Originally Posted by Josh Z
This is a thread where users try to help each other. You mentioned that you're bi-amping (passively), and yet you also say that you're not trying to add more power to your setup. I'm genuinely curious, what is it that you're trying to do?
I should think it would be obvious that he believes there might be something to passive bi-amping with the same AVR and no matter if you and I disagree with that notion and whether we are right is beside the point. He wants to try it out so let him have at it. Now as it is, I just happen to disagree that there's "no point" to it.
Clearly, passive bi-amping can have some benefits if you use a different amp (i.e. split power). My Carver AL-IIIs had an issue back in the 1990s whereby the ribbons would "snap" (rather nasty too) in this one little segment of a Japanese anime song (Heroic Legend of Arslan Vol. 3/4 track #3
entitled "深慮遠謀" (which I believe translates to "Deep Thought") just past one minute into the song). If I switched amp channels or cables, it didn't matter and yet sending the SAME channel to the left speaker would NOT do it at all. I called Carver. They sent someone out to look into this. You could actually see ribbon damage (tiny little crinkles) when you took the ribbon out. They replaced the ribbon. Still did it. They replaced the crosssover. Still did it. They replaced the woofer. Still did it. The tech guy was absolutely puzzled. We tried playing it with bi-amping using both stereo channels on one speaker. The problem disappeared like magic. They gave me a free spare ribbon and I bought a second amp and never had the problem again. I eventually bought an active crossover as well (I figured I might as well since I'm already bi-amping).
Now technically, I tried using the SAME amp to power both ribbon and woofer separately and whatever weird interaction that was going on via the crossover did not go on using both channels. Now a stereo power amp doesn't share the same power supply quite the same way these newer AVRs do (i.e. you can't get more than the rated power for one channel without bridging), but then really, you can't do that on an AVR either. True, they're sharing a common power supply, BUT there's a maximum limit to how much power you can get out of one channel no matter what and that limit on the 8500 is 150 Watts into 8 Ohms officially, at least. So what happens if you bi-amp in STEREO mode? Well, believe it or not you probably now have 150 Watts x 4 channels (It's a 13-channel amplifier so it isn't going to bring down the maximum output for just 4-channels, as far as I can tell. Yes, running all 13 you're not going to get 150W out of each at the same time. But 4? I'd say probably darn close.
So, unless I've made a miscalculation, by "bi-amping" with the 8500, he can get more power to ONE speaker than the AVR would allow him to have with just a single amp and that's because of the maximum single channel limit of 150W RMS. In other words, you could theoretically get something closer to 300W per speaker maximum using bi-amping in stereo mode. Thus, that mode would have probably 'fixed' my problem above in passive bi-amping even though I'm using a common power supply because it's still getting more maximum power because until it starts hitting the overall power supply limit, you're going to get more power from 2-channels than just one due to the 150W limit of the device. The power supply appears to be rated for 900W total (including video, etc.) I'm betting it could still easily do 300Wx4 <> 150Wx2.
Maybe I've overlooked something and if I'm wrong, I'm wrong, but it sure seems like there COULD be a purpose to bi-amping on a single AVR like the 8500. Would you get that power increase with all channels driven? No. But you'd be no worse off than if you were just using 2-channels. But in stereo mode....up to 3dB more output maximum (probably not needed if you're bi-amping for tweeters, but depending on the speaker design...). Now my Carvers are different from most box speakers. They are two-way speakers and the ribbons use just as much power as the 10" woofers because they're hard to drive and play 150Hz-20kHz on a stock unit (my active version is 250Hz-20kHz to get rid of a notch frequency). So more power could come in handy. Seeing as I'm hitting the limits at 170W into 4 for the ribbons + 350W into 4 for the woofers (the ribbon amp is going into protection on some music cranked), I went ahead and ordered another 350W amp for the ribbons instead, which should give me just over 3dB more headroom on the ribbons and match the woofers so the 8500 simply would cut it (they're rated 190 into 6 and only give a dynamic power into 4 of 280W).