[Moondingo1993]

I’ve been trying to become a little more educated on phase shifts and the effect crossovers have on phase, and to take a break from all the reading wanted to try playing with phase on my current amp to see if I notice a change. I saw someone said that most bridgeable amps are actually marked backwards and that both binding posts are positive when bridged (the - on Chanel 2 is electrically +). Which would mean when not bridged the speakers are actually reversed in phase, correct? I happen to be running a four channel bridged for my 2 front comps, so if I reverse the polarity on one side will it change the phase or will it not since they are both positive? Couldn’t find a post that specifically answered my question. also just out of curiosity, does the HPF on the amp itself affect phase at all?

 

[gijoe]

I've never read that bridgeable amps are marked backwards. No, swapping one wire will not flip the phase, swapping both wires will. Do not bridge it any way other than how the manufacture tells you to bridge it.

 

[Moondingo1993]

Here's how it works......

All amplifiers use 2 positives (driven) for bridging, all (most) amplifiers have a positive (driven) and a ground for the speaker. The negative of the second channel is actually the INTERNAL driven lug and the positive is the GROUND.

Here's why.

Bridging works by inverting the phase on one channel, you can still use two speakers wired correctly, they will be out of phase, wire the second backwards and they will be In phase and IN absolute phase. By going to the two positives you are doubling the voltage at the outputs (one channel is swinging up while the other is swinging down) in this app both speaker terminals are "live" and there is no ground reference.

Pro amps do this with a switch, the switch simply comes off the preamp stage of channel A, inverts it and drives channel B with that, this ensures the same gain on both channels, it's mono, driven with only one channel of preamp, you then go off the two positives for a voltage double, Chb's preamp just pisses in the wind, often thru a resistor to prevent internal oscillation.

Car amps are "pre bridged” although they are labeled +-+- they are wired internally +--+. The phase of channel B is flipped from the get go and chB's output labeling is backwards. This was hinted at in the original post of this amp when I suggested driving headphones then finding out I had to invert one channel. So when you wire + chA and -ChB you are actually wiring + and + internally and bridging happens by simply monoing the inputs and matching gains. Some amps have a bridge switch which is simply a summing network.

There is a couple reasons this is done and has proven in the pro world to make a difference. The technical reason is that most LF information is mono anyway. Let’s say it is hooked up "conventionally" and you get a kick drum hit. Since amplifiers are bipolar and half of a channel amplifies the positive pulse and the other half does the negative side, both speakers pull off of the positive and negative section of the power supply at the same time. By bridging the amp or flipping the phase of one side, during the exact same impulse each speaker is pulling from different sides of the bipolar supply. So on a positive swing chA is pulling from the positive side of the PS but chB is pulling from the negative side, flip the phase of the speaker and both cones move in the same direction but the power supply is effectively balanced. This has been proven to increase headroom.

So on these amps ch's 2,4 and 6 have the phase inverted naturally so bridging channel one needs to take place between ch2, 4, or 6. It won't work by bridging between another odd number.

The input section needs to be modified to mono odds and evens on this amp, no biggie, switch 2 wires or curt two traces and re-route.

whole thread was

Inverting speaker polarity.

I read one time in a home audio forum that some older units would sound better if you inverted the polarity. Nowww Im pretty new to the whole car audio business..although I do read up a lot on it and I installed my whole (modest) system by myself. I have a set of pioneer tweeters in my dash...

www.diymobileaudio.com

 

[Moondingo1993]

That’s what I was reading so did I just misunderstand the post?

 

[Moondingo1993]

And I meant swapping both wires, just on one side. Like treating the bridged four Channel as a regular 2 channel.

 

[dumdum]

Use the channels as marked on the amp, they are marked correctly! Simple as that! You are taking something you don’t understand and trying to apply it to a situation you don’t really need to do anything about

yes swapping the wires around on bridged channels will swap the phase, the same as with any speaker, it’s no different ??

and yes the hpf will effect phase, the same as any crossover does

 

[Moondingo1993]

fair enough, even if It wasn't going to apply to me I still wanted to try to understand what I was reading. I don’t just go playing with wires without knowing what will happen. unfortunately you can’t raise your hand and ask for clarification when researching on your own.

 

[dumdum]

I've never read that bridgeable amps are marked backwards. No, swapping one wire will not flip the phase, swapping both wires will. Do not bridge it any way other than how the manufacture tells you to bridge it.

He is correct, the input to one side is flipped in phase and the output is flipped back, when you bridge it you effectively use the circuits as a push pull circuit ?? But you are also correct the amplifier is marked correctly, use this and you won’t go wrong

He also wants to know if you swap the speaker leads round on a bridged channel will the phase be reversed, the answer is yes, the same as reversing the cables on any other channel, bridged or not ??

