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Discussion Starter · #1 ·
I was wondering if a dirty/scratched disc can cause knocking sounds while playing? I'm pretty sure it isn't my speaker and can only conclude that the disc is causing the knocking sound. It only happens at specific parts of the disc. Anyone know? It's a DVD is that matters. Thanks.


Calvin
 

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Sounds like the disk is the culprit. But I would first listen to it on a pair of headphones to acquit your speaker.
 

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"Knocking" is a description that sounds like a woofer bottoming out -- the knock is caused by the spider slamming against the basket and/or the voice coil slamming into the bottom of the pole piece gap.


It would be VERY common for this occur with Dolby Digital recordings because of the extreme recording levels for the low frequencies in modern movie soundtracks. Combine this with anything but a very robust subwoofer and/or the excessive subwoofer levels most people set on their systems, and this sort of problem is almost guaranteed to occur at high listening levels -- especially with any ported speaker where the bass on the disc can easily be recorded below the tuning frequency of the speaker, resulting in uncontrolled cone excursion.


The most likely place for this to occur would be on front speakers set to full-range (Large) or on subwoofers that are being overdriven.


Conversely, proper system configuration settings, appropriate for the quality of the equipment, can easily prevent this from ever occuring. To solve the problem, we'd have to know what is in your system, how it is configured (large/small/crossovers), whether or not you've calibrated with a Radio Shack meter, and which speakers are knocking.
 

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Another possibility is that the surrounds (the foam that surrounds the cone) on your woofer has failed. Although this is more of a "clunk". In any case, it is easy to visually inspect them. Depending on the speaker, you might wish to either replace the driver or replace the surround. Not a difficult job, just very time consumng to do it right.
 
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