Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

In article ,
(Svante) wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Constant magnetic fields are very easy to shield. You simply cancel it
with another constant magnetic field.

A magnet in repelling the orientation is placed on the end of the
speaker magnet and then the whole thing is covered with a heavy ferrous
metal cap. The magnetic fields still leaking through the metal cap are
opposing and cancel not too far from the speaker.

You can buy these kits for normal speakers. How well a kit works
depends on how well the field of the inverted magnet matches your
speaker.

In article ,
(Svante) wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Constant magnetic fields are very easy to shield. You simply cancel it
with another constant magnetic field.

A magnet in repelling the orientation is placed on the end of the
speaker magnet and then the whole thing is covered with a heavy ferrous
metal cap. The magnetic fields still leaking through the metal cap are
opposing and cancel not too far from the speaker.

You can buy these kits for normal speakers. How well a kit works
depends on how well the field of the inverted magnet matches your
speaker.

In article ,
(Svante) wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Constant magnetic fields are very easy to shield. You simply cancel it
with another constant magnetic field.

A magnet in repelling the orientation is placed on the end of the
speaker magnet and then the whole thing is covered with a heavy ferrous
metal cap. The magnetic fields still leaking through the metal cap are
opposing and cancel not too far from the speaker.

You can buy these kits for normal speakers. How well a kit works
depends on how well the field of the inverted magnet matches your
speaker.

In article ,
(Svante) wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Constant magnetic fields are very easy to shield. You simply cancel it
with another constant magnetic field.

A magnet in repelling the orientation is placed on the end of the
speaker magnet and then the whole thing is covered with a heavy ferrous
metal cap. The magnetic fields still leaking through the metal cap are
opposing and cancel not too far from the speaker.

You can buy these kits for normal speakers. How well a kit works
depends on how well the field of the inverted magnet matches your
speaker.

On 15 Feb 2004 10:13:38 -0800, (Svante)
wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Google "magnetic shielding" and you'll get these hits and mo


http://www.magnetic-shield.com/shielding.html

http://www.mushield.com/design_guide.html


Google is your friend!

--
John Fields

On 15 Feb 2004 10:13:38 -0800, (Svante)
wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Google "magnetic shielding" and you'll get these hits and mo


http://www.magnetic-shield.com/shielding.html

http://www.mushield.com/design_guide.html


Google is your friend!

--
John Fields

On 15 Feb 2004 10:13:38 -0800, (Svante)
wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Google "magnetic shielding" and you'll get these hits and mo


http://www.magnetic-shield.com/shielding.html

http://www.mushield.com/design_guide.html


Google is your friend!

--
John Fields

On 15 Feb 2004 10:13:38 -0800, (Svante)
wrote:

Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Google "magnetic shielding" and you'll get these hits and mo


http://www.magnetic-shield.com/shielding.html

http://www.mushield.com/design_guide.html


Google is your friend!

--
John Fields

"Richard Crowley" wrote in message ...
"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

So, that is why there aren't "cups" to buy that fits on any driver? I
would suppose this balancing is individual for every driver model.

"Richard Crowley" wrote in message ...
"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

So, that is why there aren't "cups" to buy that fits on any driver? I
would suppose this balancing is individual for every driver model.

"Richard Crowley" wrote in message ...
"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

So, that is why there aren't "cups" to buy that fits on any driver? I
would suppose this balancing is individual for every driver model.

"Richard Crowley" wrote in message ...
"Svante" wrote ...
Some drivers have magnetic shielding to not disturb
CRT screens, and obviously it works. During my
education, however, I was told that DC and LF magnetic
fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

Generally, they use either extraordinary means to make sure
the magnetic circuit is completely closed (little or nothing
escapes to the outside), or else they apply "opposing magnets"
to reverse whatever field is escaping.

You are correct that shielding it "after the fact" is
extraordinarly difficult.

So, that is why there aren't "cups" to buy that fits on any driver? I
would suppose this balancing is individual for every driver model.

(Svante) wrote in message . com...
Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

A couple of misconceptions:

1. It is not "terribly hard to shield." There are a number of
ways it can be done:

* proper design of the magnetic circuit, such that the gap
is operating at just about but not much above saturation,
the gap is the only high-reluctance part of the total
magnetic circuit, that the magnetic circuit is optimized
so that the total flux in the magnet is maintained essentially
throughout the entire circuit, etc.

* the judicious use of reverse-polarity bucking magnets to cancel
the field at intermediate and farther distances

* In conjunction with the above, a mild steel (moderately high
permeability) magnetic cup surrounding the magnet system.

* the use of non-ferromagnetic materials in everytwhere but the
magnetic cricuit itself, i.e., aluminum, magnesium, etc.,
baskets.

2. No, "supraconductors" or maybe superconductors are NEVER used
because they are utterly unnecessary. The materials needed to
accomplish the measures above are very common, very ordinary.
They are just properly used in a careful design following well-
understood engineering principles. Using these proper design
techniques, low external field emissions are actually EASY to
obtain.

