HD Theater 500 phase

[StealthESW]

I purchased a HD Theater 500 and I have it connected to a Denon AVR-790. When using the auto setup the Denon says the Center channel is out of phase. I have checked the speaker wires and I have the correct polarity. The out of phase error follows the center speaker no matter where it is plugged in. I have replaced the center speaker and the new one has the same error. I contacted Klipsch Support. The first time I was told to replace the speaker, so I did. I called them again after getting the replacement and now they tell me the speaker was designed to be out of phase.

Is there anyone out there that could explain to me if the speaker should be out of phase or not? If it is, what is the benefit of the speaker being out of phase?

[*-)]

[Professor Thump]

There are two terms I want to clarify. Phase is the reference of one time signature vs another. We usually think of phase in terms of sign wave signals normally because it is easier to describe. Sign waves cycle 360 degrees of angle. At 180 degrees the two signals are opposite and cancel. This term would be considered Out Of Polarity (OOP) at 180 degrees.

It is the Labor Day weekend so I am out of the office but there are two scenarios that I can think of.

1. The tweeter is out of Polarity. This is some times the case in two way designs because this tends to allow the crossover to mesh more smoothly in the frequency response, especially if there is a single pole filter on one driver in the system. What most people don't realize is that the phase usually revolves several if not MANY cycles from 20-20 kHz. The tweeter might be out of polarity but it is In Phase. If your receiver is correlating phase at a higher frequency such as 3 kHz it will define the speaker to be OOP.

2. The woofer or the center speaker system is out of phase. This could be an error in the assembly of the speaker. You can fix the system buy wiring the speaker out of phase. If you disconnect the center speaker cable from the receiver and connect a AA battery to the speaker cable the woofer should move out, away from the cabinet. We normally use a 9V battery but that may be too large for the woofer and burn the coil. If the woofer does move out the polarity is correct for this speaker.

Do the vocals (dialog) sound good when playing via the center? If so it may be okay.

Monday I can check to see what the design intent was. (I didn't design this system)

...On a side note. When the manufacturer is checking phase they are usually incorrectly stating what they are checking. Normally they are inferring Polarity instead of Phase. It all depends on the reference signal and how they test.

If you have two speakers the same distance from you and you are checking phase, if you move one speaker back 6 inches while checking with a 1 kHz tone you have moved the correlative phase between the speakers 180 degrees. The speakers are canceling the tone on axis, so the only sound you hear is indirect reflections in the room.

Do the vocals (dialog) sound good when playing via the center? If so it may be okay.

If the image is center then the polarity is In Polarity. If the image is skewed and to the sides of the room (phantom image) the polarity is Out Of Polarity or Reversed Polarity.

I hope this helps.

[StealthESW]

Thank you for your reply.

I tried the battery test. Unfortunatly, the design of the speakers will not allow them to be tested that way. It appears that the battery charges the speaker like a capacitor is in the cabinet. I do hear a click when I touch the wire to the battery, but there is not enough movement from the speaker to tell if it is moving in or out. I can then measure 1.5 volts across the speaker wire. It does not dump the voltage as expected from a capacitor. Instead it slowly releases the voltage across the meter.

Please, let me know if the speaker is designed to be out of phase. It was explained to me the speaker should be in phase by one tech and should not be by another. So as you could imagine, I am a bit confused.

I do know that the center speaker has one tweeter and two woofers. I don't know if that matters in the way the speaker would be detected by the microphone conected to the receiver.

I think it is odd that I would get two speakers with the same problem.

Thanks.

[Andy W]

As mentioned by Mark there could be more than one thing going on, and since I don't know what test method is used by the receiver, I can't say exactly what the problem might by.

There is phase and then there is polarity. Phase can be anywhere from zero to 360 degrees (technically it could be more, e.g. delay, but in the steady state, meaning a continuous sine tone, we just talk about phase from zer to 360 degrees). Polarity is either zero (in phase) or 180 (out of phase).

All of the speakers are checked at the factory for polarity, and it would probably take three or more process failures to yield a speaker that has reversed polarity. However if the tests on the assembly line is set up incorrectly then everything coming off the line would be wrong, so yes as Mark said, we'll check with the acoustic engineer on this particular issue.

Some receiver have a digital delay in the DSP that can compensate for distance variations in the placement of the loudspeakers. If the center channel and left and right speakers are all on the same plane (straight line on a enterainment center for example) the center speaker will be closer to the listener than either the left or the right. For all of the speakers to be the same distance from the listener they would have to be place on the arc of a circle. This affects relative phase between the speakers, and it affects time of arrival.

