Help! my center speaker is distorting my display!

bently

Grip
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Jun 19, 2001
Messages
22
yesterday(3/30/03), i upgraded my mirage frx center to a mirage omni cc center channel speaker. and it was causing some distortion on my 36" sony xbr direct view display (36xbr450).

when i increase the volume to around 80 to 90 db, i would see some wavy lines from the upper portion on my screen and would gradualy diapear as it reaches the center portion of the screen, much like a water ripple effect.

i did not have this problem when i was cranking my mirage frx center to the same db level.

to make sure that it was the omni cc that was causing this distortion, i played the same scene again from the dvd but i raised the omni cc a foot above from the top of the TV, and the ripple effect disappeared.

anyone know the reason why it's causing this distortion and probably suggest a solution.

thanks
bently
 

Scott Merryfield

Senior HTF Member
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Dec 16, 1998
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It sounds like your new center speaker is not properly magnetically shielded. If this speaker is specifically designed as a center channel, it should be properly shielded, which means your unit may be defective.
 

bently

Grip
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Jun 19, 2001
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i just spoke with customer service of mirage speakers and they said that their engineers are kinda buffled by this.
but they are guessing that power on the crossover maybe generating magnetic fields.

some how this seems logical since there is no distortion when i have the center channel in low volume, and the distortion only appears when i have the volume cranked up to about 85 to 90 db.

anyway i'll try a new speaker and see if this is an isolated problem, but if it happens again...then theres a problem with their design.
 

Dennis Gardner

Stunt Coordinator
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Dec 12, 2002
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The reason may be your upgrade, I suppose you are getting more bass than before. My 35 inch Sony does the same jumping at volume and I have read on other sites that a number of Sonys exhibit these traits. When at volume, lift the center speaker just off the surface of your monitor to see if it subsides, if it does, vibration is the cause. Put a soft cloth or felt under the center channel speaker to insulate the vibes going through your tube. It allowed me to get another 10db in volume, extending it to around reference levels without the interference.

This happened when I upgraded from a small Polk center tha housed 2 3 inch mids to the 350Ls with 4 mids and more bass extension.


Dennis
 

Doug_B

Screenwriter
Joined
Feb 11, 2001
Messages
1,081
I had this same problem with my center ch speaker when I had my TV with the speaker on top. First noticed it while playing U-571 and then noticed it more frequently with other loud material. It was a vibration-oriented disturbance in the top 1/3 of my display. Even before I ditched the TV, I moved the speaker onto a stand. 65 lb speakers don't belong on top of TVs anyway
.

Doug
 

bently

Grip
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Jun 19, 2001
Messages
22
okay i took a big towel, folded it to give enough cushion between the speaker and the TV but the ripple was still there.
so i lifted the speaker from the TV to about an inch or two so there would be no physical contact, but the ripple or distortion was still present.
so tomorrow, i'll be bringing the speaker back, so we can try it on their sony xbr demo and see if it has the same effect. and if it does then we will try another speaker (same model), if it will do the same...

i'll post the test result tomorrow

thanks for the replies

bently
 

bently

Grip
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Jun 19, 2001
Messages
22
well i returned the speaker and they just gave me another one to try out but the same thing happened.

so it is a design problem.

now i have to look for an alternative center that would match my omni 250 fronts.

i would like to stick with the omnipolar technology so my options is either to a lower model and go with an omnisat or go to a model higher and get the om-c2.
 

Brian L

Premium
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Jul 8, 1998
Messages
3,131
I agree with the other posters that this is vibration related. Had the exact same problem with a Klipsch center.

I called their tech support (great people to talk with, BTW) and they confirmed that the speaker did have the correct bucking magnets (that is what does the "shielding, BTW). He tipped me off to the vibration thing. In my case, even lifting it a few inches off the top of the set did not eliminate the distortion.

You may just need to come up with a better way to isolate the TV from the speaker. I ended up with three large stick-on rubber feet (no voo-doo stuff, just Sears hardware store).

Of course, not all speakers are the same, Yours may have something in its design that makes vibration isolation difficult.

Good Luck.

BGL
 

Rich Malloy

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Apr 9, 2000
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Brently, is it possible in your setup to place the center speaker on a stand below and infront of your screen? If so, place it on something temporary to see if it still causes magnetic interference. If not, then I'd recommend you do this for many reasons in addition to preventing the present problem. TVs are not intended to be "speaker stands". They are large, highly resonant boxes that diminish the sound quality. Do this before considering alternate (and likely unmatching) speakers.
 

