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Last modified July 5, 2015


Human Parameters

It has for a long time been understood that high-intensity acoustic noise emissions adversely affect human well-being, performance and health, but it isn't until recently that science is beginning to understand that also low-intensity noise, like the unintentional sound often emitted by equipment and machines intended for use in offices and homes, may affect these parameters.

Since there might be connections between the acoustic aspect of information technology (IT) ergonomics, well-being, and presumed effects on performance and health, this page deals with them all.


Adapted Technology

Berkeley University of California here summarizes the value of ergonomics:

"Ergonomics originated during the Second World War to overcome performance failures due to human error in new high tech defence systems. Because of its success, ergonomics is now routinely applied in the design and development of most military and aerospace systems. Industrial applications of ergonomics are increasing in response to the need to improve the productive use of human resources, the quality of working life and occupational health and safety."

"People working in ergonomically designed workplaces or using ergonomically designed products, will tire less quickly, be less distracted by discomfort and ambiguity, less muddled by confusing displays and instructions, less frustrated by inconvenience and less stressed by excessive physical demands. This will mean a lower probability of error, less likelihood of accidents, less time correcting mistakes and better morale. The cost of ergonomics depends where in the lifecycle of a systems it is applied. Applied early in the planning stages, costs will be less: existing budgets will simply be better spent. Applied as a reaction to serious problems, then costs will be higher."

Ergonomics, also known as Human Factors, is the application of scientific information concerning humans to the design of objects, systems and environments for human use.


The Ergonomics of Sound

The ergonomics of sound can be summarized as a working to achieve the highest possible signal-to-noise ratio in the sound environment, and to minimize interference when the sound isn't carrying any meaningful information. The ergonomics of sound thus not only treats unwanted distracting sound: Optimized and relevant signals, warning sounds, and perfect speech intelligibility are all of the same importance.


Where a Low Noise Level is Vital

The Arlanda air traffic control tower is a modern example of a working site where acoustic considerations are included in ergonomic thinking.


High up in the sky, with an amazing view over the airport where airplanes are taking off and landing more than once a minute at peak hours, the air traffic services are working with a number of technical systems, including a new advanced ground radar system, a new communications system, new radar presentation systems as well as flightplan, weather and lighting systems. Nonetheless the only perceivable sounds in the tower are the low voices of humans.

This optimized acoustic environment has been achieved with low-noise air condition, sound insulating windows, floors covered with sound dampening mats, and lastly by keeping keyboards, mice and screens in the tower, but putting the noise emitting components of all the in the tower necessary information technology in a server room at ground floor. The servers and system units are connected to the tower 83 meters up using so called KVM extenders and fibre modems.

Air traffic controller Bengt Collin (right image) appreciates his quiet working environment. He remembers how he many years ago used to work at a site where he had to stand background sound from a radio: "It took some time before I realized what made me so tired after a working day", Bengt says.


The only perceivable sounds here 83 meters above ground are the low voices of humans.

The Swedish Civil Aviation Administration, Luftfartsverket, is well-reputed for its safety knowledge. Optimized acoustics are part of Luftfartsverket's work to create "harmonic environments", where also interior design and positive human relations are of importance; at working sites where every effort has to be made to minimize the risk for human error. The Arlanda air traffic control tower, put in to operation December 23, 2001, is the latest example of this implemented knowledge.

The Swedish Civil Aviation Administration's upper sound pressure level limit for traffic control service areas is 35 dBA. This authority regards the work to minimize acoustic noise emission of information technology equipment not only necessary because it adds a specific amount of unwanted and distracting sound to its high-tech working sites, but also because it tend to rise the average noise level due to people rising their voices to make themselves heard.

An other reason, except for acoustic noise emissions, for keeping servers and system units out of air traffic control operating areas is that the Swedish Civil Aviation Administration believes it is vise to keep man and machine separated as much as possible: "Man and machine shouldn't breathe the same air", says Per Kjellander, responsible for implementing much of the ergonomic thinking at the new Arlanda air traffic control tower. Lastly, keeping electro-magnetic fields and heat emissions as low as possible is also achieved by separating servers and system units from air traffic control operating areas.

Arlanda, the largest airport in Scandinavia, is located north of Stockholm, Sweden.

Photographer at Arlanda: ©Tomas Risberg.


Information Technology Ergonomics

The IT equipment product group comprizes personal computers (PCs), printers, copiers, fax-machines, projectors and some other products.

IT ergonomic thinking can be divided in to three main subgroups: IT equipment must be as easy as possible to understand and use, it must not distract, and it must not cause adverse effects on human performance or health.