In the straight line scenario, the sound from the center channel will arrive to the listeners ear ahead of the left and right (assuming the listener is sitting in front of the center speaker). Some receivers have the ability to delay the center speaker in order to compensate for this, since it's not always possible or aesthetically pleasing to move the left and right speakers out into the room. However either method will compesate for the early arrival of the center channel sound (or late arrival of the left and right depending on your point of reference). The DSP however can only delay sound... it can't advance it.

The amount of relative phase shift between the center and left and right speakers depends on the distance between the speakers, the distance to the listener and the frequency (low frequencies will have less relative phase shift that high frequencies)... but if you compensate for the difference in the distance to the listener the rest will take care of itself.

But if in fact your reveiver is checking for absolute polarity (it would usually do this with a clicking sound rather that a continuous tone) and not just relative phase, I would be interested to know that too.

You are correct that there is a capacitor in the crossover network and this will limit your ability to check polarity with the battery test. Also since the center channel has two woofers the crossover network might be slightly different (again we'll check with the engineer) and might affect a pulsed signal differently enough to confuse the receiver.

If the entire speaker is reverse polarity, swapping the speaker wires will fix it. If the just the woofer or tweeter was wired out of phase then it won't.

[Andy W]

If the image is center then the polarity is In Polarity. If the image is skewed and to the sides of the room (phantom image) the polarity is Out Of Polarity or Reversed Polarity.

This is a good point.

[Professor Thump]

You are correct that there is a capacitor in the crossover network and this will limit your ability to check polarity with the battery test. Also since the center channel has two woofers the crossover network might be slightly different (again we'll check with the engineer) and might affect a pulsed signal differently enough to confuse the receiver.

If the entire speaker is reverse polarity, swapping the speaker wires will fix it. If the just the woofer or tweeter was wired out of phase then it won't.

Ah yes... I forgot about the cap on the woofer even. I am not use to designing such small speakers. Well... unless they are real small and go in your ear.

[Trey Cannon]

The center and sats are all built with the positive input going to the positive lead on the woofer /s. All the tweeters are in polarity with the woofer.My guess is that you are relying on the receiver to much. I am not a big fan of the measurements made by receivers.The one way to know for sure it the center is wired wrong inside is to take it apart. 8 screws and look. My guess is that it is not. The connectors on the wires from the network to the woofers are different sizes. There is not much chance of putting them in the wrong place. The tweeter has the same size connectors. It could be wired wrong. But if it were wrong, the speaker should not have passed end of line testing.

Here are some pictures I took. Sorry that they are not so good, but you can see the size difference in the connectors.

HDT500sat.pdf

[StealthESW]

The receiver tests the speakers with a clicking sound. I did reverse the wires and the speaker does test in phase. I don't see any screws on the speaker.

So far it looks like maybe the speakers were assembled with the polarity reversed?

Please, let me know if you guys can find any other info on my issue.

[colterphoto1]

The ultimate test : "Do the vocals (dialog) sound good when playing via the center? If so it may be okay." - P Thump.

Michael

[StealthESW]

Actually, the center speaker sounds kind of scattered. The set I had before, the center was more focused. If that makes any sense to anyone.

[StealthESW]

The center and sats are all built with the positive input going to the positive lead on the woofer /s. All the tweeters are in polarity with the woofer.My guess is that you are relying on the receiver to much. I am not a big fan of the measurements made by receivers.The one way to know for sure it the center is wired wrong inside is to take it apart. 8 screws and look. My guess is that it is not. The connectors on the wires from the network to the woofers are different sizes. There is not much chance of putting them in the wrong place. The tweeter has the same size connectors. It could be wired wrong. But if it were wrong, the speaker should not have passed end of line testing.

Here are some pictures I took. Sorry that they are not so good, but you can see the size difference in the connectors.

I don't see how to get the rubber plugs out of the speaker without causing damage to them. Also, I do not want to void my warranty on the set. The information you guys have given me so far has been very helpful.

If you have any tips to get the plugs out and sure that this would not void my warranty please let me know.

I see that the speakers would most likely be wired correctly. However could the wires connecting to the rear terminals be in the wrong place. Your picture does not show that connection. Also, would the tweeter, if wired wrong cause the speaker to be out of phase?

[StealthESW]

I looked at the speaker again and I still can't figure out a way to get the thing open. Any info?

[*-)]