500-800RPM target: Scythe 120mm S-Flex SFF21D or SFF21E?

davidh44 · Post by **davidh44** » Mon Feb 09, 2009 4:42 am

I'm thinking of running primarily in the 500-800rpm range. Am I better off getting the 800rpm SFF21D or the 1200rpm SFF21E? (i.e. which one has a better sound profile in that range?)

victorhortalives · Post by **victorhortalives** » Mon Feb 09, 2009 5:23 am

davidh44 wrote:I'm thinking of running primarily in the 500-800rpm range. Am I better off getting the 800rpm SFF21D or the 1200rpm SFF21E? (i.e. which one has a better sound profile in that range?)

I can only offer unhelpful advice !

400rpm to 700rpm - get the 1200rpm version.
800rpm - get the 800rpm version.

700rpm - both are OK.

Overall, I would go for the 1200rpm version.

Xobim · Post by **Xobim** » Mon Feb 09, 2009 6:23 am

The 800 RPM S-flexes have a tendency to stall when undervolted, so I'd go with the 1000rpm model for that matter.

As for sound on the 800RPM models: very quiet. I can hear some whirring and a soft bass-drone when I place my ear next to the fans. Most sound will come from turbulence.

blackworx · Post by **blackworx** » Mon Feb 09, 2009 7:00 am

I've got both and I'd say that below 800rpm the E is practically indistinguishable from the D. Add to that the flexibility of the E and the reported QC issues with the D (grinding/clicking) and I'd say go for the E.

If you really crave ultra low RPM then try the D. I get mine reliably down to 360rpm @ 6V with no stalling issues, but tbh the negligible noise difference between that and the E at the same Voltage (~600rpm) is barely worth the loss of cooling.

davidh44 · Post by **davidh44** » Thu Feb 12, 2009 8:37 pm

Excellent advice, thanks.

Xobim · Post by **Xobim** » Fri Feb 13, 2009 1:16 pm

However, I'd recommend the low-speed or mid-speed (if you want to undervolt it) Slipstream fans. My two S-flexes (D- variant) started to make whining sounds after a year of usage. I've replaced them with 5V slipstreams, and they run silent enough.

davidh44 · Post by **davidh44** » Thu Feb 19, 2009 12:17 am

Does anyone know what RPM the SFF21E (1200rpm version) spins at with the 5V and 7V mods (ie. undervolting without a fan controller)?

davidh44 · Post by **davidh44** » Thu Feb 19, 2009 12:19 am

Xobim wrote:However, I'd recommend the low-speed or mid-speed (if you want to undervolt it) Slipstream fans. My two S-flexes (D- variant) started to make whining sounds after a year of usage. I've replaced them with 5V slipstreams, and they run silent enough.

Does your low-speed slipstream (the 800rpm version) start up reliably at 5V? The equivalent S-Flex doesn't.

blackworx · Post by **blackworx** » Thu Feb 19, 2009 1:58 am

davidh44 wrote:Does anyone know what RPM the SFF21E (1200rpm version) spins at with the 5V and 7V mods (ie. undervolting without a fan controller)?

Seek and ye shall find

7V = 610RPM/32CFM
5V = 410RPM/14CFM

davidh44 · Post by **davidh44** » Mon Feb 23, 2009 2:24 am

Thanks.

I'm quite happy with the SFF21E undervolted, but think I will try Slipstream next time around.

pcy · Post by **pcy** » Mon Feb 23, 2009 2:39 am

Hi,

blackworx wrote:
davidh44 wrote:Does anyone know what RPM the SFF21E (1200rpm version) spins at with the 5V and 7V mods (ie. undervolting without a fan controller)?
Seek and ye shall find

7V = 610RPM/32CFM
5V = 410RPM/14CFM

In fact, as those figures demonstrate, both fan speed and CFM vary idirectly n proportion to input voltage (for any given fan) quite accurately enough for our purposes.

Peter

pcy · Post by **pcy** » Mon Feb 23, 2009 2:53 am

Hi,

victorhortalives wrote:400rpm to 700rpm - get the 1200rpm version.
800rpm - get the 800rpm version.

700rpm - both are OK.

Overall, I would go for the 1200rpm version.

I think you may be seeing sample variation in the manufacturing process here, not an actual difference between models.

In my experience two such fans will be identical, except in the power of their motors (differnt number of windings per coil). At the same rpm I'd expect the different models to be indestinguishable (subject to sample variation) and I'd also expect the min reliable starting speed to be the same.

Xobim wrote:The 800 RPM S-flexes have a tendency to stall when undervolted, so I'd go with the 1000rpm model for that matter.

I use Yate Loon 120mm and 140mm fans. I have never had any problems with the failing to start or stalling at 5V.

In general, I can get them down to about 300 rpm - (3V +/- depending on the fan) without stalling, but that's when attached to a PWM controller, which gives them a 2 sec blast at 12V to ensure they start before turning the speed down.

Peter

500-800RPM target: Scythe 120mm S-Flex SFF21D or SFF21E?

500-800RPM target: Scythe 120mm S-Flex SFF21D or SFF21E?

Re: 500-800RPM target: Scythe 120mm S-Flex SFF21D or SFF21E?

Re: 500-800RPM target: Scythe 120mm S-Flex SFF21D or SFF21E?