I just purchased an Antec P183 v.3 along with a Seasonic X-650 PSU and it didn't occur to me before that the orientation of the fan in the Seasonic might not be so good for this case. The PSU is essentially isolated in a small channel at the bottom of the case. Because the fan intake for the PSU is on the bottom of the PSU, it makes for an extremely tight (like 1/2") space for air to enter the fan since it's right up against the bottom of the case. I could flip the PSU over and since there would be a little more room between the top of the PSU and the divider that separates the bottom case channel with the upper area. But even then, it's a gap of about 1 1/2". This PSU is obviously designed to be used in the main champer of a case where the CPU and motherboard is and the P183 is mostly designed for a PSU where the airflow comes in from the front of the PSU and exits the back (instead of bottom to the back).

Does anyone think this matters? I could consider cutting out the divider between the upper and lower chambers although that obviously defeats the point. Also if I turn the PSU upside down, the plugs will have to travel a little farther to get to where they need to go and I'm worried about things becoming a tight fit.

nothing to worry about. it will get plenty of airflow in there. just mount it with the fan to the top.

The P183s have to come with their PSU, the CP850 or CP1000, period.
A Seasonic X is a waste of money (~37 USD on NewEgg) inside a P183.

The reviews on this site seem to suggest that the X650 would be quieter than the CP850. Am I reading this wrong?

http://www.silentpcreview.com/article986-page5.html

The only question is if the airflow makes things even worse for the X650.

I also want to do a question: Which PSU do you believe would be quieter, in idle, inside an Antec P183 V3? Seasonic X-850 (840W), Antec CP-1000 (840W) or Antec CP-850 (768W)?

The reviews seem to suggest that the X-850 would be quieter (I gather it's similar to the 650). For one, the fan in the X-850 actually stops spinning at low loads at which point it would be just about silent.

the p183 has at least 20mm more space than my mini p180, and more airflow potential with the opening at the front of the case. so airflow wouldnt be a problem.

as for the charts: the x650 is quieter until you start pulling more than 250w. if youre not planning on pulling more than that, then what the hell are you doing buying a 650/850w psu?

airflow wouldnt be an issue, but if you need 250+w then go with the cp-850.

I mean you have to interpret also those data.
With a baseline accurate within 1dB, it's pratically the same having 10 or 11 or 12dB.
Muffled in the bottom chamber a 12dB PSU is also virtually indistinguishable from a 10dB one: I swapped an M12D with a X-750 inside a Raven, and after a year or so I can say it was a waste of money.
About airflow, the P183 has renounced to the stock bottom chamber fan (with reference with the former P180/P182) right for the availability of the CPX form factor PSU: we can argue that its external inline fan has a role in bottom chamber thermals (IMO often inline arrangement are to be preferred in Antec enclosures).
Moreover the CP-850 is the CPX clone of the Delta-made Antec Signature, one of the best server grade unit available, and if you need more than 250W DC it should be equal or quieter than the X-series (as Seasonic controllers has always been very aggressive).

The only serious drawback (a true Achille's heel) I see nowadays for the CP-850 is its substantially inferior efficiency: if it were not an issue, then I think the CP-series should be definitely preferred for this specific application.

Eventually, does the X-650 work good in the P183? For sure, but to me it's a waste of money to have somehow slightly inferior electrical performances and chamber thermals, with no substantial better noise level.

I can see that argument for the lower power levels but I'm more interested in what happens at high load. In the table in that article at 6-700W, the X-650 registers at 32db and the CP-850 at 44db. That's a big difference.

I guess you're referring to wrong row: it's the bottom one which is nearer to the P183's bottom chamber scenario.
Therefore the CP850 has an advantage of 7dB at 500W, and 8dB at 650/700W DC.

I was referring to the table below with the measurements from the anechoic chamber. But in those two tables above, I think the top row is the important one. The bottom row are the results of running the PSU out of the box in a cool room. There's very unrealistic. My PSU is obviously going to be inside my case and the ambient temperature is not nearly so cool. I assumed that the hot box test was meant to represent a more realistic scenario but I can't seem to find any definitions of the "hot box" on the site. If the hot box refers to a test under extreme conditions than maybe I have misinterpreted the data.

The hot box scenario is more representative of a top mounting PSU, where all the system heat up the PSU due to convection (heat naturally rises).

The open air scenario is more representative of a bottom mounting PSU, where the fan can suck air more fresh, and no hot components (GPU, CPU) heat up the PSU itself.

But maybe the question is: do you really need 600W DC? Under which conditions?

Ah, so maybe I didn't choose the best option but I guess I'll see if I can tell. I'm betting it doesn't really matter. I can't say I know exactly how much power I'm going to use but this is meant to be a high-end gaming rig. I've only got one video card in it at the moment but perhaps I'll add a second one later. I think I've got a little overhead with this PSU but I wouldn't feel comfortable with a smaller one.

Honestly, don't worry about it. I have the same exact combination and it works excellent. I have the X650 facing upwards and all is well. I figured since the fan doesn't kick in at all for me when i'm not gaming (under 20% load), what little heat it does generate will simply rise up through the fan grills when the fan isn't running.

Even during heavy gaming, the PSU remains completely cool to the touch, whether the fan is on or not. I'm totally blown away by this PSU.