Why is my speaker identified as being Reverse Phase?

[milleniumaire]

Just before Christmas I got myself a Pioneer sc-lx82 amp and I have just replaced my old front Sony satellite speakers with some floor standing Monitor Audio RX6's to match the sub, rear and center speakers. I've bi-amped these and ran the MCACC setup for the first time.

It identified the front right speaker as "Reverse Phase"! I checked the cables (all were correct) and then switched the cables between the two front speakers and ran MCACC again. It now identified the left speaker as "Reverse Phase". It looked like it was an issue with the cable as it had moved with the cable, so I now switched the Left and Right connections on the amp (including the rear surround left and right as these are used for bi-amping).

MCACC now identified the front right again as "Reverse Phase", so the issue seems to be with the right speaker connections on the amp, not with the speakers or the cables as this is the only constant i.e. any cable connected to the front right and rear surround right are causing that speaker to be identified as "Reverse Phase".

What is Reverse Phase?
Why does my amp seem to be causing one of my speakers to be Reverse Phase?
Why would this only be an issue for anything connected to the right or rear right speaker connections in the amp?
What is the affect of Reverse Phase on sound quality/speakers?

 

[BlueWizard]

I suspect it has more to do with the placement of the microphone and room reflections than it does with the actual speakers.

Try shifting the placement of the microphone; higher, lower, slightly left or right, angle, etc....

Also, consider reflections in the room. If you have curtains, try closing the curtains during the test.

Remember the amp is listening to the speakers in the room, and trying to make some determination based on what it hears. If the microphone is sitting in a null point, or is picking up a strong reflection, it is going to be confused.

Can you describe your setup? Meaning, can you describe the room and the placement of the microphone during the tests?

Steve/bluewizard

 

[deckingman]

Just to elaborate on Steve's reply. In simple terms, the speaker cones should go in and out together. If the phase is reversed on one speaker, then one cone will go in while the other goes out. This can result in certain sound waves cancelling each other out, and/or giving a sort of "difuse" sound. The auto calibration "thinks" this is the case but if the wiring is correct, then it will be something to do with the room acoustics/speaker/microphone placement which is giving the same effect.

 

[milleniumaire]

I don't see how it can be anything to do with the speaker, the cable or the room acoustics when the microphone was left untouched and therefore in exactly the same position throughout my 3 tests.
As I have said, the reverse phase message moved between speakers as I moved the speaker wires on the amplifier. The speakers themselves did not move!
This suggests to me it is an issue with the amplifier and not anything else.
If it was caused by the room acoustics then I would expect the same speaker to be affected every time, regardless of which speaker cables where connected to which amp connections!

 

[BlueWizard]

When you switched the wires around on the speakers, it is true the speaker didn't move, but the speaker DID move differently, and as a result, the room acted differently.

Likely to check phase, it compare what it hears on the Microphone to what it sent out. If there isn't a huge phase or timing difference, then the amp assumes the speakers are in phase. If there is a slight timing error between what it sends out and what it gets back, then it assumes they are out of phase.

But, the amp never really knows, it assumes based on the limited information it is able to pick up.

If something interferes with that information, then it assumes wrong.

Try what we said, move the mic, better yet describe the location of the mic in detail. If you have it sitting in your favorite listening chair, then it may be picking up a reflection off the chair itself.

Rarely does the amps built-in setup get it right. More often it gets you in the ballpark and you have to tweak it from there. Even under the best of circumstances, in my limited experience, people have to run the setup several times to get setting that make logical sense.

This isn't the first time this has happened. I recall someone asking about a similar problem recently, though I don't remember the resolution to it.

If the speakers are connected correctly, then the amp is wrong, but not wrong in terms of broken, instead, wrong it terms of simply mistaken. Now we need to determine what is causing the amp to make that mistake.

Perhaps other with more experience than myself can weigh in on this.

Steve/bluewizard

 

[Alan Mac]

I
This suggests to me it is an issue with the amplifier and not anything else.
If it was caused by the room acoustics then I would expect the same speaker to be affected every time, regardless of which speaker cables where connected to which amp connections!

I have a Pioneer VSX-LX70 which also has the MCACC set-up facility.
I do not have a problem with the MCACC but my speaker arrangement in the room is very symmetrical.

Suppose that in your case there is for some reason a problem with the right front position:

If all the loudspeakers except the front right (FR) are in phase with each other, then you should expect an instruction to “reverse phase” (ie. reverse the speaker cable connections) to speaker FR.

The amplifier software assumes that the amplifier output terminals labelled “front right” are indeed connected to the speaker situated at the front right of the listening position.

If you actually connect the amplifier terminals labelled “front left” to the loudspeaker situated on the right front listening position (which is the suspect position) then the amplifier software will detect the “fault” from the loudspeaker situated front right but will report it as being on the left front side.

That’s not really the fault of the amplifier software. It has been given false set-up information by the user!


Alan

 

[Mark.Yudkin]

Your analysis is very good, and all evidence points to a really simple issue, viz. the right speaker cable is connected back to front at the amp. To fix, you simply need to switch the cable going into the red post with the cable in the black post for the channel identified as having the phase reversal.

As you correctly state, room effects are so extremely unlikely that we can safely exclude them (Occam's razor). The fact that it moved with the wire also serves to lessen the likelihood to lower than being hit by a meteor.

If the wiring really is correct, there is the remote possibility that there is a wiring reversal issue within the amp, for which a repair would be needed.

 

[Alan Mac]

I agree with Mark that it does seem plausible that the right front speaker cable is connected the wrong way round at the amplifier end. However I thought this had been ruled out as you had “checked the cables and all were correct” ?


Alan

 

[milleniumaire]

I've checked and double checked the cables etc. and all are correct.

I did determine that moving the microphone closer to either speaker results in the "Reverse Phase" message disappearing when I re-run the test. I tried moving a large leather seat out of the way of the right speaker and this resulted in no reverse phase message being displayed so it looks like the sound is reflecting off the seat and being delayed slightly from reaching the microphone, thereby causing the amp to think it has been reversed (I guess).

My setup is symmetrical - Pioneer 500A centred on the front wall (bracket mounted) with a Monitor Audio Radius 205HD mounted above it. At the rear are two wall mounted Monitor Audio Radius 180HD's and the two new floor standing Monitor Audio RX6's at the front. The Monitor Audio RSW12 sub is situated to the left and side of the room. The microphone is placed in my usual seating position which is directly in the center of the wall adjacent to the TV. I propped it up on pillows so it was about head height.

The chair is situated to the right against the wall. If I were to slightly angle the front speakers in towards my seating postion then their fronts would not be obscured by the chair, however I have them facing directly towards the back of the room and I guess the right speaker is being "obstructed" by the chair.

Now that I've determined the cause of the Reverse Phase message I assume I simply ignore it as there isn't much I can do about it!

 

[deckingman]

You can safely ignore it. That's to say no harm will be done. It may sound "odd" but then very few of us have ideal room accoustics. It seems like you have to choose, or find a compromise, between where the furniture should go for the best accoustics, and where it can go for other "lifestyle" reasons. Of course, there is absolutely no reason why you can't move things around a bit when you want to do some serious listening, then put things back after.

 

[milleniumaire]

Thanks to everyone who offerred advice.

 

[tool03]

Does it have an impact on the MCACC measurement when the speaker was connected wrong?