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IT Noise
Last modified September 10, 2017


 

The Process of Hearing

The process that in the end results in a more or less conscious awareness of being subject to, for example, a running PC's sounds starts with the emitted energy of vibrating bodies in mechanical parts in the machine, and the turbulent air flow of its fans, putting a lot of the surrounding air particles into movement. When many of these air particles move in the same frequency, and in the same direction, will pressure waves be built. Some of those air pressure waves eventually reaches the PC user's ear.

The mechanical components in the human organ of hearing will translate the air pressure waves back to vibrations, and transmit them to the organ of corti, where they will be be converted to nerve impulses for the brain areas responsible of handling sound information.



Transformation of vibrations into sound waves


Transformation of vibrations into sound waves: Sound waves are created when atmospheric particles alternately are squeezed closer together than normal, then pulled farther apart than normal. Courtesy and © of Norsonic.


 
 
 

Pure Tones & Noise

The frequency range of human hearing is generally considered as 20 20,000 Hz. The upper range varies greatly among individuals and decreases with age and noise exposure.

A pure tone is a single frequency tone. Its opposition is the physicist's definition of noise: a uniform spectrum of pure signals; here tones.


 
 

updatedThe Two Unintentional Side-Effects

Two unintentional side-effects are responsible for sound emissions from PCs and other kinds of information technology equipment: One is the unintentional sound itself. The other is heat.


Unintentional sound

Mechanical devices most often generate sound as a side-effect. PCs commonly contain two groups of mechanical devices that account for the major part of emitted sound; storage devices and fans:


  • Storage devices
  • Almost all PCs use hard drives to store and read data. There are mechanical and non-mechanical hard drives. Non-mechanical hard drives run noiseless. The sound from mechanical hard drives emanate from vibrations of their rotating discs and reading heads. Other mechanical storage devices are readers and writers for BlueRay, DVD, CD discs, and ocassionally still readers and writers for floppy, MO, Zip, Jaz and some other disc formats.


  • Fans
  • Fans are used for active cooling purpose; because the electronic components of the computer, especially the processors, the hard disks, the power supplies, some main board chips and modern graphics cards generate heat. If some of the parts of a PC runs too hot will the machine cease functioning, or catch fire. Fans represent an easy, quite safe and inexpensive solution for to cool PC components. Sound from fans emanates from vibrations of their bearings and from airflow.

    Note: Although not being mechanical devices do some computer screens contain components that can vibrate; thus might also some screens emit a bothering sound, even if this is rare today.

    Interior of a typical harddisk.

    The interior of a typical mechanical harddisk whilst operating. Click here to download a movie with sound. Courtesy and © Hardware Analysis.


     

    Unintentional heat

    As with sound, is the heat generated by electronic and mechanical components of IT equipment also an unintentional and unwanted side-effect. The more skillful we become in designing electronic circuits and mechanical components, the less heat will also be generated. Today, however, as still most of the PC industry, magazines and users primarily are competing, writing and talking about having the fastest possible components, the trend is not clear towards IT equipment components running cooler.

    If the power dissipation from personal computer processors (CPUs) would continue to increase in the same speed as it has from 1985, would they ten years ahead emit 4 700 watts!
    (source Mikrodatorn No 1, 2003 p 24)


    The Transmeta Crusoe CPU dissipates little heat

    Most PC processors dissipate a lot heat, some don't.
    Courtesy and © Transmeta™ Corporation.


     

    Keeping sound in but letting heat out

    One of the main problems with unintentional PC sound emissions is that we want the heat generated by the different components out, but not the sound. Increased heat will tend to decrease function and shorten life time of electronic components. Thus the main problem we face when trying to avoid distracting IT noise emissions is heat - if heat wasn't an IT problem noise wouldn't either. Then we could easily enclose whatever noise emitting part in sound insulation, but now we can't, because the sound insulation would not only isolate the sound, but also the heat; worsening the heat problem. Nontheless are still most of today's IT equipment and parts not built aware of their own temperature.

    You can read more on the important relation between unintentional IT equipment sound and heat, and a sustainable solution to these issues, at the Intelligent PCs page of this site.


