Another amplifier bridging question

[lumisonic]

If an amplifier is being driven non-bridged to the constant onset of clipping but not beyond and the levels are satisfactory, is it better to operate it at that level or bridge it and run it at a reduced level? I’ve read that bridging can stress an amp. But at a reduced level bridged, I was wondering which would be better for the amp.

[Bill Fitzmaurice]

Only bridge if the amp can't deliver the voltage swing to drive the speaker to full output.

[Gregory East]

Seeing as the amp is already full tit you wouldn't be breaking any rule by bridging it. so you could give it a try amd seen if it runs cooler or hotter. Cooler would be better I imagine.

[Bill Fitzmaurice]

Seeing as the amp is already full tit you wouldn't be breaking any rule by bridging it.

Not if it delivers too much voltage and isn't limited.

[Gregory East]

Hpw does the cooler better proposition fare?

[Israel]

throw the full story pal which amp and which speaker(s) do you plan to use with?

[Bill Fitzmaurice]

Hpw does the cooler better proposition fare?

It doesn't. When you bridge you don't necessarily reduce current, especially if you're running too low an impedance. An amp rated for 4 ohm operation per channel is only good for 8 ohm operation bridged. As is always the case there's no such thing as a free lunch.

[Gregory East]

I assumed he wouldn't have asked if didn't have enough impedance, my bad. Assuming he was asking because he had an8 ohm cab my proposition was based on two amps putting out the same power as one might well individually heat up less for a start and also cool waste heat more effectively resulting in lower component operating temperatures. Or not.

When you say the current isn't necessarily less I get lost.

[Rune Bivrin]

I assumed he wouldn't have asked if didn't have enough impedance, my bad. Assuming he was asking because he had an8 ohm cab my proposition was based on two amps putting out the same power as one might well individually heat up less for a start and also cool waste heat more effectively resulting in lower component operating temperatures. Or not.

When you say the current isn't necessarily less I get lost.

Well, given the same impedance and the same voltage the current will clearly be the same.

Regarding the heat you might be surprised. For a class AB amplifier the dissipation is typically highest at half the maximum output power. Running bridged at the power level equivalent to full power of one channel will actually be running two channels at half maximum power, which will mean more heat with no particular benefit.

For a class D amp the calculations are a little different; power losses are generally proportional to output current. But still, running bridged means the same current through two output stages, so there will be more heat.

[Gregory East]

Not stuff you read about on a cereal box eh!

[lumisonic]

Sorry, I should have offered more information. Please let me know if I need to include any other variables.

This is just to help me understand some of the concepts of amplifier bridging, and amps in general. I see how the load impedance would matter and whether the amp is rated for 4 or 2 ohm loads.

I was thinking about my QSC RMX1450:
280 W - 8Ω/ EIA 1 kHz / 0.1% THD
1400 W - 4Ω/ EIA 1 kHz / 1% THD

In my hypothetical query I would be running limited parallel inputs into two 8 ohm loads, one on each channel pushed to the max. When bridged the load would be the two 8 ohm loads wired in parallel for a 4 ohm load using an amp rated for being stable for a 2 ohm load.

Assuming the system is adjusted to remain the same SPL level, and disregarding the increase in distortion I thought the amp might not have to work as hard if it is bridged into a 4 ohm load.
1) Is that correct?
2) If so, would it be better to reduce the limited input to the amp, turn down the amp settings or both?
3) Does the increase in distortion affect the amp?
4) How audible would the increased distortion most likely be?
5) After reading the last explanation (valuable information) , how would the heat factor?
5) Is it OK to run an amp non-bridged into an 8 ohm load full tilt (onset of clipping) contiuously?

I do sit around thinking about this stuff but I don’t have the opportunity or the equipment to test it at this time so…

I thought I would ask

[Bill Fitzmaurice]

Forget the watts, they don't matter. Does each channel have enough voltage swing to drive the cabs to full output? If they do don't bridge. If they don't bridge, but in either case be sure your limiter is set so that the amp can't exceed the speaker voltage swing capacity.