Ive had a few couple of cases with 120mm fans, and although i thought they would be quieter they were infact louder, but the best thing is to use a fan controller, use water cooling for your processor and gpu and possibly your chipset (main heat sources for hot air in case) and usually cases come with a fan strapped to the hdd cage, so all you need is one for ur hdds pulling air in and one at the back pushing out, in my lian-li im annoyingly using 1 front, 2 back, 1 top, plus the processor/gpu and chipset fans, and its not too loud but its annoying sometimes, i need to get round to getting water cooling
use water cooling for pro/gpu/chipset (some or all) and then all you need depending on case layout is one fan in and one fan out
1 exhaust at the back - this is pretty quiet
2 intake at front - these are way too loud for me, but this is due to the airflow being obstruted. These fans sit on HDD modules, and are basically attached to a metal plate with holes in. This means that the air is drawn into the PC directly onto this metal plate, and causes a lot of turbulence within the fan, therefore causing the noise. I plan to solve this by getting some Zalman Fan Mates to reduce the fan speed, and cutting out some of the metal.
Overall though, I would say that 120mm fans can provide improved airflow with reduced noise. The 120mm fans I have are spec'd at 29dB and provide 56CFM @ 2000rpm. An equivalent 80mm fan would provide 32.4CFM at 27.85dB @ 2500rpm. As you can see, the the airflow is far superior on the 120mm fans, allowing you to add a controller to reduce the noise and still have good airflow.
There are also quieter fans out there that you could use. For example, Akasa produce some 80mm fans at 18dB, but with reduced airflow. I personally was looking for some SilenX 120mm fans that provide the same airflow (around 56CFM) at 14dB, but I am having difficulty finding a retailer that sells them where I live (Spain).
I'm addicted to getting my comp to dead silence, as is everyone at that site and on their forum.
But yes, I agree that it depends on the fan you get and the voltage you run the fan at. A fan controller is necessary if you want near-silence. I've found that with my threshold for noise tolerance, any fan at 12v is annoying. Good fans will be nearly inaudible at 5v, the voltage required to start the motors on most fans, and they'll still circulate enough air to keep your box cool.
The only fans that have 3-speed selection are Antec tricool, which are by no means the best 120mm's.
The best 120mm fans are made by Yate Loon (who also makes Nexus fans for 3 times the price of their own), which are REALLY cheap on ebay and Papst.
Avoid Thermaltake. They falsify their noise ratings.
Yeah-- those are bad ratings. Silenx is notorious for bad marketing. Watch out for any quoted noise levels that are not in proper format, which is db/ meter (the meter thing is necessary, otherwise they can measure the db at 5m and not worry about false advertising claims.
I dont know which fans Lian Li use in their cases, but when I recently installed a new motherboard in one of their cases (model number pc7 plus) the fans were inaudible to my untrained ear.
I'm pretty sure they're Panaflo, which is panasonic's fan brand. Those are quite good, as well. Remember that the lower the rotational speed, the quieter the noise, so if you want extreme quiet, each brand has their "slow," "medium," and "high" rpm fans for each size and series.
I am using a Antec Sonata with a Tricool 3 speed 120mm fan set to the medium setting ~1080rpm, and a Zalman 7000cu on my AMD64, and the thing is about as loud as when the central air heater or AC kicks on and is pushing air out thru the vents which is to say you don't hear it much unless it is at the dead on night when it is really silent outside. At the same time, between idle and load the CPU temp is ranging from 22C to 35C with room temp at around 20C.
BTW to get to this level of silence, I had to replace the 6800GT's hsf with a Arctic Cooler NV silencer, and replace the harddisks with quieter one, as well as those with less vibration. Because it doesn't take long to realize the 120mm is hardly long pole in the tent with respect to the noise issue.
All my personal systems have panaflow, they are great, various speeds available for each size, my HTPC has 2x120's 1x90, and 2x80's and it's almost as quit as my stereo receiver unless I'm playing games.
I was thinking of buying a case with 120mm fans but would like to know if they are too loud? Also, are case cpu heat pipes really worth the extra cost? Let's hear some pro's-n-con's.
I think there's a basic law in rotor dynamics which says, in easy terms, that the bigger the blade (also depending on angle) more air can be moved at slower speeds. The surface area on a 120mm blade is greater than on a 80 or 90mm, therefor it can spin slower and move just as much air as a 80 or 90mm that has to spin faster.
I've got a pair (in and out) of 120mm for my Antec case. The fans are a bit loud sometimes, but I do have them installed with heat sensors which control speed relative to the ambient temperature in the case. On idle, they tend to be very quiet and don't bother me while surfing the web...