4-channel amp produce distortion when bridged???

[keep_hope_alive Premium Member]

i know that the actual output you attain is based on available amplifier power. we have to recognize how much volume a system is capable of while keeping audible distortion to a minimum. you can always go louder, at the price of audible distortion. when i talk about usable volume, i always mean usable volume without audible distortion.

most people are faced with a decision: do i run active with my 4 channel amp, or do i bridge it and run passive?

answer is: it depends. it depends on the amp and the components and the install.

i prefer active, but that means (given the same amp) you operate with much less headroom. headroom is huge - and gives more available power while also offering more dynamic range at higher listening volumes.

that is what i've noticed over the years. ideally, you'd buy another amp, bridge both, and run active.

 

[akheathen Premium Member]

wait, did you just say it takes less voltage for the same power? that only works for ohm load. same voltage= same power for the same load. however, it puts less strain on each side, and takes half the voltage per channel, since it is divided between 2 channels, plus, you have less loss, since you have 2x the components doing the same work. in 4ch amps, the 4 channels are made symmetrical, and perform as such, so if you feed 2 bridged channels the same signal, the only real performance change would be one channel inverts, and works when the other is resting, so you get a push-pull collaboration, on some, and others, double up. either way, you ahve 2x the parts doing the same work, and yes, they sync together, so sq is not sacrificed.

 

[PrinceCharming 10+ year member]

Ok so after reading up a bit I have decided I will probably go active, but how exactly would I go about that? Because I dont really want to use my amps active x-over. I don't really know much about going active since I had planned to just use the passive crossovers.

 

[keep_hope_alive Premium Member]

wait, did you just say it takes less voltage for the same power?

Because bridging combines the non-inverted and inverted signals, the voltage on each channel is half what it would be if you were non-bridged to achieve the same voltage across the load. Voltage seen across the speaker is the same, so power is the same. But what matters in terms of distortion is how hard you are driving each channel. Bridging is easier on the amp. Output current is less and voltage on each channel is less to achieve the same power as a non-bridged configuration.

Does this make sense to everyone or should I sketch something up? I can do that for the cause. This is a common topic.

 

[av83 10+ year member]

This is why I pay attention to tech threads you participate in, @keep_hope_alive ;

Having an acoustic and electrical engineer in the forum is a win for everyone.

 

[keep_hope_alive Premium Member]

I have seen a lot of people explain bridging as the amplifier as "seeing" half the impedance load. But this is a misnomer as it implies that current is increased.

If you compare 4 ohm bridged vs. 2 ohm stereo you get the same power output (on most 4 ch amps) but bridging results in half of the current. That I should have clarified. This is what I mean by less current.

Current is determined by voltage, so when comparing bridged vs. non-bridged at the same voltage across the load, total current is equal but each channel shares it.

 

[akheathen Premium Member]

yah...basically, what i just said. to be more technical. most 4 channel amps have the pairs of bridging channels running off 3 legs of rail power. a negative power, shared neutral/common, and positive power. when you run a 4 ohm speaker off each channel, and feed them the same signal@ same settings, it is the same as if you series'ed a pair of 4 ohm speakers running 8ohms bridged. it runs from positive power to negative power. you basically have 2x the voltage available with the same current capability. there is the factor of better driver control, via the push-pull effect vs. push and fly-back, where the speaker would have more effect on the amp. it's quite simpler math than you might think.