Would this work to shield monitor speakers?

[RWhite]

I have two sets of monitor speakers, some new Event 20/20s and an old pair of Yamaha S8Ms. The later are sort of the Grandparents of the NS-10. I had recently set up my upstairs computer room so that I could do some "mastering" on that computer, using an Audiophile 2496. So I had initially set up my new Events there, and everything was fine.

To make a long story short, I wound up moving the Events to the basement "main" studio, and brought the Yamahas up from the depths they have inhabbited for years. When I set them in place upstairs and fired everything up, I was dismayed to find that the Yamaha speakers (unlike the Events) have no magnetic shielding at all, and even from 15" away they project a bright spot onto the corner of my computer monitor.

I can't move them any further away, but I did have an idea. I remember that many years ago a guitar tech once told me some techniques for eliminating hum from a Stratocaster guitar. Part of the procedure was painting the inside wood area around the pickups with a special lead-based paint.

Would it be possible to do this with the monitor speaker - open up the back, and paint the interior wood areas with this stuff? And would this in any way risk damaging the speakers themselves?

 

[djc]

I don't know if you would even have to go to that far. I was reading in a post a few months back, where someone had put (or suggested putting) metal plates on the side of the speaker facing the monitor. That might work, and it might only have to be like a 10 gage plate or something. Just a thought.

 

[RWhite]

I actually tried using Aluminum foil for that purpose, but it did not have any effect.

 

[webstop]

In order to shield the speakers you need to apply opposite maginetic field to the speakers' magnet.
For example Yorkville sells magnetic shielding for their speakers as an option. It is simply a pair of pretty big magnet rings, which are supposed to be glued to the back of the drivers' magnets.
According to Yorkville tech it is common way of shielding, although it reduces efficiency of speakers to some extend...
This is what I've been told...

 

[knightfly]

I'm the guy that posted about the steel plates - I used 1/8" steel plates between the monitor and speakers - also tested with super magnets instead of speakers. Without the plates, I could get the magnet about 8" away from the side of the monitor before distortion started. WITH the plates, I ended up TOUCHING the plate with the magnet (150 pound lift rated, about 1" x 2" x 4") and STILL had no signs of dis-coloration or distortion.

You should be able to, with plates about the size of your monitor speakers, place the speakers within probably 2" of the display with no ill effects.

The steel plates don't get RID of the magnetic field, they just re-direct it so it doesn't affect the monitor... Steve

An added plus - Unlike lead, your kid can chew on the steel plates and still not (necessarily) grow up to be as wierd as I am... :=)

 

[Bigus Dickus]

Yes, a ferromagnetic plate (steel or iron most commonly) of sufficient thickness will redirect the magnetic field lines, and effectively sheild the other side (for your purpose).

The best magnetic shielding is alternate layers of ferromagnetic and non-ferromagnetic materials. For example, steel, copper, steel, copper, steel. VERY effective, but also costly. Sometimes non-ferromagnetic materials can also act as a shield (one copper, lead, or brass plate, or aluminum of sufficient thickness) but it works by a different mechanism (not important here though).

Bottom line... if it's just affecting the corners of your monitor, then some scraps of sheet steel of 16 gage of heavier will probably do the trick.

 

[RWhite]

Thanks for the info... while I may still try the paint solution, I'll also have a look arround my neighborhood auto junk yard.

And I don't have kids, so I don't have to worry about infants chewing on the lead (unless you count my drummer)

 

[barefoot]

Conductive paint won't work. You need a magnetic material like iron or steel. An L shaped piece of 1/8"steel the same height as the monitors that covers the entire computer monitor side of the cabinet and wraps about half way around the back side of the cabinet should work.

barefoot

http://barefootsound.com

 

[barefoot]

Oh, I forgot to mention why it won't work.

Electrically conductive shields like Bigus Dickus mentioned only work for fluctuating magnetic fields like those from power transformers. Only superconductors can block static magnetic fields like those from speaker magnets. So unless you want to submerge your lead paint in liquid helium its not going to have any effect.

barefoot

http://barefootsound.com

 

[sonusman]

barefoot! Thanks!!! Need to shield my Event 20/20's and a pair of NS 10's. I can get steel for cheap from a couple of friends.

Ed

 

[sonusman]

Hey barefoot, would 1/8" thick STAINLESS STEEL work for this too? It would look much better.

Ed

 

[barefoot]

Hey barefoot, would 1/8" thick STAINLESS STEEL work for this too? It would look much better.

SS isn't a good choice. Its alloys vary in their ferromagnetic properties, but most have significantly less permeability than steel - especially 316 stainless. You'd need a very thick piece for it to work. Soft steel, or even better, iron is best. Also, you can get away with thinner steel if you wrap it further around the cabinets and make the bend radii as large as possible. My cylindrical speakers were very easy to shield with just an inner lining of sheet metal.

barefoot

http://barefootsound.com

 

[sonusman]

Thanks barefoot. One more question though.

Are there any other materials that might look a little better if used on the outside of the box? John Sayers suggested lead impregnated polysomethingoranother maybe. He differed to what you thought though.

Ed

 

[barefoot]

I don't know of any primarily lead alloy that works as a magnetic shield. I remember seeing a company online that sells thin Mu Metal sheets and foils for magnetic shielding. I don't recall the company name though. Mu Metal is several times more magnetically permeable (magnetically "conductive") than steel and you can probably get away with just having it on the video monitor side of the cabinet. But it's expensive.

barefoot

http://barefootsound.com

 

[knightfly]

If you want the mild steel to look better, you could have it chromed :=) the pieces of mild steel I used were 1/8", because I had a couple of scraps that thickness. Not sure how much thinner you could go. Mine were just straight 12 x 14 flats, no bends or curves or anything... Steve

 

[sonusman]

Thanks everyone for your input. Mild steel it is. I will find a way to make it look good.

Ed

 

[NeuzGrouper]

This has got me thinking....

Hmmmm....If your spekaers aren't shielded, can the magnetic field around a computer monitor (when it is in use) damage or in any way alter the sound from the speakers?

 

[barefoot]

Well, everything does interact. And one could even argue that the orientation of a speaker relative to the earth's magnetic field might also alter the sound. However, considering that the voice coil gap flux of a typical speaker driver is about 5,000 to 10,000 times stronger than the earth's magnetic field, and that the motor geometry would tend to redirect the earth's magnetic field in the same path as the speaker magnet field anyway, it's really not a significant issue. Same argument holds for a computer monitor.


Thomas

 

[NeuzGrouper]

Thanks! At least I don't have to worry about THAT too much...

 

[knightfly]

Right, now you'll have more time for knitting aluminum foil watch caps (they really ARE out to get us, you know... :=)