The Computer Noise Guide

By Michael Farnsworth

In order to understand what computer noise is we must first understand three related terms:

1. What is sound?

Sound is any vibrating energy we can detect through hearing or feeling.

2. What is silence?

Silence is the complete and absolute absence of sound. As the illustrious creator of Quiet PC defines sound: "Silence is the sound a rock makes when you hold it to your ear."

3. What is noise?

Noise is unwanted, undesired sound. Noise can literally harm you and those around you. It may not be evil but it is certainly "BAD", meaning not good.

How Computer Noise and Sound are Measured:

An introduction to the mystery of decibels (and this one isn't quite as easy to define, so hold on for a brief, but hopefully mildly illuminating, ride).

You may have come across the term "decibel" (abbreviated as "db") in reference to how loud a sound is. If you aren't way into physics the term can be confusing, so here's a way of thinking about decibels that may help. The range of sound humans can experience between silence and pain (yes, pain is the top end of audible sound pressure) is so incredibly, hugely vast that it can't be conveniently expressed in a scale like miles, kilometers, or gallons. Rather similarly to trying to express the distances between objects in outer space for which we use "light years" (the distance light travels in one year at a speed of 186,000 miles per second) and yet not exactly the same, we use decibels to express a range of energy that increases logarithmic-ly. The numbers get too crazy to think about without some type of scale to help us in our thinking process.

Once more in English ... decibels describe a logarithmic increase in energy as opposed to a linear increase in energy. Wait a minute, I meant "English", not physicist-ese. One more time please, from a different angle. Decibels are used describe sound energy in relative units, not absolute units. Let's try some examples that may be used as a handy reference to what decibels mean to us in the real world and in a useful way.

Human hearing is so sensitive that if it was any more sensitive we would constantly be able to hear the beating of our own hearts. In fact, when you walk into a special chamber (an "anechoic" chamber) that absorbs all reflected sound and which is also completely isolated from all external sound anyone with halfway decent hearing does indeed hear the beating of their own heart. Normal human hearing is so sensitive we can hear molecules of air moving if everything else is completely silent. Pretty wild, huh? In other words, with normal hearing we are capable of detecting pressure variations of less than one billionth of atmospheric pressure and the threshold of hearing corresponds to air vibrations on the order of a tenth of an atomic diameter. That just impresses the heck out of me, I mean really ... tenths of an atomic diameter? Gives one the impression that noise could possibly re-write your DNA sequencing.

Okay, so this proves even really tough men (and women) are very sensitive (unless they are deaf). Back to decibels ... they are used to describe how loud sound is in relation to the base point of silence. Perfect silence is stated as "0 db of sound pressure level" (SPL). The ambient sound level (the average volume level of audible SPL) of a well-designed recording studio is approximately 30 db. If you are in a good recording studio it will probably appear to you to as if there is no sound at all unless someone is making some, but even special, very well-designed air conditioning (HVAC) systems will create very low levels of noise simply by creating airflow. We can use this concept for a reference point however, 30 db ambient sound is pretty darn quiet for most of us. Well, there's a caveat ... if the sound in there is not at a frequency that is distracting or annoying then that volume level may be acceptable. Generally, the measurable ambient sound in a recording studio will be low frequency (just the air slowly moving as it is circulated) and we tend to feel low frequencies as much or more than we actually hear them. The lower the frequency, then less we tend to hear it and the more we feel it. I can't resist pointing out that when Janis Joplin was asked why she liked singing with a band she replied that she loved the feel of the bass on a certain anatomic proximity. You really do "feel" the bass frequencies.

Noise usually occurs at higher frequency ranges and in the ranges of audible vibration we are most sensitive to. This means that we can be annoyed by computer noise even when it's only at the 20 db level of SPL. Hey, you're starting to get the hang of this now, aren't you! The speed of vibrations which can humans can hear range from approximately 20 vibrations or 20 CPS (Cycles Per Second - one vibration equals one cycle) to 20,000 CPS. We are most sensitive to sound frequencies in the 1,000 CPS area. As a rule, only dogs and very strange people like The Beatle's recording engineer Geoff Emerick can hear up beyond 20,000 CPS consciously. "Hmmm ..." you may be wondering, "why did he say consciously?" Well, "he" (meaning: "this author") said (or more accurately "wrote") that because most of us really do hear up in the dog range at around 27,000 CPS, we just don't know when we are hearing stuff way up there. Tests prove through observations of our REM while sleeping that we do indeed respond to it, therefore we must be hearing it. And if we can hear it and it isn't something we like hearing then it's irritating ... noise.