     
     
     

    Methods to Minimize PC Noise

    In the following will unintentional PC sound emissions be named noise. This since they also mostly are more or less unwanted.


    Selection of components

    By excluding as much as possible of mechanical and/or heat generating components, and by choosing components known to be quiet and cool running, PCs can be built to run quiet.

    By choosing a small operating system one can have the computer run cooler than with a big one. This will reduce the need for active noise generating cooling solutions.


    Dampening of vibrations

    The connection between the moving parts and the non-moving in a PC is critical. The less mechanical vibrations are transmitted to other parts of the PC, the less noise will be heard. Sometimes parts of the PC will actually amplify noise. Using rubber or other non vibration-transmitting materials to fasten the vibrating PC components can reduce noise.


    Insulation

    The bearings are critical when talking about noise emissions from mechanical hard drives, since they constitute a main surface between a moving and a non-moving part in the PC. Hence we today see an increased use of less vibration transmitting and vibration generating magnetic or fluid bearings in mechanical hard drives. Ones solution to the problem of mechanical hard drive noise is to put them in sound absorbing boxes.

    An often used solution to damper noise emissions is also to insulate the whole system unit, which is put in a big sound absorbing box.

    A problem with the insulation-approach for hard disks or system units is that we have to get rid of the heat generated in hard disks and other components of the system unit, but that the sound insulating materials also tend to absorb heat - at the best threatening the reliability of different components, at the worst causing fire.


    Optimizing cooling

    Fans used together with heatsinks represent the cooling solution today most often utilized in personal computers. They have the advantage that they are rather inexpensive and good cooling solutions, but the disadvantage that they produce noise. When carefully designed, fans can be built to run quiet. Fan ducts can be a solution for either to guide cool ambient air to a hot running system component, or for to remove hot air from this component to the outside air.

    The electronic circuits of the PC can also be designed to continuously measure the critical components inner temperature, and regulate cooling according to need; so that for example fans only are used as much as they are needed at a given moment and not more.

    One way to avoid fans is to build a PC with electronic components that produce as little heat as possible, or/and taking advantage of the physical properties of air (warm air rises giving place for new cool air), thus making the fans unnecessary: Some electronic components can be sufficiently cooled by attaching heat sinks to them using natural convection.

    A bit troublesome and a little more expensive solution for to cool PC components silently is to use more effective media than air for the cooling purpose; such as water. Water cooling will most possible be the future solution for all the people conscious about a low level of noise emissions, but not satisfied with anything else than the fastest components. Heat pipes and vapor chambers represent silent, and today more often used ways to cool PC electronic components. The combination of heatsinks, heatpipes and fans is also becomming a common cooling solution, especially for portable computers.

    Zalman Tech noiseless heat pipe cooling solution for graphic cards
    A heat pipe is here utilized for noiseless cooling of a graphic card. Courtesy and © Zalman Tech Co., LTD.



    You can read more on the important relation between noise and heat, the future of PC cooling and hardware monitoring and control on the Intelligent PCs page of this site.



    Distancing

    Distancing is a frequently used solution for to minimize the noise from system units. The system unit can be put as far away as possible from the user using long cords, or put behind a wall. KVM extenders (Keyboard, VGA, Mouse extenders) can be used to put the system unit in an other room. Using a network the PC can be booted from a remote machine, thus if not for anything else eliminating the need for a local hard drive.


    Separating the power supply

    The power supply of modern PCs accounts for some of the heat generated, and when built in the system unit needs a fan. But maybe it doesn't have to be this way: It has been said that the power supply can be separated from the system unit, and connected to it with an electric cord. Then it can be sufficiently cooled just by convection, making the fan unnecessary. People criticizing this approach has said that the fan in the power supply is more a solution for the total demands for cooling of the system unit, than just for cooling of the power supply itself, and that leaking currents will cause problems using long cords.


    Active noise cancellation

    An often asked question is if active noise cancellation can be used for to minimize PC acoustic noise emissions. The answer is no. Active noise cancellation relies on ones position in relation to the noise source, and hence will an implemention of it for PCs have to force one to sit in the same position all the time for to benefit of it.


