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.


.

Last edited by Peterk312; 07-10-2019 at 07:04 AM.
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Old 07-09-2019, 09:19 AM   #2
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You could run a 1Hz sine wave at just enough level to see the woofers move and confirm if they are moving in sync. Some sound cards however filter out before that so depending on the card this will/won't work but something like that really is the most definitive as far as woofers go anyway. You don't even really need to see it well, I've been known to do this test and just place my fingers on the woofers and be able to tell if they are in phase.

For example my RME will go all the way down to DC so the test would work but all sound cards don't do that.
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Old 07-09-2019, 02:04 PM   #3
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Quote:
Originally Posted by karbomusic View Post
You could run a 1Hz sine wave at just enough level to see the woofers move and confirm if they are moving in sync. Some sound cards however filter out before that so depending on the card this will/won't work but something like that really is the most definitive as far as woofers go anyway. You don't even really need to see it well, I've been known to do this test and just place my fingers on the woofers and be able to tell if they are in phase.
That's funny you mention this. I actually tried lightly touching the woofer cone at the surround to see if I could feel a thump outwards on a kick drum. I really am not sure I'm feeling an excursion outward. Maybe I'll try what you suggest with the monitors side by side.
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Old 07-09-2019, 02:26 PM   #4
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I can't see any speaker excursion with a 1Hz sine wave.

But I did put on a Joe Locke Quintet tune called Cecil B. DeBop, not in Reaper just using VLC Player. This track has very heavy bass and drum hits. Light touch on the woofer surround and with every thump of the drum both drivers are definitely moving outward.

But this is with one of my speaker cables having reverse polarity, so it suggests something is up with the monitors and they are out of phase with each other somehow.
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Old 07-09-2019, 02:36 PM   #5
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The simplest way to check polarity, is using a 1,5V AA battery as a "sound" source...
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Old 07-09-2019, 03:28 PM   #6
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The simplest way to check polarity, is using a 1,5V AA battery as a "sound" source...
Active speakers. I'd do it for sure on passive.
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Old 07-09-2019, 03:29 PM   #7
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Originally Posted by Peterk312 View Post
That's funny you mention this. I actually tried lightly touching the woofer cone at the surround to see if I could feel a thump outwards on a kick drum. I really am not sure I'm feeling an excursion outward. Maybe I'll try what you suggest with the monitors side by side.
Right, they need to be both touched at the same time to really get a "feel" for it.
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Old 07-09-2019, 05:55 PM   #8
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The simplest way to check polarity, is using a 1,5V AA battery as a "sound" source...
Yeah, I've already been advised not to do that with active speakers...
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Old 07-10-2019, 06:42 AM   #9
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Originally Posted by Peterk312 View Post
Yeah, I've already been advised not to do that with active speakers...
If an active speaker fails due to 1,5V DC on it's hot leg, it was either dying anyways, or it is a VERY bad design...

I use that test at least once a month. Never ruined anything and it showed me a few leaky input caps on occasion.

Using a drum kit can be very confusing. I'd sooner adapt Karbo's solution, putting a very low tone on bothe speakers and comparing woofer displacement while the speakers are next to one another.
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Old 07-10-2019, 06:58 AM   #10
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Aloha,

For phasing of the woofers the self-cancellation technique works pretty well, but place the speakers very close together. Put the two speakers face-to-face with just an inch or two between them. Feed them both a signal that has lots of bass (or use a bass tone). Make sure the volume levels of the speakers are substantially the same. When they are in-phase a substantial about of bass will emanate out of the gap, when they are out of phase the bass will nearly completely cancel. This will not work quite as well if you have speakers that have a rear port or rear-facing passive radiator but you will still hear a clear difference.

FWIW...
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Old 07-10-2019, 01:11 PM   #11
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Aloha,

...Put the two speakers face-to-face with just an inch or two between them. Feed them both a signal that has lots of bass (or use a bass tone). Make sure the volume levels of the speakers are substantially the same. When they are in-phase a substantial about of bass will emanate out of the gap, when they are out of phase the bass will nearly completely cancel. This will not work quite as well if you have speakers that have a rear port or rear-facing passive radiator but you will still hear a clear difference.

FWIW...
Okay. Thank you for that. Makes sense to me.



In Reaper I set up two tracks, one panned hard left the other hard right.

Set up L/R pairs of the following test tones: 100Hz, 315Hz, 1Khz, and pink noise.

