which route should I take?

[iSLANDERxSE]

First off, let me tell you the setup I currently have at the moment. I have a 1995 BMW 540i completely stock. I have one 12" JL audio W7 and powering that is a JL Audio 1000/1. Power and ground wires are 4 gauge in thickness. The wires on my batteries positive and negative sides are the same thickness of the amps wire so I'm assuming the alternators positive to the batteries positive, engine ground to chassis, and the batteries negative are all 4 gauge. I recently took my sub to a repair shop. I took it to the shop because one day I was listening to music and the bass just cut off on me, and I play loud music all the time. I disconnected the sub and took out my DMM, checked the ohm reading and it was jumping up and down so of course I knew there was something wrong with the sub. The guy that is repairing my sub informed me that I blew my voice coil due to voltage spikes. He took a look at my set up and he told me that I have my setup all wrong. He said it will fix the problem if I ran a lawn mower battery in parallel to my main battery and from there my amp to the lawn mowers battery. I've done alot of research and most people are saying to do the BIG 3 and a HO alternator. My stock alternators spec is 140A and like I mentioned earlier I'm assuming I got 4 gauge wires. Now my question is should I follow the guys advice about having a seconday battery from a lawn mower, upgrade my alternator and wires, or retune the amp, because the guy who sold me the amp and sub had the gain a little bit past the halfway mark and that seems high to me? I would like to keep this setup as long as possible so any advice will help even if I have to drop alot of cash on a HO alternator but that may take awhile because my cash flow can't support that as of now. Oh and I'm not going to get a capacitor because all this research convinced me that it is a waste of money. Thank you for your time and advice.

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[Jeffdachef 5,000+ posts]

sounds like a bad grounding issue. Make sure there's no dust/dirt/engine sludge/paint on the surface of your grounds. Also is your starter battery pretty new? lead acid or agm? I wouldnt do the lawn mower battery at all, that guy's smoking some ****, Either get a good AGM under your hood or add an AGM to your trunk.

How are your gains, Low Pass Filters, bass boost, subsonic set up? how is your head unit setup(LPF, HPF, Sub level, bass level, EQ?)

 

[iSLANDERxSE]

My amps ground wire is directly to the batteries negative terminal because the battery is located under the back seat of the car. My battery is not pretty new but also it's not old. I'm thinking it's somewhere in between the two. As for the AGM, are you talking about those high performance batteries? I did not touch the gain so it is currently a little past the middle mark. As for the rest of the setups, I tuned it the way JL audio said on the JL Audio W7 manual. As for my head unit my bass level is set all the way down, which is -6. Everything else is set to 0. My head unit does not have LPF settings but on the amp itself is set to low pass.

 

[NIHL8ION]

NEVER just leave gain settings the SAME as they were for a previous user / vehicle / etc. - Read this, it's a very simple HOW TO guide for correctly setting your gain complete w/ a voltage chart to make it even easier yet - Link: How to properly set your amplifier gains using the DMM method - PLEASE STICKY - Club3G Forum : Mitsubishi Eclipse 3G Forums

 

[iSLANDERxSE]

So lets say he did have the gain set up too high. Can that cause the voltage spike that burned my voice coil?

 

[NIHL8ION]

So lets say he did have the gain set up too high. Can that cause the voltage spike that burned my voice coil?

- If the gain was up too high you likely clipped your sub to death so yes... I wouldn't necessarily refer to it as "voltage spike", and that is his opinion / assessment of the situation based upon his findings... Either way, Setting your gain properly is a MUST to avoid prematurely trashing your expensive car audio equipment

 

[iSLANDERxSE]

Okay I'll be sure to check on the gain very shortly. So if the gain is set right and it continues with the problem. What would be my best solution?

 

[naughtyca 10+ year member]

a little over half should not have killed your sub to a point that your voice coil ripped, you might be banging like crazy without knowing how much voltage drop you are getting and thus clipped the crap out of your sub, overpowering usually dont kill the sub its the clipping. do you have a volt meter to see what voltage you are getting?

 

[bbeljefe]

I wouldn't assume anything. Especially the size of the cable running from the alternator to the battery, because it's normally 8 gauge and sometimes 10, although being that the battery is that far away I would think even the factory would use 8 gauge. You definitely don't need an HO alternator with 140 amps and only a thousand watts but you do need a good path from the alternator to the battery and from the battery to the amplifier.

Personally, I'd do a big three with 2 gauge but 4 will work also. Make sure you have a good ground from the alternator to the chassis too, as the factory usually only does a small ground strap from engine to chassis. I would also run as large a battery as possible, preferably an AGM but at least the largest wet lead acid you can fit. Leave the lawnmower battery on the lawnmower. You'd be better off with a good capacitor than a lawnmower battery and with your battery so close to the amp, that's not even necessary.

Think of it this way. When your car is running (which is when you do most of your listening) the battery is only there as a reserve cell. The alternator provides operational current to the vehicle and is also supposed to keep a surface charge on the battery. i.e., keep it "hot" so that when you kill the ignition, the battery will be ready for the next starting of the vehicle.

With that said, design your wiring as though the battery isn't your amp's power source, and make sure all of the wire that goes from the alternator to the amp is the same size and is of ample size for the current the amp will need. In that instance and given the length, 4 gauge is sufficient but 2 gauge would be ideal, to give the system headroom for those deep, hard bass notes.

Also, if you over build the electrical supply to your amplifier, you will notice a marked improvement on how hard the sub hits and, you'll be insured against long term damage to the amplifier, sub and alternator due to stressing them to their limits.

As for gain settings, (I assume you're using the factory hu and a line level converter) you need to find someone with an oscilloscope or a DD-1 to check where the head unit signal clips and then that setting needs to be used to set the volume correctly for the actual gain setting on the amp, which again needs to be set with a scope or a DD-1.

Do that and your sub won't wind up back at the doctor's office.

 

[iSLANDERxSE]

I'll be sure to check the voltage with my DMM. I'll also check on my grounds as well. I will look into a better battery and perhaps doing the BIG 3. I do most of the work myself and I am not looking forward to changing the atlernator to the battery wire because that is the hardest one out of the three since the battery is in the back.

 

[naughtyca 10+ year member]

I'll be sure to check the voltage with my DMM. I'll also check on my grounds as well. I will look into a better battery and perhaps doing the BIG 3. I do most of the work myself and I am not looking forward to changing the atlernator to the battery wire because that is the hardest one out of the three since the battery is in the back.

when you do the big 3 dont replace the 4ga that is already there, just add to it, like add another 4 ga