The Top SPCR Quiet 120mm Axial Fans Compared + 120mmAC Fans.
Posted: Sun Oct 17, 2004 9:46 pm
Last update: July 2009
Note: For each dimensional category new additions are appended the list, so look towards the end of each category to view the more current choices.
____________________________________________________
First off, most of the info here has been tapped from guys on this forum so a big thanks to you, you probably know who you are. I decided to post this since I don't really know of a one stop comparison of quiet 120mm fans, and it seems like 120mm axial fan threads keep popping up. If a moderator could make this a sticky that would be awesome. A big thanks to ferdb for his insight in the 120x25+ extra thick axia fan sector!
Quiet 120mm x 25mm Fans (Standard Case Fan Thickness)
The Papst 4412 fans are very nice when undervolted on DC current. They are one of the best quiet 120x25mm fans for restrictive environments. They don't like PWM though. Purely noise wise, they fall in the quiet, but not the most quiet category. The Nexus and Globe (and the more recent additions to this list) options are quieter, but remember, the 4412 is moving a good bit of CFM.
Note: Both the Papsts and the Panaflos seem to be degrading in quality overall. The Panaflos seem to be degrading more so then the Papsts though.
The Evercool / Titan 120mm aluminum 120mm fans are pretty good quiet fans for a low restrictive environment @ <5V DC (lower than most other fans can undervolt). They also, like the Papsts, don't like PWM very much.
The Nexus "Real Quiet Fans" are astounding fans in the 80mm, 92mm, and 120mm categories. They work flawlessly on PWM and undervolt on DC fairly well considering their low 12V CFM. The only potential negatives about the 120mm is its orange color, its lower 12V CFM numbers (not an issue at all for most everyone though), and price compared to the Globes. Not as good as the Papst 4412 in a restrictive environment. It's one of the quietest 120mm axial at the standard 12v on the market and also one of the quietest 120x25mm case fan on the market at minimum RPMs. You can buy them at endpcnoise or siliconacoustics for a cool $20 per fan, but that might get the best $20 (times n number of fans bought) you've ever spent on your computer. The extra cost may be in part due to excellent quality control. The Nexus is predictably quiet, not requiring "cherry-picking" like other fans.
Edit 2-15-06: Note the Nexus fans are now available in a swanky black-and-white.
The Globe S1202512L-3M works flawlessly on PWM, undervolts on DC very well, and is one of the quietest fans around when operated with either of these two wattage regulators. Some chatter/clicking has been reported even at the lowest settings though. Doubt it works in restrictive environments as well as the 4412. With its ~65CFM at 12V, it is an excellent choice for when you�re willing to give up some quietness for extra CFM (i.e. max overclock bragging rights or converting a Delta screamer dude). You can buy them at mnpctech for only $8 per fan. If you looking for the absolute quietest fan and are willing to lay out the money, you really will want to spend the extra on the Nexus to avoid the Globes slight bearing/motor noise at the lowest RPMs.
Edit 3-16-05: There is now no known source for this fan, but Aleksi is working on it. (link)
Edit 5-11-05: Aleksi delivers! (link)
The AcoustiFan AF120CT is closely related to, if not the same fan as the Globe (link). One differentiating aspect compared to the Globe is that the AF120CT is transparent--a plus for LED/Cathode lovers. Note, however, the clear plastic is a little noiser material though. You can find them at siliconacoustics.
The Enermax 120mm (like this one) is apparently a Globe relation as well (link1, link2). Most Enermaxes use ball bearings rather than the quieter sleeved the quieter Globes and AcousticFans use (BB equals louder bearing noise). However, what's pulling for these fans is they are available from just about every wide-selection PC vendor and as a resultant have very good name recognition among the general computer savvy. In addition, they are usually bundled with some sort of simple speed controller. I believe this fan would be correctly considered decently quiet. On the quiet side of loud, but on the loud side of quiet. It seems to be pretty popular among "quieter" computing guys who have not yet tasted the fruit of a genuinely quiet fan or are not quite as intent on a truly quiet setup. Spend your money elsewere IMHO. Just including it here so you know where it stands.
