of
measure: organizational and/or personal).
Luminaires for artificial lighting can emit noise or enhance noise propagation through the use of hard
materials, such as acrylic glass, but can also help reduce annoyance through features such as soft fabric
diffusers. Windows are of acoustically hard material (glass) and influence the acoustic environment
substantially. If they are also utilized for ventilation, their impact is beyond any acoustic measure.
(Type of measure: technical)
For a general strategy to control noise at workplaces containing machinery, ISO 11690-1 includes
detailed information.
5.2 Controlling sound and noise
5.2.1 General
The control of the acoustic environment is by far the most complex task for the design of work
environments. The main reasons are the conflicting requirements associated with the use of sound for
communication (aural interaction) and the impact of acoustic interventions on the other environmental
factors.
In rooms dedicated to a single purpose, such as reading rooms of libraries or lecture halls, effective
measures can be taken in consideration of the task. In reading rooms, the environment is designed to
keep any distraction as low as possible, whereas in lecture halls the propagation of the sound from
the speaker to the audience is the ultimate goal. To achieve the goals for such environments, suitable
technical measures are usually taken during the planning of the building. Even then, all involved
persons’ behaviour needs to be controlled.
Use environments are more or less a general purpose space. People in that space do not only perform
their tasks. While performing their tasks they emit sound that can be meaningless to others and thus
can be considered noise regardless of its level. However, it can also be relevant depending on its content,
for example a colleague's phone conversation that has some personal relevance. In the immediate use
environment of teams, there will always be intended verbal communication (information), partly
interesting communication (information or noise) and noise, i.e. speech without any relevance for a
person or group.
The transmission ability of a room or a communication path for speech can be measured through
its physical characteristics [speech transmission index (STI)]. STI is a well-established objective
measurement predictor of how the characteristics of the transmission path affect speech intelligibility.
However, STI depends on various factors such as speech level, background noise level, echoes in the
room, reverberation time and masking effects and a variety of technical features of the technical
equipment if it is part of the transmission path (see Figure 11). In a general purpose space, a high quality
of speech transmission does not form the ultimate goal for all tasks and users. In many respects, a
control of the acoustic environment to inhibit the intelligibility of speech can be of higher value.
The control of the acoustic environment requires first an analysis to determine the best trade-off
between the achievable benefits and the efforts and disadvantages of a direct or indirect nature.
This task requires holistic thinking and acting, because a certain benefit (e.g. better intelligibility of
speech) could require measures (e.g. acoustic screens between co-workers) that can impact the work
detrimentally but also the intelligibility of speech, because one cannot see the speaker any more.
According to ISO 9241-6, measures to control the acoustic environment can be grouped into three
groups of goals (see ISO 9241-6:1999, Figure B1):
— reducing the rating level;
— optimizing signal-to-sound ratio (control of the intelligibility of speech);
— sound reduction within workrooms or immediate environments of workstations.
5.2.2 Reducing the rating level
This group of measures aims at lowering the overall sound level. The rating level (L ) is the
AR
characteristic value for noise emission. The rating level is determined for a specified time interval
(see ISO 1996, ISO 9612, ISO 11690). When determining the rating level, no account is taken of acoustic
events which serve the purpose of communication between the person at the workplace in question
with other persons (conversations, communication signals).
The equivalent continuous A-weighted sound pressure level (L ) is measured to represent a whole
Aeq
shift of 8 hours. L is a common measurement used in industry to characterize noise levels in loud
Aeq
environments. It is less suitable to characterize the potential of annoyance by impulsive sound or time-
varying sound.
Reducing noise emission from the equipment includes a variety of measures, such as silencing
telephones or insulating printers. The most recommended intervention is noise control at the source,
for example by using equipment with low emissions in the immediate environment.
The main descriptor of the noise emissions from information technology and telecommunication
equipment is the A-weighted sound power level (L ). It is supplemented by another emission quantity,
WA
the A-weighted sound pressure (L ) at the operator or bystander positions (ISO 7779).
Ap
The L at the operator position is relevant for the noise within the immediate environment, whereas
Ap
L helps describe disturbances to other workstations.
WA
Both sets of data are declared according to ISO 9296 and can be found in the product data sheet or the
product environmental data sheet.
