1. ## Sound Absorbtion

Which is better and what is the difference between sound absorbing foam tiles and rubbery flexable padding thats been sprayed with Barium.

The flexable rubbery padding has a "sound transmission class" of 27 and the foam tiles are measured in coefficients.

Tiles: http://www.stopthesound.com/sonex-va...fications.html

I assume the foam would be lighter but I'm sure there are more differences.

2. ## Re: Sound Absorbtion

I believe that they do different things. One is intended to reduce vibration (barium is heavy), the other to baffle sound. Here's some details from an old sounddomain post as applied to car audio.

Mass loading is exactly what it sounds like. You add mass to a panel to lower it's resonant frequency. [physics] Everything vibrates best at a specific frequency, but will still vibrate at every frequency to some degree. The idea behind mass loading is that by adding the extra mass, you make it vibrate at a lower period (frequency) to the point where it drops out of the audible range. For example, if you have a fixed energy input (road noise) and a fixed sound level at that energy level, when you add mass to the panel, you are are making it so that it now requires more energy to maintain the same level of output. Since it can't do that (fixed energy input) the noise level must go down. [/physics] So long story short, the heavier a panel is, the more energy it takes to move it. Since the level of energy is fixed, the noise level goes down.

Barriers are exactly like what you think they'd be. They prevent the sound from traveling from one location to another. This is done by combining methods of absorption and deflection. Usually the easiest way to absorb sound is to use a medium that can convert vibration into low level heat. Most closed cell foams are very good at this. (open cell foams are not as effective and often absorb water, causing all sorts of other problems) The best way to deflect the sound is to use a material that is stiff and dense so it won't allow sound to cause it to vibrate. The best barrier materials have a combination of both attributes in that they have a layer of foam with a layer of dense vinyl backing. This absorbs the brunt of the sound in the foam and what isn't absorbed gets reflected back into the foam by the dense vinyl so that the foam gets another shot at it.

Mass loading is particularly effective against lower frequencies as they are the highest energy and easiest to move out of the audible spectrum. Barriers and absorbers work much better against the higher frequencies in the audible spectrum.

There are several materials that attempt to do a lot of jobs at once. A good example is Dynamat Extreme and other styrene and rubber mat materials (RaamMat, FatMat, eDead, etc...). They use a mass loader like rubber impregnated asphalt and an absorber like styrene monomer to balance the properties of both. They act in conjunction as an absorbing mass loader and they are very popular for that reason.

In my not so humble opinion it is always best to use a combination of materials to achieve the best sound deadening. A layer of mass loading material to take out the lows and a barrier/absorber to take out the mids and highs give a well rounded solution to your deadening quandary.

3. ## Re: Sound Absorbtion

Going from this article it appears to me that computer stores are selling the wrong type of noise reduction material. http://www.acoustics.com/tutorial01/slide1.html

They seem to be selling the foam material (like in radio stations) which has a good noise reduction coeffecient (NRC) however that matieral is more designed for stopping reverberations in large spaces it is not a sound barrier.

It is the padding with a high sound transmission class (STC) that is designed to stop noise from one area going into another area which is really what we would be after for a computer case? Keeping the sound inside the case and not passing through the walls? We don't care that the case is producing a nice clear hum.

4. ## Re: Sound Absorbtion

Agreed.. mass loading a case panel is the way to go, ie: Antec P180 case.. triple layer side panels absorb loads of noise, making the case very quiet.

Ideally, you would want absorbtion of vibration from things like fans and hdds, and then dead panels to prevent the remaining noise from airflow(fans), and mechanical noise (hdd's, odd's) from escaping.

5. ## Re: Sound Absorbtion

Bit of a necro post, but I ran into some rubberized spray material (forgot the brand name) at Home Depot that would do well for deadening metal panels. It's similar to the stuff they show on TV that seals leaks in roof drains... the one where they show a rowboat with a screen door installed in the bottom... Anyway, Home Depot had a board up with some downspouts and other metal objects on it, all sprayed by this stuff. Sounds dead flat when knocked on. My system case isn't metal, but next one I build will have this added.