The Yate Loon D12SL-12 is used by 3R systems, the Korean company that builds most of Ahanix's cases. They can also be found in some Fortron power supplies. The Nexus 120mm is a Yate Loon under another label, only the Yate Loon spins faster than the Nexus at 12V and the Nexus's fan blade design possibly has a slighly little more curved leading edge. Unlike the orange Nexus 120mm, the Yate Loon is black. Can be rather difficult to find. Probably the ideal quiet fan as it still retains the ability to crank a bit more CFM on demand but lack the bearing/motor noise of the Globe (assuming the Yate Loon's noise charactersitics is the same as the Nexus 120 in the Nexus's RPM range).
Edit 1-18-05: Looks like the are relatively readily available now! See this thread.
Edit 12-5-05: Available from jab-tech, frozencpu, pctekonline, and tekgems. D12SM-12 Blue LED from case-mod
German vendor: silencio- gives a discount if you mention spcr.
Coolermaster SUF-S12 / A12025-12CB-5BN-L1 *Quote from frankgehry*:
Great fan with no bearing noise whatsoever. Motor noise was unobtrusive. Not quite as smooth as the Yate Loon models but [according to FG] every bit as quiet. If you are sensitive to bearing noise this may be a better choice that the Yate Loons. (link)
Thanks for your input FG!
GlobalWin NC Bearing 1202512L
Relatively loud at 12v, at 5v this fan can quiet down potentially even more so than the ubiquitous Nexus. The CFM values at 5v, however, are apparently noticeably inferior to the Nexus at 5v. So probably best as a case fan rather than on a heatsink, except maybe as an aternative to purely passive. A better choice for inhospitable environments (PSUs) than the Nexus or YateLoon due to its bearing design. Some bearing rub may be present with this fan though. The fan is also reportedly PWM intolerant.
Info here and here.
Scythe DF Series
A solid fan series made by Young Lin. The 1200rpm sleeve bearing version is in the ranks of the Yate Loon D12SL-12. The 1600rpm version may be a solid choice for delta screamer converts not quite ready to give up their old ways - a nice addition now that the Globe S1202512L-3M has for all pratical purposes become unavailable.
Discontinued, but lives on in its spiritual-successor, the Slipstream series.
Scythe S-Flex
Makes use of "Fluid Dynamic Bearing" technology. The non-800rpm models are excellent, albeit noticeably more expensive than the DFs (archaic) Slipstream series. The S-Flex with its finer-pitched blades can be the superior choice in more restrictive environments that the Slipstream, and more durable in horizontal orientation. The 800rpm @ 12v stock version of this model, The Scythe S-FLEX SFF21D, initially looked to be the choice for the quietest 120mm axial at standard 12v voltage, and good samples are indeed excellent, but this particular version's quality inconsistency gives the nod to either the venerable Nexus or nowadays the newer the Slipstream for this particular sector. The 1200rpm model S-Flex (with resistor) gets the most attention of the series.
Noctua NF-S12 Series
Excellent air flow to noise ratio, with efficient fan blade design. The same fan blade design however, specifically their coarse pitch the spacing between the blades, makes the fan unsuitable in more restrictive environments such as heatsinks and radiators. Fan undervolts well, with a nice, whooshing noise character -- though a potentially unnerving "presence" nature of the fan, present long after the fan had otherwise reached inaudible levels, is noted in the Nov06 Offical 120mm Report.
Scythe Slipstream Series *Quote from Mike Chin*:
The [Scythe Slipstream 800RPM, SY1225SL12L] was tested for noise characteristics. We didn't do a full range of airflow / noise tests, but SPL and RPM measurements were taken at various voltages. The overall noise signature of this nine-bladed fan is very smooth and quiet, mostly broadband turbulence with no tonality at all even at 12V. At 9V, it's already inaudible. Of course, spinning at just 660 RPM, it isn't moving that much air, although Scythe says the nine blades produce greater airflow at the same speed than seven blades. For many users, this fan can probably be run full speed; it's that quiet. Mike Chin
Looks like Scythe hit a home run on these guys!
