Loudspeaker Magnets and CRT TV Tubes

S

steve3d

Audiophyte
A couple of years ago, purchased one of the last Sony CRT HD TVs.

Recently heard that placing loudspeakers close to the TV set might damage the TV due to the magnets inside the speakers.

Is this true?

How close/far away (from the TV) would the speaker need to be in order to NOT damage the TV?

Anything else I need to know about positioning the speakers next to the TV? (My question only relates to damaging the TV...not how the speakers would sound).

I'm just concenrned about blowing out a good (albeit obsolete TV) by my own doing.

Thanks
 
J

Joe Schmoe

Audioholic Ninja
The vast majority of today's speakers are magnetically shielded. Check the manual or website for the ones you have.
 
J

Johnd

Audioholic Samurai
A couple of years ago, purchased one of the last Sony CRT HD TVs.

Recently heard that placing loudspeakers close to the TV set might damage the TV due to the magnets inside the speakers.

Is this true?

How close/far away (from the TV) would the speaker need to be in order to NOT damage the TV?

Anything else I need to know about positioning the speakers next to the TV? (My question only relates to damaging the TV...not how the speakers would sound).

I'm just concenrned about blowing out a good (albeit obsolete TV) by my own doing.

Thanks

Yes, that's true (an unshielded magnet can damage a CRT). I believe a few feet is plenty of distance to protect it from damage. And, no, it is not my understanding that "the vast majority of speakers are magnetically shielded." Paradigm offers it, and so does B&W...I think it is only standard on their centers.
 
Rickster71

Rickster71

Audioholic Spartan
If you already own the speakers.
If you can access the drivers.
Take the bass driver out, and see if it has a metal cover over the magnet.
That cover is the shielding.
 
j_garcia

j_garcia

Audioholic Jedi
CRT is only obsolete from the standpoint that they are large and heavy, otherwise they still provide the best picture quality period.

No, the vast majority of speakers are not shielded. A few feet is more than enough for the typical speaker to prevent any damage. You will see the effects immediately if it is too close and moving it further away should prevent problem.
 
J

Joe Schmoe

Audioholic Ninja
CRT is only obsolete from the standpoint that they are large and heavy, otherwise they still provide the best picture quality period.
True. This creates a dilemma because I currently own one of the largest tubes. I would enjoy a bigger screen, but the advantage might be cancelled by the significant drop in quality from going to another technology.:(
 
TLS Guy

TLS Guy

Seriously, I have no life.
The reason the speakers damage a CRT is that the tube is an electron gun. They actually emit Beta radiation which is why you should not sit too close. The electron beam is moved across the screen by charged plates and electromagnets. The first CRTs were long and narrow as they only had the charged plates to cause the beam to scan. The picture was small. Then it was discovered that the beam could be thrown curved by the addition of electromagnetic coils wound round the tube plates. This allowed the tube to be shortened and the screen to be bigger.

Now speakers less than 5 ft from the tube will magnetize it and distort the picture and cause colored halos.

I tube can be demagnetized. These days speakers are usually not shielded the cost of the shields is significant.

Unshielded speaker.

http://www.madisound.com/catalog/product_info.php?products_id=782

Same speaker shielded.

http://www.madisound.com/catalog/product_info.php?products_id=783
 
Alex2507

Alex2507

Audioholic Slumlord
The reason the speakers damage a CRT is that the tube is an electron gun. They actually emit Beta radiation which is why you should not sit too close. The electron beam is moved across the screen by charged plates and electromagnets. The first CRTs were long and narrow as they only had the charged plates to cause the beam to scan. The picture was small. Then it was discovered that the beam could be thrown curved by the addition of electromagnetic coils wound round the tube plates. This allowed the tube to be shortened and the screen to be bigger.

Now speakers less than 5 ft from the tube will magnetize it and distort the picture and cause colored halos.

I tube can be demagnetized. These days speakers are usually not shielded the cost of the shields is significant.

Unshielded speaker.

http://www.madisound.com/catalog/product_info.php?products_id=782

Same speaker shielded.

http://www.madisound.com/catalog/product_info.php?products_id=783
I'm seeing a $6.30 difference, not significant at all. Am I missing something?
 
j_garcia

j_garcia

Audioholic Jedi
No, I don't think shielding is a considerable increase in cost.
 