PC ergonomics

PC ergonomics has for a long time been focused on how to sit by these machines, on that it is important to take a rest every now and then, on that the keyboard and mouse should be ergonomically constructed, on that their screens should be optimized for good seeing, and on how the light should be around these machines. PC ergonomics has for a long time also focused on an invisible side effect; electromagnetic fields from their screens.

It is not until recently that something as obvious and easy recognized as IT noise has received any attention. It is not until recently unwanted sound has been included in PC ergonomics.

Some of the World's most powerful manufacturers of PC system units, and a few manufacturers specializing in low-noise computers, now publish data according to the ISO 9296 international standard for noise declaration of information equipment. Most computer purchasers, except some well-informed purchasing managers, are not told to ask for, and how to handle these nontheless quite rare figures. This situation now tend to bring the most noisy computers to the most quiet environments - to the homes.

Projector ergonomics

The most important aspect of projector ergonomics is of course that they provide an as good image as possible. This is what they are all about.

Projectors are commonly located in the middle of the listening audience, in rooms most often special designed optimal for communication humans in between. Since humans mainly communicate using sound when close to each other, does these optimized environments most often include acoustic considerations: These rooms are commonly very quiet, and their reverberation times are optimized for speech communication.

Projectors require more or less noisy fans to cool the lamps that project the image. Projectors will in most rooms special designed for perfect communication, due to their lamp cooling fans, be the main source for unwanted distracting sounds. Due to the tiring properties of their continuous uninspiring sounds, projectors are sometimes nicknamed "sleeping pills".

There is no known ergonomics society that have discussed projector ergonomics also taking the acoustic aspect in account, and projectors are still like most IT equipment, not noise declared according the international standard the IT industry agreed upon in the 1980s - ISO 9296. Many projector manufacturers now present noise data in dB, but these figures should be treated as misleading non-comparable and non-verifiable ones, since they aren't accompanied with information on if a, and in that case which standard has been used - remember - dB without standard specification is an as relative notion as the more honest and less customer-confusing notions "quiet" and "almost silent". There is now no known labeling scheme that at all include projectors in IT ergonomics. So, in this information age, will many most high educated listeners to many most high educated speakers still find themselves trying to concentrate through the humming noise of underdesigned projectors.

Printer, copier and fax-machine ergonomics

Printers, copiers and fax-machines ergonomics include that they fulfil their purpose, are easy to use, and don't distract.

Printers, copiers and fax-machines can often be put in to special rooms, where their noise emissions don't distract. For this product group we therefore often tolerate higher levels of unwanted sound. For small offices and home environments, where these printers, copiers and fax-machines often are located closer to the user but used less often, it is of main importance that they don't make any sound when in Sleep or Standby modes.

Most manufacturers now don't tell if their products are silent in Sleep or Standby modes, and most of today's ergonomic labeling schemes and IT ECO declarations don't include this important information. Many printer and copier manufacturers still don't adhere to the ISO 9296 standard, but present non-comparable non-verifiable noise declarations.


How Health and Performance Relates

If humans too often or continuously work at the edge of their capability, without enough control over their situation, will they find themselves in a negative stress situation. People will handle negative stress situations in different ways. The two main ones:

  • Some people tries to sustain performance even if it's very, very hard for them. If the negative stress situation continues for too long time will their health be adverse affected.
  • Some people give up the ambition to perform as much as they know they would be able to if the situation was optimal. They adapt to the situation without risk sacrificing their own health; at the expense of decreased performance.
  • Since performance and health are so close related will this page treat them together.


    Noise Effects on Health

    The diagnosis codes for noise exposure are Z58.0 and W42 according to ICD-10, the international statistical classification of diseases and related health problems, tenth revision.

    Health effects of noise exposure can be divided in two main groups: Auditory and non-auditory.


    Auditory health effects

    Auditory health effects affect the organ of hearing and include hearing damage caused by prolonged exposure to too high noise levels, acoustic trauma causing sudden hearing damage, temporary hearing loss after exposure to a high level of noise, and tinnitus (ringing or buzzing in the ear).

    High-intensity noise is at this site defined as acoustic noise emissions at levels where auditory health effects may take place. A common thought is that noise emission level lower than 85 dBA does not cause auditory health effects [1], but there are indications that even lower levels may cause hearing deficits if one is subjected to them for long times. If we should consider these data the auditory safe noise level becomes 70 dBA. Most of today's PCs cause a noise level at about 35-50 dBA at user position. For what is known there are no PCs or other information technology (IT) equipment that come near the noise level 70 dBA. Therefore there are no known auditory health effects involved in using information technology equipment.

