Originally Posted by dave2441
My Sony receiver has an impedance selector switch on the back for the front left and right speakers that I have been setting at 8 ohms but the center channel sounds pretty harsh (meaning too bright) so I have experimented setting the switch to the 4 ohm setting and doing this gets rid of most of the harshness in the center channel.
I can't imagine why that would be. This particular switch on AVRs is only really meaningful for bench testing, and should have absolutely minimal effect on sound quality in a real world audio system.
However, my receiver gets pretty warm doing this and I am concerned this isn't safe.
"Pretty warm" is a very subjective phrase, and it is impossible to know what it really means. You might obtain a IR thermometer and take readings of the case temperature.
Under $10 on eBay and they actually work!
Usually actual AVR overheating is due to poor ventilation.
I will note that with the impedance selector switch set to 8 ohms, the center channel sounds clearer and when I set the switch to 4 ohms, the center channel is no longer harsh/bright sounding but the sound does because very slightly muffled. It does not bother me and is hardly noticeable but I am wondering if anyone knows why this would be the case.
There is no technical reason for your perceptions.
Is the muffled sound at the 4 ohm setting a result of clipping?
The impedance switch makes only a small difference in your AVRs power output before clipping. Are you running a dance party so that you would be running your system that loud?
If it is safe to run my receiver with the impedance switch set to 4 ohms I would prefer to do that because it gets rid of the harshness in the center channel.
The position of that switch shouldn't make that much difference one way or the other. It makes an approximate 15% change in the voltage available to the output stages, which can be meaningful on the test bench with pure sine waves and resistive loads but is unlikely to make much difference with music and speaker loads.
If I did some technical tests and found that you were autosuggesting these perceptions to yourself I wouldn't be the least bit surprised.
For openers, spend $10 or so on the non-contact thermometer and get some objective data about the actual operating temperature of your AVR.
If it is not too hot to touch without severe discomfort than it is staying below 120 degrees, which should be fine.
If it is getting too hot, the most likely cause is likely poor ventilation, so if needed, fix that!