Why don't internal speakers distort CRT screens?

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Offline thedoc

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Why don't internal speakers distort CRT screens?
« on: 20/07/2012 17:30:01 »
Govindarajan Rajagopal  asked the Naked Scientists:
Hi Chris,

First for all I thank God for luckily seeing this Naked Scientist website.

My name is Govind. I am an Indian.

I am a guy who likes these kind of things. My parents and relatives tell me that, during my childhood (as well as now) I asked lots and lots of science questions which are difficult to answer.

W.R.T http://www.thenakedscientists.com/HTML/content/kitchenscience/nature/exp/magnets-and-tvs/

I read the explanation given in the above link about the effect of magnet over the screen.

But my doubt is that, normally CRT TV will have a magnetic speakers on either side of the screen.  Why, in this case, doesn't the magnet cause any distortion in the monitor?

Eagerly waiting for the explanation Chris.

Thanks and regards

What do you think?
« Last Edit: 20/07/2012 17:30:01 by _system »


Offline chris

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Re: Why don't internal speakers distort CRT screens?
« Reply #1 on: 20/07/2012 21:58:41 »
Good question; and I think the answer is that the screens are calibrated to compensate for the permanent magnets in the speakers in the same way that they are calibrated to compensate for the Earth's own magnetic field; if you want to prove this to yourself, turn your TV upside down and take a look at the picture...
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Offline Geezer

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Re: Why don't internal speakers distort CRT screens?
« Reply #2 on: 21/07/2012 19:22:20 »
The fields produced by magnets are fairly localized - their fields tend to "short circuit". Because of that, a magnet has to be positioned quite close to the electron beam in a CRT to produce deflection. On the other hand, the Earth is like a whopping great magnet, and even though its field intensity is not all that great, it is inescapable, and has to be taken into account when aligning colour CRT shadowmasks.

You can observe this with a compass. The compass has to be quite close to a magnet before it deviates from magnetic North.
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