Questions about noise

[Skulltrail]

I have been specing out various possible builds as a replacement / major overhaul to my main computer. Whereas the previous one was very much a case of performance above all else, with the next one I am far more concerned about noise levels, especially as I typically run at 50% load due to various virtual machines running in the background, and when I’m not actively using it the GPU is used for folding.

So, the questions:

1. Is noise level cumulative, or does simply the loudest component drown out the rest, not allowing for varying pitches etc.?

2. Will 4x 500GB disks in RAID be significantly louder than a single 2TB?

3. Do automatic fan controls on motherboards generally overestimate rotation requirements for fans, and as such is there much to gain in terms of quietness from using a fan controller (I was thinking of a Scythe Kaze Server)?

Thanks in advance!

[ed^chigliak]

80dB + 80dB = 83dB
80dB + 50dB = 80dB
Loud noise drowns out quieter noise.

4 drives will make more noise than 1
12dB + 12dB + 12dB + 12dB = 18dB
1 drive = 12dB
4 drives = 18dB

[Pob255]

1 yes and no

2 depends on the drives

3 depends on the motherboard


The loudest thing will be the main noise you'll hear, however pitch comes into play when you talk about sound and how some sounds can reinforce other noises.

This is where maths and reality clash, Sound is subjective when you talk about how loud a sound is the you hear.
It's not just about dB but frequency range as well.
To put it simply, you have two fans one is louder than the other however they are at different pitches, when both are on it will sound louder to your ear because while the raw dB value has not gone up the frequency range of the sound has expanded.

Which is where things start getting tricky, if you use all identical fans in your pc then the pitch and dB will be (roughly) the same so they will reinforce each other and end up with a higher dB value.
If you use different fans with different pitch and dB then you'll mainly notice the loudest and while the dB will not go up it will round louder to you because the sound is now over a larger frequency range.

Making pc's quiet does require a bit of trial and error and general experimentation.

[peterb]

80dB + 80dB = 83dB
80dB + 50dB = 80dB
Loud noise drowns out quieter noise.

4 drives will make more noise than 1
12dB + 12dB + 12dB + 12dB = 18dB
1 drive = 12dB
4 drives = 18dB

Not quite sure what you are trying to demonstrate here. 12dB +12dB is (in engineering - and mathematical terms) 24dB - it is the meaning of the terms that is important, and the deciBel is one of the less well understod units of measurement.

However the dB is a ratio on a ogarithmic scale, so comparing two signal levels, if one is 3dB up on another, it is twice the power output. However being a ratio, it is intrinsically dimensionless, and has to be referenced to something.

In audio engineering, the unit is normally the dBA - which is a sound pressure ratio with a weighting to correspond to the sensitivity response of the human ear - which in itself isn't linear.

What does that mean in terms of the OPs question. Well in a quiet room, a quiet noius will be audible, in a room with a lot of ambient noise, that same device won't be indivifdually audible, but it wilkl contribute to the ambient background noise.

So if you have a computer with one fan running all the time, and another one that cuts in and out, you will hear the second fan cut in, and the computer will be physically noisier, and possibly subjectively noisier as well - although your ear may not be able to detect the noise of the first over the second.

The type of noise is important too - you may hear the clicking of a hard drive over the broad spectrum white noise of a fan moving air, even though it may not be as loud as the fan.

Does that help you in the design? Probably not because it is a very subjective thing - and depends on where the noise generating device will be used. A computer that makes no discernible noise in an office envronment make be btrusivey noticeable in a bedroom at 2 o'clock in the morning.

[Ulti]

IIRC, as peterb says, sound is measured on a logarithmic scale.

You may find this site helpful but it's pretty much what peterb is saying: http://www.engineeringtoolbox.com/so...ity-d_712.html

[Skulltrail]

Thanks for the responses everyone, I am now a little closer to understanding this, but it seems that trial and improvement is the way to go.

In your experience, does sound absorbing foam work well?