    Note: When talking on dBA values at this page we talk on sound pressure level measures; ie what the user hear. These values are not to be mixed-up with the valuable and expensive sound power level values, which describe noise emissions as a property of its source; and thus are the better suited ones for product comparisons and buying decisions. Read more on this at the ISO 9296 page.

    The human organ of hearing

    The human organ of hearing.
    There are no known IT equipment that cause auditory health effects. Image courtesy of Dr. Beth Hartwell, University of Texas, Houston.


    Non-auditory health effects

    Presumed non-auditory health effects of audible acoustic emissions primary takes place at brain level. Secondary to brain reactions they may affect the rest of the human body. In the following will only possible non-auditory health effects related to low-intensity noise emission exposure be discussed: This because low-intensity noise is the kind of noise that may be emitted from information technology equipment.

    Low-intensity noise is here defined as noise with levels lower than the level where auditory health effects may take place, ie low-intensity noise is noise with a sound pressure level lower than 70 dBA.

    Possible adverse affects of low-intensity noise can be summarized as caused by distraction, fatiguing and speech masking. Since noise is defined as unwanted sound will all audible levels of unwanted sound from zero dBA and upwards become regarded as more or less distracting. All noise levels above 40 dBA may also cause difficulties to apprehend speech. The speech masking properties of IT equipment noise emissions are of particular importance for projector technology: Projectors are commonly located in the middle of the listening audience.

    Note that the so called "pink noise" used for speech masking in some open-office areas is something completely different to the uncontrolled "white noise" from IT equipment, and that zero dBA for mathematical reasons doesn't mean total silence.


    To be Observed

    There are no known scientific studies that have focused directly on health or performance effects related to exposure to PC noise or other IT equipment noise emissions. There are many studies on adverse health and performance effects of low-intensity noise, ie noise similar to the kind emitted by IT equipment, but scientific evidence regarding its adverse effects still remains non-conclusive.

    However, even if there isn't enough scientific proof yet (if at all necessary) we see that it is becoming universally accepted that IT noise emissions often adversely affect users' well-being and can make it harder to concentrate.

    The Silent PC® web site, although its author is a medical doctor, does not emphasize health or performance reasons for to minimize unintentional sound from computers and other kinds of IT equipment. The primary focus here is on low levels of unwanted sound for comfort for those that regard this comfortable, and for optimized speech intelligibility where IT noise emissions may hinder human communication: The primary focus here is on purchasers' freedom of choice and manufacturers' freedom of competition regarding acoustic aspects for a product group, where interested purchasers and manufacturers, even if now easier, still face difficulties to meet.


    A Word of Caution

    Putting too much focus on something that isn't possible to avoid can cause oneself severe problems. It would be most unfortunate if an increasing number of people started becoming too afraid of that even low levels of noise emissions can cause adverse effects on human health. Common sense must of course also be used when reading on unwanted sound.

    It seems, however, inevitable that some people becoming aware of their sound environment for some time will be preoccupied by it. If this thinking in any way become problematic, then there might be good to know that there are names and treatments for the disorders related to hypersensitivity of hearing: hyperacusis, misophonia and phonophobia.

    We live in an imperfect World, and unintentional unwanted machine and equipment sound is just one example of many human shortcomings. Most of us living in the industrialized part of the World also live in areas where machine and equipment noise is inescapable. Becoming afraid of that this low-level sound might cause health problems doesn't do any good: It seems much better to look upon low-intensity noise as a freedom issue, than a health or performance one.

    Nonetheless, since there most probable also exist health and performance reasons for to optimize the acoustic aspect of IT ergonomics, even if still hard to scientifically prove, and many IT manufacturers now tend to utilize such reasons in their marketing of low-noise products, this page will try to cover a little of what we know, and share some thoughts.


    "Stress and Open-Office Noise"

    The "Stress and Open-Office Noise" [2] study published in the Journal of Applied Psychology, 2000, is today's most important scientific study on how low-intensity noise may affect human health.

    The study main conclusions:

    "Three hours exposure to simulated low-intensitive open-office noise elevated urinary epinephrine levels, lowered postnoise-exposure task performance indicative of depressed motivation, and reduced use of ergonomic work-furniture features designed to provide opportunities for postural adjustments during work. Although there was psychological, motivational, and observational evidence of elevated stress from low-intensity noise exposure, workers' self-reports and a simple index of productivity did not reveal greater stress under low-intensity noise conditions."

    The Stress and Open-Office Noise paper discusses potential health consequences of long-term exposure to low-intensity office noise. The noise-exposed office workers were less likely to change their working position; indicating the possibility to develop musculoskeletal disorders. Chronically elevated epinephrine levels, as seen in the noise-exposed group, is a risk factor for heart disease.