In other words, even 20 db of junk sound at around 1,000 CPS will annoy us, it will likely make us cranky. We will be less productive, more irritable, and far more prone to feel like kicking the dog when exposed to it (the noise, not the dog). We shouldn't kick dogs (most of them, anyway), nor should we be made to feel cranky and irritable by some lousy piece of poorly-designed computer hardware. We just need to be able to figure out what is making the offending computer noise and be able to deal with it summarily. Think of it as creating a firing squad for the offending PC noise maker to be deployed once we identify who the trouble maker is (or noisy trouble makers are). Computer noise is evil. Think of the dogs!

Okay, a two decibel increase in volume can barely be detected by most people, but a six decibel increase will double the volume. Let's consider that it takes 50 watts of amplifier power to be twice as loud as a five watt amplifier. To get volume twice as loud as a 50 watt amp can produce you need a 500 watt amp and so on. With decibels the energy increase with respect to volume is even weirder. Psycho-acousticians (folks that deal with perceived rather than measured sound pressure levels) generally agree that a change of 10 dB of sound pressure level causes one to perceive a doubling of loudness. Yet, the human body perceives ten times the sound-power as being only twice as loud while 100 times the sound power is perceived as only 4 times as loud.

You can see how wacky it gets trying to do all the math, so let's use some common sense and real world examples to understand computer noise and how to get rid of it.

The Official Glossary of Computer Noise Terminology

Types of computer noise

  1. Hum:  Why do computers hum? Because they don't know the words! Seriously, a "hum" is generally a steady, low-frequency vibration like your refrigerator makes.
  2. Whir:  A whir is like a hum but at a higher frequency. Not as high as a squeal or a whine, though.
  3. Squeals and Whines:  A squeal is sort of an abrupt, intermittent whir but at an even higher frequency. A whine is similar to a squeal but steadier. Sometimes intermittent, but not as abrupt as a squeal.
  4. Rattles and buzzes:  These types of sounds may or may not be intermittent. They may occur across several frequency ranges simultaneously (and at the same time).
  5. Grinding:  A faint intermittent staccato type of sound often blended with a bit of whine.

How is computer noise created?

  1. Hum - this is usually generated by the computer's power supply and it's often amplified by the computer case. (More on that later.) Sometimes it can be generated by the larger computer fans running at medium RPM.
  2. Whir - this is most likely caused by computer case fans, CPU fans, and sometimes video card fans or power supplies. If you are playing a CD ROM or DVD it may be from the CD ROM or DVD drive spinning.
  3. Squeals and whines are often made by smaller-sized fans spinning at higher RPM speeds when starting up and/or running. Sometimes the culprit can be a hard disk drive whining.
  4. Rattles and buzzes are usually caused by noise made by components in the case such as fans, hard drives, and CD or DVD players, often vibrating the computer case.
  5. Grinding sounds are usually made by the hard disk accessing files on itself. Hard drives can also make a whining noise as they are running and this may or may not be intermittent.

How sound travels - The medium transmits the message!

Sound travels through the air from its source to our ears as waves by vibrating air molecules and in this instance the air is the "medium". Water, wood, steel, aluminum, plastic and other materials can also allow sound vibrations to travel through them as mediums, too. If a material is too thick to vibrate, such as lead, it can't transmit sound waves. Likewise, if a material is too pliant (soft) it will not transmit sound waves, it will simply absorb the energy instead. (Please note the restraint as I resist the obvious joke fodder with regards to "mediums". Floating trumpets in the dark, anyone?)

Special Note To Those Who May Be Concerned About Such Things: Interestingly enough, "sound" as interpreted in reality by quantum physics does not technically exist at all until it is experienced in our brains. Like, "Wow", dude!

Mechanical Transmission:

When one medium is in direct physical contact with another then sound wave energy will be transferred mechanically from the source medium to the new transmission medium. This is called "mechanical transmission". Sound waves can transfer from air to wood, from wood to metal, and then back to air and so on, but with every transfer from one medium to another some of the wave energy (volume, or more properly "amplitude") will be lost due to the different densities of the materials. Every different density of material will have it's own particular resonant properties meaning it will like some frequencies better than others.

Dampening (Damping), Absorbing, and Baffling Sound:

There are three ways to control sound once it has been emitted. Sound dampening (the proper term in physics is "sound damping") refers to stopping the mechanical transmission of audible vibrations in physical objects by attaching a very dense yet pliant material directly on the vibrating body. (Again, I'm resisting the temptation to exploit obvious joke fodder here.) A heavy material is often sprayed into the interior cavities of automobiles to deaden sound vibrations, for example. It works in two ways, the sound of the car stereo will be better due to the elimination of unwanted resonant self-created frequencies interfering with the music or speech being played on the sound system plus it reduces the road noise thus allowing the stereo to be heard more clearly. Sprayed materials are not recommended for use inside computers however as the operating temperature of some internal components can get very hot and many sprayed acoustic materials are potentially flammable under such conditions. There are special "barrier mass" sheets of material specifically designed to be used inside computers to prevent the case from actually amplifying the sound while transmitting the waves outside the case which are fireproof. Another method of stopping mechanical sound wave transmission from the case to whatever the case is sitting on (that could act as an acoustical amplifier and transmission medium such as a table or wooden floor) is to use computer feet made from Sorbothane or a similar material that is pliant enough to absorb and negate all the acoustic energy that tries to pass through it.

