Strange damage on speakers

[swak]

I had 2 Kef Ci200 ceiling speakes connected to a Denon Avr-1609 (75w/ch) with AWG 14 13m (~40ft) and suddenly the woofers went dead. The tweets are ok but the woofer is not working anymore. I had this problem once with two other same drivers in a very similar setup (only a little more power). the problem there showed up as extreme distortion coming from the woofer).

What is going wrong here or is that a driver design problem?

Sebastian

[hardwareguy]

Suspension damage? Check the glue bond where the voice coil meets the spider and where the spider meets the frame.

Check for rubbing voice coils as well....if its rubbing, it likely deformed due to heat.

[swak]

Yes, two rubbing coils on the first set, so overheat. Should I a change to a higher power amp or change cabling? Can this be a consequence of the highish cable run? The last damaged ones don't rub.

Can the amp be brought easier to clipping because of a long cable run?

[hardwareguy]

Now, if you *really* want to find out if its rubbing due to heat or just a bad winding process take out the voice coil. A burned voice coil will have discoloration on the windings and may smell burnt.

Check the DC resistance of the speakers for the heck of it. DCR should be a bit lower than the impedance.

Determine what's causing it first. A higher power amp wont help unless you are driving it into clipping (ie turned up to the point it sounds harsh). Cables wont help.

[hardwareguy]

The long cable run will cause a power loss but unless its *really* long (50m or more!), it shouldn't be a problem.

The amp will only clip if you crank up the volume to compensate for the loss.

[swak]

I suppose because of the high resistance the amp is turned up quite a lot, driving it into clipping and that that damaged the voice coil. Nevertheless I could not detect any strange smell on the last ones (I haven opened them), and the DCR measurement is crazy, being often several K-ohms. In the first setup the calbe run was about 25-30 mts, and wire quality, although awg 14 wire, was not high.
.

[hardwareguy]

K ohms DCR indicates a burned voice coil!

Try a larger cable on the longer runs if you want but if it's clipping, a larger amp is in order. Perhaps turning it down a notch would help. How loud do you like to listen? Its possible that these speakers just cant handle sustained high power use.

Two conductor power cord (SJ or SO types) works great for speaker wire. Ultra purity copper won't help you much at all.

Even at 30 meters you can still pass over 10 amps of current...the loss problem is fairly minor.

[swak]

The speakers are rated 100w program (max recommended amp). I don't use them, but I think they get cranked up every now and then. It can be a driver power handling issue or the amp exhausting (I dont trust much denon quaity).

I am thinking of using commercial installation amps (pro) and a source selector (other amp channels are powering more speakers, configured in 2 zones.

The first installation used power cord cable.

[hardwareguy]

Denon's lower end stuff is questionable sometimes. I suggest either a strong Onkyo or Yamaha RX series receiver or a dedicated power amplifier.

I assume you do not need surround sound...if that's true then opt for a stereo receiver instead of a surround sound unit. You'll get more amplifier for your money. You can always add power amps to a receiver be it surround or not.

If you need HDMI switching and that sort of stuff, surround receivers are your best bet when used with a power amp. (or you could get a receiver with some guts!)