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Audio Systems/Blown Subwoofer or Amplifier??

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Question
I have a Pioneer AVH-P4300DVD head unit installed in my 2002 Chevy Trailblazer LT.  I have 2 Lightning Audio LA-S412 4 OHM subwoofers installed inside of a sealed box. I have a single Lightning Audio LA-600M mono amplifier rated at 200x1 @ 4 ohms and 300x1 @ 2ohms powering the subwoofers. My fuse is new and my amplifier powers on. My amplifier, subwoofers and head unit are all professionally installed and were purchased brand new in box from an authorized dealer (who is now out of business)in Spring of 2011, so everything is of course out of warranty.  About a week ago while driving to school, I smelled smoke from my vehicle. When I parked, and opened my trunk door where my subs are located, I saw smoke coming from my left subwoofer. I turned the subwoofers off just before I got out of the truck and I heard a pop and they stopped playing. In the past I have heard it pop and it stopped firing and that usually meant my fuse needed to be changed.  When I push on my right subwoofer it moves silently, when I push on the left subwoofer, there is a scratching noise and I can smell the burn on it but see no damage. I use a 60A fuse. My question is: How can I tell if it is definitely my subwoofer that is blown or if it is both, or if it is my amplifier or wiring and if it is just the one speaker that is damaged, is there a way for me to just run my system using the one subwoofer that is still functional? I hope I have included enough information and I appreciate and thank you for any help you can give me.

Answer
Based on your excellent description of the system and the failure cycle it seems the sub voice coil has given out.  The best way to check the sub is to disconnect the wires from the amplifier and apply a d cell battery to the terminals of the sub. If the speaker is good when you touch the connection the dc of the battery will be heard as a little pop and the cone will slightly move in or out depending on the polarity of the battery connection to the wires feeding into the speaker box.  

Another test is to use a vom (Volt-Ohm-Meter, available at Walmart for $9.97) which can test the continuity of the voice coil.  

And, finally, when a sub voice coil burns down it usually breaks the voice coil away from the coil form and when you manually push the cone inward you can hear a scraping sound.

If the speaker voice coil did short out - rather than open up - it could cause damage to the amplifier as well, so be careful that way, too.

A 60 amp fuse is big, meaning it can support 600w if power, at least for a short period of time, before it opens up.  And, finally, if the sub voice coil is toast it means you have really been pumping lots of power into it.  Maybe back off the wattage a little......

Hope this helps.  Let me know if you have any further questions.  

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Cleggsan

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Audio Design Engineer; systems, loudspeakers, cd/dvd players, etc. I am knowledgeable in all high end audio equipment and installations. MAKE SURE YOU GIVE A MAKE AND MODEL NUMBER AND CAR IF IT IS AN AUTO QUESTION. Note: I am getting some who ask good questions that take a lot of time to research but then the questioner fails to read the answer. Please don't ask questions unless you are seriously looking for an answer. If you find an answer to your question otherwise then let me know with your reply. Thank you.

Experience

Have been associated with audio design, standards, testing and component systems for over 40 years.

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Life Fellow Member of Audio Engineering Society Life Senior Member of Institute of Electronic and Electrical Engineers

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Review technical manuscripts for IEEE Spectrum Write occasionally for high-end audio publications

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BSEE/MSCS/MBA

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Past Employee/advisor to several well known audio products manufacturers

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