    Shouting louder than & shutting out

    Background or headphone listening to radio, TV or music is not a way to silent a PC, but today probably one of the most commonly used methods for not having to stand hearing PC noise.

    This is what one PC user wrote to the site author: "Whilst I'm saving up my money for new silent components, I've found temporary relief from a pair of Peltor ear defenders. They're intended for people who work on building sites / airports etc; hence they reduce computer noise to almost nothing. It's not a very elegant solution, but they're comfortable (even when wearing glasses) and hopefully I can still just about hear the phone ringing / fire alarms."


    Utilizing the basic sound principles

    Awareness of the basic sound principles can make it possible to put PC noise to a minimum. Most of the solutions above are built on them. C. Gowan explains the the basic sound principles:


    Sound level goes down under the inverse square law -- in other words doubling the distance from you to the source of sound drops the level by 1/4 in an open space with no sound-reflecting or sound-absorbing surfaces. (Of course our hearing is logarithmic, so this doesn't help as much as we would like -- but it still helps a lot.) Hence the advice to get the system off the table and onto the floor.

    Sound travels via line-of-sight (like the signs on the backs of long trucks -- "If you can't see my mirror, I can't see you."). Hence the value of putting a system around the corner.

    Sound reflects. Around the corner can be worse if there is a nice reflective wall at the right angle!

    Sound is transmitted both via the air -- and by conduction in a rigid material, such as a floor or table. You may find that something near the computer is making the noise more irritating by vibrating sympathetically.

    Sound can be absorbed. This is the principle used in modular office wall systems like Herman Miller Action Office. You can experiment with a small cork bulletin board or a piece of scrap carpet on a nearby surface to absorb instead of reflect sound.


     
     
     

    Definitions of Notions Used at the Site


    Definition of PC

    When talking on PCs at this site the term is used as personal computer in its widest sense -  a PC is a computer designed to be used by one person at a time. Hence it follows that here the term PC covers all personal computer hardware systems, using any personal computer operating system.


     
     

    Definition of Silent

    The use of the word silent in conjunction with PC at this site refers to a personal computer not emitting any unintentional sounds. A silent PC here equals a noiseless PC. Out of this comes the natural fact that a silent PC at this site remains a multi-media machine; still capable of playing music and other sounds at any level.

    Low levels of unwanted sound has nothing to do with low performance. Highest possible performance is what ergonomics is all about.


     
     

    Definition of Ergonomics

    Ergonomics is the application of scientific information concerning humans to the design of objects, systems and environments for human use. Defined by The Ergonomics Society.


     
     

    Definition of Acoustic Comfort

    The notion acoustic comfort is here used for products and environments featuring comfort regarding their acoustic aspects. The acoustic comfort notion is close related to the sound quality notion. Both acoustic comfort and sound quality are subjective notions. This doesn't contradict the fact that humans in common can aggree on what sounds and acoustic environments are to be regarded comfortable. Note that acoustic comfort isn't the same as absence of sound: Total and sustained silence is very uncomfortable for most humans.


     
     

    Definition of IT

    The term information technology (IT) encompasses all forms of technology used to create, store, exchange, and use information in its various forms [1]. It refers to the collection of products and services that turn data into useful, meaningful, accessible information [2].

    The main focus of this site is on personal computers, even if much of the thinking here can be applied on any kind of information technology equipment, and sometimes on any kind of technology.


     
     

    Definition of Sound

    Sound, according to physicists, is wave motion in an elastic medium (solid, liquid or gas). Sound, according to animals with ears, is that which is heard.


     
     

    Definition of Noise

    The broad definition of noise by Webopedia (here shortened):

  • In communications interference (static) that destroys the integrity of signals on a line.
  • In general, anything that prevents a clear signal or message from being transmitted.
  • Karl D. Kryter has a very precise definition of acoustic noise: "An audible acoustic energy that adversely affects the physiological or psychological well-being of people" [3].

    To make it simply is the colloquial definition of acoustic noise used at The Silent PC® Web site: noise is unwanted sound. When talking about noise emitted from PCs at this site it's always audible noise.


