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Woofer damage from new Star Wars THX DVD?

Both woofers in my JM Lab Utopias blew with the THX intro (exploding sphere) on the new Star Wars DVD. Happened at normal listening level through my Theta Casablanca II/VTL 7.5 preamp/Halcro dm58 amps. I've not blown a driver in over 30 years of being an audiophile. I've heard that the base was boosted as much as 36db on some of these DVDs. Even though the speakers are under warranty, I'm out $1,200 for a new Focal woofer (JM Lab only covers 1 driver for this kind of damage). Anybody with information or suggestions? Needless to say, I'm not happy about eating this expense if the fault really lies with an overmodulated DVD with no warning about increased bass levels. At the verey least, I'm curious to see if this happened to anyone else. The sound level was high enough that the concern for hearing loss came to mind (I'm a physician and I don't think I'm this concern is frivolous). Thanks for any thoughts or other input.
avimar

Showing 3 responses by foreverhifi

foreverhifi
229 posts
 
Ooops!..I meant Dunlavy SCV's, not SCIV's!(when refering to the Dun's being overdriven...sorry.
foreverhifi
229 posts
 
I'm currious to know what amp you are driving your Utopias with ?
It appears to me that this is another case, in my experience with HT systems, where THE POWERED SUB SHOULD BE HANDLING THE BASS!
PASSIVE speaker systems, LARGELY should not be handling demanding bass from dd/dts soundtracks! I know far too many people play there "full range" speakers as "large" for movies in a "passive speaker system". And it's never going to have enough control over the bass drivers in a PASSIVE speaker to handle bass properly! I can CLEARLY overdrive the bass woofers on a pair of large Dunlavy SCIV's (4 X 12" woofers)when playing full range on some of the movie mixes out there. And I can do the same on other large speakers. I don't seem to have this kind of challenge driving active woofer designs, like Def Tech BP2000's or Infinity Prelude MTS's!!!
I've said it time and time again...."Unless you're using full range speakers WITH ACTIVE POWERED WOOFERS, you should be configuring your speakers as "small" on your pre/pro, and letting the ACTIVE POWERED sub handle the bass!!
The damping factor and control that's possible through PASSIVE CROSSOVER NETWORKS, isn't sufficient for dynamic transparancy in the bass reigion at the very least. In a powered subwoofer, the AMPLIFIER is RIGHT ON TOP of the bass driver, utilizing "TIGHTFISTED" control over the driver.
There's a reason THX has specified a 80hz setting for it's processing between bass woofer and main speakers...because it works!!!!
I bet what happened here was a case of Amplifier clipping, which cause the woofers to overheat and melt the voice coils! What Did JM Labs Say?
Anyway, my theory...
foreverhifi
229 posts
 
Tsrart, your theories are largely incorrect for your reference. It really doesn't work that way. What happens is largely that drivers(usually the tweeters first) get blown from being UNDERPOWERED when asked to handle more demanding levels! The amp cannot supply the current to properly control the driver(s), and therefore "clips", causing the drivers to distort, to simplify.!
It's a common misconception amoung new audio enthusiests, to think that too much power is the cause of breaking speaker components. It's not the case largely.
Also, a speaker will only respond to the signal and current that it's being fed. If you have more expensive/higher out-put potential gear, the gear isn't going to "try harder" or drive harder per se, simply because they have more potential.
It's not like a race car engine that's "more tightly wound" or anything. We're just talking about passive components that are sometimes overpushed from what they can comfortable handle. Or they are underdriven from the volume they're being asked to handle. Talking about speakers of course.
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