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...
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...
There is a good technical bulliten at:
http://www.papstplc.com/index.php?page=guest/articles/art007
that covers adding fan noise.
johnm
http://www.papstplc.com/index.php?page=guest/articles/art007
that covers adding fan noise.
johnm
FANS
Hi,
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,
Hi,
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,
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
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
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.
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.
William,
The fans I used (four 12v 40mm diameter) are rated at 24.5dB each and are certainly too noisy when running at full speed so I limit them by using a simple PWM speed controller. I use a thermistor screwed into the heatsink to sense the temperature and increase the fan speed as the amp heats up.
I designed the PWM circuit to start with a minimum of 15% duty cycle (the slowest speed before the fans begin to stall) at ambient and run up to a maximum of 50% (the point where the noise becomes objectionable) at around 40'C.
I did the following measurements by replacing the thermistor with a fixed resistor to give a constant fan speed:
No fans: 54'C
Fans @ 25% duty cycle: 43'C
Fans @ 33% duty cycle: 41'C
Fans @ 50% duty cycle: 35'C
I'd still like to replace the fans with some quieter units though, hence my original question. Even at 50% duty cycle, the fans are only audible in the gaps between songs but are still a bit too noisy during quiet dialogue passages in movies.
I'm half way through updating my Hiraga web page and will probably include details of this circuit.
Nice one.
David
The fans I used (four 12v 40mm diameter) are rated at 24.5dB each and are certainly too noisy when running at full speed so I limit them by using a simple PWM speed controller. I use a thermistor screwed into the heatsink to sense the temperature and increase the fan speed as the amp heats up.
I designed the PWM circuit to start with a minimum of 15% duty cycle (the slowest speed before the fans begin to stall) at ambient and run up to a maximum of 50% (the point where the noise becomes objectionable) at around 40'C.
I did the following measurements by replacing the thermistor with a fixed resistor to give a constant fan speed:
No fans: 54'C
Fans @ 25% duty cycle: 43'C
Fans @ 33% duty cycle: 41'C
Fans @ 50% duty cycle: 35'C
I'd still like to replace the fans with some quieter units though, hence my original question. Even at 50% duty cycle, the fans are only audible in the gaps between songs but are still a bit too noisy during quiet dialogue passages in movies.
I'm half way through updating my Hiraga web page and will probably include details of this circuit.
Nice one.
David
Re: BABYLON II
Here's the german and finnish translation:
Weil seine Ohren so klein sind, kann ein Storch kein Hase sein.
Koska sen korvat ovat niin pienet, haikara ei voi olla jänis.
But wait a second.................
What are you trying to say??
fdegrove said: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.
Here's the german and finnish translation:
Weil seine Ohren so klein sind, kann ein Storch kein Hase sein.
Koska sen korvat ovat niin pienet, haikara ei voi olla jänis.
But wait a second.................
What are you trying to say??
David,
my first try was also with a PWM circuit (MIC502) but this turned out to make the fans more noisy as with a constant (lower) voltage.
The other thing was that I found the PWM frequency back in the signal although I used a seperate power supply.
After that I just used some resistors to get the right voltage and this works just fine.
Silent fans are for example the papst 8412 NGL at 12dB wich runs without problems at 8V.
william
my first try was also with a PWM circuit (MIC502) but this turned out to make the fans more noisy as with a constant (lower) voltage.
The other thing was that I found the PWM frequency back in the signal although I used a seperate power supply.
After that I just used some resistors to get the right voltage and this works just fine.
Silent fans are for example the papst 8412 NGL at 12dB wich runs without problems at 8V.
william
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