MikeC says he never uses two intake fans, why?

[ExpertNovice]

http://forums.silentpcreview.com/viewtopic.php?t=19297
On April 19, 2005 MikeC stated the following

BTW, I'd never use two intake fans and I'd never have any fan in the front of the case running anywhere higher than ~800rpm. High back pressure from high impedance is simply not an issue with any PC I build. I'd also never have an 8k screamer running at any speed except off.

I have a "standard" setup. Intake from the lower front and exhaust at the top back of the case. Additionally, the two SCSI drives have fans, the cpu, a side fan inside the case blows air onto the MoBo downward, the PSU exhausts air out and does have an intake fan pulling air from the area of the mobo.

My system is loud.

I was planning on changing the intake, side, and exhaust fans.

I was planning on the intake to utilize two Nexus Real Silent 120 mm (D12SL-12). My thought was running two would be quieter than running one.

The exhaust fan has not yet been selected... I'm looking at:
#1 Panaflo 120mm U1A - FBA12G12U1A
AcoustiFan AF120CT
Antec 120mm Blue LED Fan

These fans have about 2x the CFM of the Nexus.

So, why not use two fans instead of one? Knowing why is more important to me than simply following instructions!


(Edited. because what was originally written about the PSU fans was 1. wrong and 2. worded incorrectly for what I had believed. Nor did the 2 wrongs make it right.)

[m0002a]

#1 Panaflo 120mm U1A - FBA12G12U1A

The U1A is an Ultra High Speed fan (L,M,H,U) from Panasonic. Most people on this forum would use the L1A if they used Panasonic.

[ExpertNovice]

#1 Panaflo 120mm U1A - FBA12G12U1A

The U1A is an Ultra High Speed fan (L,M,H,U) from Panasonic. Most people on this forum would use the L1A if they used Panasonic.

Thanks for the clarification.

That information was cut and paste quite hastily last night when my Wife called to see if I was coming home!

The changes to my list were being made after deciding not to purchase any SilenX product. They still have not fixed their stated numbers a full two years after their antics. Showing they have no remorse.

The actual models would be modified and your clarification reduces the additional reading yet to be done.

I wanted to check out Enermax or Global, but... it seems as if the fan gods are not blowing those fans my way.

[frankgehry]

All you need is one nexus running at 650rpm or less. (intake). So why would two be quieter? The first thing to do is get rid of the fans you don't need and turn the other ones down. An Acoustifan is noisy at top speed, but quiet at around 650. If you're computer is still noisy after you get the fan count down to 1 intake and 1 exhaust at slow speed then you might want to consider nexus. How can your psu exhaust air out and down. What is your side fan doing? Did you turn the psu fan around or something. Maybe you have two intake fans for the drives? You need to give more details because scsi drives and a psu that exhausts and blows air in is not a standard set up if there is such a thing. - FG

You can always search scsi cooling to see how other people have cooled scsi drives.

[alglove]

Are you sure that *both* of the fans on the power supply are exhausts? Typically, the fan inside the case (at the top of the motherboard) pulls in from the case into the power supply, and the fan at the back is the exhaust.

[ExpertNovice]

All you need is one nexus running at 650rpm or less. (intake). So why would two be quieter? The first thing to do is get rid of the fans you don't need and turn the other ones down. An Acoustifan is noisy at top speed, but quiet at around 650. If you're computer is still noisy after you get the fan count down to 1 intake and 1 exhaust at slow speed then you might want to consider nexus. How can your psu exhaust air out and down. What is your side fan doing? Did you turn the psu fan around or something. Maybe you have two intake fans for the drives? You need to give more details because scsi drives and a psu that exhausts and blows air in is not a standard set up if there is such a thing. - FG

You can always search scsi cooling to see how other people have cooled scsi drives.

>So why would two be quieter?
Example... 2 fans intaking 36.7 CFM at 22.8 dBA are quieter than 1 fan intaking 75 CFM at 35 dBA. The 2 at 22.8 would be just under 25 dBA and thus, about half as loud. At least, that is my understanding.

The fans I don't need are old and not moving enough air to keep some components (I'm not sure which) cool enough without keeping the case open.

I'm interested in cool as well as quiet. I have had all the ribbons, except for the the LVD SCSI cables, changed to round cable and ties are bundling the cables together.

This is not a high performance system by any means. A 1.4 GHZ Socket A.

