Speaker Problem or TV Problem? (1 Viewer)

[Brett Hancock]

The problem that I am having is with my Boston CRC center channel speaker. So far this has happened on both tv's that I have had. A 12 year old Mitsubishi and a new 36" sony wega, im not sure about the model numbers. The problem is that whenever there is loud dialog coming from the center channel the picture does this weird thing where lines run throw the top part of the screen, after the dialog is finished it stops. I know thats not the greatest explanation in the world but its the best I could describe it. I mainly noticed this on Shrek when they are walking through the field and it is just Shrek with the sky behind him and he starts yelling about the onions. Also during action movies it is very noticable. I contacted Boston about this problem and they said that they ran tests on my speaker and determined that there is nothing wrong with it and it should work fine. However when I use my dads VR910(also boston) on my tv it does not display this problem. So Boston sent me these little 'feet' to put on the speakers but the problem is still there. This has led me to believe that it is in fact the speaker sense I cant imagine that 2 tv's that are very different would have the same problem. Could this be causing any negative effect to my tv in the long term? Please help if you can, I know the description is vague and odd.

 

[RichN]

Brett,
Sounds like a case of speaker interference. Perhaps your dad's speaker is better shielded than yours, which is why it didn't show up then. Do you have the speaker sitting on top of the TV? If so, move it temporarily to see if the interference goes away. If it does, then you need to see exactly how close you can get it to the TV before the interference comes back, or try to shield the speaker better (others can tell you how to do that better than I can).
RichN

 

[Brett Hancock]

I probably should have mentioned before that I tried it on another tv and it didn't do the problem at all. And its not a problem that shows up when the center channel is just sitting on top of the tv. It is only when there is loud dialog. Could this be a reciever problem, the Sony that I currently have is there lowest prices 5.1 model.

 

[John Garcia]

The obvious question then is, do you have your video signal looped through the receiver? (I'm guessing you do) If so, try going direct to the TV and see if the situation persists, if it goes away, the problem is with the receiver.

 

[Brett Hancock]

I have the dvd player running through a monster s-video cable straight into the tv. I have always had it set up this way.

 

[John Garcia]

Hmmmm....tougher.
Is the receiver in any way hooked to the TV? Disconnect the two completely and see if it still happens.
Does the problem still happen if the center channel is not hooked up or is not used (or moved farther away, as mentioned before)?
If it is shielding, you could try putting a piece of sheetmetal between the two (try a local hardware store).
If you are driving this speaker to distortion with an underpowered receiver, this could somehow be the cause, but I have never seen this before.
Final though, maybe you are pulling too much current for the outlet/circuit you are running all this stuff on?

 

[Brett Hancock]

If the center channel is not hooked up or not in use it doesn't happen. And it only happens in the upper part of the tv because the center channel is on top of the tv. I have tried moving it farther away and the problem goes away but thats when it is like a foot above the tv and obviously that is not going to work for movies. These little feet that Boston sent me raised the height of the speaker and reduced the problem slightly but it was still very noticable on Lord of the Rings and other movies with loud and active scores in the center channel. However when I use another Boston center channel(different model) with everything set up the same way as before it does not display this problem, which leads me to believe that it is in fact a speaker problem. But Boston said that they ran tests and didnt find anything wrong with any part of the speaker, so that is why I am completely out of ideas.

 

[John Garcia]

Try shielding or ask Boston to swap it for a different one to try out. They ran tests, but they didn't necessarily use the same receiver and TV as you. You tried your Dad's center in your setup, but did you try yours in HIS setup? Then you would know for sure that it is not any of your gea, and is the speaker itself.

 

[John F. Palacio]

Try this Brett:

Take your center channel speaker away form the top of the TV and on the floor a couple of feet away form the TV.

Run the DVD's in question and see what happens. This is NOT a magnetic shielding problem. Shielding is to prevent the PERMANENT MAGNET from interfering.

The permanent magnet field is fixed and does not vary with the level fed to the speaker. The electrical field produced by the voice coil is confined inside this magnet and for all practical purposes does not escape to the outside world.

This is most likely acoustical interference.

 

[Johnny Mac]

I had the same exact problem with the CRC center and my Sony TV. They all do it. Even when I was in the Tweeter store looking at subwoofers, the CRC they had on top of a Mits big screen was causing the same type of interference at loud volumes. Lines of horizontal interference at the top of the screen. Got tired of trying to fix it and swapped it for a Polk CS245i and haven't looked back. Boston claimed it was the tv but no other center channel i've owned ever caused that type of interference. The Kortec tweeter is poorly shielded and that's the real problem.

