Media Cases, Air Flow Design and Room - AVS Forum
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post #1 of 10 Old 12-15-2012, 05:17 AM - Thread Starter
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I"ve built four or five PCs over the past 10 years, I'm a hobbyist not a pro. One was an HTPC build. I"ve always used mid-tower cases with ATX builds. I've always used negative pressure with no trouble, other than having to vacuum them out a couple of times a year. My latest case, Antec Sonata, has a dust filter and is super clean inside.

So typically, I have the PSU fan, the chip fan and one fan pulling out the back of the case, up high. I block all other air openings except for one or two at the bottom front of the case. I use 120 mm fans. Never had any trouble. The goal is to keep the PC as quiet as is possible.

This time I want to build an HTPC that looks like a set top box. I don't see why a negative pressure scenario won't work with it as well. And if I were to get an ATX case (I might go micro ATX, not sure yet, but my experience tells me that I would want the expansion) and put in some cards, will there be enough room to work in there?

What are the pros and cons of negative pressure in a media case?
How difficult are they to work in?
Are micro ATX components built, minimally to the same standard as regular ATX components?
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post #2 of 10 Old 12-15-2012, 09:01 PM
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I always prefered to use positive pressure because I can control the dust/debris intake; very beneficial especially when you have 4 cats. Negative pressure kind of negates the benefits of having dust filters BTW (unless you seal all other holes in the case).

As for space to work, that all depends on the case. Some have more room than others.
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post #3 of 10 Old 12-16-2012, 02:33 PM
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Here is a negative pressure setup in a Dish DVR box.


This is another negative pressure in a ITX box. Both the CPU fan (center) and exhaust fans (lower left) are PWM controlled. It is kind of a double negative pressure setup as the CPU fan also pulls. There is an air dam placed on top of the heatsink to force air thru the heatsink skive fins.


But I have possible pressure setup too. In order to keep the fan noise low, I use thermal controlled fans and thermal controllers extensively. This is a thermal controller controlling the two front fans (left side). The green dot on the right touching the HDD is a thermistor.

These two fans typically runs at less than 700RPM.
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post #4 of 10 Old 12-17-2012, 02:16 PM - Thread Starter
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Wow! Thanks.

I've read a couple of threads about slowing down the fans. If they don't connect to the motherboard, how do you do this?
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post #5 of 10 Old 12-17-2012, 02:42 PM
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Quote:
Originally Posted by dksc318 View Post

It is kind of a double negative pressure setup as the CPU fan also pulls.
It's still just negative pressure. Negative pressure means that more air is being mechanically removed from the case (ie: using fans) than blown into the case. It has nothing to do with the number of fans. Positive pressure means that more air is being blown into the case than blown out. You can have fans pushing 40CFM into the case and fans blowing 30CFM out and you would have positive pressure and vice versa.

BTW: a double negative = a positive wink.gif

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Originally Posted by Crescent View Post

Wow! Thanks.
I've read a couple of threads about slowing down the fans. If they don't connect to the motherboard, how do you do this?
Connect the fans positive wire to a lower voltage supply. ie: connect it to 5V instead of 12V
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post #6 of 10 Old 12-17-2012, 07:06 PM
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Quote:
Originally Posted by vladd View Post

...
Connect the fans positive wire to a lower voltage supply. ie: connect it to 5V instead of 12V

Some 12V fans don't turn at 5V.

Today we can have fans work smarter than that, by PWM on the MB or fans that have built in thermistors. Fans then self adjust according to the temperature of the component they are assigned to cool.
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post #7 of 10 Old 12-17-2012, 07:37 PM
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He asked specifically how to slow down fans that don't connect to the motherboard and as referenced in several threads on this site.
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post #8 of 10 Old 12-18-2012, 02:15 AM
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Fan that have built-in thermistors don't require MB to work. The front fans in my server are thermal controlled fans.
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post #9 of 10 Old 12-18-2012, 07:52 AM
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And those slow down automatically, there would be no need for him to ask how to do it. wink.gif

Some fans also have a speed switch on them that can be used to slow them down. Antec uses them a lot in their cases.
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post #10 of 10 Old 12-18-2012, 08:29 AM
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That's right, they work automatically.


AUX fan in this chart are the two front fans that are thermal controlled. SYS fan is a PWM controlled by the MB. You can see the fan varies speed by themselves controlling the HDD temperature to a narrow band. They are mounted to the front of the HDD cages.

One of these two fans is a Antec Smartcool 120mm. Gelid also makes them.
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