Depends how big the magnets are inside the speakers. Three feet would usually be enough. Seldom is it permanent, as the TV will demagnetise itself.
But there are faults in the TV which can cause the symptoms.
It's caused by a magnetised shadowmask, which is an integral part of the cathode ray tube. Situated behind the glass of the tube face, it looks a bit like a oversized shaver foil.
It gets magnetised by the earth's magnetic field all the time but the TV demagnetises itself at switch on. If magnetised, the electrons from each gun (red, green & blue) are deflected onto the wrong color phosphors, causing the colour impurity.
If your loudspeakers magnets are the cause, moving them will usually give an immediate result or at least reduce the effect.
Other things, which can cause uneven magnetic field, are..
1. Moving the position of the TV, (especially when it's on).
2. Large central heating radiators near the TV.
3. Placing TV in a confined area with surrounding stone walls.
4. Using power tools very near the TV.
5. Placing magnets against the face of the TV (a favorite for children as it creats pretty patterns), this can permanently warp or magnetise the shadowmask.
6. If the TV is dropped or such, the shadowmask can become detached or bent, this is very rare but would require tube replacement..ie. writes the TV off.
7. Misaligned tube yoke or deflection magnets.
Most common is failure of a part called a positor, which is part of the TV's automatic degaussing circuit, which activates in the TV at switch on (before the picture appears). They are inexpensive and it's a very simple repair.
Otherwise, if the cause is not a faulty component but due to magnetic field, which you can't eliminate, an engineer can usually clear it by manually degaussing the TV and the area around it.
Cobweb, January 2005
