Mains cancelling surrounds?

[ned]

When I turn off my mains, the surrounds are much clearer and distinct. It seems like the mains are canceling my surrounds. Is this a speaker placement issue?

 

[TLS Guy]

When I turn off my mains, the surrounds are much clearer and distinct. It seems like the mains are canceling my surrounds. Is this a speaker placement issue?

Under what conditions, and with what program are doing this test?

 

[Exit]

The surrounds often carry the same information as the mains but delayed in time so they produce a spatial effect (echoes). So if you turn the mains off you would only hear the original content of the surrounds. When the system is operating normally you hear the mains first, which your ears and mind interpret as coming from the mains, like intended. Sometimes you just get a sense of spaciousness from the surrounds and that is fairly common. Sometimes you do get a special effect that comes out the surrounds but that is maybe five percent of the movie time in normal movies.

 

[jcPanny]

Speaker setup

Ned,
Nice system. It would be worth while to get the Avia or DVE calibration disc and an SPL meter to help verify that you speakers are all configured with the correct level, distance, size, etc. Some THX discs like Star Wars, Cars, ect. also have a simplified calibration function.

 

[jonnythan]

It's entirely possible you have one or both surrounds wired out-of-phase with the front speakers.

Check the red/black connections.

 

[ned]

It's entirely possible you have one or both surrounds wired out-of-phase with the front speakers.

Check the red/black connections.

The speakers have been calibrated by AVia using SPL meter. No, it's not out of phase or incorrect wiring either.

I was listening to dolby Tru HD demo from CES 08. When I turn off the mains I could hear the vivid clarity of the right and left surrounds each producing different instruments source.

When I turned on the mains I could hardly hear this.

 

[TLS Guy]

The speakers have been calibrated by AVia using SPL meter. No, it's not out of phase or incorrect wiring either.

I was listening to dolby Tru HD demo from CES 08. When I turn off the mains I could hear the vivid clarity of the right and left surrounds each producing different instruments source.

When I turned on the mains I could hardly hear this.

You are not supposed to hear the surrounds!

 

[ned]

You are not supposed to hear the surrounds!

huh! please explain.

 

[TLS Guy]

huh! please explain.

For most program material the surrounds are just reproducing the ambient field, which you should not be aware of. You will only hear the surrounds if you listen to a program of antiphonal music recorded in a discrete multi channel format.

You will also hear the sounds in a movie with a discrete multi channel audio format, when there is a scene, or effects that involve the surround channels. I have noted that Hollywood makes very little demands on the surrounds as a rule. I guess they have realized the vast majority of surround speakers are rather miserable examples of the art of loudspeaker design. Some foreign films are a different matter.

 

[jonnythan]

Yeah, but turning the surrounds on shouldn't make the mains sound significantly worse.

My money is still on one of the surround speakers being wired out of phase. It's real easy to overlook some speaker wire plugged in backwards at one end.

 

[TLS Guy]

Yeah, but turning the surrounds on shouldn't make the mains sound significantly worse.

My money is still on one of the surround speakers being wired out of phase. It's real easy to overlook some speaker wire plugged in backwards at one end.

I don't see where Ned says that. He just says he can hear his surrounds clearly when he turns off his mains and can't hear his surrounds when his mains are on. That is what one would expect.

 

[jonnythan]

Sorry, had it backwards. Turning on the mains shouldn't cancel out the sound from the surrounds.

 

[TLS Guy]

Sorry, had it backwards. Turning on the mains shouldn't cancel out the sound from the surrounds.

In a properly set up system, you should not be aware of the surrounds, unless there is program from the direction of the surrounds. If you are aware of the surrounds, that is a set up error.

 

[jonnythan]

I think that's something of a semantic argument.

 

[TLS Guy]

I think that's something of a semantic argument.