 

[Johnny Mac]

You got me curious again Brett. I called Boston and spoke with one of the reps. He didn't think it was the tweeter but thought it actually might be a problem with the crossover which would back up what John said. It would also explain why the higher priced Lynfield units don't exhibit the same problem. Different crossover. They are going to do some tests with The Patriot and LOTR and get back with me. I'll let you know what I find out. He did say you could try turning it upside down to get the crossover further away from the TV.

 

[John F. Palacio]

A speaker with a well braced and dampened cabinet will produce most of the soundfield from the drivers. A less well designed cabinet that resonates can transfer a lot of energy through the cabinet to the TV set.

That's why I suggested placing the speaker away and not physically touching the set.

 

[John Garcia]

Yes, shielding of the motor structure of the drivers is obviously not the issue, but using some type of shielding between the speaker and TV may solve the issue, since it IS some type of electronic interference. I would guess it is either the specific design of the crossover, or a field generated by one of the inductors when driven hard, especially since it is not an isolated issue.

 

[John F. Palacio]

John Garcia says: "If it is shielding, you could try putting a piece of sheetmetal between the two (try a local hardware store)."

Regular metal will do nothing for magnetic fields. It has to be Mu-metal which is expensive and not available at your corner hardware store.

Put a large magnet against a tin can with nails inside and prove it to yourself!

 

[John Garcia]

Sorry, you'll have to define "regular" metal, as many metals posess some level of ability to inhibit magnetic fields. This obviously varies, depending on the composition of the metal.

I doubt "Mu-metal" is carried in many local stores. While I should have been more specific, I didn't think most people would know what austenitic 16ga. stainless steel was or where to find it.

Put a large magnet against a tin can with nails inside and prove it to yourself!

Sorry, I'm failing to understand this one. "Tin" cans are magnetic, as are some nails. I don't think this really has any relevance, nor does it prove anything, nor would putting a tin can thus equiped, between the speaker and TV, make any difference.

 

[John F. Palacio]

Almost ALL metals are permeable to magnetic fields which means the will PASS MAGNETIC FIELDS.

Mu Metal is specifically formulated to act as a shield for magnetic current. Just about any other metal will not act as a shield.

Tin cans as well as just about ANY OTHER METAL are NOT MAGNETIC per se but can be magnetized if subjected to the influence or in other words placed in the proximity of a strong magnetic field. They can also be demagnetized by being placed in an alternating magnetic field and removed very slowly or the field decreased very slowly.

The nails in the tin can are resting in the bottom of the can. If you place a large magnet on the side of the can you will see the nails being attracted and moving towards the magnet. And what this proves, Mr. Garcia is that the magnetic field of the magnet has gone RIGHT THROUGH the walls of the tin can to attract the nails.

In the exactly the same way the "shield" that you suggested be placed between the speaker and the set will pass whatever magnetic field is present in the speaker.

Therefore accomplishing NOTHING!

 

[John Garcia]

Tin cans as well as just about ANY OTHER METAL are NOT MAGNETIC

Well, that is COMPLETE, and UTTER BS. So if most metal is not magnetic, then I guess someone just decided to make refrigerators magnetic so we can buy funny little magnets to stick to it? Not likely. Magnets don't stick to the steel sheetmetal in your car? Try again.

First off, ANY ferrous metal IS magnetic, period. This is a FACT, not open to debate. Even "nonmagnetic" steel still possesses a degree of magnetic properties because it still contains IRON. I don't need to prove this, it has been known for a few hundred years... I've been working with materials and manufacturing processes for over 15 years, I'm not pulling this stuff out of my thin air.

Well, last night, just for kicks, I stuck a rare earth magnet next to a tin can (Dennison's Chili) and low and behold, it was magnetic. An ALUMINUM can would be a different story... When the magnet is attached to the metal, the metal now maintains it's own field, which would attract the nails regardless of the location of the magnet.

As I said, Mu-metal IS NOT the only metal that will disrupt magnetic fields, so your "theory" is BUNK. In this case, it sounds like what needs to be blocked is an ELECTROMAGNETIC field, not a magnetic one, so MU-metal may or may not work either.

This conversation seems to have degenerated into something less than useful, as it now has little to do with the original question, so I will simply agree to disagree and move on.

 

[Johnny Mac]

I think the question has been answered sufficiently for now. I'll post the Boston engineer's response when they get back with me.

 

[John F. Palacio]

"Well, last night, just for kicks, I stuck a rare earth magnet next to a tin can (Dennison's Chili) and low and behold, it was magnetic"

No it wasn't. It was ATTRACTED TO THE MAGNET!

And placing a piece of sheet metal around a speaker does not magnetically shield it! It will just transmit the magnetism right through.

Study some basic physics for the love of this forum, before you come out with all this nonsensical bable!

 

[Geno]

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