    The ambient noise intensity used under the "no-noise" condition was averaging 40 dBA. During the simulated open-office conditions were the average levels 55 dBA, with peaks up to 65 dBA.

    In summary the Stress and Open-Office Noise study tells us that chronic exposure to noise, even low-intensity noise, may have the potential to cause health problems.


    A Performance in Low-Intensity Noise Study

    A study that could show performance decrease due to low-intensity noise

    During a grammatical reasoning task noise was suddenly interrupted, and error rates went down sharply.

    The "Effects of simulated ventilation noise on performance of a grammatical reasoning task" [3] study showed a statistical significant decrease in error rates when low-intensity noise was shut off. The noise levels was somewhat high (47-57 dBD) compared to most ordinary personal computers. The so called weighting of the noise was also not comparable to ordinary PCs: PC noise is commonly weighted using the A-filter, while here the D-filter was used.

    Nonetheless is the study most interesting reading since it is one of a few ones that has been able to show effects on performance in low-intensity noise. The article discussion is also of utmost value to anyone interested in problems that might arise when trying to study adverse effects of low-intensity noise.

    The full text article is here provided free to download as pdf-file courtesy of Formas, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning. The article is Copyright © Formas.


    How Low-Intensity Noise May Affect

    The following paragraph discusses in what way also low-intensity acoustic noise emissions may possess the power to decrease human performance and to adversely affect human health.

    The hypothesis here presented is not based on scientific evidence: It is based on thoughts by The Silent PC Web site author. These thoughts are of course as everything else here, except cited items and others stated copyrighted items, the site author's copyrighted intellectual property ©.
    Fujitsu Siemens Computers® has in 2003 with permission used part of these thoughts for marketing purpose. This writing has been further improved since then.

    Fujitsu Siemens Computers is a registered trademark of Fujitsu Siemens Computers GmbH.

    "Close your ears and relax"

    Humans can not close their ears: Shutting out unwanted sound requires brain activity.

    The human brain needs dynamic work for its functioning: All awake humans will therefore during all activity, most often unconsciously, include shorter or longer pauses in what tasks they are focusing on.

    In the same way as science is beginning to understand that the mechanism behind the "burn-out syndrome" isn't primarily a too heavy workload, but the lack of necessary regular relaxation pauses, will continuous or too often repeated unwanted sounds hinder relaxation more than add to workload. This leads to the basic assumption:

    The basic assumption

    Non-auditory health effects and negative performance effects caused by acoustic noise emissions are all based on the fact that audible sound consciously or unconsciously calls for and competes for attention, and that monotonous sound decrease alertness.

    Sound calls for and competes for attention

    Attention is an active process. Active processes cost energy: In the same way as a personal computer, printer, fax machine or projector requires electric power to do its job does the human brain need energy to execute its tasks. Like the personal computer is the human brain limited in what it can accomplish. Each moment is only a certain amount of energy and capacity available. Like it costs electricity, processor power and consumes RAM (memory) to have many programs active in a PC, does it require brain energy to keep several tasks going on at the same time. (This is Psychology's and Neuroscience's theory of "Working Memory".)

    The human brain processes information. IT acoustic noise emissions can in some aspects be regarded as information, but this information is limited to tell us that a machine is on, and how this machine sounds when on. Since most IT users will have other indications that the PC, printer, copier or projector is on, will their brains treat the sound telling that the machine is on as unnecessary and useless information. Hence do most of us not say that we are continuously listening to a PC's, printer's, copier's or projector's sound, but exposed to its noise.

    Reactions to being subjected to repeated or continuous unnecessary and useless information include annoyance, feelings of lack of control and even helplessness; and second to this stress with its physiological and behavioral effects.

    Note: Those people that like to continuously hear the kind of sound emitted from information technology equipment will of course not experience any adverse effects of listening to it; in the opposite will their health and performance probably benefit of it.

    Annoyance and tiredness

    Even if some people don't bother much about the sounds emitted from fans, hard disks, storage devices and other mechanical components of information technology equipment, would few choose to continuously listen to a recording of them: The unintentional continuous sound of information technology equipment is by most people regarded an unpleasant kind of sound. Most people dislike what is unpleasant, and want their world to be as comfortable and enjoyable as possible. Annoyance is a natural reaction to being exposed to something unpleasant.