Edit May '08: Attack of the 120 Scythes
Quiet 120mm x Thicker than 25mm Fans
The Panaflo L1A 120mm, unlike the Japanaflo L1A 80mm fans, is not really considered in the most quiet fan category. It still can be pretty quiet though, esp. a 'good' one on a lower undervolt, and it is not uncommon to see it being used by some of the more hardcore quiet gurus. Most (basically all) will want to look at other options though unless you are willing to accept a lot of not so good to pretty bad samples in the hunt for good ones.
The following are slightly edited quotes of Ferdb's posts in this thread. I highly recommend you take the time to read the original posts too! Thanks for your input Ferdb! A word of warning to the not too technically oriented, the following are AC fans. You will want to sick with DC fans, which are highlighted red.
Quiet 120mm x 38mm AC Fans
The Globe Motors A47-B15A-15T2-100 is an 120V AC fan. If you connect 2 in series across 120V they run about 950rpm and are very quiet, comparable to a Nexus undervolted to about 9.5-10v. They flow substantially more air than the Nexus and since they are thicker they should handle backpressure better but I have not actually tested their performance with backpressure yet. Note: Ferdb has seemed to have dropped this fan in favor of the Sunon 2123XST.
The Sunon DP200A-2123XST (2123XST) is a 240V AC fan and runs 1300-1350rpm on 120V. At this speed it makes more noise than the Globe Motors fans but only because of the higher RPM. Slowed down to around 900 rpm it is almost inaudible at 1 meter in open air and pushes a good amount of air. Even at the 1300rpm level it is much quieter than the Panaflo L1A DC brushless. Almost no motor or bearing noise, it is all airflow noise. Easily the best airflow vs noise ratio of the 120x25+mm lot. Probably one of the best 120mm fans available when undervolted. It has a better airflow to noise ratio than the Nexus (for a given airflow it's quieter than the nexus / for a given quietness it moves more air) and performs gloriously in restrictive environments. Reduce the RPM with a series resistor to desired level. For more information see ferdb's posts on page 2 and <this> thread by ferdb.
Addition 1-18-05:
The Sunon A1123/A2123 HST, unlike the 5-blade 2123XST, is a 7-blade fan with about 25% better flow at 0.2in H2O pressure difference. Air flow is rated at 112/124 CFM at zero resistance, and volume is 43/46 dBA [DrCR: At 240V I assume]. A bit louder, but I'm guessing most of that is probably air flow noise. There are several other fans that could fit the A1123 model number, so be careful to make sure you get the right one. It's got an Aluminium alloy frame, is described as "High Air Flow", and rated at 0.28/0.31 in H2O peak pressure.
Compared with the Nexus 120 and Sunon 2123XST at similar rpms, the A2123 make a little more noise than the 2123xst but the higher airflow more than makes up for it and it comes out ahead on CFM/noise. At comparable CFM through the radiator the A2123 has a better CFM vs noise ratio than the 2123XST or Nexus 120. The A2123 fan blade's shape is much different than that of the 7-blade Nexus, but the CFM vs RPM ratio of the two are very close. The Fan noise is a higher pitched than the 2123XST at the same rpm because of the two extra fan blades, and is similar to the Nexus in tone. The A2123HST has almost no bearing noise at all (in my [ferdb's] samples).
For Radiator applications the A2123 comes out as the best performer, the advantage over the Nexus or 2123XST being moderate. Both the A2123 and 2123XST are heavy metal 38mm thick fans which 'weigh' against them from a mounting and weight issue [DrCR: Very punny. ].
