Hi SatKartr,
I just had a conversation with Tom Cumberland, our chief R&D engineer who designs all of our electronics, including the A1400.
First, he asked me if you are running a center channel and it seems you are. Do you have it set to "Small"? It should be, because if you have it set to Large, the center can't reproduce low bass and any deep bass routed to the center might cause the woofers in your center to hit the magnet structure, producing the popping noise.
Next, Tom told me that there are several points within the Yamaha where distortion may occur. If an especially "hot" (loud) digital signal hits the Yamaha's DSP processor and if it's so-so, it may not handle the hot signal, causing distortion, which would be fed through to the A1400 and reproduced by the M80s. Another possibility is that even if the Yamaha's processor handles the hot digital signal, the peak in the gain might cause the Yamaha's preamp section to clip, which would also feed through to the A1400/M80s.
Finally, he pointed out that if you don't have a subwoofer and you are listening at levels you quoted of 107 dB SPL, it's possible that the LFE deep bass, which should go to a subwoofer, is going to the M80s and overdriving the M80's woofers so they hit the magnet structure, causing the pop. By the way, that won't damage the M80 drivers--it just makes an unpleasant sound.
As to the Yamaha shutting down, it may well be a product of the DSP board clipping or the preamp section clipping as described above. As JohnK pointed out, the impedance setting should have no effect whatsoever because none of the Yamaha's internal power amplifiers are being used.
Regards,
Alan
Thank you so much for your post, Alan, that gives me a lot more things to consider.
The center is set to "small," although it's funny that you mention it, because before lowering the impedance setting, it seemed there might be a popping sound coming through the center as well.
Since the Yamaha shut down, I tend to favor the hypothesis that the Yamaha DSP may be having difficulty handling a "hot" digital signal, especially deep LFEs at high volume.
I'm glad to hear that the M80s will not be damaged!
I am getting a lot of LFE bass out of the M80s, it seems even more so with the lower impedance setting; however, with regard to the 107 db SPL, keep in mind that I am using a Radio Shack digital SPL meter, and I was getting a louder popping sound at 90-100 db SPL with the higher impedance setting than with the lower impedance setting at 107 dbls. This again would seem to point to the 663 as the possible weak link in my setup rather than the Axiom equipment.
Thanks guys for your input, I have a much better idea of the likely culprits, I'm looking forward to plugging in the sub when this may become a former "ghost in the machine" or if not, truly with the SPLs I am able to achieve without appreciable distortion at the lower impedance setting I will be quite satisfied until I can replace the 663, wherein lies the root source of the problem I feel quite confident, although only time will tell.
