80 mm vrs 120 mm, which is better?

NetTechie · Post by **NetTechie** » Thu Jun 03, 2004 8:40 pm

I want to build a silent pc, as silent as possible. I've not yet purchased my case (nor any of the components for that matter). I read a lot about Panaflo L1A fans. How do they compare to a 120mm? I was thinking maybe it'd be better to put two panaflo's instead of one 120mm, and run the 80mm silent speed. I do need a fairly good cooling solution, since my main use of my computer is the 3D games... sometimes played nonstop for over 6 hours at a hit. The system will run just about 24/7.

loren_brothers · Post by **loren_brothers** » Thu Jun 03, 2004 9:52 pm

I personally feel that single 120 will make less noise than 2- 80's at the same rpms. Try a nice evercool Al with a bay mounted fan controller. That way when you are gaming you can increase RPMs if you start to heat up and the rest of time have it running slow to keep things quiet.

Uberman1080 · Post by **Uberman1080** » Fri Jun 04, 2004 7:50 am

Ok, anyone can feel free to contradict me on this, im not 100% sure im right. but anyway. In theory the area for air expelled with a 120mm fan is roughly 113cm. Where as with a 80mm fan its 50cm, so even if you have 2x 80mm fans your still not getting the same area to expell the air, no matter what the CFM.
Also it makes sence now to use the 120mm fan because it is only 1 fan as opposed to 2, so less hub noise, less blades moving air = less noise. and less rpm = less noise. so all things being equall id go with the single 120mm fan.
Thats not taking into account any form of grills though.

lucienrau · Post by **lucienrau** » Fri Jun 04, 2004 9:14 am

You might want to do a search in the Fans forum as this has been gone over many many times there.

shathal · Post by **shathal** » Fri Jun 04, 2004 1:03 pm

Mark me down as a vote for the 120mm fan (points to his Evercool 120 mm Alumium).

Bear in mind that 2x 80 mm fans need not only higher revs (each) to put through more CFM, but also enter harmonics, which increases the perceived dBA by a fair bit.

yermolovd · Post by **yermolovd** » Fri Jun 04, 2004 3:19 pm

So it means I'm screwed, because I have two 80mm Panaflos

Altough, at 5V I dont hear them.

Reading the forums over, now I regret I bought 80mm Panas, instead of 120mm fans. Oh well, too late.

SpyderCat · Post by **SpyderCat** » Fri Jun 04, 2004 4:10 pm

Uberman1080 wrote:Ok, anyone can feel free to contradict me on this, im not 100% sure im right. but anyway. In theory the area for air expelled with a 120mm fan is roughly 113cm. Where as with a 80mm fan its 50cm, so even if you have 2x 80mm fans your still not getting the same area to expell the air, no matter what the CFM.
Also it makes sence now to use the 120mm fan because it is only 1 fan as opposed to 2, so less hub noise, less blades moving air = less noise. and less rpm = less noise. so all things being equall id go with the single 120mm fan.
Thats not taking into account any form of grills though.

That's one way of looking at it.
Here is another view:

At the same RPM the tips of the 120mm fan move through the air at a higher speed than the tips of an 80mm fan.
Tip vortices are giving most problems (ask any sailor)
So I would vote for 2 80mm fans, each fed with a different voltage to prevent interference.

josephclemente · Post by **josephclemente** » Fri Jun 04, 2004 5:09 pm

There was another thread here not too long ago where the majority stated two 80mm fans are better than one 120mm, when moving the same amount of air.

I was surprised by the popular opinion. I always thought 120mm was the way to go.

I'm not sure what is really the best.

1398342003 · Post by **1398342003** » Fri Jun 04, 2004 5:21 pm

One thing to consider is that the wavelength of the sound produced by a 120mm fan is lower and more difficult to dampen than that of 2 80mm fans. I have found this from personal experience. I have two similarly loud fans; (when not dampened) a 120mm and an 80mm, and using the same amount of dampening material, the 120 is more audible than the 80.

Personally I'd recommend using a pair of 92mm L1As, not 80mm ones, but either should be fine. I have heard that 92mm Panaflo fans usually have some clicking noise though.

Wedge · Post by **Wedge** » Fri Jun 04, 2004 5:59 pm

1398342003 wrote: Personally I'd recommend using a pair of 92mm L1As, not 80mm ones, but either should be fine. I have heard that 92mm Panaflo fans usually have some clicking noise though.

I would go for an undervolted 92mm L1A before using a 120mm fan. Good air movement, less noise than a 120mm. Not sure which is quieter between two 80mm vs a single 120mm (because I have never done a direct comparison).

Uberman1080 · Post by **Uberman1080** » Fri Jun 04, 2004 8:57 pm

That's one way of looking at it.
Here is another view:

At the same RPM the tips of the 120mm fan move through the air at a higher speed than the tips of an 80mm fan.
Tip vortices are giving most problems (ask any sailor)
So I would vote for 2 80mm fans, each fed with a different voltage to prevent interference.

Id never thought about it that way SpyderCat, it makes alot of sence though.

Also just a question about running 2 80mm fans at slightly different voltages next to each other as to not to deal with harmonics, wouldnt that end up with a vibration problem? 2 sources close together vibrating at different frequencies?

On the wavelegnth side of things i personally dont think a 120mm fan is too bad really, its the higher frequency fans like 60mm or even AMD's old 50mm 7000RPM fan that really kills me. That said i dont think id want to go much higher than 120mm

TheWesson · Post by **TheWesson** » Sat Jun 05, 2004 12:03 am

Yes, it's interesting ...

