What the H ll Happened Here?

I was listening to music two nights ago and heard what sounded like low level scratching through one speaker, then it went away. A short while later it happened again but this time the sratching was coming from both speakers with reduced bass response. Then, I lost bass in one speaker completely with maybe 1/2 output from the other. Tweeters seem OK but hard to tell as they sound kinda bad without the rest of the spectrum.

By the way, I have Harbeth C7s which are two ways.

I thought the problem may be tubes in the pre-amp so I plugged in a passive that was just boxed away, same problems. Tried another amp, CD player (with and without the DAC), same problems. Swapped speakers from side to side, problem with woofers went with them. Then I tried pressing slightly on the woofers, doing so causes changes in the distortion. So I'm pretty damn sure it's a problem with both speakers, but what the hell happened? And to both speakers at the same time?? I noticed no electrical surges, power problems of any kind.

Guys, any ideas as what's going on???
Your voice coils may be shorting out in contact with the magnets. Maybe burned or melted from extreme use? The crispy bits could cause interference. With the amp off, and lightly pushing the woofer cones inward through their travel with your splayed fingers, can you feel the scratching of the voice coils in their gap? They ought to travel freely and be noiseless.

I had a pair of Dynaco A-25 10" woofers that both evidenced scraping behavior after about 30 minutes of play. When they were cold they acted and sounded fine. The problem arose after taking them from prolonged hot attic storage. I attributed their failure to corrosion but never tore them apart to see for sure. Please post the solution if you find one.

I did what you suggested and do hear a light but definite scraping sound from both woofers. I was playing organ music and then Hendrix (odd combo, eh?) and it was right after this the problem arose. However, I wasn't playing that loud and am using a Plinius 50 wt amp with more than enough power for my small room. Also, one woofer is outputting no sound whatsoever.

I presume I'll have to ship them to the importer for repairs? Or does anyone know someone in the southeast Michigan or Ann Arbor area who could do this? What actually needs to be done?

By the way, I've heard nothing about Harbeths being hyersensitive like this. Anyone have similar experiences with the C7s?
I had a similar problem with Paradigm speakers, blown voice coils. Mine were overdriven by my son (damn that rap music) and he blew tree of the four woofers. I odered relpacement woofers from Paradigm; a snap to replace but not cheap.
You may have a warranty issue although it's hard to convince customer service people the speakers weren't overdriven/abused. Good luck.

I'd also have that Plinius amp checked out thoroughly before putting it back in service. If any of its active deviced failed, it could have been putting out DC to the speakers causing the woofer failure. If you have a voltmeter you could turn the amp on without speakers connected and measure the DC volts at the speaker terminals after giving the amp 5 or so minutes to stabalize. If it's any significant amount, then you'll probably need to send the amp back for service too.

My feeling is that some sort of failure within the electronic chain was responsible for the speaker's failure... You need to isolate that problem before hooking up good speakers.
The fact it's in both woofers indicates the odds are good that it was electronics related so definitely get the Plinius checked out.
If the voice coil was fried you would smell it! Sometimes they smoke, but you would smell an aweful burnt electronics smell. yes, your amp must have put out DC. Be most careful and get it checked out right away.

To be sure, simply remove one woofer and look at the voice coil. If copper and clean that is not the issue. If black, you found the problem!

Disconnect the woofers and measure them. Most probably and unfortunately, you have damaged these drivers. IF so, then it shouldn't be yr amp that's at fault (spurious noise fm the amp would have taken out the tweets first).
The best thing is to write to Harbeth -- they don't use off the shelf drivers...
Excellent info and advice, guys. I have plugged in two expensive Pinnacle speakers and am running them to see if anything else happens. I bought them new 6 years ago at 50% off for $115.00 pair at Accutronics Audio when they were going out of business and the owner, Arnie, was setting up Audiogon. Thought they'd work in my wife's bedroom system but they've never been out of the box since purchase. So far no problems.

If something happens to these then it may indeed be the amp but I don't think so as it was a one time occurance. It may also be, as stated above, an electrical problem in house as we've recently had a couple of other odd things happen around here. I've called a good electrician to come out and "trouble shoot".

And, no, I did not smell anything burning whatsoever. Will take out the woofer that is giving no sound and see what's what. I understand Harbeth builds their own woofers and will send them an e-mail to discuss.
Found out what problem was. Seems there was a voltage surge into our house and also house next door. Turns out my wife's laptop is also damaged as is a clock radio used in the basement. I'm going to make an insurance claim and see if this will be covered.

Had a friend who has been modding his own hi-fi stuff for 25 years (such as fully modded Quad 63s, various tube amps, etc.) check the speakers and the woofers are blown. Somehow the tweeters survived as did the crossovers. New woofers cost $300.00 each since Harbeth builds their own Radial drivers. Time for a properly designed power plant!
When I bought my speakers (Paradigm active 40's and ADP's. I don't have a CC, so if anyone knows where I can get one, I'd be greatful), I realized these were hard to get. So what I did is spend $200 and I put in a whole house surge protector. If you get a surge, it's much easier (read: cheaper) to replace that $200 dollar protector than probably any other electronic equipment in my home...and I have toys!