When inverting phase on one track for all but the pink noise, the sound was completely cancelled out. Pink noise left just a high pitch when phase was inverted, but lost all low frequencies completely. Same results when both tracks for each test tone were panned center.

So yet another test that indicates AS CONNECTED, the monitors were in phase with each other. But note --I'm still using one speaker cable that has reverse polarity, which is a fix for a pair of monitors that are OUT OF PHASE with each other.

So yes, more evidence that the monitors really are out of phase with each other for some reason. Still only guessing why...

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Old 07-10-2019, 04:01 PM   #12
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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...One says V 1.10 and the other says V 1.20....
If they were originally bought as a pair shouldn't they be identical? So what's their history? It seems that they were manufactured at different times and a deliberate change was made for some obscure reason.

Did you or a previous owner buy them separately? Did the retailer decide it was OK to provide two different versions as a pair? Last one of V1.10 and first of V1.20?

If you can open one up just swap the two wires at the speaker. If they are spade connectors it'll only take a second.
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Old 07-10-2019, 04:12 PM   #13
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If you can open one up just swap the two wires at the speaker. If they are spade connectors it'll only take a second.
I was able to get the speakers out and observe the wiring, which looks to be correct polarity to each driver. What you suggest is interesting to try, but these are active monitors and I don't know how they connect at their respective power amps. Are you saying to swap connections at both tweeter and woofer?

If you really want to know the history of these. I purchased them some time in 2004. I got them from Sweetwater. What they did was send me two (they didn't come in "matched pairs"), but one of them had obviously been returned and had cosmetic damage. I didn't like that they tried to sell something used at a price like it was new, so I requested a return. They sent me back a single monitor. I don't believe at the time I checked the firmware versions, and like I said above I always assumed they were not defective, despite having had problems with mixes.
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Old 07-11-2019, 08:02 AM   #14
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Yes, the woofer and tweeter should both be swapped. Photograph the connections first, then assuming different colour wires you can confidently return them to their starting point. You would then no longer need your reversed lead - a situation that could be forgotten at some future date.

However your question about the tweeters raises another question - what exactly went wrong here? Was one of the monitors incorrectly wired somehow (just the woofer and not the tweeter)? If so which one? If the woofers and tweeters are incorrect relative to each other you'll get frequency response problems around the crossover frequency, and that might already be the case with one of the monitors. If you fix the right one (by swapping only the woofer), fine. If you fix the wrong one then both monitors could have a lumpy response. If you do nothing at all, you might still have one with a lumpy response.

That second paragraph is all just speculation, sorry if I've opened a can of worms!
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Old 07-11-2019, 08:27 AM   #15
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Hold on...
Put down the screwdrivers just yet.

Grab a mic (a shit 57 will do in a pinch). You're going to record each speaker.

JS Tone Generator plugin.
Record 3 tones from each speaker separately. A high, mid, and low frequency. Pick something that's in the range of each driver in the speaker. (Two tones if these are only two way speakers.)
Then record a frequency sweep on each one. This will let you look at the cross-over points for any phase issues.

Mic in front of left speaker. Record. Beep Boop Bum Sweep. Repeat for the right.

Zoom in on the waves you recorded. You'll see if anything is out of phase and be able to evaluate each driver. There's no reason for any of this to be a mystery or difficult to evaluate. But real quick, out of phase speakers in stereo will throw everything to one side of the room.
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Old 07-11-2019, 11:12 AM   #16
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Quote:
Originally Posted by alanofoz View Post
- what exactly went wrong here? Was one of the monitors incorrectly wired somehow (just the woofer and not the tweeter)? If so which one? If the woofers and tweeters are incorrect relative to each other you'll get frequency response problems around the crossover frequency, and that might already be the case with one of the monitors. If you fix the right one (by swapping only the woofer), fine. If you fix the wrong one then both monitors could have a lumpy response. If you do nothing at all, you might still have one with a lumpy response.
Like I said above, as marked with a red dot on the drivers for + polarity, the drivers are wired correctly. I cannot see how they are connecting at their power amp outputs because I can't get the back plate off the cabinet and don't want to damage it.



Click on the above for a larger image. The connections appear to be correct polarity for both monitors. Red + for woofer. Tweeter has Blue + which you can't see in the photo (that's not a white wire coming from the + connection at the tweeter). I was going to check with a battery only because it's possible, though unlikely, that the woofer polarity may have been marked incorrectly.
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Old 07-11-2019, 11:23 AM   #17
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Quote:
Originally Posted by serr View Post
Hold on...
Put down the screwdrivers just yet.