Comparison at full power:
80mm L1A - 24 CFM, 21 dB
120mm L1A - 69 CFM, 30 dB
3 80mm L1A's - 72 CFM, 26 dB

So there you go, multiple 80mm fans are better in this case.

19200 cm sq for 3 80 mm L1A's.
14400 cm sq for the 120 mm L1A. It's a little more space efficient.

Let me add that I can verify this from personal experience; I have 80mm and 120mm L1A's strewn about at this moment. I'd pick 2 12v 80mm L1A's over 1 7v 120mm L1A any time.

FYI 3 dB is about a "noticeable difference" and I do notice it.

the wesson

1398342003 · Post by **1398342003** » Sat Jun 05, 2004 1:56 pm

Uberman1080 wrote:
On the wavelegnth side of things i personally dont think a 120mm fan is too bad really, its the higher frequency fans like 60mm or even AMD's old 50mm 7000RPM fan that really kills me. That said i dont think id want to go much higher than 120mm

The lower frequencies are less annoying, but it is harder to dampen them than higher frequencies given the same material.

burcakb · Post by **burcakb** » Sat Jun 05, 2004 2:41 pm

A very unscientific comparison for you:

A single 80mm acoustifan at 12V pushes a lot more air and is a lot more silent than a 120mm acoustifan at 7V.

I have a Sonata case with a 120mm acousti @ 8.5V and an Aopen H600 case with two 80mm (one globe M @ 5V and a vantec stealth @ 8.5V). The two 80mms push more air than the 120mm at about the same noise level.

Truth is 120mm are damn hard to quiet in the first place. I'll be trying my luck with a noiseblocker blacknoise pro next and see if that helps

NetTechie · Post by **NetTechie** » Tue Jun 08, 2004 10:40 pm

I sure appreceate the input guys. I think 120 and 80mm are both good, but the mention of lower freq. being harder to silence is a good point.

3700BQE/Sonata cases may not be the best route... it's 120mm only. I sleep about 4 feet from my computer, which is on most of the time, so absolute silence if it is possible would be priceless. However, cases are the subject of my other topic here.

TheWesson · Post by **TheWesson** » Wed Jun 09, 2004 1:15 pm

Looking at the fan database, here's a rule of thumb I would like to propose:

Make a number for 1 or more fans: ((total CFM)/(total sq cm cross section)). The lower this number is, the lower the noise is.

I propose this because one 120mm L1A @7v has a similar cross section, a similar CFM, and a similar noise level to two 80mm L1A's at 12v.

However of course the low pitched vibration is an issue.

It also depends on the quality of fan manufactury, of course.

the wesson

NetTechie · Post by **NetTechie** » Wed Jun 09, 2004 2:58 pm

What are these evercool aluminum fans? Are they worth it? Are they really better than Panaflo's for their silence?

shathal · Post by **shathal** » Wed Jun 09, 2004 3:04 pm

There is - oddly enough - an entire thread about that.

See here:
http://forums.silentpcreview.com/viewtopic.php?t=7274

I believe that should answer everything?

Edit:
Corrected the link with the missing character...

Bosk · Post by **Bosk** » Fri Jun 11, 2004 10:17 am

NetTechie wrote:I want to build a silent pc, as silent as possible. I've not yet purchased my case (nor any of the components for that matter). I read a lot about Panaflo L1A fans. How do they compare to a 120mm? I was thinking maybe it'd be better to put two panaflo's instead of one 120mm, and run the 80mm silent speed. I do need a fairly good cooling solution, since my main use of my computer is the 3D games... sometimes played nonstop for over 6 hours at a hit. The system will run just about 24/7.

My vote for 120mm fans.

I've noticed they tend to push more air at the same or even lower noise levels then their 80mm buddies.
And is it just me or do most 80mm fans tend to "squeal" in a way which 120mms never do? I find i can't get rid of this kind of high pitched noise at anything more than 7v at least, and most "quiet" 80mm fans really dont move much air at those speeds.

TheWesson · Post by **TheWesson** » Fri Jun 11, 2004 10:50 am

Ehhh ... then you should construct a "160mm fan" out of 4x 80mm L1A.

160mm construct @ 5v:
2 dB + 6dB = 8 dB.
10CFM x 4 = 40CFM.

A practically inaudible 40 CFM!!

160mm construct @ 7v:
9.3 dB + 6 dB = 15.3 dB.
14 CFM x 4 = 56 CFM.

56 CFM at 15.3 dB sounds *FAN*tastic to me.

Or, 160mm construct @ 12v:
21dB + 6 dB = 27 dB
24CFM x 4 =96 CFM.

96 CFM at 27 dB - that kicks the rear end of any 120mm fan *I* ever heard of.

Where this goes, in my mind, is that silent PC types should get a tower case (like for servers) that has places to put 4 80mm for intake and 4 80mm for exhaust. 40 CFM at 8 or 11 dB is unequaled ...

Don't worry about *quiet* fans so much - what you need is a LOT of fans.

Katana Man · Post by **Katana Man** » Fri Jun 11, 2004 11:34 am

I have built hundreds of computers in my past, and the cases with dual 120mm fans are by far the quietest I've built. 80mm fans tend to have a higher "whiney" pitch.

Not only that, but the use of 120's have produced cooler running components. My technique (which many people are scared to do), is to run dual 120mm's with low airflow restriction. This involves using "modder's mesh" modification to the front grill. The end result is the ability to run the 120mm fans in the 4.8-7V range. Get yourself some dual Papst 4412's 120mm fans, and you'll have a hard time hearing if your computer is on.

80 mm vrs 120 mm, which is better?

80 mm vrs 120 mm, which is better?

Re: 80 mm vrs 120 mm, which is better?