    A particular property of IT equipment noise is that it continues as long as the equipment is on. Because of this will we, if annoyed by the sound, continuously have to try to put it to an unconscious level of our minds. Since this continuous active suppression of information costs brain energy will it tire us. We want to be as alert as possible when using IT equipment. The tiring property of low-intensity noise will therefore add to our annoyance towards it.

    The tiring aspect of continuous low-intensity noise will be most prominent as we already are tired. We will thus become more annoyed by noise when not thoroughfully rested than when we are, and more annoyed at the end of a working day than at the beginning. Most obvious is the tiring and annoying effect of noise for very tired users trying to focus by the PC late at night in a quiet working or home environment, and for a tired audience in a dark room having to stand the noise of an underdesigned projector.

    Lack of control

    Annoyance is a reaction that calls attention to the fact that something is wrong. Something wrong is natural to try to make right. Humans will therefore try to find a solution to what annoys them. If we can't find a solution to what annoys us will we experience lack of control.

    Because of our World's imperfection there are numerous sources of annoyance humans can not avoid. Most people therefore have the capacity to handle annoyances that they can not respond to.


    If humans experience too much of lack of control, will the total experience be perceived as helplessness. Today's working situations are often very hard, and humans do today often experience too little control over their situation. The amount of work in today's World is often more or less over the limit what a human can handle to feel comfortable. Lack of control on what repeated or continuous sounds one is exposed to can here become part of a feeling of helplessness.

    The theories on so called "learned helplessness" are often applied on acoustic noise emissions. These theories focus on human reactions in prolonged or too often repeated unsolvable conflict situations.

    Negative stress

    In a more or less continuous feeling of helplessness at the same time as having to perform complicated tasks, humans will find themselves in a state of negative stress. Stress reactions include arousal, increased levels of hormones necessary for "fight and flight" reactions, elevated blood pressure and the heart beating faster.

    If negative stress continues over too long time will secondary reactions occur: sleep disorders will be a first sign, and may be aggravated if one has to stand acoustic noise in the bed room. Secondary to too little or disturbed sleep, and too much of arousal at daytime, will one see changes in brain function, decreased performance, memory deficits, learning difficulties, headache, hypertension and stomach problems.

    In the end of this spectrum of stress reactions can one see psychiatric disorders like depression, anxiety syndromes, abuse and "burn-out", musculosceletal disorders, coronary heart disease and stroke.

    Note: The Silent PC Web site deals with acoustic noise emissions from information technology equipment. They can of course not alone be held responsible for reactions like the ones above, but it seems possible that they sometimes may take part. Scientific evidence here lacks, as said above.


    The Feeling of Relief Sign

    While many people these days are becoming aware of the fact that they easy become distracted by IT noise emissions, are many people not, and some can declare that they don't bother about low-intensity sound from machines and equipment at all, and never become distracted by it. People are also here different.

    Annoyance caused by acoustic noise emissions is often unconscious. This is not to say that all people not bothered by the sounds that most other people define as noise emissions actually are, but many people will agree on that they have experienced a feeling of relief as the ventilation with its smooth almost non-hearable sound shuts off at a late working day. Other people will say the same on PC noise, and clearly declare that they don't let their machines and equipment be turned on a minute extra if not in use.

    The exact meaning of the feeling of relief when low-intensity noise is shut off seems to require further research.


    The Human Brain's Signal Processing

    Has anybody regularly visited a cinema where background noise was included in the experience? If so - did you like the noise? No, probably not. In this respect movies can be regarded as examples of how we want our surroundings to be to be able to enjoy and experience as much as possible. Would you accept and like a stereo or telly not only taking use of its speakers for the sound it was made to handle, but also emitting some extra sounds from other parts of the equipment?

    We healthy humans are very, very good at excluding unnecessary and useless information from our consciousness. We are fully capable of handling the most often heard continuous flow of unnecessary acoustic noise emissions from today's technology, but it costs some of our brains' energy to do it - energy that instead can be used to enjoy wanted sounds, communicate and to perceive and process useful information.

    The human brain's signal processing capacity is vulnerable. People suffering of too much stress, or of some disease affecting their brains, will early discover they have problems with sorting out important from unimportant information. Acoustic noise can to those people become handicapping. Elderly people also find it more problematic to sort out information from noise.

    Sorting out important information from noise is something very advanced, and technically complicated to accomplish. Healthy humans' brains are, compared to most of our technology, still superior in signal processing.


    "Coexistence of Attention-Based Facilitation and Inhibition in the Human Cortex"

    The "Coexistence of Attention-Based Facilitation and Inhibition in the Human Cortex" study [4], from where the image below stems, presented evidence that is consistent with the existence of an active modulatory attention mechanism by which task-irrelevant input in the auditory cortices of the human brain is suppressed.