Bottom line is that the Sunon A2123 is the best airflow to noise ratio fan I've found for radiator use. If you want the ultimate performance, you can achieve it with this fan. However the Nexus 120 is fairly close in performance and has the added convenience of being light weight and running on 12V.
And additional note by pdf27:
The fans have a little bit of 50Hz hum (I think I can hear it @ 2m in free air, but only with a fluorescent light @ 4m turned off!), and the rest of the noise is vibration. The fan bodies are aluminum (look like castings) so are fairly heavy, and that should help vibration when installed.
Special thanks to pdf27 in addition to ferdb for his input on the A1123 and his offer to order some for all us State-side. For more information on the A1123, see the second half of this thread.
AC Cons:
Not as easily speed controlled and a 120V relay (such as a pump relay) may be needed to switch the fan(s) on with your machine. Note, vibration isolation/isolators is essentially required to avoid a ton of vibration noise. Also, the A1123 has a metal frame/case and could present mounting issues due to its weight.
To the newbies, feel free to post questions! To this forum's core, feel free to comment on if you believe any aspect of this comparison to not be correct. If a fan is not on this list then it's probably not a quiet fan (e.g. Vantec anything-but-Stealth), but most assuredly go ahead and ask anyway, esp. if it is a more obscure fan or if the same fan is also marketed under a as of yet unknown to me different label.
Also, bear in mind there are multiple choices in quiet fans, but it would be extremely hard to say which is the 'quietest' as there are so many other factors like CFM, resistively, character of noise, technique of lower rpms, etc. In some cases 'hard-core' silence gurus simply have to agree to disagree and realize the variation in circumstances and a fans' attributal consistency. Things are less subjective in recent times now that there are many proper reviews completed by MikeC and co (look for the fan roundups).
For you new guys having a hard time choosing and don't want to undervolt, buy the Scythe Slipstream 800RPM or the Nexus, both very solid quiet fans at the default 12v, with the Slipstream edging out the Nexus. If you are willing to undervolt and/or want those extra rpms for whatever reason, the higher RPM versions of the S-Flex like the S-Flex SFF21E 1200rpm or nowadays the Slipstream SY1225SL12M is the route to take (I'm a fan of 1200RPMers @5-6v myself). For budget builds, the cheaper priced YateLoon D12SL-12 is choice now that in recent times they are common and gloriously affordable. Their quality control isn't as good as the cherry-picked Nexus fans, but their higher 1350rpm speed over the Nexus is perfect for running straight off a 5v line rather than a variable resistor. In general though, the superior and also reasonably affordable Slipstream is the route to take for all but the most budget of builds.
If you have the electrical and perhaps modding know-how, room for a thicker fan, the need for higher pressure, and don't mind AC, by all means go for the Sunon!
Note: Most quieter computing guys will never need more CFM than ~1000rpm as half that will often suffice with proper heatsinks, and there are numerous solid options mentioned above for the guys a little too timid to try undervolting right off. Still though, the Globe S1202512L-3M (archaic) Scythe SFF21F or Slipstream 1600rpm are perfect for Delta screamer converts as their undervolted quiet potential is far better than most other fans with such 12v CFMs. The Sunon is perfect for heatercores or other high-restrictive environments, but you have to be prepared to take on its AC and AC-related undervolting issues.
DrCR
_________
Update June '07: Hard to believe this thread is 2.5years old now. We're starting to get serious lab results nowadays thanks to Mike & Co. A _big_ thanks to you guys! Be sure to check out the Fans and Controls article section for the latest testing results in this sector!
Edit 9-13-07: I have absolutely fallen in love with the S-Flex SFF21E 1200rpm for when you are willing to spend the premium over the wonderfully cheap D12SL-12 YLs. Recommended with a variable DC-voltage controller like the FanMate though.
Edit 2-28-08: Comments added for the excellent Slipstreams and reorganized a bit.
Edit 5-20-08: Official Slipstream Fan Roundup added and thread reorganized a bit.
