Magnetically shielded against LCD and amp?

[ccsakura]

Hi there everyone it's my first time to come into the technical forum(kept wondering around Home Theater section previous time) . Will the speakers which are not magnetically shielded affect the LCD and reciever or not??? I was wondering about this for long time because the magnetic was mainly dealing with the machines that rely on magnetic field(like CRT's tube). Sorry kinda stupid in physics and mechanics . Thanks in advance

[lynnm]

Unshielded speakers will have no effect on either the receiver or an LCD screen. As you mentioned conventional TV's use magnetic fields in their deflection circuits,( ie. the circuitry that steers the electron beams within the picture tube which cause the phosphorescent pixels to light up an create an image). This circuitry's magnetic fields can interact with the magnetic field radiated by a speaker and create distortion. LCD display technology does not utilise magnetic fields and therefore LCDs are not effected.

I am a computer technician and on occasion have installed LCD monitors for users whose conventional monitors displayed serious video disortion. In one case the cause was an elevator motor.

Initially we were at a loss because we got complaint calls and one or another of us would go the users' workstations and could find no problem let alone a cause. One day one of my collegues rode the elevator up to that floor while I was checking out the ongoing complaint. I had as usual not seen anything out of the ordinary and asked him to come take a look. About 20 seconds before he arrived at my position the monitor in front of me began fluttering and distorting. It was at that point that we figured out that the elevator was the culprit. The offending elevator motor was powering one of the six elevators that stopped on that floor and was the car closest to the work area whose workers were being effected.

[WMcD]

The strong magnets in speakers do mess up a CRT. The electrons (cathode rays) are deflected by magnetic fields. A bucking magnet applied to the magnet on the driver can reduce the fringing of the field and eliminate the problem. Another solution is the use of very permiable iron around the magnet can prevent the field from getting out.

BTW, you might be wondering about the speakers used in CRT based TVs. Obviously, they have been in there, close to the CRT ever since TVs have been made. I saved some speakers from a Sony which died. There are shielding cups over the, admittedly, small magnets. The speakers were the size of tweeters, in my view.

OTOH, liquid crystal display are made up of little cells which can be switched to transmit or absorb light just like the digits on our wrist watches. There are no electrons traveling in a vacuum. Hence they are not effected by magnetic fields.

The magnets in speakers put out a constant field. Therefore the don't modulate anything in receivers, amps, etc.

One other thing is that a CRT can be a problem. The oscillators which sweep the electrons from left to right have high frequency components. They drive magnetic coils in the deflection yoke of the CRT. This is what paints the video picture.

However, these fields can get into amps and receivers and cause a buzz.

Best,

Gil

[D-MAN]

I have my corner horns in the "TV room" and have 2 pair of 15" woofers sitting on the floor in front of the big screen pending storage. I noticed the screen was quite fuzzy and out-of-focus at the bottom. Moved the drivers, and it straightened right up. That's what I get for being lazy!

DM

[ccsakura]

Thanks alot for clear explanation(especially for those LCD part, since I didn't really understand how LCD works too much) . Gee I was nearly to get the speakers without shielded and the reciever just sit next to the position that I'm going to place the speakers. Thanks again .

[Johnny dB]

bumped

I found my answer in the Search.