Okay, so if all of this is true, then why is it such a problem?
simply because many speaker "engineers" are simply clueless as
to their existance and how to apply them. Many magnets are poorly
designed and sloppily manufactured. A lot of magnet assemblies
have far more hard magnetic material (e.g., the ceramic magnet
ring where the energy is actually stored) than is needed to achieve
the necessary gap flux and the result is the excess energy spilling
out of the circuit (you can only stuff so much flux into the soft
metal parts, such as the front plate and the pole piece: any more
magnetically saturates it and all the excess energy now goes into
the space around it).

It's CHEAPER in the SHORT RUN to badly design a magnet: you just
slap parts together. Yes, it's harder to design it properly, but
that just requires the right expertise, and that expertise is not
so common amongst the manufacturers of loudspeaker drivers.

(Svante) wrote in message . com...
Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

A couple of misconceptions:

1. It is not "terribly hard to shield." There are a number of
ways it can be done:

* proper design of the magnetic circuit, such that the gap
is operating at just about but not much above saturation,
the gap is the only high-reluctance part of the total
magnetic circuit, that the magnetic circuit is optimized
so that the total flux in the magnet is maintained essentially
throughout the entire circuit, etc.

* the judicious use of reverse-polarity bucking magnets to cancel
the field at intermediate and farther distances

* In conjunction with the above, a mild steel (moderately high
permeability) magnetic cup surrounding the magnet system.

* the use of non-ferromagnetic materials in everytwhere but the
magnetic cricuit itself, i.e., aluminum, magnesium, etc.,
baskets.

2. No, "supraconductors" or maybe superconductors are NEVER used
because they are utterly unnecessary. The materials needed to
accomplish the measures above are very common, very ordinary.
They are just properly used in a careful design following well-
understood engineering principles. Using these proper design
techniques, low external field emissions are actually EASY to
obtain.

Okay, so if all of this is true, then why is it such a problem?
simply because many speaker "engineers" are simply clueless as
to their existance and how to apply them. Many magnets are poorly
designed and sloppily manufactured. A lot of magnet assemblies
have far more hard magnetic material (e.g., the ceramic magnet
ring where the energy is actually stored) than is needed to achieve
the necessary gap flux and the result is the excess energy spilling
out of the circuit (you can only stuff so much flux into the soft
metal parts, such as the front plate and the pole piece: any more
magnetically saturates it and all the excess energy now goes into
the space around it).

It's CHEAPER in the SHORT RUN to badly design a magnet: you just
slap parts together. Yes, it's harder to design it properly, but
that just requires the right expertise, and that expertise is not
so common amongst the manufacturers of loudspeaker drivers.

(Svante) wrote in message . com...
Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

A couple of misconceptions:

1. It is not "terribly hard to shield." There are a number of
ways it can be done:

* proper design of the magnetic circuit, such that the gap
is operating at just about but not much above saturation,
the gap is the only high-reluctance part of the total
magnetic circuit, that the magnetic circuit is optimized
so that the total flux in the magnet is maintained essentially
throughout the entire circuit, etc.

* the judicious use of reverse-polarity bucking magnets to cancel
the field at intermediate and farther distances

* In conjunction with the above, a mild steel (moderately high
permeability) magnetic cup surrounding the magnet system.

* the use of non-ferromagnetic materials in everytwhere but the
magnetic cricuit itself, i.e., aluminum, magnesium, etc.,
baskets.

2. No, "supraconductors" or maybe superconductors are NEVER used
because they are utterly unnecessary. The materials needed to
accomplish the measures above are very common, very ordinary.
They are just properly used in a careful design following well-
understood engineering principles. Using these proper design
techniques, low external field emissions are actually EASY to
obtain.

Okay, so if all of this is true, then why is it such a problem?
simply because many speaker "engineers" are simply clueless as
to their existance and how to apply them. Many magnets are poorly
designed and sloppily manufactured. A lot of magnet assemblies
have far more hard magnetic material (e.g., the ceramic magnet
ring where the energy is actually stored) than is needed to achieve
the necessary gap flux and the result is the excess energy spilling
out of the circuit (you can only stuff so much flux into the soft
metal parts, such as the front plate and the pole piece: any more
magnetically saturates it and all the excess energy now goes into
the space around it).

It's CHEAPER in the SHORT RUN to badly design a magnet: you just
slap parts together. Yes, it's harder to design it properly, but
that just requires the right expertise, and that expertise is not
so common amongst the manufacturers of loudspeaker drivers.

(Svante) wrote in message . com...
Some drivers have magnetic shielding to not disturb CRT screens, and
obviously it works. During my education, however, I was told that DC
and LF magnetic fields are terribly hard to shield, unless
supraconductors are used. So how does it work?

