[Miney]

Hey! 

Could use some expertise... a bit baffled by what happened to the woofers of my Cantons. 



System details here.

My dealer replaced the aluminum drivers, and Rotel found no problems with the receiver - fortunately all under warranty - but could offer no insight whatsoever as to how this might have happened, other than to suggest it should have been quite audible.

No crazy parties, no scientific experiments, no explosions.  It's highly likely we've never exceeded 100 decibels.  No circuits tripped.  Everything else connected to the Isolator is working fine.  It's just my wife and I here, plus a triune of labs who have no interest in anything they can't eat.

I'm just interested in making sure this doesn't happen again...  29 days left on the warranty, and I'd really like to get something when trade time comes around. 

Thanks,
Paul

[*Scotty*]

It looks like metal fatigue that led to stress fracturing. It could be a result of the metal alloy chosen for the cone and or faulty fabrication of the cone which left stresses behind in the metal to name a couple factors that could contribute to the cone failure.
 If it happened to you the chances are very good that this happened to a whole lot owners with models that used this production run of woofers. It would be nice if the company could give you some assurance that this would not happen again.
Scotty

[Æ]

Are you sure someone didn't kick it or punch it?

[Doublej]

Both woofers I assume. I agree it looks like some sort of manufacturing defect. I wonder if perhaps temperature or humidity played a role in the failure.

The good news is that if you are nearly out of warranty you'll get another five? years out of them before the problem reoccurs.

If you can get past the customer service folks to a company engineer you might be able to get an answer. Or if you find someone knowledge about driver design outside the company they might be able to shed some light on the problem.

Major bummer, how expensive were the speakers?

[jetengr]

I'd speculate that it is not due to a defect in the cone. 

Is the box sealed? The n=8 pattern provides a clue, it is too uniform, not man-made so to speak, and the surround looks to be undamaged, which is a clue.....suprising given the stiffness of the metal cone.
Also, the condition appears to be worse on the bottom (lower half) of the cone, perhaps another clue......

It could be cone buckling from a very rapid forward coil excursion, which the driver/cone was not designed to absorb....the cone may not have had time to react to due to it's mass and cabinet internal pressure (suction?) resisting the rapid coil excursion.  In other words, the coil moved faster than the cone and the air inside the cabinet, causing the cone to buckle & tear (kind of like sucking the air out of a empty plastic water bottle?).

I imagine the metal is ductile, probably aluminum? So no brittle fracture or fatigue, just bending, deforming and tearing from a catastrophic "impact" type loading. The unharmed surround never saw load, the air in the cabinet and cone mass inhibited cone excursion. 

Also, on the lower half of the cone the failure appears more severe. This could be from the rapid internal pressure gradient where higher pressures resulted where the cabinet wall boundaries are closest (less compliant air?). 

I could be totally wrong.  Just my .02.

[JLM]

Both woofers of both speakers?  Being so symetrical, I'd guess it was due to an overload of some sort. 

If both speakers, could there have been a power surge (if fast enough surge protectors can't help)?  Any other damage of anything in the home?

If just one speaker I'd peak at the crossover.  As mentioned above, with the surround in good shape I'd think about a high frequency/high spl signal did this.

[Miney]

Thanks all for chiming in...

Both (aluminum) woofers of both speakers.  Tweeters and crossovers checked out fine.  The left was still producing output, but not the right.  Visually, the damage was nearly identical.  They are rear ported.

As suggested by jetengr & JLM, the dealer thinks there was a very fast / strong burst (my terms), like someone max'd the volume, turned it on and then quickly off, and the resulting extreme excursion basically tried to pull the driver through the basket.  That'd surely be a memorable sound... so I figure it must have happened while we were out.

There are a number of other devices connected to the isolator:  TV, DVR, CD, zone amp, low voltage cabinet lights, and fans in the cabinet...  All continue to function normally.   

No kick-boxing tournaments were hosted.

