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Old 28th October 2002, 12:18 PM   #1
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Default Adding fan-noise decibels.

Hi everyone,

I thought I understood the decibels scale but now I'm not so sure.... I'm planning to add some fans to my Hiraga Classe A to bring down the temperature of the heatsink and would like some clarification about my noise calculation figures....

Say I have a fan that makes 14dB(A) of noise.

I add a second fan so total noise level is 17dB.

Add a third fan and noise becomes 20dB.

Adding a forth fan makes the total 23dB.

Now, 23dB is 9dB more than the noise produced by a single fan, but it takes a 10dB increase to be perceived as a doubling of noise. So although I've quadrupled my air moving capability, the total fan noise has almost - but not quite - doubled.

Is the above correct? I believe it is but it does seem a bit counter-intuitive!

Nice one,
David


BTW, I tried searching the archives but any search containing "dB" is rejected because all terms must be at least three letters...
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Old 28th October 2002, 04:20 PM   #2
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It sounds correct to me. My textbooks always said that 3dB was a "noticeable increase" in percieved sound level while 10dB was "twice as loud".
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Old 28th October 2002, 05:15 PM   #3
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There is a good technical bulliten at:
http://www.papstplc.com/index.php?pa...rticles/art007
that covers adding fan noise.
johnm
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Old 28th October 2002, 06:02 PM   #4
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David,

According to the article above, your assumptions are correct.
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Old 28th October 2002, 06:10 PM   #5
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Thanks guys - that answers my question.

BTW, the author of the document given in Crown300's link (Ian McLeod) is Papst's UK technical sales rep that I actually met a couple of years ago! Guess I should have given him a call....

Thanks again,
David.
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Old 28th October 2002, 06:18 PM   #6
herm is offline herm  United States
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From the article:

New SPL = 30 + 3=33dB

Using the above formula for the addition of identical fans:

3 fans add 4.7dB(A)
4 fans add 6.0dB(A)
5 fans add 6.9dB(A)
6 fans add 7.8dB(A)
7 fans add 8.5dB(A)
8 fans add 9.0dB(A)

-herm
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Old 28th October 2002, 11:06 PM   #7
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Default FANS

Hi,


Quote:
I'm planning to add some fans to my Hiraga Classe A to bring down the temperature of the heatsink and would like some clarification about my noise calculation figures....
To lower the noise level you could try to run them at lower then standard voltages:i.e a 12V fan at 9V and so on.
That would make them a lot more quiet.
Dig into PC overclockers worlds and you may find a handful of tips.

From an audiophile standpoint I would make the heatsinks a bit bigger but don't forget that this design sounds at it's best when running hot.
That's Class A doing it's job.

Cheers,
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Old 30th October 2002, 10:41 AM   #8
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Daatkins,


14dB still is quite loud. I´ve used two papst 12dB @12V fans and they are audible at about 5 meters distance when everything else is silent.

Reducing the voltage to 8-9V has made them close to in audible at 1m distance.

What I want to say is that everything above 10dB probably is too loud when you´re listening to music.

If your class A is already working without fans even very slow (and silent) fans should reduce the temp by at least 10°.

william
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een ooievaar is geen konijn want zijn oren zijn te klein!
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Old 30th October 2002, 11:04 AM   #9
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Default BABYLON II

Hi,

Because his ears are too small a stork is no rabbit at all!
Porque sus orejas son tan pequenitas la cegogna no puede ser conejo!
Puisque ses oreilles sont tellement petites une cigogne ne peut pas etre un lapin!


Still missing:German,Portuguese,Italian,Svensk,Norsk.... .

Ciao,

Roger Rabbit.
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Old 30th October 2002, 11:07 AM   #10
UrSv is offline UrSv  Sweden
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Efter som hans öron är för små är storken alls ingen hare!

/UrSv

PS. That would be slightly poetically adjusted Swedish
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