 

[Moondingo1993]

Use the channels as marked on the amp, they are marked correctly! Simple as that! You are taking something you don’t understand and trying to apply it to a situation you don’t really need to do anything about

yes swapping the wires around on bridged channels will swap the phase, the same as with any speaker, it’s no different ??

and yes the hpf will effect phase, the same as any crossover does

Well the reason I’m trying to understand all this is because I’ve been having problems where I know a certain sound should be coming from both sides in a song, but I only hear it on one and have been trying to figure out if it’s a phase issue or just simple off axis beaming as it usually is higher frequencies it happens with. And instead of just blatantly asking for help would like to have a general understanding of as much of the science as I’m capable of.

 

[gijoe]

He is correct, the input to one side is flipped in phase and the output is flipped back, when you bridge it you effectively use the circuits as a push pull circuit ?? But you are also correct the amplifier is marked correctly, use this and you won’t go wrong

He also wants to know if you swap the speaker leads round on a bridged channel will the phase be reversed, the answer is yes, the same as reversing the cables on any other channel, bridged or not ??

Yeah, that's where I got confused. The amp will be marked on the outside to give the correct polarity, so by using the markings the speakers will be in phase. I thought he was implying that the phase would be wrong if you wired according to the markings. That's also why I mentioned to follow the manual with regard to bridging. It sounded to me like he was asking if moving one wire over in bridged mode would flip the phase, instead of swapping both the positive and negative wires with each other. In bridged mode, only use the terminals that the manual shows, if you want to flip the phase swap both wires around.

 

[F150Man]

I’ve been trying to become a little more educated on phase shifts and the effect crossovers have on phase, and to take a break from all the reading wanted to try playing with phase on my current amp to see if I notice a change. I saw someone said that most bridgeable amps are actually marked backwards and that both binding posts are positive when bridged (the - on Chanel 2 is electrically +). Which would mean when not bridged the speakers are actually reversed in phase, correct? I happen to be running a four channel bridged for my 2 front comps, so if I reverse the polarity on one side will it change the phase or will it not since they are both positive? Couldn’t find a post that specifically answered my question. also just out of curiosity, does the HPF on the amp itself affect phase at all?

I have always been told one can believe half of what they see and none of what they hear. Good advice nowadays.

 

[Moondingo1993]

guess I don’t fallow what your referencing to Specifically, although i know the saying. the link is what I was talking about,added it when I realized I probably condensed The information poorly to try to make the question faster.

 

[syc0path]

I saw someone said that most bridgeable amps are actually marked backwards and that both binding posts are positive when bridged (the - on Chanel 2 is electrically +). Which would mean when not bridged the speakers are actually reversed in phase, correct? I happen to be running a four channel bridged for my 2 front comps, so if I reverse the polarity on one side will it change the phase or will it not since they are both positive? Couldn’t find a post that specifically answered my question. also just out of curiosity, does the HPF on the amp itself affect phase at all?

U'r asking 2 different questions here...

1st of all, phase and polarity are related, but not the same. Phase indicates the relationship between 2 signals, and they can be anywhere from 0° to 359° apart from each other -- at 360°, phase would be back at 0°. At 180°, they would be exactly opposite each other and would tend to cancel each other out. Polarity is much more blunt -- correct polarity is 0°, reversed polarity is 180°.

Now let's talk about the idea that + terminal has voltage potential and the - is just a ground. While this is generally true, it's just a convention -- there is no physics or electrical reason why it should be this way. Multi-channel amps take advantage of this fact to simplify bridging. In fact, the + terminal on the left channel and - terminal on the right channel are usually where the voltage potential comes from.

And yes, the signal from the left and right have opposite polarity. But since the voltage rails from left and right hook up to opposite ends of their respective speakers, the opposites cancel out and both speakers play at the same polarity. Think of it this way -- say u want to move air thru a room from the west to the east. It doesn't matter if u blow in the air from the west or suck it out from the east -- it's still moving in the correct direction. So, as mentioned, hook up your speakers as marked on the amp and your polarity will be correct.

Getting back to your crossover/phase question, crossover slope affects the phase of the signal at a rate of 180° per 12dB of slope. So a 12dB/octave crossover will reverse polarity, and that in turn can be corrected (reversed again) by switching the speaker wires -- or often by changing a setting in the HU, DSP, or other processor. Depending on about a million factors, reversing the speaker wires may or may not sound better.

 

[Moondingo1993]

yea, i really would like a DSP so I can play with crossover slopes and phase. wanted to try to understand these things better before spending the money on one just to find out I don’t know how to use it.