Hi all,
After reading through a lot of reviews on the web, and a lot of people's comments about noise in their comps, I decided to clear up some things about noise and how we hear it.
The problem is best summarized this way: I have one fan rated at 34 dB. If I add another one why isn't it twice as loud???
The answer is that the dB scale is logarithmic and not linear, like the sound is. Okay, let's explain (ack! some high school math!). I'll be using a simple model to explain it, since trying to handle real world problems exactly is a bitch. First off, we have a fan turning round and round, moving air and generating sound. This sound is a wave in the air, marked by high and low pressure changes. Eventually this sound wave hits our ears, where it gets interpreted into noise.
We'll represent the sound generated by S and the noise we hear by N. The reason that the dB scale is used is that it behaves similarly to the way we hear (not exactly though), but it's good enough for an approximation. The dB scale is defined as 20*log (in base 10). So, N = 20*log(S). Adding another fan, doubles the SOUND generated, and the new amount of noise generated is:
20*log(S+S) = 20*log(2S) = 20*log(S) + 20*log(2) = N + 6 (approximately).
So what do we see here? Adding on a second fan won't double the noise, it'll increase it by 6 dB. For really, really quiet sounds (less than 6 dB) this more than doubles the noise, which seems somewhat counter intuitive. Now then, of course this isn't exact. Everybody knows that a 46 dB delta isn't twice as loud as a 23 dB ultra quiet fan. So where's the problem? The decibel scale works pretty well for normal noises, but, as is to be expected the simple mathematical model really isn't that close to how we hear close to our barrier of hearing. Thus while a 40 dB fan isn't twice as loud as a 20 dB one, an 80 dB one is about twice as loud as a 40 dB one (though 80 dB is some serious, serious noise). The scale can probably be made more accurate by shifting and scaling it to the range of human hearing, but nobody's after an exact result anyways, especially when using a simple model.
Well, that's about it. You can use this is a rough guide for calculating the total dB your system's putting out.
Hope it's been informative.
After reading through a lot of reviews on the web, and a lot of people's comments about noise in their comps, I decided to clear up some things about noise and how we hear it.
The problem is best summarized this way: I have one fan rated at 34 dB. If I add another one why isn't it twice as loud???
The answer is that the dB scale is logarithmic and not linear, like the sound is. Okay, let's explain (ack! some high school math!). I'll be using a simple model to explain it, since trying to handle real world problems exactly is a bitch. First off, we have a fan turning round and round, moving air and generating sound. This sound is a wave in the air, marked by high and low pressure changes. Eventually this sound wave hits our ears, where it gets interpreted into noise.
We'll represent the sound generated by S and the noise we hear by N. The reason that the dB scale is used is that it behaves similarly to the way we hear (not exactly though), but it's good enough for an approximation. The dB scale is defined as 20*log (in base 10). So, N = 20*log(S). Adding another fan, doubles the SOUND generated, and the new amount of noise generated is:
20*log(S+S) = 20*log(2S) = 20*log(S) + 20*log(2) = N + 6 (approximately).
So what do we see here? Adding on a second fan won't double the noise, it'll increase it by 6 dB. For really, really quiet sounds (less than 6 dB) this more than doubles the noise, which seems somewhat counter intuitive. Now then, of course this isn't exact. Everybody knows that a 46 dB delta isn't twice as loud as a 23 dB ultra quiet fan. So where's the problem? The decibel scale works pretty well for normal noises, but, as is to be expected the simple mathematical model really isn't that close to how we hear close to our barrier of hearing. Thus while a 40 dB fan isn't twice as loud as a 20 dB one, an 80 dB one is about twice as loud as a 40 dB one (though 80 dB is some serious, serious noise). The scale can probably be made more accurate by shifting and scaling it to the range of human hearing, but nobody's after an exact result anyways, especially when using a simple model.
Well, that's about it. You can use this is a rough guide for calculating the total dB your system's putting out.
Hope it's been informative.