2x 92mm or 1x 120mm for case (SX1030) exhaust, and dBa question..

[MB]

posted this question in another board, but maybe you gurus can shed more light

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I'll be picking up an Antec SX1030, and was thinking of the following mods.

- 2x 92'mm Panaflo fans on the back instead of the 2x stock Antec 80mm (I've seen this mod already)

or....

- 1x 120' Panaflo fan on the back instead of the 2x Antec 80mm (haven't seen this one, but looks possible. I already have a steel plate cut from the bottom of an old AT case). This will require a little more work, but I think it can be done. Has anyone done this?


My questions are:

1.) will the 2x 92'mm Panfalo's be that much louder than 1x 120'mm fan? (I'm asking because the dBa levels don't necessarily give a correct reading of actual perceived noise, or what we really hear )

* 2x 92'mm = 85CFM @ roughly 31dBa

* 1X 120'mm = 68.9CFM @ 30dBa

2.) are my computations for the dBA of the 2x 92'mm fans correct? (1 is rated 42.7 CFM @27dBa)

3.) what is a better configuration and why?


although the higher CFM of the 2x92'mm fans (and easier mod) is appealing, I don't want to have a noisy setup. (can't stand the noise)

I've checked out other cases with 120'mm exhaust slots (Chenbro Junior), but I'm leaning towards the Antec for the greater space and larger amount of drive bays.

this is my first mod, and hope you guys can help me out.

Thanks all.

 

[GERRY136]

welcome!!!
yuve sure come to the right board for help. i havent been here long but the help is really superb.

one thing im fairly sure of is the panaflow 120mm L1A is probably the quietest 120 around.
i have heard that if u use multiple fans that are exactly the same speed and db that they all cancel out eachother, ie: 3 80mm fans at 37db sounds like 1 80mm fan at 37db.
now im not sure if this i true and seems kinda odd but im not a pro at this and im sure one of the veterans here will correct me.

wish u luck bro!

 

[MB]

GERRY.

thanks.

I always thought that each additional fan adds 10% of the dBa level of the quietest fan. don't remember where i read that from though.

you could be right as well about the dBa levels cancelling out.

it would be nice to hear from someone who know for certain what the real deal is.

hey, I see you have a Slot A as well. I've got an 800 on a K7V. happy with it, despite of everyone seeming to be running Ghz+ systems ;D amazing how you're running @850 on a 200watt PS though!

 

[William]

the 10% figure is wrong. You can have 100fans running at 50 decibels but the total db level of the area will be something like 60 at most. It is the way the decibel formula works, but of course, being the great physics student, i forgot what is was so you could calculate it. ;D

 

[Hoot]

I have Panaflo 120x38s and 92x25s. I also have two Sanyo Denki 92x32mm fans. The Sanyo Denki 92x32 fans run quieter than the 92mm Panaflos by a small amount and deliver better airflow, especially in circumstances of elevated static pressure. I highly recommend you consider a pair of them instead of a pair of Panaflo 92x25 or a single 120x38.

Hoot

 

[KaHNZa]

every time you double the sound output. ie add a second fan of the exact same rating, your sound level is evectively doubled. Add 3dB to the original fans rating. So, 1 92mm is 27dBA. 2 is 30. 3 is 31.5. 4 is 33. Now I don't think I'm making sense. Hope this helps alot. I may ask my step-dad. He knows about this stuff.

 

[William]

KaHNZa (Jun 17, 2001 03:25 a.m.):
every time you double the sound output. ie add a second fan of the exact same rating, your sound level is evectively doubled. Add 3dB to the original fans rating. So, 1 92mm is 27dBA. 2 is 30. 3 is 31.5. 4 is 33. Now I don't think I'm making sense. Hope this helps alot. I may ask my step-dad. He knows about this stuff.

*Modify* I just deleted everything because I was kinda wrong and kinda right, so to explain I have my physics book and a TI-89, lets get cracking!