Grab a mic (a shit 57 will do in a pinch). You're going to record each speaker.

JS Tone Generator plugin.
Record 3 tones from each speaker separately. A high, mid, and low frequency. Pick something that's in the range of each driver in the speaker. (Two tones if these are only two way speakers.)
Then record a frequency sweep on each one. This will let you look at the cross-over points for any phase issues.

Mic in front of left speaker. Record. Beep Boop Bum Sweep. Repeat for the right.

Zoom in on the waves you recorded. You'll see if anything is out of phase and be able to evaluate each driver. There's no reason for any of this to be a mystery or difficult to evaluate. But real quick, out of phase speakers in stereo will throw everything to one side of the room.
Yes. What you describe about sound thrown to the side (almost sounded like behind the monitors) is exactly what was happening. 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 sounded 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 was dead center in the stereo image. That's supposed to be indicative of the speakers being out of phase. Only when I reversed polarity on one of the speaker cables, I got the expected results with the test.

The test you describe is interesting. I will try that later.
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Old 07-11-2019, 11:45 AM   #18
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In case it wasn't clear, render the test samples you use first. That way you have them right there in a track on the screen to compare phase with the speaker recordings you make.

The test sample from the tone generator will be the master. You'll be able to look at each driver and see if it's correct or reverse polarity in the recordings. So not only one speaker vs the other but each one against a reference.
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Old 07-11-2019, 05:38 PM   #19
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I believe I did this test accurately, without using a master track for reference, to show the monitors are out of phase with each other. Here's my procedure:

1. Removed the COM port serial cables from PC to monitor and between monitors so that no Windows application was being fed to the monitors. Checked input levels and matched with a 1 kHz test tone. Checked all EQ bands were at 0 db gain. Checked both monitors were on preset 1 (flat setting).

2. Setup an AM 52 condenser mic (just happens to be an Alesis mic) 8 inches away from the front of the speaker, diaphragm centered between the drivers.



3. In Reaper, set up panned L/R pairs of tracks each with the JS Tone Generator plugin. Each pair was set for 100Hz, 1kHz, 2.5kHz, and 6kHz.

4. Recorded two test conditions:

Test 1 - Both speaker cables normal polarity (+tip/-ring/sleeve, TRS jacks)

Test 2 - One speaker cable on one side reverse polarity (-tip/+ring/sleeve)

Note: Test condition 2 was my current fix given I suspect the monitors are out of phase with each other. If I'm right, then Test 1 should indicate out of phase wave forms in Reaper.

Procedure: I started with the Right monitor, which was the speaker that has the sticker that says "Positive Phase." I simply played the test tone first then hit record for each Right Side track. I believe doing it this way allowed me to maintain time alignment for the tones between the two monitors. When done with Right monitor, I moved the microphone to the same position at the Left monitor and repeated the recording.

Results Test 1

Here's the wave forms captured in Reaper with speaker cables having normal polarity:


100 Hz



1 kHz



2.5 kHz



6 kHz

--in every case above, the wave forms are out of phase with each other.

Results Test 2

Remember, before recording the output of the monitors I had to reverse polarity on one of the speaker cables, which is a fix for monitors that are out of phase with each other. Test tones:


100 Hz



1 kHz



2.5 kHz



6 kHz

In test condition 2, because these monitors are out of phase with each other I compensated by reversing polarity on one of the speaker cables. The wave forms indicate the speakers are now in phase with each other.

Unless I did not do a valid test above, I think there's no doubt at this point that the monitors are out of phase with each other.

Last edited by Peterk312; 07-11-2019 at 05:43 PM.
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Old 07-11-2019, 09:42 PM   #20
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I think what I'm going to do next is a sweep test with monitors in phase (same setup as above for each speaker) and see if there's any obvious irregularity. These are supposed to be 50Hz - 20kHz +/- 1.5dB.
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Old 07-12-2019, 08:10 AM   #21
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I wanted to share this too:

There was a Sound on Sound article on these monitors that I know influenced me to buy them. The article is still up https://www.soundonsound.com/reviews...olinear-720dsp

In the article Paul White says:
Quote:
The speakers have a decent degree of bass extension (50Hz-20kHz is the quoted figure ±1.5dB), while remaining tight and well controlled. The mid-range was also open and detailed, while the high end was smooth and open, due in part to the use of soft-dome tweeters. Overall the stereo imaging was very good, and the mix was presented with depth as well as width —something you don't always get in this price range.
He says he was impressed by "depth," but what I heard as "depth" in these monitors was actually due to the out of phase relationship of the sound being thrown to the sides or sounding at times like the sound was behind the monitors. Now that I've gone through extensive testing and more critical listening to determine there's actually an out of phase relationship between the two monitors, I'm not sure if Paul White was hearing the same thing and never realized it may have been a distortion.

