Bridging two mono amps?

I recently did an install of two Alpine mono M350 amps each running its own Type R sub at 2 ohms. I kept the gains low since I knew the wires I used and the car itself won't hold the current draw.

Sure enough the customer wasn't satisfied with the output so he took it to someone to make it "bump". To no surprise the fuse blew and he called me to fix it.

Anyway long story longer, I expected to find all the gains tuned up but instead I see each amp is wired to both subs simultaneously. That is the positive lead of one amp went to one sub and the negative lead went to the other sub, same with the other amp. In essence bridging the two mono amps

I told him whoever did that was an idiot, but I couldn't prove it seeing that it actually worked. The fuse blew because the gains were turned up, not identically mind you.

So my question is what can go wrong in such a set up provided the gains are properly set? My guess is audio output is the same as wiring normally so doing that was just being redundant.

And what if there were only one sub in the situation? my guess is the sub would sound just as loud as one amp but each amp would only work half as hard and thus cooler.

I thought I saw a diagram of such a setup in a sony manual years ago but my mind could just be playing tricks.

Any input is appreciated as I don't want to tell this guy I know better till I can back it up with some hard logic.

Give us a more accurate description of how the subs were wired. You have two amps and four voice coils here.

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Top Secret, I can tell you but then my wife will kill me.

the only time yo can bridge a amp is if it has  slave/master switch and u have to wire the slaved amp negative wire to the master amp's negative and the postive wire from the slave to the negative of sub and the postive wire to the positive of the sub

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4-15" RF T2
6-7" RF Component sets
8 Planet Audio 900d
10 Batcap800
1 250 amp alt
1 300 amp alt
2" sound deadner roof,doors,floors

Each sub is wired at 2 ohms. Outside the box just has one terminal cup for each sub. So the Dual voice coils are not an issue here.

Again they played fine, but I'm just not sure what problems would arise in the future if I left them alone.

That slave/master thing seems interesting. what good are those type of amps; do you get double the power or something?

Yeah, I think the term used is "strapped" when you can set up the amps in that configuration.  The crossfire vr1000D for example is strappable.  It produces over twice the output of just one amp and is perfectly safe to do.  Not all amps are capable of this and I wouldn't even think about leaving it that way personally.  But if it works I don't know.  I don't really understand the first post though.  It seems like turning the gains down is just a "band-aid" solution to the problem.  Why would you use wires you know wouldn't work?

Allow me to clear up a few things:

This is a crude sketch of what they did


It was a mistake to say I used the wrong wires, I used 4 gauge. There are three amps in this system pushing close to 1000 watts RMS. The largest fuses I had at the time were cheap 50-60 amp AGU, the ones with defective solder.

Also his alternator is weak, idling at about 12.9 volts on average and maxing at 13.4

Since I knew this knuckle head would max his volume I kept the gains down knowing that a dip in voltage would cause the fuses to blow prematurly and potential charging system failure.

So I guess there are such a thing as strappable amps, but my question still is what damage can be done in the above diagram. As far as I can tell there is no benefit in audio output, so doing all that was just a waste of time. But what do I tell this guy that doesn't seem to care about my MECP cert and my years of experience at Best Buy.

I don't want to say its bad "because I said so" In his mind it played louder than what I did, so I don't know what I'm taklking about.

Yes, there are such things as strappable mono amps.  I do not believe the Alpine M350 is one of them.  Never connect the outputs of two amplifiers together unless you want to fry the output of one or the other or both!  In the wiring diagram you posted above, neither sub should work unless they are connected together internally somehow, and if they are connected together you should NOT wire your system this way.  Doing so can fry one or both amps.  Disconnect them now and let us know how the woofers are connected together.

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A sure way to melt them both. If he doesn't like your diagnosis, give him Alpine's 1-800 number and let him ask them directly.  It amazes me how retarded people can be.

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Mitchell Whitney, Installer/technician
Mainstreet A/V

the why u have them wired in the diagram is just like straping them together. ur not doing it at the amp but at the subs ur lucky ur just popping fuses, like DYhon stated the M350 isn't bridgable at all  don't u hate when someone second guesses ur work and when they do things get missed up and they run back to you for you to straighten up someone elses work.

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4-15" RF T2
6-7" RF Component sets
8 Planet Audio 900d
10 Batcap800
1 250 amp alt
1 300 amp alt
2" sound deadner roof,doors,floors

That happens because you are cutting and pasting from an editor like Word.  Do not do this.  Compose your posts on line or in a plain text editor like Notepad.  Please read the Forum Rules.

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After days of reading tech docs, MECP books, other posts, manuals, and my own tests, I've came up with a somewhat more detailed answer to my question.

I'm still no expert but my belief is there is no way to "fry" the amps unless the outputs are either short-circuited together or subject to very low impedance. Therefore in the previous diagram or similar situations, the amps should be fine as long as a suitable sub is hooked up to the circuit.

However, there is potential for damaging subs; especially if both amps are not set exactly the same. This would be due to either extreme excursion, clipping, overheated voice coils etc....

I came to my conclusions by first understanding the principles of bridging in 2-4ch amps and how mono amps work in relation to those.

In a bridgeable amp, for each channel only one terminal has a signal while the other references ground. The second channel is inverted but on an opposite polarity thus giving an identical output. When both channels are bridged you get double the output.

"Strappable" mono amps use this same principal because the positive terminal drives the signal while the negative is a ground reference (like a single channel in a 2ch amp). The second amp will have a switch that will allow you to invert the positive signal and use it as a negative, thus doubling your output if you use both amps together.

The Alpine M350 in my example (like many other Class D amps) don't work on this principle. In essence it's already internally "bridged" because both the positive and negative have a signal (regular & inverted).

"Bridging" two of these as the diagram showed would not have any positive effect on audio output but possible a negative effect if both amps weren’t in sync. If anything it would be a neutral effect; like cutting two apples in half and putting two halves together, you get one apple and a waste of time.

Yes you can bridge two mono amps, only if they were designed to do so, otherwise it's pointless and potentially dangerous to the subs.

So that's the long answer to my question with a why and a how.

Thanks for all the previous responses from you guys. Someone please correct me if I’m wrong about anything I've said.