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 Post subject: illustrative example of effective low(er)-noise cooling
PostPosted: Tue Jan 14, 2003 12:50 am 
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looks like tom's hardware guide (thg) (http://www.tomshardware.com/) does a non-spectacular socket a cooler round-up.

overall, not an incredibly interesting read, and notably, low-noise favorites around here, thermalright, and to a lesser extent, alpha novatech, coolers, are not represented.

however, that's not the point i wanted to bring up. a quick skim through the article, and i couldn't fine how thg measured noise. nevertheless, i'm going to assume that at least for comparative purposes, it's relevant. take a look at the noise/thermal resistance table:

http://www.tomshardware.com/cpu/20030113/cooler5-39.html
(a 2-D distribution graph with Rth on one axis and noise on the other would've been nicer, imo, but i digress.)

what i thought was most interesting was the comparison between two heatsinks that use the same fan in the table- the vantec aeroflow VA4-C7040, and the swiftech MCX462-U + Y.S. tech PD1270155B-2F (a.k.a. 5600 RPM TMD fan).

the vantec has same-to-lower thermal resistance, while being over 16x quieter than the swiftech.

i think this is a good illustrative example of effective cooling. understanding the fundamentals on what makes these two examples so different can help any noise-reducing seeker in their quest for effective and quiet cooling.


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PostPosted: Tue Jan 14, 2003 1:23 am 
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16X quieter? :!: Looks like a misinterpretation. Tom's shows a 13 dBA difference (45 vs 58 ), which is very surprising, given they are apparently the same fan. That translates to maybe 2.5 or 3 times, subjectively. 10dBA = 2x, 20dBA = 4X.

Also looks like an error by Tom's. I have a hard time believing the data reported. It COULD be that one of the fans is the 4500 rpm version and the other the 5500 rpm, but I've heard that difference, and it is nothing like 13 dBA. It could be they made a typo?

Same fan, pressed up against the HS -- yes, different ones, but pressed right up in both cases -- showing a 13 dBA difference? I just don't buy it. Unless one HS had zero impedance and the other blocked 90% of the airflow, this just does not seem possible. I have tried a high airflow fan jammed up against all kinds of different HS -- never have I heard anything even remotely approaching this type of difference.

Someone write THG & have them double-check?


Last edited by MikeC on Tue Jan 14, 2003 9:37 am, edited 1 time in total.

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PostPosted: Tue Jan 14, 2003 2:11 am 
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hmm, am i missing something here? dB is logarithmic. thus a doubling in sound intensity means a 3 dB(A) rise. thus, 13 dB(A) rise should have a sound intensity slightly greater than 16x. hmm... i must be missing some subjective weighting... i do seem to recall that 10x sound intensity means perceived loudness is doubled. let's see if i can recall that...

if i seem to recall correctly, the formula for perceived loudness is something like-
Quote:
perceived loudness = 0.3 * ( physical sound intensity)

right? then 13 dB sound intensity is a little over 3 dB of perceived loudness. thus, slightly over a doubling of perceived loudness, which is what your were telling me, mike :D

man... time to look up those equations again. feel free to correct or clarify anything. i'm far from positive on those equations from memory.

sidenote, i checked the fans used in the thg article before post thg to make sure they were both the same. the model number is given in the article for the mcx measurement (TMD 5600 RPM), and the stock fan for the aeroflow is the 5600 RPM TMD according to the vantec sight.

i don't discount that the results may be exaggerated as we aren't told how the noise was measured, but i think we can agree that the vantec is much quieter. 2x quieter? dunno, but i think it's much quieter.

however, rather than turning this into a comparative post, my intention of the post is more for discussion fodder about airflow/heatsink/fan design for low-noise performance rather than so-and-so heatsink A is 2x quieter the so-and-so-heatsink B. heck, your response already helped me to recall how to calculate perceived noise!


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PostPosted: Tue Jan 14, 2003 4:39 am 
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hyum wrote:
hmm, am i missing something here? dB is logarithmic. thus a doubling in sound intensity means a 3 dB(A) rise. thus, 13 dB(A) rise should have a sound intensity slightly greater than 16x. hmm... i must be missing some subjective weighting...


Dont forget, that your ears have a kind of built in compressor, quiet sounds appear louder than they actually are, and louder sounds appear quieter than they actually are in terms of dBA. So a 3dB increase in sound level is a doubling in amplitude, but your ear 'compresses' this increase such that it takes an increase of 10dB for your brain to think that the sound level has doubled.

(It should probably be pointed out that the type of compression here is absolutley nothing to do with mp3 compression!) The dynamic range is compressed so that you can hear a much wider range of volumes.

That percieved loudness formula is effectively the same as Mikes statement about 10dB increase 'sounding' twice as loud :)

_________________
Computers should be seen and not heard...


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PostPosted: Tue Jan 14, 2003 10:24 am 
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Time to post links to acoustics info sites again. Here is a good one:
http://www.faqs.org/faqs/physics-faq/acoustics/

Going back to that Swiftech vs Vantec HS noise difference: if they're saying a 13 dBA difference is arising from the difference in fan/airflow turbulence effects alone, I say no way.


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