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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.
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sean
6,231 posts
 
I did the same thing Will. I could not understand how that could damage ANY system, even at massive volume. I turned my pre / pro up seven notches higher than normal ( and i like it LOUD ) and nothing even flinched. There just isn't that much bass during the opening THX "electrified exploding sphere" sequence. Something is really wrong somewhere. To blow up a driver ( let alone two ) with that big of a motor structure would really take a lot of brute force over an extended period of time. Either the drivers themselves should have never been shipped out the door ( defective ) or the amp has got BIG, BIG problems. Sean
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spluta
58 posts
 
Sean... is it possible for the drivers to blow
if they are sent a signal that is simply below their
achievable level? So this could be a problem caused
by a PRE/PRO capable of sending a signal below 20hz
and the speakers not being capable. I know in some
of the newer PRE/PROS you have an option of declaring
a sub as either THX or non-THX. And if you do declare
your SUB or MAINS as being THX a lower signal will be
passed. I remember reading about this problem somewhere
a while back...

I also played THX intro on mine and think unless he had
the volume UP WAY TO HIGH this shoulent have happened.
sean
6,231 posts
 
Spluta: As i mentioned above, feeding a high level signal that is below the point of resonance to a vented speaker system will cause the woofer to throw wildly i.e. make excursions that can be dangerous to the woofer itself. I doubt that this is the situation with this specific case though as there really isn't a great amount of deep bass in the THX intro to that movie. Sean
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spluta
58 posts
 
Ok thanks Sean... You know I have an old pair of Fisher (flame thrower) three ways in my band room... Perfect
canidates for the EXtreme FLOGGING flayling wolfer test..
I bet 400wpc will do it. I will put on goggles and ITS ON!
I will call it my own form of THX certification.

Ill will post results...
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