Axiom Home Page Forums General Discussion Home Theater Crackling speakers

Whatever you say, Epic.

The setting on the preamp was less than 0 db, maybe -4db maybe less.

The Yamaha has a 6 ohm setting (which manufacturer states is also suitable for 4 ohms for the front speakers), I have been advised before here on the forum to stick with the 8 ohm setting; however, I have switched to the 6 ohm setting for the moment and it seems to be working better, still can't really tell until I have a free moment without the fam around to experiment a bit.

Before when I had the XPA 2, running the 663 at the 6 ohm setting did not trigger the infamous protect circuit on the XPA 2, but it wasn't loud enough for those moments when you want to crank up the sound a bit. Now with the A1400-2 the system seems to have plenty of head room on the 6 ohm setting, and the overall experience seems more smooth, e.g., as if the volume control increments on the preamp are smaller, making the "volume dial" more spread out, so to speak.

I admit that I did not think that the pre out section of the 663 would overdrive the inputs of a power amp even on the 8 ohm setting with volume output of 0 db or less (and it seems it would be immaterial to the preamp what ohm speakers are downstream from the power amp), so I am a bit mystified, however I lack time and inclination to do a lot of troubleshooting that might damage the speakers.

In addition the kicker for me was when the 663 shut down spontaneously, that just shouldn't happen under normal circumstances when reproducing material at 0 db or less, and suggests there may have been an overload within the preamp itself before possibly overdriving the power amp input(s).

Charles, again the reason for strongly suggesting that manual directions to set a lower impedance number be disregarded is that this in no way "optimizes" the receiver for lower impedance speakers, as some imagine. It's a safety precaution to keep the UL happy by reducing the chance for overheating at high volume levels and it does this by reducing the maximum voltage that the power supply can output by something on the order of 25-30%. Since power is proportional to voltage squared(Ohm's Law again)this sort of reduction roughly cuts the maximum power capacity in half, as test labs such as S&V have reported. For example, if the maximum voltage output was 40 volts otherwise, setting the lower impedance switch or menu setting might reduce this to about 30 volts or a bit less and power capability would be roughly halved.

Whatever better results you may get from your experiments, there doesn't appear to be a reason that setting the impedance lower would be a positive factor.

So here are my latest observations and loose reasoning/weak hypothesis:

We watched a dvd tonight and the peaks were up to 107 db (volume setting was +4.5 db) before mild almost subtle popping sounds kicked in, keep in mind that loud, nasty popping sounds were evident at 90-100 db before with the 8 ohm setting, so this was a definite improvement, although clearly not a solution. Also I should point out that I would not have noticed these sounds currently if I had not been trained to do so by previous experience, they were mild rather than obnoxious by comparison.

All cases of "popping" sounds going back the past 2 months or more (?) have only occurred during HT LFEs, never during music playback, even at similar or even higher db levels.

It makes no immediate sense that an LFE would cause a high frequency pop like a gunshot (not really a close example but just for comparison sake).

I have no subwoofer (waiting for Godot) and it has been documented that the M80s are limited with regard to the LFE frequency range.

I suspect that with no subwoofer to receive deep LFE output the preamp has nowhere to discharge the power output and this may cause the popping distortion I am experiencing during LFEs.

Everything else besides LFEs sounds perfect, actually LFEs sound smoother, louder, and better since I set the 663 to a 6 ohm output setting; although I couldn't swear to this since I have obviously done no DBT, it seems unlikely to attribute a much softer almost negligible "pop" to listener artifact given a 10 db increase in SPLs.

Perhaps others know better but I have no way to check this out except to wait a few weeks until the sub comes; of course this could be massive wishful thinking on my part since I am hoping this problem goes away at that point, or that at least I achieve something closer to the peak volume I would like have in play without the sonic defect kicking in.

JohnK, I don't think this in any way contradicts the info you have shared, given that according to my understanding it is not a good idea to run an amplifier at high volumes without a resistor downstream to discharge the power output, because then the power has nowhere to go other than toward some form of implosion.

Perhaps my thought process is way old school or off base, perhaps they have error correction built in to correct such issues nowadays, if so I'm sure you will all let me know the error of my ways (of thinking), at any rate the system is working much better and I will have nothing to report until the sub arrives, I will let you all know if I achieve greater workability at that point.

Sat(still had Charles on my mind from a previous reply for some reason), no I can't even hazard a guess as to why the situation would be improved at the lower impedance setting(if after switching back-and-forth that still appears to be the case). The suggestion about the pre-amp output wouldn't appear to be part of the explanation either(the lower impedance setting affects only the internal amplifier in the 663 and has nothing to do with the pre-amp section). The mystery remains.

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

I realize what you're saying makes theoretical sense except I remember without a doubt empirically that one of the reasons I sent the xpa2 back was that I couldn't get much sound out of it at the lower impedance setting, whereas the higher impedance setting caused it to go into protect; not sure what the 663 is up to with their settings, that should not be the case with preamp output yet it seems to be so.

That is one of the reasons I felt compelled to post, it seemed to me that the weak link, for whatever unknown reason, might be the 663 and it was unfair to persist with the assumption that the xpa2 was the weak link without better clarity.

Alternatively, as Alan has suggested, the lack of subwoofer may have been the culprit, which I will test later and report my findings.

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.

I wonder if it was that crackling/popping signal that was setting off the XPA-2? When you couldn't get much sound the signal was too low for the XPA to worry about, with a stronger signal it would sense the distortion and go into protect.