Okay, here is the formul for figuring out decibels.

[Decibell]=10*log[(sound intensity of object)/1*10^-12]

Ok. So lets just say we have an object that has a sound intensity of 4*10^-3 W/m^2. using the formula we get that this object has a dB level of 96dB. Thats loud. Now lets put two objects. When doing this we just add up the intensities like this

[Decibell]=10*log[(intensity of A+intensity of B+.........)/1*10^-12]

So for two objects the intensity is 99dB. That is louder, but not much. Now lets have a hundred of these going. Thats 116dB which is still louder, but not by a whole lot for a hundred objects. In fact, that is just about a 15% increase in sound over two objects. So thats how it works and why having two is not twice as loud. I hope this helps, is edifying, and that I didn't confuse you too much.

 

[MB]

Hoot.

I'm having a look at the Sanyo-Denki fans right now.

william.

Thanks for the formula. gimme some time to make some sense of it first. ;D

Thanks to everyone. It seems the best bet is still the 2x 92mm fans (as long as they have low dBa levels), as they will be pumping out more air, a better ration as well compared to the 1x 120mm fan...right so far?

 

[GERRY136]

MB (Jun 16, 2001 11:12 p.m.):
GERRY.

thanks.

I always thought that each additional fan adds 10% of the dBa level of the quietest fan. don't remember where i read that from though.

you could be right as well about the dBa levels cancelling out.

it would be nice to hear from someone who know for certain what the real deal is.

hey, I see you have a Slot A as well. I've got an 800 on a K7V. happy with it, despite of everyone seeming to be running Ghz+ systems ;D amazing how you're running @850 on a 200watt PS though!

yeah its 200 watts but i took apart a hard drive cooler with dual tiny fans and tried to use them in other places but after few boots i could hear my psu groaning tilli unpluggd them lol. so im at my max but have some pretty hefty stuff on the way!

 

[Flash]

What y'all may be missing here is that a few dBa difference can make a *big* difference in the amount of sound you hear. The decibel scale is, I believe, geometric, so 90 dBa is not twice as loud as 45 dBa--it's like a 1000 times as loud (or some big number louder anyway). Unfortunatley I don't know the exact formula/ratio.

 

[William]

well my physics book said otherwise even though I had always heard this.

0dB is our starting point.
10 dB is ten times as intense as 0dB
20 dB is a hundred times as intense as 0dB
30 dB is a thousand times as intense as 0dB.
And so forth.
But due to the nature of our hearing we perceive 20dB to be twice as loud as 10dB even though sound is a lot more intense.

 

[KILLorBE]

I think y'all forgot one thing (I could be wrong) and that is Frequency (or two: MAP Maximum Air Pressure), A fan that produces 30 dB @ 6000 Hz sounds much louder than a fan that produces 30 dB @ 20 Hz (you probably won't hear it at all).
And since larger fans (most of them) have lower RPM the frequency is also lower.
All I want to say is that a large fan might sound less annoying than 1 or 2 small(er) fans at the same dB level, and it might also push/pull more cool air through your system since most of the larger fans have higher MAP.

Sorry if this confuses you MB, but IMHO I would go for the 120 fan.

 

[William]

oh yeah, frequency is a totally different animal. That is why the Delta is so annoying is because its frequency is much much higher than allmost all other fans.

 

[Karsta]

I have Sunon KD1212PMB2-6A voltage dropped with potentiometer (now about 6 V) in front for intake and Papst Multifan 4312M dropped with resistor to 8.5 V on top for exhaust. Both 120 mm's. MB temp same as room temp or sometimes 1° higher. Additionally slowed down 80 mm fan for PSU. Case temp ranges from 24° to 26° (about 2 cm from HSF )

I switched to them from 92 mm's because of noise. If I remember right 2 92 mm fans connected in series to drop the voltage on top was also a good and effective solution.