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Shielding a subwoofer? Monitor is not happy.

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BobA:

Just place the sheet between the speaker and crt with it closer to the speaker.   Degauss your monitor and see if it makes a difference.    If it does nothing then Zebidee is right about it being basically an old wives tale.

specfire:

It is NOT an old wives tale, the property of the material required is that it be ferromagnetic  http://en.wikipedia.org/wiki/Ferromagnetic.  The success of the shielding is dependent on the material used and its thickness. 

If a magnet will stick to it, that is a good start, however, it is not a foolproof method.  In otherwords, one man's cookie sheet may not necessarily be like another man's cookie sheet. 

Many metals can be used to form an alloy with which such things as cookie sheets can be made, so even if a magnet "sticks to it", it may not have enough ferromagnetic material to be effective for your application.  Often aluminum will be a significant component of most metal consumer goods even if there is some iron in them as well.  (aluminum is not ferromagnetic.)

Dedicated shielding material is expensive because it uses expensive metals such as cobalt, magnesium or nickel.  BTW, most speakers sold as "shielded" do not use such expensive shielding materials.  The dedicated shielding material is used in applications that must guarantee a certain level or degree of shielding such as in medical devices or in particular industrial applications where an errant magnetic field might wreak havoc to a particular manufacturing process etc. 

When it comes to consumer goods such as speakers and CRT's, really bad things don't happen even if the shielding is not very good (in other words, no one dies, at worst, the CRT has a colour haze or ring.)

I personally would go to a hardware store and get some flat sheet metal (usually found in the heating section amongst all of the ductwork.)  and then cut it to size to form a dedicated enclosure. 

Good luck.

spec

Zebidee:


--- Quote from: specfire on August 23, 2007, 05:47:56 pm ---It is NOT an old wives tale, the property of the material required is that it be ferromagnetic.  The success of the shielding is dependent on the material used and its thickness. 

--- End quote ---

Hey Spectre, I agree with you 100%.  Why I say "old wives tale" is because simple iron or steel sheeting is not nearly powerful enough to counter the magnetic field of your average powerful speaker.  Commercial mag shielding materials are like 20,000 times more powerful.  But also expensive.

Telling you guys, I've done this experiment but always happy to watch someone else have a go :)   Like I said, love to be proven wrong and learn something new.

jcoleman:

Most speakers are magnetically shielded (those that are, anyway) by essentially reversing the magnetic field outside of the area that drives the voice coil.  In other words, another magnet is applied that supplies an inverse field, thus cancelling out the field of the magnet supllying power to the speaker.  This is non-trivial for a DIY-er.

Coleman

Zebidee:


--- Quote from: jcoleman on August 23, 2007, 08:29:46 pm ---... In other words, another magnet is applied that supplies an inverse field. ...
Coleman

--- End quote ---

Wow, no I've learnt something new!  I've often wondered how they did that relatively cheaply for multimedia speakers and similar.

Incidentally, I'm shocked to say that MOST of the old original arcade cabs I've worked on originally used UNSHIELDED speakers  ???, and in many cases closely positioned speakers would have had a significant affect on the original monitor - WTF  !%#$%@ :censored:.  I STRONGLY recommend to anybody with an original cab that they check their speakers out closely, and replace as necessary.  For example, I've had 6w unshielded original cab speakers that have caused distortions to my SHIELDED sony video monitor, which was at least 6-8 inches away.

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