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Xiaou2:
One time I bought some AC fans from a Surplus place. They were like 1.5" thick, with 3 large blades. I believe they came out of
those ancient + massive HP Laserjet printers. They were loud AF... but they also moved about 30 times as much air as any PC
fan that Id ever owned. I shoved a carrot into the blades to see how bad it might be to run them without the Grills... and it had
the power to actually chop the carrot clean, like a food processor.

If you want a quieter fan.. you would probably better to use a DC based PC fan. You can use one of the larger diameter fans,
for even less noise + greater overall air movement.

Most arcades were noisy enough, especially when you are playing at a decent volume.. that you would never hear
the cooling fans that were inside of them.

Zebidee:
Some fans are quieter than others. Sometimes they just get a little old/worn, and sometimes they get a bit dry and just need a little lubrication.

You could always lifting up an edge of the sticker in the middle, and putting a few drops of fine motor oil into the sleeve/bearings.

bobbyb13:
This thing is new and all metal and the blades are really moving some air so I imagine what I am hearing is just blade noise.

I does kind of remind me of a model plane I had when I was 10!

Suspect that it will get a bit quieter with time and I am going to get to install the audio system tonight it appears and then maybe get going on the bezel shroud by this weekend so it may be a non issue anyway.

Get building everybody!
I think I'm catching up to some of you!
:cheers:

Zebidee:
You can do a lot with fans. Always easy to swap in a different fan that might be quieter/larger/flashier whatever.

If you go DC for the fan, you can throttle the speed by installing a resistor (appropriately rated) on the active input line. This both limits current and creates a simple voltage divider (in this case the other "resistor" is the impedance in the fan's coils). You can (for example, with a 12v fan) throttle 12v input down to around ~7v and the fan will still turn, just slower (and therefore quieter).

The trick is getting the right resistor value. I suggest good-old trial-and-error, because every fan will have different impedance characteristics anyway. Also, the coil's impedance (R) goes up as current increases, so it's R value will decrease as the resistor value increases. Because of this, you can't measure the coil impedance directly with a DMM (AFAIK), but once you install a "test" resistor you can easily calculate the impedance value by using the known or observable values (voltages, resistor) and applying normal voltage divider rules (or one of those online calculators if you are lazy like me).

You could even use a potentiometer (pot), at least until you know what resistor value you want. I guess the same logic applies to AC fans, but doing this kinda thing with DC feels safer.

Technically it is also possible to use the fan's third input (if it has one) to throttle fan speed, but this requires a logic controller as it works by switching the fan on/off really fast. You could probably control fan speed by using the Pi itself (but I don't know very little Pi lore), or perhaps an Arduino, but (ironically) that all sounds much more complicated to me.

Sorry for the long post, hope it is relevant ;)

Falken Hawke:
If you want to get ambitious, a honeycomb composite "cowling" or shroud can be made to go around the fan and heatsink along with ducting to redirect the blade noise to the bottom of the cabinet. basically the same thing turbine engines have that makes them louder front and back versus side-to-side.

Assuming it's like my 386 PC I installed an AC fan on 'cause it's what I had, ;D it's blade noise.

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