Edit 7-9-09: Supplemental comments (black text) added, removed, and modified as needed. S-Flex comments clarified.
Note: For each dimensional category new additions are appended the list, so look towards the end of each category to view the more current choices.
____________________________________________________
First off, most of the info here has been tapped from guys on this forum so a big thanks to you, you probably know who you are. I decided to post this since I don't really know of a one stop comparison of quiet 120mm fans, and it seems like 120mm axial fan threads keep popping up. If a moderator could make this a sticky that would be awesome. A big thanks to ferdb for his insight in the 120x25+ extra thick axia fan sector!
Quiet 120mm x 25mm Fans (Standard Case Fan Thickness)
The Papst 4412 fans are very nice when undervolted on DC current. They are one of the best quiet 120x25mm fans for restrictive environments. They don't like PWM though. Purely noise wise, they fall in the quiet, but not the most quiet category. The Nexus and Globe (and the more recent additions to this list) options are quieter, but remember, the 4412 is moving a good bit of CFM.
Note: Both the Papsts and the Panaflos seem to be degrading in quality overall. The Panaflos seem to be degrading more so then the Papsts though.
The Evercool / Titan 120mm aluminum 120mm fans are pretty good quiet fans for a low restrictive environment @ <5V DC (lower than most other fans can undervolt). They also, like the Papsts, don't like PWM very much.
The Nexus "Real Quiet Fans" are astounding fans in the 80mm, 92mm, and 120mm categories. They work flawlessly on PWM and undervolt on DC fairly well considering their low 12V CFM. The only potential negatives about the 120mm is its orange color, its lower 12V CFM numbers (not an issue at all for most everyone though), and price compared to the Globes. Not as good as the Papst 4412 in a restrictive environment. It's one of the quietest 120mm axial at the standard 12v on the market and also one of the quietest 120x25mm case fan on the market at minimum RPMs. You can buy them at endpcnoise or siliconacoustics for a cool $20 per fan, but that might get the best $20 (times n number of fans bought) you've ever spent on your computer. The extra cost may be in part due to excellent quality control. The Nexus is predictably quiet, not requiring "cherry-picking" like other fans.
Edit 2-15-06: Note the Nexus fans are now available in a swanky black-and-white.
The Globe S1202512L-3M works flawlessly on PWM, undervolts on DC very well, and is one of the quietest fans around when operated with either of these two wattage regulators. Some chatter/clicking has been reported even at the lowest settings though. Doubt it works in restrictive environments as well as the 4412. With its ~65CFM at 12V, it is an excellent choice for when you�re willing to give up some quietness for extra CFM (i.e. max overclock bragging rights or converting a Delta screamer dude). You can buy them at mnpctech for only $8 per fan. If you looking for the absolute quietest fan and are willing to lay out the money, you really will want to spend the extra on the Nexus to avoid the Globes slight bearing/motor noise at the lowest RPMs.
Edit 3-16-05: There is now no known source for this fan, but Aleksi is working on it. (link)
Edit 5-11-05: Aleksi delivers! (link)
The AcoustiFan AF120CT is closely related to, if not the same fan as the Globe (link). One differentiating aspect compared to the Globe is that the AF120CT is transparent--a plus for LED/Cathode lovers. Note, however, the clear plastic is a little noiser material though. You can find them at siliconacoustics.
The Enermax 120mm (like this one) is apparently a Globe relation as well (link1, link2). Most Enermaxes use ball bearings rather than the quieter sleeved the quieter Globes and AcousticFans use (BB equals louder bearing noise). However, what's pulling for these fans is they are available from just about every wide-selection PC vendor and as a resultant have very good name recognition among the general computer savvy. In addition, they are usually bundled with some sort of simple speed controller. I believe this fan would be correctly considered decently quiet. On the quiet side of loud, but on the loud side of quiet. It seems to be pretty popular among "quieter" computing guys who have not yet tasted the fruit of a genuinely quiet fan or are not quite as intent on a truly quiet setup. Spend your money elsewere IMHO. Just including it here so you know where it stands.
