Which Scythe fan is a better choice? (S-FLEX or SlipStream)

[netmask254]

I raise this question for two reasons:
1 I saw in latest Puget Serenity review, they updated the case fan and CPU fan to Slipstream, while the previous case fans are S-FLEX. Does it indicate that SlipStream is a better choice in practice?

2 I have used a SFLEX-E as CPU fan (undervolted to 600rpm) for almost two years. In a recent listening test (10-cm nearing my ear), I found it generates very significant click noise (larger than its wind noise). Meanwhile, I have another Noctua S12 fan (800rpm) also used for two years, I'd like to say it's much better in that listening test and has very little click noise. It makes me hesitate that although S-FLEX (FBD) has an extremely long declared life time, in practice it's easier to age out and becomes noiser after some time using (I don't know whether it's my sample's problem but wish so).

Could you share your experience? Thanks a lot!

[Modo]

I've had an opposite experience. My two S-FLEX fans were running fine for two years. I replaced them with SlipStream fans to see what everyone was so loud about, but these seem slightly more audible at the lowest speed I use (about 550 rpm). I'm guessing that at these low noise levels sample variance and usage plays a big role.

As to a manufacturer switching expensive fans for a cheaper model, I'm sure you can figure that one out.

[Das_Saunamies]

Slip Streams are supposedly softer in noise signature, and I can vouch for the 800 RPM SS I have vs the S-FLEX Es I ran at similar RPM for gaming. The SS makes more of a whoosh sound and the S-FLEXs mix in a bit of mechanical noise. Much better at sucking air through filters or when mounted horizontally though, less RPM drop vs my (admittedly weak) SS.

Both are still smooth as silk to my ears, it's like comparing different steel alloys for hardness to me. Today I would pick the PWM option though, no contest.

Neither of my fans has ever had clicking, even though the S-FLEXs have gotten really dusty at times. Could be sample variance as suggested.

Since the human ear adjusts to loudness if you let it, the signature is what counts (how annoying the sound is). Pick what you like best - I'm currently scooting along fine on Arctic Cooling F12 PWM fans that are not as silky-smooth, but do the job just fine for half the money.