stability question

[thaar411 10+ year member]

I have an orion 800.4 xtr amp. The rear channels are rated as follows: 100x2 at 4 ohms, 200x2 at 2ohms, or 400x1 at 4ohms. Does this mean that in mono mode, it is not stable at 2 ohms? If so, why is this since it is stable to 2ohms in stereo mode? thanks.

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[Prowler573 5,000+ posts]

I have an orion 800.4 xtr amp. The rear channels are rated as follows: 100x2 at 4 ohms, 200x2 at 2ohms, or 400x1 at 4ohms. Does this mean that in mono mode, it is not stable at 2 ohms?

Yep. That is exactly what it means.

If so, why is this since it is stable to 2ohms in stereo mode? thanks.

Almost all amps (not all, but most) are stable at a lower impendence in stereo mode than they are in mono mode.

 

[ljb211087 10+ year member]

In mono mode, both channels see half the load, i.e. in stereo mode 2 ohms is the equivalent of having 4 ohms (as there is 2 ohms present on each channel) in mono mode, 2 ohms in mono would mean your amp is stable at 1 ohm in stereo

 

[flakko 5,000+ posts]

In mono mode, both channels see half the load, i.e. in stereo mode 2 ohms is the equivalent of having 4 ohms (as there is 2 ohms present on each channel) in mono mode, 2 ohms in mono would mean your amp is stable at 1 ohm in stereo

i got confused by that comment lol

in some amps you can run fine daily at a lower impedance level. for example, my Merlin MD22, only 4 ohm stable bridged, i ran it daily at 2 ohms for a week or so. got a little hot, but it was okay.

so it depends on the amp i guess.

 

[ljb211087 10+ year member]

sorry i was confusing, if you want to be confused more then the technical reason is:

In bridged mode, the voltage is effectively doubled, hence you get double the power, at this point running at 4 ohms mono takes as much power as 2 ohm stereo. It's hard to explain but it comes down to ohms law. Anyways, you're probably more confused than ever now. At the end of the day, running lower impedances (below manufacturer recommendations) will in most caases lead to damage

 

[thch 10+ year member]

math is a bit off. power scales with V^2. double voltage means double current means 4x power. each channel still puts out its normal voltage, but must provide double current, thus each channel sees V/(2I), or 1/2 the load it would see with the speaker attached only to it.

overbuilt amps might be run at lower impedances. its probably not the best idea, but its not like people haven't tested the limits of any other peice of equipment.

 

[ljb211087 10+ year member]

P=VI

V=IR

P=I^2*R

When voltage is doubled in the case of bridging, the following happens

P=2VI

Therefore P=2V^2*R

For example if voltage was 10v in stereo and 20v bridged, then @ 4ohms

In bridged- (20)^2*4= 1600 watts

In stereo- (10)^2*4= 400 watts

So bridging has the effect of quadrupling the power output for a given load. As most amps cannot do this, by doubling the impedence, the power is halved which makes the amp much happier. This is why most amps can only handle twice the rated stereo impedance. Eg. 2 ohm stable per channel, 4 ohm stable when bridged