The Yate Loon D12SL-12 is used by 3R systems, the Korean company that builds most of Ahanix's cases. They can also be found in some Fortron power supplies. The Nexus 120mm is a Yate Loon under another label, only the Yate Loon spins faster than the Nexus at 12V and the Nexus's fan blade design possibly has a slighly little more curved leading edge. Unlike the orange Nexus 120mm, the Yate Loon is black. Can be rather difficult to find. Probably the ideal quiet fan as it still retains the ability to crank a bit more CFM on demand but lack the bearing/motor noise of the Globe (assuming the Yate Loon's noise charactersitics is the same as the Nexus 120 in the Nexus's RPM range).
Edit 1-18-05: Looks like the are relatively readily available now! See this thread.
Edit 12-5-05: Available from jab-tech, frozencpu, pctekonline, and tekgems. D12SM-12 Blue LED from case-mod
German vendor: silencio- gives a discount if you mention spcr.
Coolermaster SUF-S12 / A12025-12CB-5BN-L1 *Quote from frankgehry*:
Great fan with no bearing noise whatsoever. Motor noise was unobtrusive. Not quite as smooth as the Yate Loon models but [according to FG] every bit as quiet. If you are sensitive to bearing noise this may be a better choice that the Yate Loons. (link)
Thanks for your input FG!
GlobalWin NC Bearing 1202512L
Relatively loud at 12v, at 5v this fan can quiet down potentially even more so than the ubiquitous Nexus. The CFM values at 5v, however, are apparently noticeably inferior to the Nexus at 5v. So probably best as a case fan rather than on a heatsink, except maybe as an aternative to purely passive. A better choice for inhospitable environments (PSUs) than the Nexus or YateLoon due to its bearing design. Some bearing rub may be present with this fan though. The fan is also reportedly PWM intolerant.
Info here and here.
Scythe DF Series
A solid fan series made by Young Lin. The 1200rpm sleeve bearing version is in the ranks of the Yate Loon D12SL-12. The 1600rpm version may be a solid choice for delta screamer converts not quite ready to give up their old ways - a nice addition now that the Globe S1202512L-3M has for all pratical purposes become unavailable.
Discontinued, but lives on in its spiritual-successor, the Slipstream series.
Scythe S-Flex
Makes use of "Fluid Dynamic Bearing" technology. The non-800rpm models are excellent, albeit noticeably more expensive than the DFs (archaic) Slipstream series. The S-Flex with its finer-pitched blades can be the superior choice in more restrictive environments that the Slipstream, and more durable in horizontal orientation. The 800rpm @ 12v stock version of this model, The Scythe S-FLEX SFF21D, initially looked to be the choice for the quietest 120mm axial at standard 12v voltage, and good samples are indeed excellent, but this particular version's quality inconsistency gives the nod to either the venerable Nexus or nowadays the newer the Slipstream for this particular sector. The 1200rpm model S-Flex (with resistor) gets the most attention of the series.
Noctua NF-S12 Series
Excellent air flow to noise ratio, with efficient fan blade design. The same fan blade design however, specifically their coarse pitch the spacing between the blades, makes the fan unsuitable in more restrictive environments such as heatsinks and radiators. Fan undervolts well, with a nice, whooshing noise character -- though a potentially unnerving "presence" nature of the fan, present long after the fan had otherwise reached inaudible levels, is noted in the Nov06 Offical 120mm Report.
Scythe Slipstream Series *Quote from Mike Chin*:
The [Scythe Slipstream 800RPM, SY1225SL12L] was tested for noise characteristics. We didn't do a full range of airflow / noise tests, but SPL and RPM measurements were taken at various voltages. The overall noise signature of this nine-bladed fan is very smooth and quiet, mostly broadband turbulence with no tonality at all even at 12V. At 9V, it's already inaudible. Of course, spinning at just 660 RPM, it isn't moving that much air, although Scythe says the nine blades produce greater airflow at the same speed than seven blades. For many users, this fan can probably be run full speed; it's that quiet. Mike Chin
Looks like Scythe hit a home run on these guys!
