Originally Posted by DoctorM
As kikkenit2 said, the more I read, the more it looks like official support of 4 ohms is largely a UL certification and if you had it you don't want to actually engage the 4ohm setting. It's a nanny that makes your speakers perform worse.
Buying a good quality AVR is more important. At that point I stayed up till the crack of dawn researching units that officially handle 4 ohm, and units that should be good enough to handle 4 ohm.
The short list ended up having a log of last year's models: Denon x2000 (better bang/buck than getting an s900 or x1100), Yamaha RX-V675 (or v577 (neither has HDMI 2.0)), NAD T 748V2, Onkyo TX-NR727 (the 737 is out of budget and the 727 is still a bit high).
The Onkyo is the only one that officially claims to support 4 ohms.
That said, I think I'm back where I started.
At this point I'm looking for opinions or comments on my nearly solid decision: Yamaha RX-V675. (The v775 seems to have no useful upgrades, not even more power.)
The M&K's are supposed to be pretty efficient for 4 ohms, all low frequencies are sent to the powered sub anyway, I'm only running 5 speakers not 7, and the Yamaha should(?) have decent enough circuitry to handle it all.
Am I crazy, wrong or misguided? (Is Audysey a compelling reason to go Denon?)
Edit: Is there a way to tell if a receiver has enough muscle to run 4 ohms? Some formula with the wattage or something? Even the x4000 is only rated for 6-16 ohms. Same with the NAD.
It's hard to state specifics here. But I will try to list what I think are the key points
- It seems most receivers should handle a 4 ohm load, the unknown is at what volume level does it overheat (or in the worst case shutdown)
- It's not about receiver power as you might think of it; knowing how much power a receiver can put out to 8 ohms does not tell you how much it can put out to 4 ohms; the power it puts out would seem to be depending on the specifics of the power supply, and how the protection circuits in the receiver work
- It's been suggested by a few people before, that mid level receivers can handle 4 ohm speakers as a general rule, but you need to ensure they have proper air space for clearance ( manuals often give some info on recommended clearance)
- If you are running your system at a "reasonable" volume, like -10 dB below reference, the theory says you need little power to hit peaks in movies and way less power for average levels in movies ( less than a watt,) which should be easy for a receiver to handle
- If you are playing music, your average power output is higher, but if you listen at reasonable level ( 90 dB peaks or less for example,) it seems like a pretty safe bet a receiver will handle 4 ohm speakers
- Audyssey seems to be well liked; YPAO seems to be less sophisticated, but I am not sure how much work has been done it recently