>How can your psu exhaust air out and down.
http://www.antec.com/us/productDetails.php?ProdID=20430#
I know not all PSU's have 2, or even 1, fan. Are you saying this is a rarity?


>What is your side fan doing?
it is mounted to the frame inside the case and is blowing air down onto the motherboard. I plan to move it so it is blowing air directly on the memory.

>Did you turn the psu fan around or something.
No. It is, however, a fan and small heat sink that was put on in 2001. I believe it is pulling air away from the cpu rather than toward it.

(FYI: The PSU went and took out the memory and MOBO. To minimize the cost I replaced only the items lost. To speed up the process An Antec Truepower 430 PSU was put in because it was the best they had. My new computer will probably be using a Seasonic and I may even replace the one in the current computer at that time. They did not have 1 GB of Corsair DDR memory so 2 GB was put in. By the time we were done I wish I had just rebuilt the computer. Live and learn.)


>Maybe you have two intake fans for the drives?
The SCSI drives have a fan wrapped around them to keep them cool. They run at about 35c. They are only 10k rpm ultra 160 SCSI's purchased 4 years ago.

They are at the top of the case and their fans exhaust air directly toward the case exhaust fan.

>need to give more details because scsi drives and a psu that exhausts
>and blows air in is not a standard set up if there is such a thing. - FG
I obviously did not word my original statement correctly. It has two fans. One exhausts air outside the case. The other blows air down and toward the mobo. My original statement suggest that both fans are an exhaust.

Hey, I'm exhausted right now! Sorry about the confusion and thanks for the help.

My problem now is that the fans are not cooling the system well enough. It did before so I'm not sure what the problem is now.

Since I'm about to build another computer (waiting on the Antec P180 case) I'm reasearching components. Starting with the Case, PSU, and fans. The next computer will use more passive cooling because of the faster cpus and video cards. This computer is a four year old backup.

[ExpertNovice]

Are you sure that *both* of the fans on the power supply are exhausts? Typically, the fan inside the case (at the top of the motherboard) pulls in from the case into the power supply, and the fan at the back is the exhaust.

After rereading what I wrote I realized the confusion.

Plus, from your statement I was confused. The tech told me that it was a fan blowing air onto the MoBo. When he told me that I suggested that would create a lot of turbulence with the other fans (side and cpu) and was assured otherwise.

Now I realize that he probably said it caused air to blow over the mobo (by pulling) rather than blowing air onto the mobo.

THAT makes much more sense to me.

Sheesh. I will attempt to edit my original post.

[Tibors]

For a silent PC we try to place all needed fans as far from the listener as possible. So we bury them inside the PC or put them on the back. Then we try to create an airflow path as free from obstacles as possible, so the fans don't have to work against a lot of backpressure. With low backpressure two fans in series will not produce a notable increase in airflow over a single fan. So a fan both in the front and the back will not give you a lower case temp than only a fan in the back.

The only reason left to use a front fan is cooling of the HD's. The front fan better directs the airflow to the disks and breaks up the (poorly cooling) laminar airflow you would otherwise have in that part of the case.

If I understand your setup correctly, then your SCSI disks each have a fan attached to the disk itself. This means you probably don't need a front fan at all. Or you could get one quiet front fan pointed at the disks and ditch the fans on the disks. A third idea is not to use an intake fan and mounting one fan horizontally between both disks.

[ExpertNovice]

Thanks for interpreting my confused and erroneous verbage describing the PSU fans.

The SCSI drives are not over heating, as far as I can tell.

I thought that an intake fan at the lower front of the case would help the flow of air to be directed over the mobo and up into the exhaust fan and out of the case. Almost an "S" shaped air flow.

From what you have said that fan doesn't matter. Since it is currently the fan that is moving very little air I thought it was the primary problem with cooling in my system.

Ok, I'm learning but slowly. Backpressure could be a problem because the PSU is near the top and the video, mobo, etc (all but the HDD's) are near the bottom of the case. thus a LOT of wires. neatly tied and round where possible, still, a lot of wires.

[Tibors]

From what you have said that fan doesn't matter. Since it is currently the fan that is moving very little air I thought it was the primary problem with cooling in my system.

It might still be the primary problem. Fans in series move only as much as the slowest of them. E.g. a fan in the front that only moves half the air that the fans on the back (case and PSU) want to exhaust, actually works as an air brake. In that case just a hole would allow more air to flow.

Luckilly this is easy to test and free (as in free beer, not free speach ).