Edit May '08: Attack of the 120 Scythes
Quiet 120mm x Thicker than 25mm Fans
The Panaflo L1A 120mm, unlike the Japanaflo L1A 80mm fans, is not really considered in the most quiet fan category. It still can be pretty quiet though, esp. a 'good' one on a lower undervolt, and it is not uncommon to see it being used by some of the more hardcore quiet gurus. Most (basically all) will want to look at other options though unless you are willing to accept a lot of not so good to pretty bad samples in the hunt for good ones.
The following are slightly edited quotes of Ferdb's posts in this thread. I highly recommend you take the time to read the original posts too! Thanks for your input Ferdb! A word of warning to the not too technically oriented, the following are AC fans. You will want to sick with DC fans, which are highlighted red.
Quiet 120mm x 38mm AC Fans
The Globe Motors A47-B15A-15T2-100 is an 120V AC fan. If you connect 2 in series across 120V they run about 950rpm and are very quiet, comparable to a Nexus undervolted to about 9.5-10v. They flow substantially more air than the Nexus and since they are thicker they should handle backpressure better but I have not actually tested their performance with backpressure yet. Note: Ferdb has seemed to have dropped this fan in favor of the Sunon 2123XST.
The Sunon DP200A-2123XST (2123XST) is a 240V AC fan and runs 1300-1350rpm on 120V. At this speed it makes more noise than the Globe Motors fans but only because of the higher RPM. Slowed down to around 900 rpm it is almost inaudible at 1 meter in open air and pushes a good amount of air. Even at the 1300rpm level it is much quieter than the Panaflo L1A DC brushless. Almost no motor or bearing noise, it is all airflow noise. Easily the best airflow vs noise ratio of the 120x25+mm lot. Probably one of the best 120mm fans available when undervolted. It has a better airflow to noise ratio than the Nexus (for a given airflow it's quieter than the nexus / for a given quietness it moves more air) and performs gloriously in restrictive environments. Reduce the RPM with a series resistor to desired level. For more information see ferdb's posts on page 2 and <this> thread by ferdb.
Addition 1-18-05:
The Sunon A1123/A2123 HST, unlike the 5-blade 2123XST, is a 7-blade fan with about 25% better flow at 0.2in H2O pressure difference. Air flow is rated at 112/124 CFM at zero resistance, and volume is 43/46 dBA [DrCR: At 240V I assume]. A bit louder, but I'm guessing most of that is probably air flow noise. There are several other fans that could fit the A1123 model number, so be careful to make sure you get the right one. It's got an Aluminium alloy frame, is described as "High Air Flow", and rated at 0.28/0.31 in H2O peak pressure.
Compared with the Nexus 120 and Sunon 2123XST at similar rpms, the A2123 make a little more noise than the 2123xst but the higher airflow more than makes up for it and it comes out ahead on CFM/noise. At comparable CFM through the radiator the A2123 has a better CFM vs noise ratio than the 2123XST or Nexus 120. The A2123 fan blade's shape is much different than that of the 7-blade Nexus, but the CFM vs RPM ratio of the two are very close. The Fan noise is a higher pitched than the 2123XST at the same rpm because of the two extra fan blades, and is similar to the Nexus in tone. The A2123HST has almost no bearing noise at all (in my [ferdb's] samples).
For Radiator applications the A2123 comes out as the best performer, the advantage over the Nexus or 2123XST being moderate. Both the A2123 and 2123XST are heavy metal 38mm thick fans which 'weigh' against them from a mounting and weight issue [DrCR: Very punny. ].
Bottom line is that the Sunon A2123 is the best airflow to noise ratio fan I've found for radiator use. If you want the ultimate performance, you can achieve it with this fan. However the Nexus 120 is fairly close in performance and has the added convenience of being light weight and running on 12V.
