Do windows let out noise unnecessarily?

engseng · Post by **engseng** » Fri Jul 09, 2004 10:57 pm

Well, I've seen all kinds of windows on casings, including the unique Lian Li aquarium window. But I wonder if windows let out noise unnecessarily.

A window would be useful to see if the fans in my case are running or seeing if the water cooler is not leaking anything. I'm not the type to install lights and all the other kinds of stuff. But if windows let out more noise than it should, is it a better choice to choice the non-window side-panel if I want to shut off more noise?

TimO · Post by **TimO** » Sat Jul 10, 2004 2:28 am

Considering sound transmission loss through a case side panel, you should not have to worry about a case with a window allowing more noise through than a solid panel. The difference in sound transmission between a typical 0.8mm steel panel, a 1.5mm aluminum panel, and a 1/8" polycarbonate window panel is insignificant.

I have attached (see below) a very basic graph of the sound loss through these panels. I say very basic, because the lines should not be perfectly straight as they are shown. However, most of the dips in tranmission loss that do exist on the plots would occur at higher frequencies, for such thin panels. (Actually, at these thicknesses, aluminum would probably turn out to be the worst of the bunch.)

At any rate, for the levels of noise we are talking about within the case, there will be no audible difference in sound transmission between the different panel materials. They will all block almost all of the sound from transmitting through them.

Of much more concern is how many openings there are between the noise sources inside, and you, the observer outside, as it is primarily through these openings that the sound escapes. With proper quiet equipment, you can worry less about these openings.

One last concern: There is surely some benefit to using sound absorption foam within the case, on the side, top and bottom panels. Consider, therefore, if at some point in the future you may try for that extra dB of attenuation. You can certainly put foam on the inside of a clear window, but you lose the window feature, and it would look quite ugly.

Personally, I would go for the window, and assume that you won't need acoustical foam inside the case, at least not on that panel. You are right, there is a big advantage to being able to monitor the inside of your system without pulling the case apart.

Hope this helps.

Tim

peteamer · Post by **peteamer** » Sat Jul 10, 2004 4:25 am

Welcome to SPCR TimO.

Nice input.

Is noise/acoustics a field of interest for you ?

Pete

TimO · Post by **TimO** » Sat Jul 10, 2004 4:55 pm

Thanks for the Welcome, Pete.

Yes, acoustics and noise control are definitely of interest to me -- I'm actually an acoustical physicist/noise control engineer, and have been reading the articles on SPCR for several months now. I've seriously been thinking about getting into the business of silent computing, perhaps designing for one of the hardware manufacturers. It also may be more fun just building, seeking quiet components. Anyway, I couldn't help but respond to that last question.

Thanks again,
Tim

Cave Creek, Arizona, USA

efcoins · Post by **efcoins** » Sun Jul 11, 2004 1:40 pm

You said
"there will be no audible difference in sound transmission between the different panel materials."

But according to your graph there is about 5dB difference between a window and a solid side pannel. 5dB seems quite substantial to me.

josephclemente · Post by **josephclemente** » Sun Jul 11, 2004 2:11 pm

This first window I ever did was made out of glass. I wonder if glass is better from a noise perspective?

TimO · Post by **TimO** » Sun Jul 11, 2004 3:30 pm

Hi efcoins,

You said
"there will be no audible difference in sound transmission between the different panel materials."

But according to your graph there is about 5dB difference between a window and a solid side pannel. 5dB seems quite substantial to me.

Good question. What I actually said was, "for the levels of noise we are talking about within the case, there will be no audible difference in sound transmission between the different panel materials."

You're absolutely right that 5 dB would be an audible difference, if you were actually hearing that. But you probably never will. Suppose your heat sink generates 30 dB at 1m. Since most of the fan noise is above 500 Hz, then even the loudest part of the noise getting through the worst panel will be at most 15 dB. Most of the noise will be below this, for all the panels. The implication here is that the noise getting through any of the panels will be inaudible relative to the noise escaping through case openings. If the noise is inaudible, then the difference between the panels is inaudible, regardless of the theoretical difference on the plot.

Put another way, if you could seal your computer in an airtight box, it wouldn't matter which material the sides were made of, because you wouldn't hear the thing regardless. Any of the panel materials would block the noise pretty much down to the noise floor.