    PET scan visualizing how distracting sound can affect human brain function

    These PET scan images superimposed on MRI scan images shows a healthy medical student's brain function when performing arithmetical tasks at the same time as being exposed to irrelevant speech. Some brain areas are found significantly modulated: (A) Shows bilateral decreases in the auditory cortex. (B) Shows an increased activity in the left posterior parietal cortex. Courtesy and © Karolinska Institute and Hospital, PET Cognitive Neurophysiology, Sweden.

    Note: PET images showing how prolonged exposure to information technology acoustic noise emissions affects the human brain will most probably look a bit different to these ones. This is because of the differences in how Man perceive speech and noise. This study, and the two below, are here used for to visualize and prove the fact that distracting sounds not only are perceived as annoying, but actually causes changes in brain function.


    "Background acoustic noise and the hemispheric lateralization of speech processing in the human brain: magnetic mismatch negativity study"

    The results of the "Background acoustic noise and the hemispheric lateralization of speech processing in the human brain: magnetic mismatch negativity study" [5] confirmed the increased role of the right hemisphere in speech-sound processing in noise, suggested in previous studies. The study data indicated that this shift of a functional dominance towards the right hemisphere may occur due the recruitment of some additional neural structures in the right auditory cortex that do not participate in speech-sound processing to such extent in the absence of noise.

    The auditory stimuli in this study were presented in three conditions: in silence and in constant white noise of two levels in which the signal-to-noise ratio was estimated to be 15 and 10 dB (here referred to as noise-low and noise-medium conditions, respectively).


    "Noise affects speechsignal processing differently in the cerebral hemispheres"

    The "Noise affects speechsignal processing differently in the cerebral hemispheres" [6] study explored the effects of acoustic noise on the cerebral asymmetry of speech perception measuring magnetic fields of the brain elicited by consonant vowel syllables in silence and white noise. It was found that background noise affected brain responses to these stimuli differently in the left and right auditory cortices. The results suggested an increased right hemisphere role in speech sound processing in noisy conditions, involving the recruitment of additional right auditory cortex structures.

    The noise conditions were the same as in the study above.


    Human Response to Sound

    Depending on how loud a sound is, on what quality it has, the listeners former experience of sounds, his or her condition, the sound source and the context in which the sound is heard will humans regard it more as an okay sound or more as noise. Important aspects of human apprehension of sounds are therefore:


    Loudness is a subjective response to the amplitude of sound. It is a human judgment of the intensity of a sound.

    Sound quality, noisiness & annoyance

    A sound's "noisiness" represent the degree of annoyance it causes: Every hearing human has his or her own personal relation to the world of sound. It is therefore difficult to make general rules on what sounds are to be regarded pleasant or unpleasant, and on what kind of noise is more or less annoying.

    Science, however, reveals that the frequency spectrum of a noise is important in how it is perceived. In general are high-pitched sounds perceived as more noisy than lower pitched ones. Noise also containing easy discriminated pure tones are more often perceived as more annoying than if they are not present. In general, it is also easier for people to stand sounds when they provide meaningful information. Hence it is easier for the car driver to stand his motor's sound; informing him that he travels at the right speed using the right gear, than it is for the PC user to stand the sound emitted from his or her machine; simply telling that the machine is on, and how it sounds when it's on.

    A particular property of the sound emitted from a machine is that as long as the machine is doing its job will it emit the sound. This fact will add to the possibility of becoming annoyed by sounds from machines.

    The term sound quality can be used to summarize how humans in general perceive a sound, and for to improve this aspect in product design. An example of good acoustic design is the sound of a Harley-Davidson® motorcycle; where the rhythm of the sound share similarities with human or horse heart beating, and its other characteristics with the power of thunder.

    Harley-Davidson is a registered trademark of Harley-Davidson Inc.

    The context

    The context in which the sound is heard is important on how it is perceived. In a noiseless environment may also a very quiet piece of information technology compete for attention. As one tries to sleep will also very quiet machines produce sound enough to make it harder. In distracting environments and situations will noise be perceived as more annoying than in other ones.

    The personal condition

    Tired people and people in stress face greater difficulties to concentrate in noise, and if aware of the noise will they regard it more annoying than when thoroughly rested and relaxed. People suffering of depression are also easier distracted by noise. En extreme example are people suffering of burn-out syndrome, who most often are extremely sensitive to even the most quiet sounds.