Mike Sloan

Second Unit
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May 18, 2002
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456
I don't think it is caused by vibration. When you turn up the volume you are increasing the magnetic field from the "improperly" shielded speaker. You could build a stand for it that would lift the speaker a few inches off the TV.....I have the same problem.
 

bently

Grip
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Jun 19, 2001
Messages
22
well heres an email from mirages customer service

Bently, after sitting down with our x-over design engineer he explained what is happening:

As electrical current travels through the coil in the x-over it becomes magnetized. As the volume goes up, so does the electrical energy and magnetic field. The magnetism created is negligible and in all on TV tests that have been performed here, not one speaker, not even engineering samples in pre test phases have ever created enough magnetism to gauss a television set (over the last 10 years). This includes some of our Energy Veritas line of speakers that have a much more complex x-over network with many more coils. They strongly believe that it has to so with the sensitivity to magnetism of your particular TV set- the x-over is acting within its intended parameters.

The OmniCC has the x-over network mounted on the bottom of the unit and therefore exposes the small magnetic field to the television set. The FRX-C has its crossover mounted higher up on the speaker and does not cause a problem.

I have a couple of options that I would like to discuss:

1/ We send you a pair of MacroMount bracket- free of charge and you can mount the center channel on the wall
2/ You either downgrade to an Omnisat or Upgrade to an OM-C2. Our engineer doesn't believe that the Omnisat or OM-C2 will create a magnetic field as strong as the OmniCC and cause problems with your sensitive TV Set.
3/ We investigate if we can have the speaker modified for your particular application- ie the x-over is moved in the enclosure...I don't think that this will work in your application because the OMNICC has few options for x-over positioning.

Please advise on how you would like to proceed.


i must say that i'm impressed on how fast they answer their emails...any way i opted for option#1 since i do not want to place the center on the floor since i have a very energetic 5 yr old kid.
 

Doug_B

Screenwriter
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Feb 11, 2001
Messages
1,081
Or you could mount the speaker on a stand in front of the TV per Rich's suggestion and use Option 1 on your 5 yr old
.

Seriously, I wonder if there is enough magnetic force with the high volume mode to attract a small, light piece of metal. May be worth a try as a means of lending add'l credence to Mirage's suspicions and decreasing the probability that it's vibration-related.

Doug
 

Rich Malloy

Senior HTF Member
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Apr 9, 2000
Messages
3,998
Mounting a speaker flush to the wall can diminish imaging and boost bass response... in other words, it might sound muddy and boomy.

No chance of putting that puppy on a stand, huh? Such a nice speaker... seems a shame not to!
 

bently

Grip
Joined
Jun 19, 2001
Messages
22
Well out of curiosity, i went and got the top of the line omni-c2. this is a really big center channel speaker thats 2ft across and 12 inch deep

i placed the omni-c2 om top of my 36" tv and fired it up.
i used the same dvd scene to test out the center channel w/c is a scene from pixar's award winning short film: "For The Birds"...but unfortunately the same ripple effect came on my screen every time the big ugly bird would sqwack!


so i guess my only option is to either wall mount my center channel or just place it under the tv.
 

Brian L

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Jul 8, 1998
Messages
3,131
I don't think it is caused by vibration. When you turn up the volume you are increasing the magnetic field from the "improperly" shielded speaker. You could build a stand for it that would lift the speaker a few inches off the TV.....I have the same problem.
Well, I guess it could go either way, but when I had the problem, the problem did not exist at low volume, but when cranked it did.

While I agree you are increasing the electrical signal, which could lead to magnetic distortion, you are also cranking the drivers and causing more vibration.

When I fought the problem, the scene I used to test was the trailer for Disney's Dinosaur that is on Tarzan. The climatic scene in the trailer would do it every time (when cranked). Once I put the rubber feet under the speaker, problem solved.

Methinks its vibration, but the proof will be in the pudding.

Brian
 

ChrisAG

Supporting Actor
Joined
Aug 26, 2001
Messages
503
I had the same problem with two Mordaunt-Short centre channels. At first I thought they were improperly shielded, but it is more likely sound vibration. I don't mean "vibrating drivers" that transfer by contact to the TV, but rather the relatively powerful sound vibrations that travel through the air when you crank it up. This would explain why the TV still has the ripples when you lift the speaker up a couple of inches. The same result is seen in your computer monitor if you rap it on the side - try it.

When I changed TV stands the centre speaker was moved to a separate shelf under the TV. Not the easiest solution for those without such a stand, I realize.
 

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