TLS Guy

TLS Guy

Seriously, I have no life.
I'm seeing a $6.30 difference, not significant at all. Am I missing something?
Yes you are missing something. Price points. Now most speakers would use two of those drivers per side plus a tweeter. That is six shields in all. So we have $37.8 in shields. Now lets add 40% for the distributor or agent/importer and we have $52.92. Now add 40% for the dealer and we have $74.

Now those markups are conservative for the trade. I did not include the increase in freight, from the increased weight.

Now the shield adds nothing to the sound of the speaker. Increases in the MRSP like that really count.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Agreed.
I stamped tin cup?
I wouldn't think so.
A stamped tin cup will shield nothing. There are special metal formulations that have to be used to mask a magnetic field. After all the metal magnet surround does not shield the magnet does it?
 
C

chadnliz

Senior Audioholic
Damage will only happen if you can see it, if you have purple, green, red, corners...or any discoloration when you should see all white screen (for example) then there is a problem..............if you see nothing then nothing is wrong.
I have a Sony 34 XBR WEGA CRT unit and at one point had my mains flanking the unit which have 3 10' Woofers and are NOT sheilded, at 18 inches from TV I had no issue, anything closer and I could see the effects of the magnets easy.
 
j_garcia

j_garcia

Audioholic Jedi
Yes you are missing something. Price points. Now most speakers would use two of those drivers per side plus a tweeter. That is six shields in all. So we have $37.8 in shields. Now lets add 40% for the distributor or agent/importer and we have $52.92. Now add 40% for the dealer and we have $74.

Now those markups are conservative for the trade. I did not include the increase in freight, from the increased weight.

Now the shield adds nothing to the sound of the speaker. Increases in the MRSP like that really count.
Volume sales and scales of economy will reduce that total cost, not to meniton we aren't likely looking at the raw price since Madisound is a distributor also - meaning we are seeing some markup there already. The shields probably cost a company less than a dollar each. We are also talking about a driver that cost quite a bit, so an additional $6 is nothing and I would not expect a driver with a distributor price like that to be going in an inexpensive speaker...
 
Alex2507

Alex2507

Audioholic Slumlord
Yes you are missing something. Price points. Now most speakers would use two of those drivers per side plus a tweeter. That is six shields in all. So we have $37.8 in shields. Now lets add 40% for the distributor or agent/importer and we have $52.92. Now add 40% for the dealer and we have $74.

Now those markups are conservative for the trade. I did not include the increase in freight, from the increased weight.

Now the shield adds nothing to the sound of the speaker. Increases in the MRSP like that really count.
The driver you posted is aprox. $180. A difference of aprox. $6 for a shield is less than 3%. If you start multiplying shields needed for set of mains, you may as well keep multiplying and include center and surrounds but when you're done don't forget to compare the over all cost of the shields to the price of the entire speaker package. IMO it is not significant.

I do respect the fact that you know plenty about this hobby but when you come up with a $74 figure as a significant difference I think you should also include the aprox. cost of the speaker package you have described. I'm going to guess that it would be well in excess of $1000. Closer to $2000 is what I'm really thinking.
 
J

Joe Schmoe

Audioholic Ninja
Most of the speakers I have looked at (both in stores and online) list magnetic shielding as a feature. It is very common.
 
TLS Guy

TLS Guy

Seriously, I have no life.
The driver you posted is aprox. $180. A difference of aprox. $6 for a shield is less than 3%. If you start multiplying shields needed for set of mains, you may as well keep multiplying and include center and surrounds but when you're done don't forget to compare the over all cost of the shields to the price of the entire speaker package. IMO it is not significant.

I do respect the fact that you know plenty about this hobby but when you come up with a $74 figure as a significant difference I think you should also include the aprox. cost of the speaker package you have described. I'm going to guess that it would be well in excess of $1000. Closer to $2000 is what I'm really thinking.
I might have picked a bad example. I used it as I use those drivers, and knew where to find the pictures. However the shield will cost the same if the driver is $20 or $200. In fact I think that shield is cheap. The cost of Mu metal is significant.

Anyhow there must be price point issues otherwise all drivers would have them and few do.
 
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