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Old 07-12-2019, 08:16 AM   #22
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Looks pretty conclusive all right!

If you were to render those test samples first, you'd be able to see the waveform and then tell conclusively WHICH speaker is reverse polarity. But you proved that not only are the two speakers running reverse polarity from each other, it's also the entire speaker (both drivers). So the connection to the built-in crossover (before the signal is split to the two built-in amps).

If I were betting on a race, I'd speculate that the one not labeled "positive phase" is reverse. I'd further speculate that them eventually catching what was a mistake (reverse polarity on the input) was "fixed" by introducing an "updated" model named "positive phase". But that's just taking a poke at them for no good reason. But then releasing an updated model speaker in reverse polarity from your previous one is kind of asking for it.

You mentioned a digital connection on these speakers? Purely academic but it might be interesting to see if they're still reverse with a digital input. I'm not familiar with a digital audio connection over a serial com port. You mean that old 9 pin serial port from late 20th century?

I'd rewire the input jack on the reversed one. (You may be able to correct for the digital input if you find the analog signal coming out of the built-in DA converter. Should be feeding the same input to the built-in crossover.) Then I'd scribble on the front with a sharpie "positive phase". That way people will ask you what that's about and you can tell them about Alesis screwing up.

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Old 07-12-2019, 08:59 AM   #23
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Looks pretty conclusive all right!
Yes. And I can't thank you enough for suggesting this kind of test.

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If you were to render those test samples first, you'd be able to see the waveform and then tell conclusively WHICH speaker is reverse polarity.
I think I can still add that to the test project, right? Just add a track above each pair of test tones with the JS plugin and I can record the output of the plugin without a mic? Or do I need to do the test over again?

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If I were betting on a race, I'd speculate that the one not labeled "positive phase" is reverse.
That's the speaker that also has the later firmware version. One of the only things I've been able to get out of a tech support rep from Alesis is that the firmware revision may have been because of a change to "internal parts." On that sticker that says "Positive Phase" it says the words "MICRO EEPROM," and that's some kind of memory chip controller. I don't know if that's what was changed between the two monitors, but it would be a plausible reason for firmware revision. Just wish Alesis would give me a definite reason. You'd think they still have archives on this, but the rep seems too disinterested.

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You mentioned a digital connection on these speakers? Purely academic but it might be interesting to see if they're still reverse with a digital input. I'm not familiar with a digital audio connection over a serial com port. You mean that old 9 pin serial port from late 20th century?
The serial port is not for audio signal. It's only for communicating with the PC through a Windows application (XP believe it or not) by connecting from the PC to one monitor and then that monitor to the other. The Windows application allows you to assign the monitors to a Channel, and then from the PC you can change trim, EQ, mute, and presets to both monitors at the same time. This works perfectly with both monitors, as I can tell from the LCD screen in the front. The out of phase relationship appears to be due to something else.

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Originally Posted by serr View Post
I'd rewire the input jack on the reversed one. (You may be able to correct for the digital input if you find the analog signal coming out of the built-in DA converter. Should be feeding the same input to the built-in crossover.) Then I'd scribble on the front with a sharpie "positive phase". That way people will ask you what that's about and you can tell them about Alesis screwing up.
I still have one issue though that makes me lack confidence in using these as reference monitors. These monitors have a spec that says the frequency response is 50Hz - 20kHz +/- 1.5 dB. I don't know if reversing polarity on one monitor is going to alter this. That's one reason I was going to record a sweep and look for obvious irregularities in output. You'd think though it's the out of phase relationship that causes irregularities, but you'd have to record both speakers at the same time to detect that. I think I need to do this:

1. Sweep with each speaker individually (as per above procedure), both in phase and out of phase. If the out of phase condition shows irregularities in response then the quoted spec should be okay if I go ahead and use these by swapping polarity on one monitor.

2. Sweep with both speakers both in phase and out of phase, again to detect if there are odd irregularities. I think here I have to put the monitors close to each other and the mic fairly close (maybe a foot away) so that the room acoustics don't get picked up.