I beg to differ. I'm listening to my rig now and I'm not aware of the surrounds or center backs. For most program that is the way it should be. If I started being aware of the speakers creating the ambient field, I would recalibrate, and trace the problem. I don't see what is a semantic argument about that.

Ned was worried he was not aware of his surrounds, when his mains are playing. That is as it should be. He needs to leave his rig alone and enjoy it!

 

[jcPanny]

Receiver mode

Try this receiver/pre-amp configuration:

For listening to music, use 2 channel or 2.1 mode.

For watching movies, use 5.1 or 7.1 surround sound.

If is quite possible that your speakers would sound worse listening to music in a 7-channel stereo or Dolby PLII mode then in 2 channel mode. There is no need to "corrupt" the souce material with DSP processing.

 

[Jack Hammer]

Another possibility is the OP's system may be underpowered, I didn't see any mention of what was being used to drive those speakers. Maybe the fronts are using up all the power. Something to consider.

It's also my understanding that speakers that have the +/- wires correct can still be out of phase due to room/setup variations. A test disc, or the audio setup portion on most THX dvd's, will offer a phasing test to help determine that.

Jack

 

[TLS Guy]

Another possibility is the OP's system may be underpowered, I didn't see any mention of what was being used to drive those speakers. Maybe the fronts are using up all the power. Something to consider.

It's also my understanding that speakers that have the +/- wires correct can still be out of phase due to room/setup variations. A test disc, or the audio setup portion on most THX dvd's, will offer a phasing test to help determine that.

Jack

I think this issue of phase is an interesting topic, and in terms of speakers for surround misunderstood.

We have already had members say that when testing with the disc you mention, state that they get an out of phase error, even though the speakers are wired correctly, and they wonder if their speakers are faulty.

So how does this happen. Unfortunately easily. Lets take a two way speaker, with second order low and high pass filters. In many of those the crossover puts the two drivers 180 degrees out of phase at crossover. Therefore to avoid a null at crossover the tweeter is wired out of phase.

Now for each order in a crossover, the bass driver lags 45 degrees and the tweeter leads 45 degrees. Now the drivers have phase changes of their own, so the actual phase of tweeters, woofers and filters is all over the map.

So I think you can see that any combination is possible. Now when drivers have phase angles 125 degrees to 225 degrees apart, then there will be significant cancellation, maximal when the phase error is 180 degrees.

I think this is a big part of matching mains and centers. There the phase has to match precisely. When you get into surrounds the witches brew continues. So really for optimal results the speakers have to have the same designer who designs all the speakers to work together in a coherent fashion.

You won't solve it by reversing speaker connections usually, just change the phase cancellation form woofer to tweeter and vice versa.

You know I'm a huge fan of people designing and building their own speakers, this is just another reason why. I know this probably sounds of the wall to most, but I really believe all true enthusiasts should learn the art, especially in this multichannel era.

 

[Exit]

My YAPO (built in receiver auto calibration) tells you when you get a speaker out of phase. Don't most receivers have something equivalent nowadays. If not don't the test disks run some kind of check. If he says he has the phase correct I have to believe one of the top two methods were probably used.

YAPO also set the speaker's distance from the listening area and the relative volumes from each speaker. I would have to assume that this has also been performed correctly.

I don't think there is a setup error, but rather the normal functioning of the surround sound system like I mentioned before. I think the systems ok and it is time to listen to it more. Try some Star Wars movies. There should be some use of the surrounds for fly by sound effects in those. Once you hear the surrounds putting out special effects you can rest assured the system is working ok.

 

[Jack Hammer]

...If he says he has the phase correct I have to believe one of the top two methods were probably used...

...I would have to assume that this has also been performed correctly...

Whereas you may be right, the process of elimination says we need to clarify that he actually did use a test discs phase check. All we have to go on his statement,

"No, it's not out of phase or incorrect wiring either."​

How was that determined, by looking at the wire colors or by using a test disc?

It could still be an amplification, or lack of issue. Ned, what are you using to power the speakers?

Jack