Tim

TimO · Post by **TimO** » Sun Jul 11, 2004 3:48 pm

josephclemente wrote:This first window I ever did was made out of glass. I wonder if glass is better from a noise perspective?

Glass has similar properties to aluminum, as far as sound transmission is concerned. Of course, you would need thicker glass than aluminum to alleviate the breakage factor. Again, this would not likely make a practical difference in noise containment.

Tim

efcoins · Post by **efcoins** » Mon Jul 12, 2004 7:58 am

I see, thanks for the explanation
But you also said
"There is surely some benefit to using sound absorption foam within the case, on the side, top and bottom panels"

If the existing side pannels block virtually all sound from passing through them, the how can lining the case with sound absorbtion material make any difference?

If the material blocks off some holes in the case, that would make a difference, but people report worthwhile improvements by just increasing the sound absorption of the case pannels.
You appear to be saying that increasing the sound absorption of the pannels helps, but reducing it makes no difference.

TimO · Post by **TimO** » Mon Jul 12, 2004 7:24 pm

efcoins wrote: But you also said
"There is surely some benefit to using sound absorption foam within the case, on the side, top and bottom panels"

If the existing side pannels block virtually all sound from passing through them, the how can lining the case with sound absorbtion material make any difference?

Again, good question. There are two different effects we are talking about here. One is blocking sound transmission *through* the panel. The second is *absorbing* sound that is bouncing around inside the case.

The side panel material (steel, aluminum, plastic, etc.) affects how much sound is blocked, and I think we have established that it probably doesn't matter what material is being used.

The absorbing foam lining the panels hardly affects sound transmission through the panels, but what it does do is absorb sound inside, so less will find its way out through the openings. Neither is the absorption foam meant to cover any holes, but simply to reduce sound that otherwise would reflect off the inside case panels and eventually reach the openings to the outside.

So, while I would not expect a change in panel material or thickness to improve sound reduction, I would definitely expect sound absorption foam lining the panels to do so.

Tim

efcoins · Post by **efcoins** » Tue Jul 13, 2004 8:56 am

Thank you

Bort · Post by **Bort** » Thu Jul 15, 2004 10:24 pm

I guess the next step would be double glazing for the window, and maybe even a dual layer metal case. I know car manufacturers sometimes use a double layer firewall to block out the engine noise - two layers of metal, I think with damping material in between.

Mercedes have even started double glazing the side windows to block out noise.

Double layering the case metal would be a tricky for a DIY job though.

TimO · Post by **TimO** » Thu Jul 15, 2004 11:52 pm

Bort wrote:I guess the next step would be double glazing for the window, and maybe even a dual layer metal case. I know car manufacturers sometimes use a double layer firewall to block out the engine noise - two layers of metal, I think with damping material in between.
...
Double layering the case metal would be a tricky for a DIY job though.

You're right, it would be difficult to implement DIY layering.
But again, I really don't think using thicker, or better sound blocking, material would make a difference anyway. As I alluded to earlier, the noise problem is due to the open-air path that exists between the noise sources and the observer outside the case.

Beyond quieting the actual sources, then as far as casement is concerned, it would be much more helpful to: 1) seal as many gaps/holes as possible between inside of case and out, 2) use sound absorption material inside case, 3) prevent case from vibrating. I believe #1 may be more important than many realize.

I read a thread recently (http://forums.silentpcreview.com/viewtopic.php?t=13092) which described acrylic cases as perhaps better for quietness, because 1/4" acrylic stops sound better than typical case steel or case aluminum. In theory that is true, but enhancing the sound transmission loss of the case panels will not likely achieve much effect (see previous posts in *this* thread for explanation). Again, #1 above should be considered. Small openings let out a lot of noise from inside the case.

In the thread referenced above, several stated there that perhaps acrylic should be used as a quiet case. Well, I agree that it certainly *can* be used, and just as effectively as a non-acrylic one (except for the aesthetic problem with adding absorption material inside). But again, the real issue is not the sound blockage, but the openings. If acrylic case panels "seal" better than non-acrylic, thus better eliminating gaps, then there would be an inherent advantage, but not because of the increased sound transmission loss due to the panel material or thickness.

Cheers,
Tim

Do windows let out noise unnecessarily?

Do windows let out noise unnecessarily?

Case window won't negatively affect noise.

Thanks for the welcome