Paul

[Big Red Machine]

I did that to one of Jim's aluminum drivers in the V3 center once.  I did not drive it excessively, it just crinkled and failed, similar to your failure, but exactly the same.  No rhyme or reason for it other than fatigue or manufacturing flaw of some kind.

[*Scotty*]

Paul, it looks like you are driving these speakers with a HT receiver, go into the setup menu and select "small loudspeakers". This should keep the bass out of your speakers and help prevent a repeat of the damage you experienced.
 Many people make the mistake of driving their speakers full range and coming in underneath them where they are rolling off with their sub-woofer. If this is how you have your system setup this may have contributed to your problem. Also if you are not home, turn the system off. If a transient voltage spike comes through the house while you are away this action will save your system.
Scotty

[jetengr]

Basket impact seems unlikely (does the basket have 8 support legs?).....the voice coil bottoming-out first should preclude clashing. 
I was thinking the other way around, the coil pushing forward, the cone resisting......all happening faster than a human could turn a knob. 
Although not exactly driver cones, see my gallery for some examples of cone buckling.

You might want to measure the crossover capacitors with an LCR meter if you haven't already, just to be sure. 

Darn solar flares . 

[charmerci]

Maybe it was a turn-on/turn-off thump/surge that did it.

[J Fallows]

This looks a lot to me like a LARGE inward excursion.

My understanding is that some on some drivers, depending on architecture, the voice coil or more
specifically the former will bottom on the back plate before running out of suspension travel. So you hear a thump.

In this case the suspension travel looks to be limited by the surround. So maybe the voice coil has pulled
on the cone and the surround real hard.

It's possible that a big DC- voltage was involved. I don't think that a manufacturing problem show in both woofers at the same time.

And of course we can never rule out that maybe I'm all wet

[J Fallows]

Oops, didn't notice that some of that had been covered already.

[Tyson]

This is why paper/carbon/hexacomb drivers rule!

[Æ]

It's possible that a big DC- voltage was involved. I don't think that a manufacturing problem show in both woofers at the same time.

And of course we can never rule out that maybe I'm all wet

A "big DC" would indicate something terrible happened with the amplifier. A small amount of DC is usually present, but it only causes very slight dynamic offset of the woofer voice coil and some minor voice coil heating. To get that big of a bang, would have required that the amplifier to be driven way beyond clipping! Accidentally drop the tonearm on the record with the volume knob all the way up and the woofer cone will jump right out of the speaker.

[jetengr]

This is why paper/carbon/hexacomb drivers rule!

If we could just train spiders to spin cones (no pun intended)......

[Æ]

This is why paper/carbon/hexacomb drivers rule!

Paper is hygroscopic! Not to mention that most paper eventually turns brittle.

[srb]

Paper is hygroscopic!

Untreated paper is, but coated paper isn't.

Anyway, I recommend aluminum cones, but not ones where the material is bent, stamped, streched, woven, cracked or otherwise stressed into submission.  I prefer cones made from a 2.5" thick, 16 pound solid billet of aluminum and CNC machined until only a .008" thick, 1 ounce cone remains!

http://www.ygacoustics.com/UploadFiles/file/PDF/YG%20Acoustics%20BilletCore%20Brochure.pdf

Steve

[Æ]

Anyway, I recommend aluminum cones, but not ones where the material is bent, stamped, streched, woven, cracked or otherwise stressed into submission.  I prefer cones made from a 2.5" thick, 16 pound solid billet of aluminum and CNC machined until only a .008" thick, 1 ounce cone remains!

Here is an interesting video, if you haven't already seen it. Absolutely worth watching even if somewhat poorly produced. Just wait till you get to the automated manufacturing processes, totally high tech.

http://www.youtube.com/watch?v=ZMTAceNVsfw

I just love FOCAL drivers.

[Miney]

Theories abound!

To clarify...  these are full range monitors.  Being driven by a Rotel RX-1052 - not an HT receiver.

For more info on the AM-180 drivers, see page 6 of this white paper.

Thanks again for the feedback.