Why arent all amps 2 ohm stable?

[johnk_10]

i always run my crown xti 2000 bridged into a 4 ohm accugroove or my 1212/6 (also 4 ohms) and it's actually cleaner and louder with less distortion than when i run either cab off of one side of the amp.

 

[gnjpowell]

It requires a larger, heavier and more expensive power supply to make full power at 2 ohms. If the marketing guys decide the average target buyer for the amp in question would not likely use the 2 ohm capability they may decide a lower price justifies no 2 ohm support. A very typical product marketing and design price/performance compromise. Same reason most car makers no longer offer a big-block V8 option... few people want or use it.

 

[babebambi]

do you actually know how bridging affect your amp?

No, that's now how it works. Two 4 ohm cabs in parallel is 2 ohms. Always. You can't get 1 ohm resistance from two 4 ohm cabs.

But the point is moot anyway because now that I think about it, I was describing the whole situation incorrectly.

When I used two 4 ohm cabs I would run each one from it's own power amp in the 4pro. It was only when I ran one 4 ohm cab (club shows) that I tried to figure out the difference between running that one cab from the bridged output, or from only one of the power amps in the 4 pro. That was the only time I ran it bridged, and I remember thinking that it wasn't quite as clean sounding.

 

[Bob Lee (QSC)]

No, that's now how it works. Two 4 ohm cabs in parallel is 2 ohms. Always. You can't get 1 ohm resistance from two 4 ohm cabs.

When you run an amp in bridged mono, the net effect on the two amp channels is that they see half the load impedance. This is because the two channels are running as mirror images of each other.

So when one channel is putting out, for example, +4 volts into a 4Ω load, the other end of the load isn't zero, but -4 V. A voltage of 8 V across a 4Ω load produces 2 A of current. That's 2 A from one output, through the load, and into the other. So one channel has to put out 2 A when its output is +4 V; that means the load impedance it sees is 2Ω. The other channel has -2 A when its output voltage is -4 V; that means the load it sees also is 2Ω.

 

[Bob Lee (QSC)]

It requires a larger, heavier and more expensive power supply to make full power at 2 ohms.

Typically, it also takes more output devices and their associated circuitry.