Last edited by Peterk312; 07-12-2019 at 09:08 AM.
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Old 07-12-2019, 11:56 AM   #24
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I'd do this:

Render/freeze a couple second long sample of each test tone. Just 100Hz and 6k are fine too. They're each clearly within each drivers' range respectively.

Then play from those samples when you record the speakers.
You'll have:
<original sample>
<left speaker recording>
<right speaker recording>

You only need to record it with normal connections. Reversing the polarity of the input is academic at this point.

You might want to reverse the left and right inputs to the two speakers and make another pass though. Just in case someone wants to ask if it could be the outputs on your interface.

And OK, there's no digital input.
It sounds like one of these is simply wired up reverse polarity on the analog input. Unless there's digital signal processing ability in those things. And that includes the ability to flip the polarity. And then different firmware would have different defaults...
Could be. All speculation on that bit though.
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Old 07-13-2019, 03:56 AM   #25
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There's a real DSP in there. And it seems Alesis changed polarity to remedy complaints that the analog input was wired in reverse...

If you're adventurous, you could try running the Win 98SE software that controls the EQ and see if there's a polarity flip in there. That needs a serial cable between PC and monitor. Presumably a null-modem 9 pin D cable.

If you're even more adventurous, you could try load the same firmware on both.

Me, I'd just wire up a custom cable and be done with it. Or can you flip polarity on one side of the master in Reaper?
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Old 07-13-2019, 07:15 AM   #26
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If there's DSP in there...

Is there a mode that connects the analog input coming from outside directly to the analog input to the speaker's crossover input? Because if there is, I'd want to bypass the AD and DA conversions needed to get in and out of that DSP! Lo grade AD/DA conversions is how you make things sound shitty for no good reason. Actually flashing matching firmware would be an elegant and proper solution. (Presumably over that old serial connection. So a serial to USB adapter... Careful with that. Cheaper ways to find paperweights.)

Next choice (ruling out bypassing DSP and/or if it's the root cause) would be to flip the polarity on the input jack. Unless it's so built up with a PCB soldered jack to make it a PITA. Something is just appealing to me about hand writing "positive phase" with a sharpie on the front of the thing following that.
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Old 07-13-2019, 03:45 PM   #27
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Hmmm... I'd still prefer to swap the wires at the speakers. No soldering, no non-standard leads that will probably be forgotten down the track. Leave a note inside the box, re-assemble & move on.
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Old 07-15-2019, 01:41 PM   #28
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Did the test again with a reference waveform (top track). I simply rendered the JS Tone Generator first, panned the track to one monitor only and played the tone while recording the same monitor's output.

TRS speaker cables had normal polarity (+tip/-ring/sleeve).

The monitor on the right is the one with the "Positive Phase" sticker.


100 Hz


6 kHz


So, as predicted, it appears the monitor that does not have the "Positive Phase" sticker is the one that has inverted phase. This test confirms (again) that both the tweeter and the woofer have inverted phase.

I think I'm going to just reverse the wiring to the drivers on the monitor that has the problem. There are clips that just pull off. Given they're a pair might as well make it permanent that they're in phase with each other.

The other test I did was a sweep, 5Hz - 20kHz, and I was going to look for irregularities in the waveform that might indicate the monitors are still not functioning according to spec (50Hz - 20kHz +/- 1.5dB) but I realized I don't have a microphone that has a flat enough response for that kind of test.
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Old 07-15-2019, 01:59 PM   #29
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alanofoz is right. Reverse at the speaker.
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Old 07-15-2019, 02:18 PM   #30
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I also forgot to mention that I did rule out that my interface (E-mu 1616m) is the problem by swapping the L/R outputs to the monitors. Same results when the monitor without the "Positive phase" sticker is connected to the Right output of the interface instead of the Left: Inverted phase compared to the reference tone waveform.
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Old 07-15-2019, 02:49 PM   #31
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Quote:
Originally Posted by alanofoz View Post
Hmmm... I'd still prefer to swap the wires at the speakers. No soldering, no non-standard leads that will probably be forgotten down the track. Leave a note inside the box, re-assemble & move on.
Sounds a bit uncertain to me, as you're switching after the DSP. That DSP -might- do phase corrections on the tweeter. I don't think Alesis is doing it, or they would probably mention it for marketing reasons, but we don't know.

