Subwoofer Mystery

See if you can solve this one :confused:

THE SETUP: brand new Cerwin Vega XL300.1 amplifier powering 1 4-year-old JL Audio 10W3, which is a dual voice coil (4 ohm) subwoofer.

The amp is rated at 270W RMS at 4 ohms; the sub handles 250W RMS.

THE PROBLEM: After only 5 minutes of distortion-free operation, my sub amp shuts off and goes into protected mode. At this point it is almost hot enough to burn your hand. I tried disabling the subwoofer output from my head unit to see what would happen, and even with no music it still clicks into protected mode and gets hot. Next I turned the gain all the way down to the minimum, but still the same result.

The wiring done by my installer may be to blame, but I'm not knowledgable enough about dual voice coil subs to be sure. With two positive and two negative outputs on the amp (+) (-) (+) (-), he's got two wires connected to the same positive output on the far left, and two wires connected to the same negative output on the far right. I was under the impression you either wire each voice coil independently as if it were two speakers (one wire to each of the 4 outputs), or you wire it in parallel (one wire to far left positive output and one wire to far right negative output) like this (http://www.crutchfield.com/learningcenter/car/subwoofers_wiring.html?suboptions=2%2DChannel%5F1% 2D4ohm%2DDVC&amptype=2%2DChannel).

Installer thinks the subwoofer is "going out" and may need to be replaced. Is it the subwoofer, a faulty amplifier, or a bad install job? Any help is much appreciated :bow:

It's a monoblock amp, so he can go off of the same terminals without any problems... he just split the signal there rather than at the sub

however, this leads me to believe he ran 2 positives from the amp (one to each voice coil positive) and the same with the negatives

that would mean the DVC 4 ohm sub is wired in parallel -- so the amp is seeing a 2 ohm load rather than a 4 ohm load, which it is not stable at (I assume)..

the only way to make that sub/amp combo work is wire the voice coils in series to create an 8 ohm load... you'll lose power, but at least it will play -- otherwise, purchase a single 4 ohm voice coil sub, or a dual 2 ohm voice coil sub

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just curious...who installed this? a friend? or a business?

The Vega XL300 is advertised as being stable at 2 Ohms, so that shouldn't be a problem for it. I questioned the installer's wires for two reasons. First, the amp's manual recommends the independent wiring of each voice coil. Secondly, it says when the amp goes into protected mode to make sure the speaker leads are not touching each other. If you think his method is valid then maybe I am barking up the wrong tree.

The install job was done at a shop and I don't know the guy personally.

I forgot to mention that the amp this one replaced would go into protected mode occassionally too. That one was a 2 channel amp wired to each voice coil independently, and it would only happen after 3+ hours of constant listening. That was one of the reasons I wanted to replace it...it was a cheap Boss Audio amp. Maybe the installer's point about the JL woofer going bad has some merit?

But then why does the thing shut off after 10 minutes when there isn't even any signal going to it? :confused:

I do not know how your amp is wired internally -- wire it per the manual then, separately. Who knows how he has the voice coils wired up either...

Sorry I wasn't sure it was stable at 2 ohms...assumed 4 only because you mentioned the power it puts out at 4 and that the subs were DVC 4 ohm -- so thought someone forgot to account for series/parallel wiring.

Definitely try using all amp channel outputs per the manual, and power each VC individually. Take it back to your installer and make him look at it for free if you do not wish to....it will take him minimal time, so he shouldn't have a problem with it..

the same happened to me man i had a concept 2 channel 4 ohm amp (100w) and i was running it with a kikker cvr (12inch) and it was working good for a while. then i got another amp wich was a 600w amp and 4 ohms too. i decided to use the bigger amp with the kikker it worked good, then i came accros a 15 inch crossfire bmf 1528, which was rated at 700w with 2 ohms. worked good after about 2 months the amp just stopped working i thought the the amp had given out so i went back to the concept and wired it up and again after a few minuts of playing it would go to the protect mode and i never found the problem. at fist i didnt know if it was the sub or the amps so i went to my friends and wired the speaker with one of his amps and it was good. but i got mad and sold the sub and i have no system in the car. i have a new amp a autotek street machine sx2300. i dont know what subs to run with it any ideas.
thanks frank

Disconnect wires from sub and use tester to measure voice coil resistance. Post it here.
Disconnect RCA's and sub from amp and measure "idle" voltage on amp output, from where you disconnected subs. Post it here. Should be close to zero.
Amp bias compensation can go south, feeding sub constantly with several volts without a signal leading to overheating.
Hope it helps.

Wish I had a tester.:cry:

Wish the installer wasn't an hour away from my house too.:cry:

The terminals on the sub are very difficult to get to with that custom 10" fbody box. Before I go screw with the wiring, is it even possible the subwoofer would be the cause the problem? That's the shop's stance on the matter, and I would like to know if they are full of $#^@ and trying to squeeze me for more money. I just don't understand how the thing is overheating without any signal from the head unit...

Wish I had a tester.:cry:

Wish the installer wasn't an hour away from my house too.:cry:

The terminals on the sub are very difficult to get to with that custom 10" fbody box. Before I go screw with the wiring, is it even possible the subwoofer would be the cause the problem? That's the shop's stance on the matter, and I would like to know if they are full of $#^@ and trying to squeeze me for more money. I just don't understand how the thing is overheating without any signal from the head unit...

Get a simple tester for like $5 from Walmart. Sub can cause a problem if it has voice coils melted. If you follow the steps I posted before you can figure your problem in 5 minutes.

nice, these guys know there stuff...very well explained.....as far as why stuff like this happens though, I believe it's easier to assess the problem in person, or if you can atleast upload some pics of the install...

and by the tester, I believe this guy is talking about a voltage meter, buy one somewhere that can measure resistance in Ohms (Omega symbol)......your sub without connection to anything should measure the posted Ohm across the terminals

nice, these guys know there stuff...very well explained.....as far as why stuff like this happens though, I believe it's easier to assess the problem in person, or if you can atleast upload some pics of the install...

and by the tester, I believe this guy is talking about a voltage meter, buy one somewhere that can measure resistance in Ohms (Omega symbol)......your sub without connection to anything should measure the posted Ohm across the terminals
depending on the sub, it will usually not read posted ohms since those are nominal impedances -- resting resistance is typically lower

since when can a voltage meter measure resistance? ;) But yea, he is talking about a DMM/tester