what rpm does a 120mm fan run @ at 7v?

[poohbear]

hello, i've been trying to find the ideal noise level for my system's exhaust fan to run @ 24/7 and bought a vantec fan controller to achieve that. does anyone know what rpm a 120mm fan run at @ 7v? my vantec fan controller only supports 7v-12v. is 120mm fan running @ 7v good as an exhaust fan? right now the bios controller on my mobo runs it @ 731rpm in silent mode (completely silent) and 1600rpm @ full load, which is way too loud and i hate it. my 120mm cpu fan runs @ 1300rpm which is a perfect balance. would 1300rpm be 7v? im guessing 731rpm is 5v, would that be correct?

thanks in advance.🙂

oh, and im guessing brand name would'nt matter since they're all 120mm fans connected to a fan controller, yea?

 

[Zepper]

Different fans will run at different speeds at 7V. A fan controller is good for slowing higher speed fans to a reasonable noise level while having CFM in reserve if you happen to need it. Check out the fan tests at XtremeSystems for more info.
http://www.xtremesystems.org/f...&highlight=fan+testing

There is an earlier test as well linked from the one above.. Unfortunately they don't put voltage dots on the curves, so you'll have to figure that out for yourself.

www.silentpcreview.com also has fan tests more oriented to quiet - the above tests are more oriented to performance. And remember that PWM fan controllers don't change the voltage, they always run at around 11V, what they change is the delivered power. Linear/analog fan controllers like the Rheobus actually change the voltage applied to the fan.

.bh.

 

[Billb2]

Different fans will run at different speeds at 7V
Different fans will deliver different CFMs at the same speed
Different fans will provide different noise levels at the same CFMs.

Since the two things you are concerned about are noise and heat, volts and RPMs are of little importance to you. What you're looking for ia the fan that will deliver the CFMs you need at the lowest noise level, no matter what the voltage or RPM is.

But, what many people don't realize is that as a fan works against more back pressure, the less air it will move. It's called a P/Q curve.

So two different fans with the same CFM ratings, at the same voltage, the same RPM, and at the same noise level can blow different amounts of air through your case. The problem is that you'll never find a test that reflects your exact use conditions (RPM, volts, noise and air through YOUR case). That's where rheostats come in. You pick a fan that's slightly more than you need and slow (and quiet) it a little more with a rheostat. The problem with rheostats is that all the current the remove is directly converted into heat. Also note that some fans will not start up at voltages lower than 0.7v, or even worse, won't start up every time at reduced voltages.

 

[DSF]

What's wrong with running the fan in silent mode? What are your temps like when you're doing that?

 

[poohbear]

thanks for the replies folks!

Originally posted by: Billb2
Different fans will run at different speeds at 7V
Different fans will deliver different CFMs at the same speed
Different fans will provide different noise levels at the same CFMs.

now, how can different fans @ the same voltages push less/more air? isnt it straight forward w/ all fans that are 120mm that run on the same voltage? the same egnineering, the laws of phsyics and what not? is my 120mm silenX fan really more silent because of special engineering? it thought that was all bullocks, a 120mm running @ a certain voltage would push the same amount of air like any other 120mm running @ that same voltage, yeah?

Originally posted by: DSF
What's wrong with running the fan in silent mode? What are your temps like when you're doing that?

well, w/ the exhaust staying at 731rpm (controlled through my bios), the case temps get much higher than im comfy w/. My cpu goes past 53c under load, which im not comfy w/ considering its still winter here, so in the summer u can imagine how hot that'd get. My 8800gt has an S1 accelero w/ the fans on it, so im not too worried about that.

 

[heymrdj]

poohbear, fans differ by blade design. The sharper the angle of the blade the louder it's going to be, but it will also push more air. So it's a balance of finding a fan that runs where you want.

Case and point: The Scythe SFF21E puts out 49cfm at 800RPMs at just 20db using 7 blades. The Delta EFB1212L 120x25mm Triple Blade Low Speed puts out 50 CFM at about 1700RPMs at about 28db using only 3 blades. The 3 blades are not as aggressively angled, which is why even at those RPM's it's not loud.

Point: All fans are different.

 

[DerwenArtos12]

Originally posted by: heymrdj
poohbear, fans differ by blade design. The sharper the angle of the blade the louder it's going to be, but it will also push more air. So it's a balance of finding a fan that runs where you want.

Case and point: The Scythe SFF21E puts out 49cfm at 800RPMs at just 20db using 7 blades. The Delta EFB1212L 120x25mm Triple Blade Low Speed puts out 50 CFM at about 1700RPMs at about 28db using only 3 blades. The 3 blades are not as aggressively angled, which is why even at those RPM's it's not loud.

Point: All fans are different.

also keep in mind that, generally speaking, the one with greater surface area to each blade will have a higher static pressure rating. That static pressure rating will actually determine it's performance on something that is going to create a lot of back-pressure, like a heatsink or a radiator.

 

[poohbear]

Originally posted by: heymrdj
poohbear, fans differ by blade design. The sharper the angle of the blade the louder it's going to be, but it will also push more air. So it's a balance of finding a fan that runs where you want.