    The sound source

    A factor of importance regarding the apprehension of sounds, is that the annoyance a sound causes also depends on the listeners psychological attitude toward the sound source: It is easy to understand that people working with bad designed operating systems and other software, and people afraid of adverse health effects of using information technology equipment easier will become distracted by this technology's noise emissions, than the ones working with perfectly designed software and not afraid of any adverse effects of the technology they use.

    The ones that understand that noise isn't something unavoidable, the ones that understands that it doesn't cost that much to minimize unintentional sounds from machines and equipment, will also easier become annoyed than the ones that simply think they have to accept the noise as a necessary part of reality. This example of how we can react to the noise source was written to The Silent PC™ Web site author in May, 2002:

    "Quite a marketing scheme you've got here. I had not noticed the noise my computers made while I was sitting around them until I read your webpage. Now, considering that I am an MIS associate at a firm and work around anywhere from 2-200 computers at once, I am finding the noise quite unbearable. Thanks a whole lot. Now I can barely function around computers which used to be my life. You should really have a warning message on your website to people who use computers often. It's like showing a professional wrestling fan a video tape of all of his/her favorite wrestlers saying that what they do is fake and remarkably easy."

    The scientific field that studies how we react to sounds is called psychoacoustics.


    Buying the Pig in a Poke

    Since there are no scientific studies exactly related to low-intensity noise exposure from information technology equipment, we can not be sure that it causes any health or performance effects. For the moment we don't know if there are any adverse effects of even very low but continuous noise exposure, even by equipment emitting lower than the declared A-weighted sound power level of 5.5 - 5.8 B per ISO 9296 most commonly allowed in today's only on rare occasions adopted labeling schemes for information technology equipment intended for some sort of average working environments.

    When allowing just one single machine to emit this much noise, you must take into account the additive effect of other noise sources; and that people in noise tend to rise their voices: In the end will this result in higher total noise figures. You must also consider in what way also continuous or often repeated exposure to low-intensity noise from information technology equipment in the home environment affect humans; if added to already noisy working environments.

    As said at this site before: Noise limits for IT equipment might sometimes be of some value, but since noise always must be heard in its context, is it better to have its exact figures declared in a comparable way. Buyers will then be free to choose what they regard comfortable; and industry will provide itself an important incentive for to compete and profit also on the acoustic comfort aspect of product quality. Read more on this subject at the Introduction, ISO 9296 and Noise Labels pages.


    The Freedom to Choose

    Richard Stallman founder of the GNU project

    Richard Stallman isn't bothered by PC noise emissions unless he is trying to sleep in a room with one.

    Richard Stallman is the programmer that in 1984 founded the important GNU project for "copylefted" free software. The today well-known Linux® kernel takes use of GNU software, and the resulting operating system is therefore often referred to as GNU/Linux.

    Asked what he thinks on PC noise emissions Richard answers:

    "In general PC noise emissions don't bother me unless I am trying to sleep in a room with one. So the noise issue simply is not important to me. I sympathize with people who are bothered by noise, but I can't make a strong statement about it myself."

    After a little time of thinking the GNU project founder returns:

    "In the 1970s at MIT, we used one of the first bitmap display terminal systems. It was a joy to program, but the monitor emitted a high-pitched noise all the time. After a while you would stop noticing it--but there was a suspicion that long use might damage the user's hearing. Later, in the 80s, I found I had some hearing loss. I don't know whether those terminals were responsible, but it shows that noise is an important issue for all equipment that will be next to a user's desk."

    Note: Richard Stallman here also talks on auditory health effects of IT noise emissions. Referring to what has been said above there are today no known information technology equipment emitting so much noise that it can affect human hearing.

    Linux is a registered trademark of Linus Torvalds.


    The World Health Organization

    The World Health Organization, the United Nations specialized agency for health, was established on 7 April 1948. WHO's objective, as set out in its Constitution, is the attainment by all peoples of the highest possible level of health. Health is defined in WHO's Constitution as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

    An important WHO statement that coincides with this site author's thoughts on purchasers' freedom to choose and manufacturers' freedom of competition is this one:

    "..people should have the right to decide for themselves the quality of the acoustical environment they live in."

    The sentence can be found at the WHO page Guideline Values, which also might be of interest for IT manufacturers wanting to refer to consensus on noise limits for marketing purpose.


    The IT & Noise Counteraction

    Even if the main focus for The Silent PC™ Web site is on low noise levels for comfort for those that regard low noise levels comfortable, this page has tried to explain how also low-intensity acoustic noise emissions, by calling for and competing for attention, may be involved in processes adversely affecting human well-being, performance and health.

    It can also be concluded that by calling for and competing for attention, acoustic noise emissions actually counteract the very purpose of information technology: When utilizing information technology attention is our brain's foremost tool.

