OT: Speakers vs TV Monitor...?

Jay Gladwell wrote on 12/21/2006, 9:12 AM

Can shielded speakers still cause problems with a monitor's images? I was under the impression that the shielding prevented any interference with the monitor's image.

If not, just how close can you place such speakers to a monitor?

The reason I ask is because the apparent problem I was having with my new monitor (the technician swears there's nothing wrong with it) is due to the placement of the two speakers (Fostex 6301B) I'm using.

Any information/suggestions would be welcomed.


Comments

Billy d wrote on 12/21/2006, 10:56 AM
In general anything that has a varying voltage creates an EMF (Electro Magnetic Field).
Devices such as Loudspeakers and CRT's have lots of wires wound into coils and have quite high amounts of varying voltage/current running through them. They therefore develop large EMF's in the space surrounding them.
I believe the intensity of the EMF falls off as the square of the distance, just like light (which is an EMF). (not sure about the square bit, may be cube of distance - whatever - it's not linear)
And just as you can shield yourself from light so too with the much lower frequencies involved with loudspeakers. However these lower frequencies are more difficult to shield because they do things like going round corners and through things.
So although you have "shielded" loudspeakers the shielding is not perfect and (remembering the square of the distance thing), you should place your speakers as far away as practical from your monitor.
How close can you place them? As close as the point at which they start to screw up the picture on your monitor, then back off a bit.
farss wrote on 12/21/2006, 12:38 PM
Only CRT monitors, LCDs are quite immune.
The very best magnetic shielding comes from Mumetal, haven't a clue as to its actual composition but back yonks ago when we used fully magnetically shielded CRT monitors that shielding doubled the price of the monitor. I doubt monitor speakers use anything that expensive, I think they make some effort at keeping the magnetic circuits fully closed to minimise leakage.
How close can they go, just watch the monitor / TV, once you see purity errors they're too close.

Bob.
Billy d wrote on 12/21/2006, 3:31 PM
Mumetal is a laminate of several layers of metal one of which was copper (I think).
It was used over the top of the erase, record, and play heads of pro tape recorders back in the 60's. By Ampex anyway.
Pretty expensive stuff as you say.
busterkeaton wrote on 12/21/2006, 3:35 PM
The first experiment to try to plug the monitor away from the speakers and then move it closer and closer to the speakers and see what happens. If possible with just the monitor and speakers nothing else around.

What is the apparent problem you are having.

The first thing I thought of was not the speakers themselves, but your cables. Piles of cables can sometimes generate a lot buzz or noise. If you find you are having noise, trying laying the cables perpendicular to each other (I believe that's right) which should lower the EMF field.
craftech wrote on 12/21/2006, 7:20 PM
Jay,

The last time I posted regarding the problem with your monitor I said:

"Sounds like either the tube degause cirt is faulty or you have another appliance close to the display. Sometimes changing the position of the display will cure this. Techs often use a strong magnet to degauss the tube, but I would send it to the closest authorized factory service center ASAP."

You said that the tech could find nothing wrong meaning (I assume) he didn't see the blotches and uneven image you saw at home......is that correct?

If they were an official JVC authorized factory service center, they would have kept it longer (in my opinion) if they found nothing wrong. There are regional techs that make the rounds to the JVC factory service centers every week to verify that "nothing is wrong".

If in fact nothing IS wrong then said interference can come from anything that produces a strong magnetic field or RF.Those speakers are shielded and as such they should not be exhibiting enough of a field to cause that much distress with your monitor. Unless, of course there is something wrong with them.
A computer and especially a cable modem certainly will cause a problem, but that usually exhibits itself as video noise or herringbone patterns.

Hook the monitor up at a neighbor's house and try it. If I had to guess, I would say the "tech" is full of it and there is probably something actually wrong with the monitor. Of course, you probably should also give more details as to what transpired. It's a little vague.

John
Jay Gladwell wrote on 12/21/2006, 8:18 PM

Well, John, all I can tell you is that I got the shop from JVC's site. They were listed as a "Preferred Service Center." They had it since Monday. Hopefully, I can pick it up on Friday.

I asked the guy to try a few more tests, because I didn't want to drive 100 miles round-trip to find the same problem.

I don't know what else to tell you. I'm not trying to be vague.


farss wrote on 12/22/2006, 4:26 AM
But what is the problem?
Areas with offset colors, aka purity errors?

Magnetic fields are the most likely cause, if not the only cause. But it could be anything, I've had it caused by the mains feeds running under an office, metal furniture that's become magnetised.
Best test is to try moving the monitor elsewhere and see what happens.
craftech wrote on 12/22/2006, 4:34 AM
Well, John, all I can tell you is that I got the shop from JVC's site. They were listed as a "Preferred Service Center." They had it since Monday. Hopefully, I can pick it up on Friday.

I asked the guy to try a few more tests, because I didn't want to drive 100 miles round-trip to find the same problem.

I don't know what else to tell you. I'm not trying to be vague.
============
Jay,


When you go to pick it up tell him you want to see it working before you take it home.


When you get it back try it at a neighbor's house or a different location in your house and if the problem still exists ship it to a FACTORY service center. That is where I brought mine. I drove about the same distance, but if it were a "preferred" service center I wouldn't have taken it there. I would only send it to a place that services only JVC. I am sorry you are having so much trouble with the monitor. If you get it working properly I am sure you will really like it.

But please, have the tech show you the unit working properly before you accept it.

John
Jay Gladwell wrote on 12/22/2006, 5:42 AM

John, where do I go to find a FACTORY service center?


craftech wrote on 12/22/2006, 9:09 PM
John, where do I go to find a FACTORY service center?

===========
The nearest of these to you.

16 Chapin Road, Suite 910
Pinebrook, NJ 07058
(800) 582-5825

705 Enterprise St
Aurora, IL 60504
(800) 582-5825

1500 Lakes Parkway
Lawrenceville, GA 30043
(800) 582-5825

5665 Corporate Avenue
Cypress, CA 90630
(800) 582-5825



John
John_Cline wrote on 12/23/2006, 8:59 AM
The shielding on shielded speakers generally prevents the magnetic energy from the speaker magnets from "leaking" out the sides of the speaker. The back of the speaker is a little less protected than the sides but the front is always difficult to fully shield. You can usually place the speakers directly to the side of a video or computer monitor. If you place the speakers further back, the magnetic energy coming from the speaker magnet out the front of the speaker will mess with your CRT monitor.

John
craftech wrote on 1/9/2007, 5:18 AM
Jay,

How did you make out with the monitor problem??

John
Grazie wrote on 1/9/2007, 5:31 AM
Yes, Jay-man? Any good?
Jay Gladwell wrote on 1/9/2007, 6:34 AM

I'm still wrangling with JVC to get this taken care of.