That unit from the article sounds very temperature sensitive. I'd be wary of throwing a precision unit like that out of spec and out of calibration.
FWIW I've noctua-swapped so many things including an oscilloscope.
The last rubidium oscillator I played with, had to heat the vapor cell within the physics package, but then prevent that from overheating the rest of the unit, so it specified mounting to a heatsink. There was no heatsink recommendation given, just a certain package temperature as reported by sensor value X in the diagnostic data page. Get below that and you're golden. Get too much below that and you're wasting extra energy in the heater. Which is harmless, it just drives power consumption up.
So depending on how the unit's thermals work out, a slightly less aggressive fan may end up being mildly beneficial.
One of my slightly embarassing ones was the fan on one of my Nanlite lights was always on, do I thought to swap it with a noctua one so at least it'll probably be quieter.
When I took it apart, it turns out it was already a 12cm noctua... Black edition.
You can also get non-Noctua hydrodynamic bearing fans with polycarbonate blades and silicone mounts which are supposed to be very quiet, but I've never compared one against a Noctua. Anyone done a comparison?
In the case of this Rb oscillator, it is temperature sensitive, but also built for pretty extreme environments.
I'm not too worried about this particular application, because the clock will be in an air conditioned environment, and I'm monitoring the clock accuracy to +/- 2ns from another GPSDO / rubidium clock. The performance before and after the fan swap is within my measurement noise for 24H, though I haven't done 30+ day measurements and ADEV comparison. Still working on a consistent test setup.
Considering the new airflow rating is 9.4 m^3/h (vs 16.8[2]), yes it sounds like plenty of headroom.
[0] https://safran-navigation-timing.com/wp-content/uploads/2023...
[1] https://cdn-adepci5.actonsoftware.com/acton/cdna/28343/f-bf4...
Not with Noctua and the likes, not always at least. These fans are quiet, but they are not made of magic fairy dust. They simply max out at lower flow rates than some of the the noisy, high-RPM fans people replace with them. Those 40 mm Noctuas, apart from voltage options, don't really come in many varieties.
It's a trade-off - you definitely lose the upper end of the device's original temperature range, but if it's stable under your conditions - great. How do you find out? Well, you replace the fans and check if it sizzles or not.
And funnily enough, a LOT of equipment these days isn't made with formal thermal design, they simply throw in high-cfm fans and... check if it sizzles. It usually doesn't because there's plenty of headroom. It's loud, but who cares since it's not meant to sit on your bench.
Source: replaced PSU and chassis fans in countless pieces of network and test & measurement equipment.
The Mac Studio that replaced it is practically silent and very energy efficient, while not being significantly slower.
When I was in highschool, I bought a secondhand Poweredge 1800-something hoping to make it my new home server after the Pentium 4 desktop I had been rocking. It was so fucking loud, I couldn't find a place to keep it that wasn't audible throughout the house. My parents were not happy.
The rounded pins present minimal resistance to incoming air streams and Incoming air streams can enter from all directions (omnidirectional).
Round pins generate extensive air turbulence.
I'm guessing the more splayed the pins, the greater the air turbulence and it allows for air movement in all directions; the time / gps chipsets are meant to run cool.
For the little story, back in the early beige PC days (think 386 and 486), quiet PC fans didn't exist. It was all super noisy, and typically at a fixed speed.
And, coming from the Commodore 64 and then Commodore Amiga that were silent machines, this was driving me crazy.
So 18 y/o me managed to source some proper fans out of Japan (Panaflo fans IIRC) and I went bug my neighbor, who was studying to become a chip engineer...
I came to my neighbor with an idea: "Why not lower the fan speed when the PC ain't too warm and then only speed it up when the PC gets too warm, you know, like a car's fan adapts to temperature?" (cars would do that: they'd start spinning a huge fan to cool down the water in the car's radiator, but only once the water would be too warm).
And so my neighbor drew a little electronical circuit and we bought "thermistors": I would "calibrate" them with boiling water in my mom's kitchen and then we'd install the circuit with the thermistor in the PC's PSU, with Panaflo fans.
So basically: back in the 386 and then 486 days, I already had quiet PCs. I'd "muffle" my HDD in an enclosure, opened on top (so that heat could dissipate, on which I'd put a 7V panaflo fan [I'd take the 12V and the 5V and create 7V]).
Once the PC world began to wake up and the likes of Be Quiet! and Noctua became a real thing, I was delighted. My current main rig has a Be Quiet! PSU and a Noctua fan for the CPU. I cannot thank such companies enough.
P.S: for what it's worth my neighbor later on moved to southern California and became an early Broadcom employee and he's been much more successful than me for he was the real smart cookie. We're still friends to this day.
Usually these boxes are at remote sites or in already-loud test racks, so the noise isn't a concern.
The Noctua is rated for lower CFM, so if you are already at a slim margin for thermals, switching to a quieter fan is not necessarily a good idea.
I do wish more manufacturers would go to 60 or 80mm fans instead of the 40mm ones common in this gear. Power supplies especially!
Any idea how much it costs?