severe voltage drop, bad alternator?

"Even if you do add a high-output alternator, which is, ultimately, not a bad idea (again, research this purchase EXTREAMLY carefully.. I've bought 3 different rewound alts from 3 different ppl and never had ONE of them put out more than 10v at idle) you will still require a proper deep cycle battery to maintain any semblence of system reliablity." 

That right there is where your assumption of an alternator wont do anything.  When you get an alternator re-wound in a stock case there isn't much room to play with so something has to be compromised, aka the idle output..  If you purchase a quality alternator (at least $1 per amp) you wont have that problem.  I have always spent good money $300-$400 on alternators and have achieved excellent results.  With my mechman alternator I could sit at a stop light with the bass cranked on a bass cd and not get light dimming. (3000WRMS System)

Now, as for your missunderstanding on how adding more batteries is the answer that is very wrong. If you have time to do so I would study some electrical characteristics, for example how a capacitor charges and discharges in a rectified AC circuit. A battery can only charge to its source voltage (the alternator), If the alternator is only putting out 10 volts, your battery will NEVER read more than 10 volts, its simple fact.  No matter how many batteries you install, heck, say you install 50 deep cycle batteries in a veh and crank that bass with a bass track on repeat and go on a road trip for a few hours, I am willing to bet that the car wont start after you turn it off. An extra battery will only help in 2 situations 1) as a current source for when the veh is turned off, or 2) as buffer or filter when the charging source is able to supply more than the demand.

Im sure fellow Electrical Engineer's on here can provide a more detailed explaination if you request, were all here as a hobby to help educate and learn, I was once in your position and now im here with only 2 more years of school left and I'll be making the amps people on this site will be frying.

Amplifiers today generally have circuitry that shut them off when the input voltage drops below ~10v or so..  You ought not hear distorted output, rather, output for a few seconds, then nothing, then a few more seconds of output.  I'd be suprised if you damaged the amp itself.. you'd need a bad ground or shorting wires or something like that to damage the amp. 

Not really suprised here... you amplifier really doesn't have all that much to do with total output..  you're re's are in REALLY small enclosures, sealed, and they're only 10's.  The cone area on that L7 has got to be almost as much as the 2x10's..those square subs really move more air than comparative round subs.  Nevermind the fact that the box is ported... a huge increase in volume and output right there alone.  Always remember astro, your enclosure has FAR MORE to do with output/sq than ANY OTHER factor in your system... save possibly the shape/size of the vehicle itself.  Air movement is what produces sound, and the shape/design of your box goes the farthest to influence this.

Anyway, point being, if you didnt' kill your alt or battery with all your tribulations, I don't see how you could've hurt your amp.

I'd get/build a different box for those 10's anyway..  maybe ~2cft, tuned to 30 - 35hz....   but as the two different sub configurations stand, the L7 would require considerably less power to get considerably lounder.

Some thoughts while reading this thread..

Alternator rating is *max* output.. which typically doesn't happen at idle. Most alternators also can't output max rated output for long without overheating and failing..

Starting current for a car is generally 100+ amps or more.. the rule of thumb I use is 1 amp for each cu in of engine displacement. A 3.4 liter engine would draw approximately 150-200 amps.

When system voltage is 12.8v and higher, no current is flowing out of the battery. The alternator is supplying all the power required by the vehicle. The battery only supplies current when system voltage drops to approximately 12.4v.. this means that from 14v down to 12.4v the alternator is doing all the work. Once 12.4v is attained, the battery starts draining. While a larger battery bank will help maintain higher voltage during times when the alternator isn't capable of supply the needed power, the larger battery bank does place more of a load on the alternator when recharging. Some alternator manufacturers recommend sizing the battery bank to no more than 2x the max alternator output. Example would be a 100a alternator should be hooked to a battery bank with a capacity no greater than 200 Ah. (in contrast, whereas a battery will not provide power until system voltage drops to 12.4v or so, a capacitor supplies power as soon as the voltage drops to less than what the capacitor is charged to)

Battery voltage and alternator voltage are the same.. less any voltage drop in the wiring.

While it was an acceptable method to check an alternator/generator in older vehicles to disconnect the battery with the engine running (if the engine continued to run then the alternator is good) on todays vehicles there stands a real good chance of smoking electronics due to the possibility of voltage spikes (due to the loss of the damping effect of the battery)

to address astro88's situation directly, if the alternator is working properly and the wiring is sound, then you are probably using more power then the alternator is capable of providing. You are correct that by installing a larger battery bank you load the alternator more; your best solution would be to either reduce the power draw or increase the power output of the charging system. However, if by your comment that the lights dim with the blinker on (assuming the stereo is off) then this indicates a possible problem elsewhere.. voltage drop measurements would be critical at this point to establish that the wiring is in good condition.

Any questions?..

Jim

At the time I had that stereo I was running a 225 amp Mechman alternator with a smaller pulley as recommended by them for my motor, which is why it ran so well, just wanted to add that

However I do have to confess I didn't thoroughly real all the posts to get your complete understanding of the plan at hand.