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Blew Subs From Audible thumps at 0 volume

Old 02-10-2009, 11:26 AM
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Blew Subs From Audible thumps at 0 volume

I may be new to the forum but I've been in to car audio for quite a while and have set up many systems from low end to high end.
My newest issue has me totally stumped as to what I should do to identify the cause. This is going to take a while to type out/read so please bear with me.

I'll first list the specifics and equipment
Pioneer DEH-6000UB HU
JL 500v2 Mono amp
Hertz HX 250 10" Subs (2 of them/ SVC 4ohms)
Wired in parallel so there is 250w per sub.
Using heavly insulated RCA cables
4 AWG Power wire
This is the first couple days with the new system. I previously ran a 140w RMS audison amp to a 250w RMS Hertz ES 250 sub. The setup was in for 1.5 years until I got bored of it, still pumped like crazy for one 10 on 140w RMS.

I was at a light listening to my music (rock) at about 1/2 volume. At this point I was listening very closely and happened to hear a thump periodically. It then hit me that is sounds exactly like distortion from the subs. At this point I immediately reduced the volume to 0 on my head unit.

At zero volume on the head unit I could still hear a " thump, thump, thump, thump, thump, thump, thump, thump" at a rate of maybe 4 "thumps" per second coming from the subs. These thumps were quite loud. I left the volume at zero and it stopped after maybe 3 seconds, I was relieved. Then I moved the car forward to make a left turn and during the turn the thumps came back. To stop it from happening I turned the deck off.

I didn't have much time to diagnose the problem when I arrived at my destination so I just made sure that all the connections on my amp were still properly in place. At this point I knew there was damage to the voice coils.

When I drove back home the same thing happened, the thumps were happening while playing at any listening volume, and when I raise the volume one notch I can hear a distorted thump sound coming from the subs. It's only periodical and plays very clean when it is not occuring.

The voice coils had been burned from this distorted noise and are currently being looked at by the place I bought them from. At this point I don't know what to do. Why am I getting a clipping/distorted thump type noise from my subs at zero volume?

I can not let this happen again as the subs are quite expensive. What is creating this noise? The deck sending a signal out at zero volume, which is then amplified and sent to the subs? Or the RCA cables picking up interference and sending it to the amp to be amplified? Or the amp itself? How can I further diagnose the problem with out blowing up everything? For as long as I've been in car audio I've never experienced this thump type noise and especially when the deck is at 0 volume.

Thanks in advance
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Old 02-10-2009, 12:11 PM
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i had a similar experiance not to long ago. turned out the amp was deffective 2 weeks in. the customer disconnected the fuse for the amp to make it stop but all it did is thump every second and you could see the amp going from green light to red light ( protect )

have you diconnected the RCA from the amp completely??? if you did it my be the amp that is screwed up
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Old 02-10-2009, 12:59 PM
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Orrr It could be your pioneer deck. I have seen a few cases where the internal pre out amplifier does something, and produces this thump.
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Old 02-10-2009, 01:05 PM
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Sounds much more like a amp issue and it's power supply losing ground.
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Old 02-10-2009, 01:14 PM
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the funniest thing about your post is that somehow u knew there was damage to the voice coil? and somehow u knew it was burnt and some place was lookin at it for you? You do realize that you cant see the coil unless you cut it out of the rest of the the sub's structure.........with a knife. So is this place gonna cut your sub open? or do they see thru the magnet? anyways.

its probably your amp. pull the rca's out of the amp and see if it still happens, if it does then its your amp 100%. either the power supply or the input stage.

and i can also tell you 100% that your coils are not blown or burnt.
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Old 02-10-2009, 09:33 PM
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There's really nothing funny about my post. I've never invested this much money in to a system and now that I have, it's not too good knowing an unknown problem is blowing up my subs.

What I forgot to mention in my above post (and I apologize for this) is when I quickly looked over my wiring when I arrived at my destination I could smell that very distinct odour. It wasn't the amp that created this odour as I couldn't smell anything from it. When I got close to my subbox and popped one of the screw covers from my sub mount screws off I could slightly smell it.(sealed box)

Around 5PM yesterday (9th) when I got home I pulled my amp and box out of my car to be certain where the smell was coming from. The first thing I did was remove the screws and pulled the sub out of the box. It was very clear when the sub was pulled out, that it was the cause of the odour. The second sub, same thing when held up close.

With my other hobby that odour is very distinct of wire that has been over heated resulting in melted insulation - burned voice coils in this case. You don't have to rip it apart at this point to determine it's the voicecoil. To be sure even a multimeter can be used to see if there is a loss in impedance in the voice coil. When the insulation is burned away on the coil, one turn of the coil can be shorted with the next turn of the coil ect, decreasing the overal resistance of the voice coil.

I hope this clears up why I "knew" it was the voice coils.

Around 6 PM I headed to the place that sold me the subs - East Hamilton Radio. They were very good about it and have always been pretty good as long as I've been a customer there. One of the managers told me that it is covered under warranty and will be replaced or repaired. Only down side is a 1.5 month wait but it was really a big relief.

This is why I stated how can I diagnose the problem without blowing up another sub(s) Is there any other way I can test if the amp is outputing this thump signal without using a load that could be potentially blown? Could I place a voltmeter on the speaker terminals and watch for eratic jumps in output voltage when there is no input signal/rca's?

I do greatly appreciate the help guys.

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Old 02-11-2009, 02:10 AM
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a sub with a blown coil would not make any sound, it would not even make those pops or thumbs you are talking about.

what you smell was the glue on the coil heating up. this happens all the time and there are many reasons why this can happen. this is probably in no way caused by the thumbs. The smell has probably been there ever since and happens everytime you bump your system loud. You just never smelt it before b/c its a sealed box.
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Old 02-11-2009, 07:12 AM
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Alright, EHR told me the coils had been burned. And to be honest I've never smelt anything like that before in any of my previous subs. The odour from the subs did not smell anything like glue, it smelt like burned insulation from wire.

How ever I don't have the subs anymore so it is not of concern.
Could I place a voltmeter on the samp speaker terminals and watch for eratic jumps in output voltage when there is no input signal/rca's?

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Old 02-11-2009, 07:40 AM
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Originally Posted by ryan_t888 View Post
Could I place a voltmeter on the samp speaker terminals and watch for eratic jumps in output voltage when there is no input signal/rca's?

Yes but you'll also need a load(speaker, resistor) on the amp and a fast DMM(a cheap analog one will be easier to read).
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