Anyone know why anyone would do this?
They've got the 2 channel amp, bridged it and then connected two subs up in series. So positive of amp to pos of sub 1, neg of sub 1 to pos of sub 2, neg of sub 2 to neg on amp.

should've wried the subs in parallel unbless of course the amp sucks and can't handle the low impedance.

it's some rockford fosgate punch amp. basically mate bought the car, crashed it, and i stole the sound system, this wasa couple of months ago and i was just wondering about it then. the previous owner really liked there rockford stuff.

what type of subs?

the biggest reason i can think of is that the subs share a common chamber, and as such require the same signal, amount of power, etc

bridging the 2 channel amp turns it into a mono output, meaning it's impossible to get a difference between 2 channels that would affect performance

You'd still get all that wiring in parallel on the brdiged channel. What's the differences in parrellel and series?

It's a Rockford Fosgate Punch series amp and two of the same RF Punch series subs.

who knows, the amp i got can't bridge it self so i just connect left neg to left pos and visversa on the right

parallel halves (for two subs) the impedence of the subs, allowing the amp to deliver more power.

eg. you have two 4Ohm subs, and a amp capable of driving loads at 2 or 4 Ohms.

In series you present the amp with 4+4=8Ohms the amp will struggle or not work at all.

In parallel you present the amp with (4*4)/(4+4) = 2Ohm.

Now for power calculations you need to know the voltage output of the amp (we'll guess 70V here), and the impedance of the load (the subs).

For series: 70V / 8Ohm = 8.75A (current) which 8.75 * 70V to get power = 612Watts

For parallel: 70V / 2Ohm = 35A which 35 * 70 = 2450Watts.

These numbers a guesses, and amps/subs aren't perfect so the numbers will be different, but the idea is there. The amp can drive a 2Ohm load harder than an 8Ohm or 4 Ohm load (as long as the amp is "2Ohm Stable").

It depends on a number of factors.

Most class A/B amps dont bride down and run a 2ohm load so you can wire them for an 8ohm load and the amp will have no problems driving them (although you will get reduced power at higher impedences).

The other possibility is that the subs are 2ohm subs (or dual voice coil 4ohms) and wiring that way will provide a 4ohm load.