    Lastly, since it isn't too complicated to build quiet IT equipment, and manufacturers, resellers and purchasers are beginning to find ways to meet also regarding IT products' acoustic aspects, will we in the future most probably "hear" more of it.


    Further Reading

    The Ergonomics of Sound: Selections from HFES Annual Meetings, 1985-2000. ISBN 0-945289-21-9.

    ICBEN - International Commission on the Biological Effects of Noise

    ICBEN Team 3 works on non-auditory health effects of noise - linking scientific and health policy aspects.

    Noise & Health - "Noise and Health is the only International Journal devoted to research on all aspects of noise and its effects on human health. An inter-disciplinary journal for all professions concerned with auditory and non-auditory effects of occupational, environmental, and leisure noise."

    Environmental Health Report 2005 - The report describes the importance of various environmental factors for ill health in children in Sweden: "Community noise is a widespread environmental problem in Sweden and is the form of disturbance that affects the highest number of people, both children and adults."

    Noise-induced extraaural effects - by Barbara Griefahn, Institute for Occupational Physiology at the University of Dortmund.

    Components of decreased sound tolerance : hyperacusis, misophonia, phonophobia.

    Decreased Sound Tolerance: Hypersensitivity of Hearing

    Things that talk: Using sound for device-to-device and device-to-human communication - An IBM Systems Journal article.

    Designing Product Sounds - Ingemansson informs.

    International Ergonomics Association - "The International Ergonomics Association is the federation of ergonomics and human factors societies from around the world. The mission of IEA is to elaborate and advance ergonomics science and practice, and to improve the quality of life by expanding its scope of application and contribution to society."

    FEES is the Federation of the European Ergonomics Societies. Its mission is to enhance the recognition of ergonomics contributing to economic development, to quality of life, to health and safety at work, and to social progress in European Countries.

    The Office Ergonomics Research Committee is a non-profit committee of companies dedicated to the advancement of research in office ergonomics.

    Staying Healthy at Your PC

    A Critique of Pure Audition, by Malcolm Slaney, Interval Research Corporation: "All sound separation systems based on perception assume a bottom-up or Marr-like view of the world. Sound is processed by a cochlear model, passed to an analysis system, grouped into objects, and then passed to higher level processing systems. The information flow is strictly bottom up, with no information flowing down from higher level expectations. Is this the right approach?"

    Neuropshychological Mechanisms of Auditory Selective Attention in Humans: A full text article on the Web from Frontiers in Bioscience, January 1, 2000, volume 5, 84-94.

    WHO on noise and protection of the human environment.

    In the article Differentiating PCs in a 'Toaster World' Intel® and Analog Devices® provide some of the latest knowledge on how Man reacts to noise, rules out the important relation between heat and noise, and tells how it can be minimized by adding thermal awareness to the PC system.

    Progress Toward A New Standard on Classroom Acoustics for Children with Disabilities: "Research indicates that high levels of background noise, much of it from heating and cooling systems, adversely affect learning environments, particularly for young children, who require optimal conditions for hearing and comprehension."



    WWCS 2007 - Work With Computing Systems - International conference on computing sytems for human benefits in Stockholm, Sweden, May 21-24 - 2007.



    1. International standard ISO 1999-1990 and American National Standard ANSI S3.44-1996.

    2. "Stress and Open-Office Noise", Gary W. Evans and Dana Johnson, Cornell University, Journal of Applied Psychology, 2000, Vol. 85, No. 5, 779783, ©2000 American Psychological Association.

    3. "Effects of simulated ventilation noise on performance of a grammatical reasoning task", Anders Kjellberg and Per Wide, Noise as a public health problem, Swedish Council for Building Research, Stockholm 1988, pp 31-36. Full text article here provided courtesy and Copyright © of Formas.

    4. "Coexistence of attention-based facilitation and inhibition in the human cortex", P.H. Ghatan, J.C. Hsieh, K.M. Petersson, S. Stone-Elander & M. Ingvar, Neuroimage, 1998, 7, 23-29.

    5. "Background acoustic noise and the hemispheric lateralization of speech processing in the human brain: magnetic mismatch negativity study", Shtyrov, Y. Kujala, T. Ahveninen, J. Tervaniemi, M. Alku, P. Ilmoniemi, R. J. Näätänen, R.; Neuroscience Letters 1998, 251, 141-144.

    6. "Noise affects speechsignal processing differently in the cerebral hemispheres", Shtyrov, Y. Kujala, T., Ilmoniemi, R. J. Näätänen, R.; NeuroReport, 1999, 10, 2189-2192.


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