Case and point: The Scythe SFF21E puts out 49cfm at 800RPMs at just 20db using 7 blades. The Delta EFB1212L 120x25mm Triple Blade Low Speed puts out 50 CFM at about 1700RPMs at about 28db using only 3 blades. The 3 blades are not as aggressively angled, which is why even at those RPM's it's not loud.

Point: All fans are different.

wow, i never even knew that such variables were so important. thanks alot for all that info. seems there's alot more to consider than just rpm and size.😛 mind u, i got this table from the scythe site:

Model # Dimensions Fan Speed Fan Noise Air Flow Rated Current
SFF21D 120x120x25mm 800rpm 8.7dBA 33.5CFM 0.10A
SFF21E 120x120x25mm 1,200rpm 20.1dBA 49.0CFM 0.15A
SFF21F 120x120x25mm 1,600rpm 28.0dBA 63.7CFM 0.20A

i'm guessing that's still great, but @ 800rpm it pushes out 33.5cfm, and @ 1200 it pushes out 49cfm, but its still only 20db @ 1200rpm. I'm guessing that's the best fan to get then if someone wants silence at a reasonable noise level.🙂 cheers for that.

edit: ouch, it costs $20 for one of those fans, kinda like the silenx fans. is it worth all that extra money?

 

[DerwenArtos12]

Originally posted by: poohbear

Originally posted by: heymrdj
poohbear, fans differ by blade design. The sharper the angle of the blade the louder it's going to be, but it will also push more air. So it's a balance of finding a fan that runs where you want.

Case and point: The Scythe SFF21E puts out 49cfm at 800RPMs at just 20db using 7 blades. The Delta EFB1212L 120x25mm Triple Blade Low Speed puts out 50 CFM at about 1700RPMs at about 28db using only 3 blades. The 3 blades are not as aggressively angled, which is why even at those RPM's it's not loud.

Point: All fans are different.

wow, i never even knew that such variables were so important. thanks alot for all that info. seems there's alot more to consider than just rpm and size.😛 mind u, i got this table from the scythe site:

Model # Dimensions Fan Speed Fan Noise Air Flow Rated Current
SFF21D 120x120x25mm 800rpm 8.7dBA 33.5CFM 0.10A
SFF21E 120x120x25mm 1,200rpm 20.1dBA 49.0CFM 0.15A
SFF21F 120x120x25mm 1,600rpm 28.0dBA 63.7CFM 0.20A

i'm guessing that's still great, but @ 800rpm it pushes out 33.5cfm, and @ 1200 it pushes out 49cfm, but its still only 20db @ 1200rpm. I'm guessing that's the best fan to get then if someone wants silence at a reasonable noise level.🙂 cheers for that.

Silence is ver subjective and the overall sound output of a fan varies more than what is listed. Anything, and I do mean anything, within 1mm of the fan per CFM is going to create resistance and with resistance comes a noise, that noise depends on the material and size of the point of resistance. Plus, there are seperate wind noises and motor noises. The motors on some fans have a tendancy to squeel and other to tick. Ball bearing fans like the ones you listed, will be very quiet in the motor department but, given the wide blades of the fans there will be very good static pressure so you'll be more concerned with wind-noises. Also, silent is going to depend on the ambient room volume. If you have an ambiet room volum of 30db(as is common) then even the SFF21F is going to be "silent" as it will be lower than the ambient room volume.

 

[poohbear]

good points derwenartos, thanks for the clarification.

now, hey mrdj, all the 120mm fans that i have have 7 blades (3 silenx, 1 thermaltake, and a couple generic ones) so i dont see how this is unique to the scythes? does 7 blades generally mean they're quieter? im still going back to my original assumption that most fans would sound the same given the same rpm and voltage, w/ very tangible differences to the point of being imperceivable at 1 meter (the distance from my case to my ear). hmmm. im tempted to buy one of those scythes, but really i doubt they'd make a diff in terms of noise if i plug them all to my vantec controller (and run them all @ 7v). actually, i'll do some testing tomorrow to this end, i'll try all 3 different brands to see if they do indeed make a diff between them.

 

[DerwenArtos12]

Originally posted by: poohbear
good points derwenartos, thanks for the clarification.

now, hey mrdj, all the 120mm fans that i have have 7 blades (3 silenx, 1 thermaltake, and a couple generic ones) so i dont see how this is unique to the scythes? does 7 blades generally mean they're quieter? im still going back to my original assumption that most fans would sound the same given the same rpm and voltage, w/ very tangible differences to the point of being imperceivable at 1 meter (the distance from my case to my ear). hmmm. im tempted to buy one of those scythes, but really i doubt they'd make a diff in terms of noise if i plug them all to my vantec controller (and run them all @ 7v). actually, i'll do some testing tomorrow to this end, i'll try all 3 different brands to see if they do indeed make a diff between them.

7 blade fans have become the standard so the main differences between them are going to be bearing type and how curved the blades are. If these are just going to be case fans I actually like the Scythe Slipstreams. Tehy ahve more smaller blades so they're notably quieter at the same RPM compared to a 7 blade fan but, they don't have as much static pressure so they're more affected by grills, filters, heatsinks or radiators.