6. ## Re: Sound Absorbtion

That stuff can also be purchased at auto parts stores and it's not bad for mass loading. I would much rather use something butyl-rubber based and NOT spray-on because it's a lot harder to get precise application with a spray. Plus it's not necessary to load the entire panel, so you can leave sections blank and it will still have sound deadening effects, but you could perhaps hide it behind a motherboard or whatnot.

7. ## Re: Sound Absorbtion

A bit of thread necro, but:

Aside from increasing sheer chassis mass, are there any effective sound-damping options which don't interfere with thermal efficiency?

I've actually compared a couple new 120mm 1300rpm Noctua fans (with precision cut noise-reducing patent-pending "Vortex Control Notches™" on each fan blade) against a variety of new generic 120mm 1200-2400rpm fans. Airflow (at least, as measured in terms of inner case temperature) was very much the same for every fan when operated ~1200-1500rpm. But the Noctua fans measured <19dB while the others measured ~22-27dB (and in one instance 36dB). I'll admit my old Extech noisemeter ain't so accurate at these low levels, but a decibel is a decibel, and a 3dB difference means an apparent difference of half volume intensity.

Aside from Noctua's patented VCN™ - which does seem marginally effective but nonetheless looks a lot like a big overhyped marketing gimmick - I notice that it's pretty tough to find fans which have low noise and high performance. Any recommendations? For me the real deal-breaker against these Noctua fans is actually the bearing, some kind of "SSO" hybrid fluid-magnetic thing rated for a mere 50,000 hours in vertical placement only ... ie, fancy acronyms aside it's basically a lubricated sleeve-bearing, not a hassle worth 3dB, moreso since they're low-end performers with a mid-end pricetag. Incidentally, the other Noise Controlling options packaged with the fans are just extra power cables which have inline resistors to reduce voltage and rpm, yeah right paying for compromises wtf is that.

As an experiment I filled out the Noctua fan notches with tape (and made sure it's all balanced) and took another reading ... 21dB. Tomorrow's experiment will be to carefully duplicate these notches as best I can on the most similar fan I have available, to see if it changes 1300rpm noise level. Noctua's marketing literature contains fancy graphs which suggest detailed computer modelling and analysis was involved, which I probably won't bother attempting to duplicate, but I suppose different rpms would require different notch geometries, and there are probably practical limitations on this tweak.

8. ## Re: Sound Absorbtion

Actually those notches are designed not to lower the SPL but to rather change the sound of the fan so it's more pleasent/less noticeable.
It creates a more random noise which blends with background noises better than a constant droning sound that would normally come from fans.

9. ## Re: Sound Absorbtion

I'd read that in the Noctua literature, but my noisemeter is really only an addon function in my multimeter, and it only measures dB(A) ... which is apparently a frequency weighting system designed to better approximate human perceptions. The notches do knock a couple dB(A) off total measured sound output, and as best I can tell observationally they do seem to make the fan sound quieter overall (that's why I got two of them), it might be a sort of illusion designed to trick the ear/brain but it's still very convincing. All my measures were taken in a large environment filled with a moderate noise floor.

My final verdict is that the gimmick isn't worth it; the fans are substandard in other critical parameters (and perhaps I can duplicate the notching pattern anyhow). I'm actually going to talk to one of the plant engineers and see what I can learn about fluid vortex physics kinds of stuff. I've wondered before about optimum number of blades, number of rotors, angles and geometries of blades, etc ... I wouldn't be surprised if aerospace guys have all the answers and mass-produced computer fans are just arbitrary symmetrical "good enough" designs.

10. ## Re: Sound Absorbtion

Tell you what when I get home in a week I will compare noctura p12 with scythe mental typhoons and a cm silent 120mm fan.
Got a high quality SPL meter at home and if you want can measure noise at the same airflow because I also have an airflow meter will need to wait a week or so tho, house sitting atm.

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