In office environments, keyboards are among the noisiest equipment due to their use throughout the
day. According to ISO 9241-410, the sound emission of keyboards can have three categories:
— C1: suitable for meeting rooms or tasks involving concentration [35 dB(A) to 45 dB(A)];
— C2: suitable for routine office work [45 dB(A) to 55 dB(A)];
— C3: suitable for industrial workplaces [75 dB(A) to 80 dB(A)].
Selecting C1 is recommended. Since many products are not labelled, the products should be tested for
their noise emission before purchasing.
For printers, there is a correlation between the printing speed and the sound emission because the
main source is the movement of paper. Thus, purchasing a low-noise printer is not always a good option.
For the frequent use of higher-speed printers, the device should either be moved to a separate room or
an enclosure should be used. Most printers offer a silent mode, which should be used if possible.
Increasing sound absorption is a usual intervention and gives protection against noise from all sources.
All equipment, room surfaces or furniture can be considered for this purpose. The cost involved and the
achievable effects are rather different.
[34]
Two examples of this type of intervention are given in Figures 7 and 8. The calculation of the
efficiency of the measures is valid for a specified position in a workroom (Figure 7). The sound
reduction lies between < 0,5 dB and 9 dB for the specified work position (Table 2). For the other work
positions, the outcome is similar.
Key
1 Cabinet
SOURCE DGUV Information Akustik im Büro, VBG Hamburg, 2012-09.
Figure 7 — Workroom and working position
Table 2 — Variants of acoustic interventions and the effects
SOURCE: DGUV Information Akustik im Büro, VBG Hamburg, 2012-09.
The following example depicts a bigger room used for phone conversations, e.g. a call centre. An
absorbing ceiling cannot be used because of the chilled ceiling. Instead, baffles can be used. The
luminaires can be equipped with acoustic sails (Figure 8, Table 3). The lighting is installed over the
workstations.
Key
1 Cabinets
SOURCE DGUV Information Akustik im Büro, VBG Hamburg, 2012-09.
Figure 8 — Multi-person workspace used for regular phone conversation
Table 3 — Variants of acoustic interventions and the effects
SOURCE: DGUV Information Akustik im Büro, VBG Hamburg, 2012-09.
Some elements of this intervention do not cause any negative effects (e.g. wall-to-wall carpet) while
baffle ceilings require an additional height of the room. If this is not available, the room impression
can suffer. Also, the air circulation in the room can suffer from the baffles, screens and sails. Absorbing
walls and cabinet fronts limit the available colours for these surfaces. Once installed, the colours cannot
be changed without removing parts of the surfaces. The screens inhibit visual contact between the
workers. They also form an obstacle for the daylight. Usual forms of general lighting in regular rows
would suffer somewhat when screens are used.
With most of the variants, a comfortable acoustic environment through the technical measures is not
achieved. The room for which two different uses and the sound events are shown in Figure 5 can help
to evaluate the acoustic environment: the rating level for the general office use would exceed the base
level of 37 dB(A) only by about 4 dB(A) to 5 dB(A). If the task includes often telephone conversations,
the sound level is increased to about 55 dB(A). Using the same space (Table 3) for tasks where phone
conversations dominate will result in sound levels of 65 dB(A) (without intervention) that can be
reduced by up to 10 dB(A) with a variety of interventions.
Sound insulation in structural components means that the structural components (walls, ceiling,
windows) should be adequately insulated against structure- and airborne sound. Because of the
differences in room sizes, activities and interior noise level (background noise level), the acoustic
requirements to be met by the components can be adapted to the appropriate conditions (see Table 4)
The requirements to be met by the sound insulation system can be selected in relation to the background
sound.
Table 4 — Recommendations with regard to the sound insulation of structural components
for various office tasks and background noise levels (without activities and equipment) which
should not be exceeded
Level of background
Acoustic recommendations insula-
noise
Type of activity Type of room
tion and restrictions
L dB(A)
Aeq
Tasks with temporary Good noise insulation from neighbour- Single office with
concentration, tasks ing offices; very good verbal communi- normal user require- 35 to 40
occasionally repetitive cation ments
Good noise insulation from neighbour-
Tasks with temporary Multiple office with
ing work a
...