[GheeTsar]

In your experience, does sound absorbing foam work well?

In my experience, not all that well. It'll probably take the edge off the noise, but it's no magic bullet for a noisy system.

[Pob255]

In my experience, not all that well. It'll probably take the edge off the noise, but it's no magic bullet for a noisy system.

What he said, also depends on what the sound issue is you're having trouble with.
For side panel resonance, ie the side panel being vibrated and creating a hum, then sound dampening foam is very good.

[Skulltrail]

In my experience, not all that well. It'll probably take the edge off the noise, but it's no magic bullet for a noisy system.

Thanks, I'll try without first and only go for it if I really need to cut down the din further.

[Queelis]

What he said, also depends on what the sound issue is you're having trouble with.
For side panel resonance, ie the side panel being vibrated and creating a hum, then sound dampening foam is very good.

For side panel vibration I've found a very simple solution: mine was vibrating because of the stock Antec TriCool fan (replaced it with a Nexus Basic since then, no vibrations), so I've just stuck some window insulation (I've used the particular one in the shape of a D) on the chassis where it's touched by the side panel, so that I'd have to press the side panel a bit so it would close - worked beautifully

[acrobat]

Foam isn't bad but you have to be careful that it doesn't increase your temps, especially if you overclock. My system is very quiet. I used to have a very noisy computer so when I built the one I use now, I tried my best to make it much quieter. The result was even better than I hoped for. The solution seemed to just be to make sure that everything you buy is quiet. What I did is this.

First off my PSU is a Corsair 620 HX which is very quiet. You can barely hear it's fan unless you put your head near it. My case fans are Sharkoon 120 "Golf Ball" fans. They don't push a whole lot of air, but they are extremely quiet. Then I put a Thermalright 120 Ultra Extreme heatsink on the CPU which is so good that it barely even needs a fan on it. But because I like to overclock, I just put a quiet, low/medium speed fan on it. It's a Yate Loon fan but it's pretty much identical to the Sharkoon fans.

So in total there are only 3 fans in there (excluding the PSU), and they are all very quiet, and then there is the PSU which is very quiet too. So that makes for a very quiet base. Then there is the issue of hard drives.

I have 4 drives. The first three are Seagate Barracuda drives which are fairly quiet. I could have got quieter ones but performance was my priority for those. I have mounted them in the hard drive cage in my case though, and I have the cage sat on a thick piece of foam on the bottom of my case, and I have some rigid cable ties holding the cage in place so it wouldn't fall over if someone accidentally knocked the PC. So the hard drives are very quiet too. The fourth drive I keep in an external USB enclosure which lets me take it with me and transport files, and it also helps keep the volume and temperature down inside the PC too by only having 3 disks in there instead of 4.

So the PC is extremely quiet and some people even wonder if it's switched on. In the day the general noise of nearby traffic and stuff is far louder than the PC so it drowns out the sound completely. I can only even hear it late at night and even then it's just a quiet whisper.

The finishing touch was when I got a weird little bedside table I had, I painted it black to match the rest of the PC. I took the handle off and laid that on the floor long ways and I have the PC sat on top. So the PC tower is now quite low to the ground, raised just about 6 inches off the carpet, so it's almost entirely hidden to the side of my desk which means that the noise from the rear fan is sheltered by the desk a bit. So all in all it's really quiet! I plan on upgrading a bunch of components soon, but I'll be keeping my case and fans and PSU because it all worked out so well.

[Skulltrail]

Thanks acrobat - very informative. How do you give thanks?

[peterb]

Thanks acrobat - very informative. How do you give thanks?

You need 25 posts - but once you have got them, you can apply it retrospectively!

[acrobat]

Thanks acrobat - very informative. How do you give thanks?

You're welcome. I forgot to mention too that there are lots of other quiet PSU's these days, so it's not just the Corsair. I just got that one because it suited me and I really like Corsair. But yeah the bottom line is that if all your individual components are quiet, then the finished PC's should be pretty quiet too. Hope it works out