RR Copland CD speaker killer?

Jimmy, I am not familiar with that CD. Maybe it is an unusually large quick dynamic peak of maybe 10db or more. A 10db peak is twice as loud as the average sound level.If you're playing at 100db avg. and you get a peak like that with your particular system, you're gonna need over 300 watts to do it. That would account for the same behavior with the MAC 300 as they have very little headroom. This sounds like a very tough CD to me and it's likely that a lot of systems would have trouble with it, when played loud. If your speakers were just 3db more efficient(88db), then you would only need half the power(150w) to cover the peak without clipping. With a speaker efficiency of 91db, you could do it with 75 watts. Do you see how a little more efficency in speakers can go a long way in reducing power requirements?

Interestingly enough, the speakers started making the sound at about 80-85 Dbls - which was the level recorded at the peak of the drum "thwack", 3 ft. away from the left speaker. Any more than that and it got worse quickly...

Twl has done a VERY nice job on this one. Kudos to him for putting in the effort and presenting all of the figures and effort that he has. As such, i tend to agree with him. SOMETHING ( speakers or amp ) is making VERY audible signs of distress. If you continue to do this, you can expect BAD results in a short period of time.

Not being familiar with the speakers, i assume that they are vented. Playing high energy notes that are centered below the tuning of the cabinet will produce the potential for massive over-excursion. This can manifest itself as the woofer severely bottoming out which sometimes sounds like "clicking". Since many voice coil formers are aluminum and they are bumping the back plate, which is also metal, it could be conceived as a high frequency note due to it's more "metalic" or "grating" tonal character.

On the other hand, your speakers are so in-efficient that i can imagine that you could drive an amp into clipping relatively easily. The only problem with this theory is that you state that the SPL when these conditions manifest themselves is quite low, pretty much ruling out amplifier overdrive. The fact that it does not occur at slightly lower SPL's points points towards the first scenario i.e. the woofer bottoming out.

Have you ever watched the woofer as this phenomena occurs ? Is it throwing like mad ( or at least MUCH more than normal ) when you hear this noise ? While i'm not encouraging you to keep repeating this situation, you do need to find out what is going on. The only way to do that is to repeat the situation and study it step by step. If you are going to repeat this a few times, i would highly recommend letting the system / speaker cool down in-between attempts. Clipping and / or over-excursion are bad enough, let alone adding heat build-up to the situation. Sean
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Sean, thanx for your kudos. The reason I went in the direction that I did was because he stated that the noise was coming from his tweeters. Of course, you know how hard it is to diagnose something that you can't hear, so we're kind of running in the dark. Stehno says that he has heard the 6's break up pretty early on the bass, too. Could be that. But, if the noise really is coming from his tweeters, then he's clipping, no matter what the db level is. Whatever, the siuation might be, I'd say it's a bad combination of amp/speaker at best.

Another possibility of why this could happen is a low preamp/source level. This would account for the amp having to drive alot of power trying to hit normal listening levels. You could tell this right away if you have to turn up the volume knob quite high to get normal volume. The opposite could also be possible. If the source level is too high for the preamp input section, it might overload the preamp input on a high peak, thereby causing a distortion in the preamp that is passed on the the amp and then the speaker. You could tell this right away by not having to turn the volume knob up very much at all to get normal listening levels. Give us some more info, Jimmy.