Need 9cm fan with low start voltage

[netmask254]

I have a Synology DS212J NAS using Y.S. Tech FD129225LS-N as case fan, which is a 92mm fan with below specs. It's quiet but not silent thus I'm going to get a lower-speed fan to replace it.
Operating Voltage Range: 7~13.2V
Speed: 1800RPM
Noise Level: 25dBA

I have single WD Green disk installed and the cooling is never a problem (I don't think 40C is a problem for harddisk ). However, the fan speed is controlled by disk temperture. When the temperature is low, the fan is feed with a relatively low voltage. What’s worse, I don’t know it, maybe 5V or 7V (it's also hard to guess since there is no way to monitor the fan speed). If the new fan doesn’t work at that low voltage (i.e. stops), the motherboard will not be able to detect any fan speed via the 3-pin and thinks the fan is broken. Alarms are generated and the system may be shut down within some minutes.

Therefore, I quite care about the start working voltage. On one hand, I'm seeking low speed fan. On the other hand, low speed fan generally doesn't work at low voltage. I have a couple of choices, but I don't how what's their working voltage range nor the minimum speed (except the Noctua fan).
NF-B9-1600 9cm: 1600rpm, 17.6dBA, can be as low as 1000-rpm with ULNA connector.
Scythe Kama Flow2 9cm: 1200rpm, 16.9dBA
Scythe S-Flex SFF92B 9cm: 1500rpm, 17.4dBA

Does any body have experience with them (using a fan controller)? And how about their quality on noise? Thanks very much!

[Lithium466]

I'd go for Nexus basic fan, if you can buy one. Cheap, quite efficient, start under 5V, not too noisy, 1500rpm max.

I haven't tried the Kama flow 2 fan, but the S-flex is good too, maybe it will last longer than Nexus, but it is also more expensive, and personnaly I prefer the sound of the Nexus. The Noctua is in my opinion just an average fan, sure it will last long (~same MTBF as S-flex), but it is way overpriced.

You can also have a look at Noiseblocker fan, XE2 or PE1/PEP, they are also very good fans.

[Abula]

Noiseblocker NB-BlackSilentPro PE-1 92mm x 25mm Ultra Quiet Fan - 1300 RPM - 14 dBA, has a starting voltage of 5V, and lower rated top speed, so i would guess would end up quieter (but havent tried it), another to look into is Scythe S-FLEX™ SFF92A 92 x 92 x 25 mm Fan w/ S-FDB Bearing (1000rpm), but no specs into starting voltage.

[netmask254]

Noiseblocker NB-BlackSilentPro PE-1 92mm x 25mm Ultra Quiet Fan - 1300 RPM - 14 dBA, has a starting voltage of 5V, and lower rated top speed, so i would guess would end up quieter (but havent tried it), another to look into is Scythe S-FLEX™ SFF92A 92 x 92 x 25 mm Fan w/ S-FDB Bearing (1000rpm), but no specs into starting voltage.

The noiseblocker fan would be my best choice. Unfortunately it's not avaiable at all in China market, neither Nexus fan. I'm going to use Noctua fan temporarily.