     
     

    Definition of High-intensity & Low-intensity Noise

  • The term high-intensity noise here refers to noise causing auditory health affects. It is commonly said that auditory health effects take place at a continous sound pressure level of 85 dBA or above, but some scientific studies have shown that they might take place at even lower levels at long-term exposure. Therefore, an auditory safe noise level might be continous exposure below 70 dBA.
  • Low-intensity noise is here defined as noise with levels not causing auditory health effects, ie noise levels below 70 dBA. Low-intensity noise is characterized by such a low energy content that it doesn't damage hearing. Adverse effects of low-intensity noise emissions include distraction and speech masking. Read more on this at the Ergonomics page.
  • Note that Low-intensity noise is not the same as low frequency noise. Sound frequencies between 20 and 20,000 Hz are what can be heard by most young people. As people get older, the higher frequencies become more difficult to hear. Commonly low frequency noise is defined as noise with a dominant frequency content of 20 to 200 Hz. Out of this explanation comes that low frequency noise at the same time can be either high-intensity or low-intensity noise. Humans in common regard low frequency noise the most unpleasant kind of noise, and high-intensity low frequency noise thus can be extremely unpleasant.

    It might be interesting to know that tigers, whales, rhinos, elephants and some other animals communicate using low frequency sound.


     
     

    Definition of Acoustics

  • Acoustics deals with the science of sound, the transmission of vibrations in gases and solids. Although acoustics implies that you can hear signals, acoustics also deals with signals both below (infra sound) and above the highest frequencies of human hearing (ultrasound). (from NI)
  • The word acoustics is often also used as an abbreviation for acoustic noise emissions. The word acoustics seems to be prefered when wanting to market products as quiet: "Low acoustics" or "Industry's best acoustics" may sound more positive than "low noise emissions" or "Industry's lowest noise emissions". In a similar manner is "low acoustic signature" used in product marketing.

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    Further Reading

    Noise Reduction Using Dampening in Voice Coil Motors/Actuators of Hard Disk Drives - interesting reading from IBM/Hitachi.

    About Temperature

    "Noise in Computing: A Primer" - some most valuable writing by Mike Chin at SilentPCReview.

    EWALD - Exciting World of Acoustical Links from Denmark: A comprehensive collection of interesting sound links.

    "Measurements and Judgments of Sound in relation to Human Sound Perception" - a valuable report by the Danish knowledge centre DELTA.

    Design Sounds - A Swedish exhibition about sound and design. Some most interesting pdf-documents to download there.

    Acoustics.org provides easy access to information in the broad field of Acoustics. Whether you are a student, a seasoned professional, or simply an interested layperson, this site will be a valuable resource in your search for information.

    Active Noise Control FAQ

    National Instruments Corporation explains Acoustic Standards, and how the ECMA, ISO and ANSI standards are related and synchronized.

    What is a decibel?

    Handbook for Acoustic Ecology - teaches the basics of sound and noise.

    A Poor Man's Tour of Sound Levels and the Decibel by Michael R. Chial, Ph.D.

    Minimizing acoustical noise in electronic systems: An Electronics Cooling magazine article by George Maling, Noise Control Center and David M. Yeager, Motorola Corporation® describing the three elements required for a low noise design, selection of air moving devices and design of systems for low noise, quantitative limits on the noise emissions of equipment, and measurement procedures which can be used to determine the sound power level of the equipment.

    HyperPhysics Concepts on Noise

    Introduction to Sound Recording: also includes comprehensive information on sound and noise basics.

    Acoustic Overview is an Intel Corporation® article on the increasing importance of including acoustic considerations early in product design. It provides a lot basic facts on IT noise emissions, and how to master them.

    The Swedish flag - click to come to Tyst Dator Tyst Dator - on noiseless computing in Swedish.


     
     

    References

    1. search390.com Definitions

    2. ITAA - Information Technology Association of America - "The U.S. Information Technology Industry: A Brief Overview"

    3. Kryter, Karl D., "The Effects of Noise on Man", Academic Press Inc., 1985 (ISBN 0-12-427460-9).

    4. International Standard ISO 9296:1988 (E) "Acoustics -- Declared noise emission values of computer and business equipment"


     

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