Besides, some speakers have different spade connectors for + and - connections. This one too, according to the pic.
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Old 07-15-2019, 02:52 PM   #32
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Seems like Alesis & Sweetwater between them have a lot to answer for...


And the results of all your testing are pretty conclusive.
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Old 07-15-2019, 02:57 PM   #33
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Quote:
Originally Posted by cyrano View Post
Besides, some speakers have different spade connectors for + and - connections. This one too, according to the pic.
Could be a bit of a speedbump.
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Old 07-15-2019, 03:17 PM   #34
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Quote:
Originally Posted by cyrano View Post
Sounds a bit uncertain to me, as you're switching after the DSP. That DSP -might- do phase corrections on the tweeter. I don't think Alesis is doing it, or they would probably mention it for marketing reasons, but we don't know.

Besides, some speakers have different spade connectors for + and - connections. This one too, according to the pic.
Was going to mention seeing that before too. Short of that it would be an easy swap. Otherwise the jack.
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Old 07-16-2019, 08:48 AM   #35
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I managed to get the back panel off the monitor, which is where the electronics are fastened to.



The two white plugs you see are for the drivers. Red + for woofer, Blue + for tweeter. I couldn't just swap connections at the drivers because there are two different size spade connectors, and the + spade was just too big for the other wire's connector. I was also curious to look at the PC board, so I found a way to carefully tap out the back plate from inside the cabinet.

The PC board has no visible markings for polarity at the plugs for the drivers. The female plugs you see each fit over two pins. Both the male and female connectors have no markings for polarity either. I couldn't see under the PC board and didn't want to fiddle with the screws. Just makes me think this is a good spot for manufacturing error, but you can see in the image there's a stamp that says "Test-1 OK." Who knows what that was for?

What I did was remove the female plugs, and at each side there's a small metal spring (visible in the photo) that you can push in with a tiny screwdriver and slide out the wire. I just swapped the position of the wires and they slid back in. Reconnected the plugs, which only fit one way and lock in, and then reattached the drivers at the same polarity that's marked on the drivers.

Setup the monitors again and they sound exactly the same as when I was doing the easy fix of reversing polarity on one speaker cable. I did the phase tests again (100 Hz and 6 kHz reference rendered test tones) using Reaper and these monitors are indicating they are now in phase with each other, both the tweeters and woofers.

I might take a look at the PC board of the speaker that has the "Positive Phase" sticker to see if the driver wires are connected the way I just changed the wiring for this monitor.

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Old 07-16-2019, 09:30 AM   #36
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Oh, swapped the wires in the molex connectors. That works and was probably the easiest option out of your choices.
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Old 07-16-2019, 02:29 PM   #37
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It's probably a result of the XLR pin 2/3 polarity problem. Years ago, the standard was different in the US vs Europe. Wasn't a big problem, as long as everything is connected to one mixer. But if you use different preamps, it can be a pita.

Probably someone complained the XLR on these speakers was wired wrong. Probably someone with a second pair of monitors, or a sub. And reversing polarity in the firmware was the easiest fix for Alesis...

You were just unfortunate to get a swap when the new firmware came out. I wouldn't blame Sweetwater, as it is an unlikely problem. Besides, I've seen it in passive speakers too...
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Old 07-16-2019, 03:42 PM   #38
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Yes, an extremely unlikely problem. Good final result though.
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Old 07-18-2019, 04:30 PM   #39
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I just took a look at the PC board and molex connectors of the other monitor that was not indicating it was out of phase with the test tone reference wave form.

The two monitors were wired exactly the same at the PC board connection.

The manual says this about the "Flat" setting: "How is the Prolinear DSP's frequency response set at the factory? The response is set to be as flat as possible, typically +/- 1.5 db from 50Hz to 20kHz with advanced bass compensation."

So that means even the Flat setting is not bypassing DSP?

And if the DSP is always in use and differs between the two monitors, given they have different firmware versions (1.10 and 1.20), it's possible the out-of-phase relationship is caused by some difference in programming.

Or, it's possibly how the XLR/TRS female jack for the speaker cable was wired is not the same. Those are Neutrik connectors, and I think it's going to be a pain to get to that.
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Old 07-19-2019, 03:06 PM   #40
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The DSP is used to pull the frequency graph to a straight line. So, yes, that would mean it's always in the signal path.

I couldn't find anything about an "off" or "bypass DSP" switch in the software. Of course, not having the monitors and not spending hours on it, makes this a bit uncertain.
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