A couple of misconceptions:

1. It is not "terribly hard to shield." There are a number of
ways it can be done:

* proper design of the magnetic circuit, such that the gap
is operating at just about but not much above saturation,
the gap is the only high-reluctance part of the total
magnetic circuit, that the magnetic circuit is optimized
so that the total flux in the magnet is maintained essentially
throughout the entire circuit, etc.

* the judicious use of reverse-polarity bucking magnets to cancel
the field at intermediate and farther distances

* In conjunction with the above, a mild steel (moderately high
permeability) magnetic cup surrounding the magnet system.

* the use of non-ferromagnetic materials in everytwhere but the
magnetic cricuit itself, i.e., aluminum, magnesium, etc.,
baskets.

2. No, "supraconductors" or maybe superconductors are NEVER used
because they are utterly unnecessary. The materials needed to
accomplish the measures above are very common, very ordinary.
They are just properly used in a careful design following well-
understood engineering principles. Using these proper design
techniques, low external field emissions are actually EASY to
obtain.

Okay, so if all of this is true, then why is it such a problem?
simply because many speaker "engineers" are simply clueless as
to their existance and how to apply them. Many magnets are poorly
designed and sloppily manufactured. A lot of magnet assemblies
have far more hard magnetic material (e.g., the ceramic magnet
ring where the energy is actually stored) than is needed to achieve
the necessary gap flux and the result is the excess energy spilling
out of the circuit (you can only stuff so much flux into the soft
metal parts, such as the front plate and the pole piece: any more
magnetically saturates it and all the excess energy now goes into
the space around it).

It's CHEAPER in the SHORT RUN to badly design a magnet: you just
slap parts together. Yes, it's harder to design it properly, but
that just requires the right expertise, and that expertise is not
so common amongst the manufacturers of loudspeaker drivers.

I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected. Have not created the market for it yet, but the price
of used NS-10's is starting to spike, and I have quite the few woofs
standing by. . .

I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected. Have not created the market for it yet, but the price
of used NS-10's is starting to spike, and I have quite the few woofs
standing by. . .

I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected. Have not created the market for it yet, but the price
of used NS-10's is starting to spike, and I have quite the few woofs
standing by. . .

I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected. Have not created the market for it yet, but the price
of used NS-10's is starting to spike, and I have quite the few woofs
standing by. . .

(sodderboy) wrote in message . com...
I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected.

Well, no. First, the size of the reverse-polarity magnet that you'll
be attaching is important. Any ol' magnet won't do. Second, the
internal field most assuredly IS affected. In many cases you will see
a slight decrease in the electrical Q, Qe, and an attendant increase
in efficiency and other Q-dependent factors. This phenomenon has been
well know for quite a number of years.

Have not created the market for it yet,

Well, when you get around to creating it, you'll be too late,
because there are people doing it already.

but the price of used NS-10's is starting to spike,

Gee, just like their frequency response!

(sodderboy) wrote in message . com...
I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected.

Well, no. First, the size of the reverse-polarity magnet that you'll
be attaching is important. Any ol' magnet won't do. Second, the
internal field most assuredly IS affected. In many cases you will see
a slight decrease in the electrical Q, Qe, and an attendant increase
in efficiency and other Q-dependent factors. This phenomenon has been
well know for quite a number of years.

Have not created the market for it yet,

Well, when you get around to creating it, you'll be too late,
because there are people doing it already.

but the price of used NS-10's is starting to spike,

Gee, just like their frequency response!

(sodderboy) wrote in message . com...
I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected.

Well, no. First, the size of the reverse-polarity magnet that you'll
be attaching is important. Any ol' magnet won't do. Second, the
internal field most assuredly IS affected. In many cases you will see
a slight decrease in the electrical Q, Qe, and an attendant increase
in efficiency and other Q-dependent factors. This phenomenon has been
well know for quite a number of years.

Have not created the market for it yet,

Well, when you get around to creating it, you'll be too late,
because there are people doing it already.

but the price of used NS-10's is starting to spike,

Gee, just like their frequency response!

(sodderboy) wrote in message . com...
I put the pocket pen protector in my Hanes tyedye and gave the
opposing magnet theory a shot. Any studio tech dog has loads of blown
drivers, and can create mizagnetically shielded speakers. I have done
this with Auratones and NS-10's (of course!!) You tiewrap the
disembowled magnet from the "fatigued" (I came in for the session and
it was farting already) speaker and test against a CRT in different
positions. When you get to the sweet spot of field cancellation, mark
the position and epoxy the magnets together. The internal field is
not affected.

Well, no. First, the size of the reverse-polarity magnet that you'll
be attaching is important. Any ol' magnet won't do. Second, the
internal field most assuredly IS affected. In many cases you will see
a slight decrease in the electrical Q, Qe, and an attendant increase
in efficiency and other Q-dependent factors. This phenomenon has been
well know for quite a number of years.

Have not created the market for it yet,

Well, when you get around to creating it, you'll be too late,
because there are people doing it already.

but the price of used NS-10's is starting to spike,

Gee, just like their frequency response!