And additional note by pdf27:
The fans have a little bit of 50Hz hum (I think I can hear it @ 2m in free air, but only with a fluorescent light @ 4m turned off!), and the rest of the noise is vibration. The fan bodies are aluminum (look like castings) so are fairly heavy, and that should help vibration when installed.
Special thanks to pdf27 in addition to ferdb for his input on the A1123 and his offer to order some for all us State-side. For more information on the A1123, see the second half of this thread.
AC Cons:
Not as easily speed controlled and a 120V relay (such as a pump relay) may be needed to switch the fan(s) on with your machine. Note, vibration isolation/isolators is essentially required to avoid a ton of vibration noise. Also, the A1123 has a metal frame/case and could present mounting issues due to its weight.
To the newbies, feel free to post questions! To this forum's core, feel free to comment on if you believe any aspect of this comparison to not be correct. If a fan is not on this list then it's probably not a quiet fan (e.g. Vantec anything-but-Stealth), but most assuredly go ahead and ask anyway, esp. if it is a more obscure fan or if the same fan is also marketed under a as of yet unknown to me different label.
Also, bear in mind there are multiple choices in quiet fans, but it would be extremely hard to say which is the 'quietest' as there are so many other factors like CFM, resistively, character of noise, technique of lower rpms, etc. In some cases 'hard-core' silence gurus simply have to agree to disagree and realize the variation in circumstances and a fans' attributal consistency. Things are less subjective in recent times now that there are many proper reviews completed by MikeC and co (look for the fan roundups).
For you new guys having a hard time choosing and don't want to undervolt, buy the Scythe Slipstream 800RPM or the Nexus, both very solid quiet fans at the default 12v, with the Slipstream edging out the Nexus. If you are willing to undervolt and/or want those extra rpms for whatever reason, the higher RPM versions of the S-Flex like the S-Flex SFF21E 1200rpm or nowadays the Slipstream SY1225SL12M is the route to take (I'm a fan of 1200RPMers @5-6v myself). For budget builds, the cheaper priced YateLoon D12SL-12 is choice now that in recent times they are common and gloriously affordable. Their quality control isn't as good as the cherry-picked Nexus fans, but their higher 1350rpm speed over the Nexus is perfect for running straight off a 5v line rather than a variable resistor. In general though, the superior and also reasonably affordable Slipstream is the route to take for all but the most budget of builds.
If you have the electrical and perhaps modding know-how, room for a thicker fan, the need for higher pressure, and don't mind AC, by all means go for the Sunon!
Note: Most quieter computing guys will never need more CFM than ~1000rpm as half that will often suffice with proper heatsinks, and there are numerous solid options mentioned above for the guys a little too timid to try undervolting right off. Still though, the Globe S1202512L-3M (archaic) Scythe SFF21F or Slipstream 1600rpm are perfect for Delta screamer converts as their undervolted quiet potential is far better than most other fans with such 12v CFMs. The Sunon is perfect for heatercores or other high-restrictive environments, but you have to be prepared to take on its AC and AC-related undervolting issues.
DrCR
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Update June '07: Hard to believe this thread is 2.5years old now. We're starting to get serious lab results nowadays thanks to Mike & Co. A _big_ thanks to you guys! Be sure to check out the Fans and Controls article section for the latest testing results in this sector!
Edit 9-13-07: I have absolutely fallen in love with the S-Flex SFF21E 1200rpm for when you are willing to spend the premium over the wonderfully cheap D12SL-12 YLs. Recommended with a variable DC-voltage controller like the FanMate though.
Edit 2-28-08: Comments added for the excellent Slipstreams and reorganized a bit.
Edit 5-20-08: Official Slipstream Fan Roundup added and thread reorganized a bit.
Edit 7-9-09: Supplemental comments (black text) added, removed, and modified as needed. S-Flex comments clarified.