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Old 07-09-2019, 08:52 AM   #1
Peterk312
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Default Checking if monitor speakers are out-of-phase?

I discovered in an odd way thru interest in the JS Stereo Width plugin that I may have been working with monitors (Alesis Prolinear DSP) and was unaware they were not in phase with each other. I attributed some of my problems with poor mixes to my skills but may have actually been dealing with inaccurate reference monitors for the audio. Ten years or so ago I never thought that monitors costing $700 for the pair could have a defect like this.

These connect with balanced cables. I use TRS jacks. The cables were checked over and have no polarity issues or poor solder joints. The pin assignments for both the monitors as well as my interface (1616m Microdock made by E-mu, now discontinued) are the same: +tip/-ring/sleeve.

I pulled out the drivers to check the wiring to the drivers inside the cabinets. It looked correct, but these are powered monitors and I couldn't access the amplifier section to check those connections.

There are a couple things I know that are different between the two monitors but I'm not sure why they would cause phase issues. For example, when these power on there's an LCD screen in the front that indicates firmware version. One says V 1.10 and the other says V 1.20. The one that says V 1.20 has a sticker on the back that says "Positive Phase."



The other monitor does not have this sticker.

Also, you can assign these monitors to a Channel using a Windows application. The monitors connect to a PC with a COM port serial cable. When I check to see they're both on Channel 1, I get a different display. The speaker that has the "Positive Phase" sticker on the back says +Ph in addition to Channel 1. Click below for larger image. I know they are both on the same Channel, but why the +Ph only on one?



Then there's my listening tests. Out-of-phase speakers have a few symptoms compared to in-phase: thin sound, unfocused stereo imaging (especially panning center), frequency cancellation in certain circumstances that produce silence.

I had been working in Reaper on an imported Sonar project and could not get the vocal (mono track) to pan center, so I knew something was very wrong.

One of the first tests I did was go to a website: https://www.richardfarrar.com/are-yo...red-correctly/ Downloaded the file called "out-of-phase." When the announcer says "You should now be hearing my voice in phase," it sounds like a dual mono with the voice equally coming out of both speakers way to the side but definitely NOT centered in the stereo field. When the announcer says, "You should now be hearing my voice out of phase," the voice is dead center in the stereo image. That is indicative of the speakers being out of phase, yes?

I inserted a 100 Hz Sine Wave into two tracks in Reaper, panned one hard left and the other hard right. When I inverted polarity on one track there was much more bass and the sound was louder. Changed the audio clips in the two tracks to a Charlie Hunter tune. Inverting phase in this case moved all audio to the center of the mix and made the bass much louder. Sounds like the speakers were out of phase?

One fix for out-of-phase monitors is to reverse polarity on one of the speaker cables (one jack only). So, I did another set of tests with one speaker cable normal and then reversed polarity on one side:

1. Speaker cable polarity normal (+tip/-ring/sleeve)

Two mono tracks, one panned hard left the other hard right. Both tracks in phase sounded very thin but did not cancel out. It almost sounded like the sound was behind and to the sides of the monitors. Inverted the phase on one track and bass came back full, sound was in the center right in front of the monitors.

Note, inverting phase on one track and panning one side over to the other the sound cancelled out and there was silence, as you'd expect. Same with panning both tracks center, one track out of phase cancelled the sound. Put the tracks back in phase sound came back, and if I panned one side over to the other the sound was louder with more bass than hard right/hard left.


2. Speaker cable with one jack inverted polarity (-tip/+ring/sleeve)

Again, two mono tracks, one panned hard left the other hard right. Both tracks in phase sounded like more bass and louder compared to when you invert phase on one track. That's the opposite of what I got above with speaker cable having normal polarity, but here in this test I believe this is what you'd expect: Thin sound out of phase and more bass/louder when both tracks are in phase. It suggests reversing polarity on one of the TRS speaker cables has fixed a problem, yes?

If I inverted phase on one track and panned it over to the other side the sound cancelled out, as in the previous test condition. Same with panning both tracks center, one track out of phase cancelled the sound. Put the two tracks in phase and sound came back. Panned one side over to the other and the bass was basically the same, the overall sound was slightly louder.

So I got cancellation in both test conditions, but condition 1 still suggests that's when the monitors are out of phase with each other. Right?

Also for test condition 2 (reversed speaker cable polarity) I created two tracks with white noise, one panned hard left the other hard right. Moved the speakers back to their normal arrangement about 3 feet apart for good nearfield stereo imaging. With the two tracks in phase the white noise was dead centered, as you'd expect. Inverted phase on one track, and the sound was way to the side and almost behind the monitors and thinner. Panned tracks to the center, inverted phase on one track, and sound cancelled out. Again, the testing here with the white noise suggests the speakers are in phase with each other, but this is when I've swapped polarity on one of the cables, and that suggests the two monitors have some factor causing them to be out of phase with each other. I just don't know what's causing it.

Sorry for the long post, but if anybody can tell me if I'm troubleshooting this right, or perhaps another test to check phase, I'd appreciate it. I also sent Alesis an email on this days ago, but they have not yet responded.


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Last edited by Peterk312; 07-10-2019 at 07:04 AM.
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