The second method is to absorb as much of the airborne acoustic sound wave energy as possible with specially-designed, open-cell foam sheets placed inside the computer itself. These sheets act in two ways, one is to deaden sound transmission by absorbing the bulk of the energy that hits it thus damping it and preventing it from transferring into the case itself. The second advantage is that the sound waves are effectively and efficiently broken up then absorbed into the open cells therefore not reflecting the sound waves back into the interior of the compute case. Materials that dampen but do not absorb noise aren't that efficient because "bounced' internal computer noise will simply escape through the fan ports. If you look at a computer fan port when the fan is switched off you will realize there is a lot of space for noise to travel through and the same 'hole' exists even when the fan is on, just don't test this statement with your fingers when the fan is in motion. Absorbing as much noise as possible inside the case will prevent that from happening very effectively.

Eliminating unwanted computer noise by individual component selection:

The most effective approach is to simply specify before you purchase (or upgrade to if you've already purchased)  individual components that don't generate noise at all, or at least as little noise as possible depending on how heavy your hardware performance requirements are. Quiet fans are very inexpensive and there are a few other specialty components such as vibration-absorbent grommets and feet that will really cut down on mechanical transmission of sound very effectively. Also look for CPU coolers with high-efficiency heatsinks, specially designed power supplies with large, slow-moving fans or even no fan at all.

Try to find noise and SPL measurement specifications that include decibel ratings which reflect standard testing procedures such as "A" weighted and measured at one meter from the component sound source on-axis at full operational speed. There are many ways to fudge sound measurement specification and testing data. You need to ensure that you are getting honest and accurate information. Caveat emptor (translation = don't let yourself get sucked in by cretins).

If you are starting from scratch designing a system first figure out how much horsepower you need, i.e. CPU speed, number of cores/CPU's, how much memory and your required motherboard bus speeds, then you'll know what CPU's you are dealing with and you can start with CPU coolers. Look for very quiet  hard drives next and also for quiet CD /DVD drives, they almost all come with published noise specifications these days. Shop for the quiet, reliable ones from reputable manufacturers and dealers. Bear in mind that cooler operating temperatures for all components means extended component life and also that less generated heat to dissipate the less computer noise will be made doing so. If you need video horsepower look for special heatsinks first (heatsinks are silent) and video fan/heatsink combinations second to silently dissipate heat thermally. The less air you need to move the quieter your computer will be.

Choose a power supply with enough beef to run everything and still have power to spare. An under-worked component will not get as hot as one that is working really hard all the time.

Finally, choose a case that is designed to have as little airspace between panels, bezels, etc.  as possible and with thick enough panel to provide some mass that isn't prone to mechanical transmission. If you have a case outfitted with sound absorbent plus sound damping materials you will have covered all the bases along with all the cracks. You should look for cases with tight-fitting panels and bezels, the tighter the better. This will reduce buzzes and rattles, escaping noise, and acoustic amplification of unwanted noise vibrations in general.

And in The End ...

Oh yeah, back to decibels ... you don't need a sound meter to know if you're hearing your computer or not, just use your ears. Just in case you need a reference ... remember that the sound and noise level generated is the total sound of all the components inside the case including all of the fans plus any acoustic amplification from the case vibrating, plus any mechanical transmission of sound wave energy to any potential medium outside the case. If your computer is generating over 30 db of "sound" (and let's be honest: it's COMPUTER NOISE!) ... then it's louder than you should ever have to tolerate unless it's iron with way serious beef to it. Okay, the Space Shuttle is loud for a reason, I get it.

If your computer is generating 40 db of noise it's equivalent to being in a reasonable quiet library, 50 db of noise is the typical noise level found in the average household, a vacuum cleaner from five feet away is 70 db, a loud nightclub is usually from about 90-110 db and once you get to 125 db you've hit the threshold of pain. And you need to consider the content of the sound. Loud music is one thing (provided you enjoy the type of music being presented) but loud noise is very different, even at the same relative volume. The bottom line is that you can eliminate computer noise and, since the average North American now spends more time on the web than they do watching television, eliminating computer noise is even more vital to our sense of well-being. It's easy to do too, now that you know how.

Hope you enjoyed the ride.

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