Receiver tells me newly constructed center speaker is out of phase

[ct991]

I recently ran the auto setup on my Yamaha receiver and it told me that my center speaker was plugged in backwards (ie. out of phase). I just finished building the center and designed the crossover myself. It's a 3-way WMTMW design and the the mids are wired out of phase (as with mostly any 3-way) to avoid the large null in the response.

I reversed the connection to the receiver (+ to -) and the receiver seems to like it. However, I'm not convinced. How exactly is it determining that it's out of phase? Is it just basing it the mid frequencies? Also, since my crossover was designed to be wired one way, if I reverse the + and - inputs to the crossover, will this cause any issue with the functionality of the crossover?

Attached is the crossover schematic for reference (...and I'm using a Vifa XT25 instead of a Dayton RS28A).

[augerpro]

It determines the phase when you do the auto setup. Yamaha's are bad in determining this I've read. You could just set it up manually.

[cjd]

Phase can't be told by looking at the schematic.

A loudspeaker operates on an A/C signal, so there is no polarity that is important as far as safety, but there IS the possibility of needing to swap leads if the phase of your center doesn't jibe with the phase of your mains. Just like you need to take care with phase between drivers in a single speaker, it holds true for all the speakers in your room.

Only response measurements can tell us whether the speaker itself is in phase. Not really sure your process for designing that, but you used a potentially problematic topology with difficult drivers, and you don't know the answer to this question, which has me vaguely antsy. :P Plus I'm curious.

C

[augerpro]

Phase can't be told by looking at the schematic.

A loudspeaker operates on an A/C signal, so there is no polarity that is important as far as safety, but there IS the possibility of needing to swap leads if the phase of your center doesn't jibe with the phase of your mains. Just like you need to take care with phase between drivers in a single speaker, it holds true for all the speakers in your room.

Only response measurements can tell us whether the speaker itself is in phase. Not really sure your process for designing that, but you used a potentially problematic topology with difficult drivers, and you don't know the answer to this question, which has me vaguely antsy. :P Plus I'm curious.

C

Chris that yamaha does FR in a manner of speaking during the auto setup with a mic. The problem is the Yamaha's are not doing so well in deciding what is in or out phase. I would look at the settings the Auto function comes up with as a reference, since it does account for room modes. But I would do the setup manually. Also make sure it's setting bass management for the speakers properly also, crazy settings can show there too.

[cjd]

Chris that yamaha does FR in a manner of speaking during the auto setup with a mic.

Oh, that part I know about. It was a later comment questioning if thing would work right with a switch of the wires that had me wondering. Then again, I don't remember when I learned there was such a thing as phase. I DID know it was an A/C signal from way back when I was a wee lad and that it didn't matter this way or that how you wired the speaker to the amp.

You can often tell by playing different types of noise, R-L first, R-C and then C-L. In each case you should get some "phantom" imaging between the two being tested. Out of phase will put that out of whack, easily tested by manually wiring two out of phase.

C

[ct991]

I DID know it was an A/C signal from way back when I was a wee lad and that it didn't matter this way or that how you wired the speaker to the amp

That's what I figured but I wanted someone else to confirm that.

[cjd]

Heh. I'm just giving you a hard time. This stuff gets messy some days. Heck, half the time I don't have a clue what I'm doing and just happen to be wearing good pants.

[augerpro]

OP i just reread your post. I think the Yamaha may have been "correct." Depending on how the L&R are wired, the center may have been seen as out of phase with them due to the mid.

Try Chris's trick. You're Yammy should be able generate pink noise, or find a cd or file that does. There should be a good stereo image if the L&R are in phase. If they aren't the image will collapse and it will just sound "wrong" I don't if works well with determining a center channel though, I've never tried it. How did you check a center Chris?

As far as switching the wires at the reciever, it's fine, the XO won't care one way or the other.

[ct991]

but you used a potentially problematic topology with difficult drivers

cjd: Can you elaborate on this? This was basically the first crossover I did from scratch but I thought it was ok (not perfect - but good enough for me for now). I did plan on some tweaking but I'm trying to learn more first and listen to what it sounds like now.

Thanks for the info guys

[Dennis H]

Does your center have a similar XO to the LR? I think (not sure) the receivers determine 'phase' by looking at the initial direction of the impulse response, i.e. they're trying to get the tweeters in phase. That could be a problem with 2-way mains and a 3-way center. What you really need is for the woofers to be in phase because the wavelengths of the woofers are long and they need to combine well. At tweeter frequencies, the wavelengths are short and you won't get the different speakers combining in phase if you're even a few inches off axis so that's less important.

What I do to check phase is set the two speakers facing each other a few inches apart and play a mono signal through them. Swap the wire polarity and whichever way gives you the most bass is the correct way.

[kingpin]

Heh. I'm just giving you a hard time. This stuff gets messy some days. Heck, half the time I don't have a clue what I'm doing and just happen to be wearing good pants.

Uh Oh......... 8O :roflmao: :lol:

[technimac]

Out of Phase?

I use the YPAO auto set-up with my Yammie RX V-1500 and it works very well.
So well, in fact that it once left me with humble pie crumbs all over my chin. :W
After completing my Audax HT MTM quad, I hooked them up and ran the YPAO auto set-up, only to be informed that the left surround was "out of phase".
That's crap, I thought, every one of those crossovers were triple checked during the hook-up. :M
But I was curious and decided later to check the wiring.
So I popped off a driver, checked the XO and sure enough, the positive and negative connections of one of the woofers was switched. 8O
Now that's only one out of two woofers on an MTM, so I think the Yammie YPAO worked pretty well in this case. :T
Once I reconnected them correctly and ran the YPAO auto set-up again, all was OK in the "phase" department.
If I were to "set it up manually", how would I be able to quickly determine that one woofer in an MTM was "out-of-phase"? :huh:

[augerpro]

The level on that speaker would probably have to be higher then the other one. And you should notice the sound difference.

[cjd]

The phase check L-R works L-C and C-R as well - you just have to center yourself between the L and C, so they effectively become L and R (disable or disconnect any other speakers).

cjd: Can you elaborate on this? This was basically the first crossover I did from scratch but I thought it was ok (not perfect - but good enough for me for now). I did plan on some tweaking but I'm trying to learn more first and listen to what it sounds like now.

Well, any horizontal MTM alignment runs into serious trouble off-axis. The higher you cross, the worse it is. Add to that the breakup behavior or the RS drivers, which can sometimes be tricky to deal with (until you figure out HOW and then it's not too bad at all). Without understanding the transfer functions and seeing the net resulting response I can't actually say what kind of issue you'll have. But I find my MTM is only good to 15 or 20 degrees off-axis at best at 2100Hz, which is one of the reasons I pushed it down to 1800 and now recommend that. 4th order acoustic I think it is still. It'll still probably have issues much beyond 20 degrees off-axis, you just can't defeat the physics. And you made it harder on yourself by adding another set of woofers, which may or may not also have issues - depends on their spacing and on their crossover point and slope.

C