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Old August 15th, 2008, 08:23 AM   #1
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interference from magnets?

Hello, I just made myself a little soundbag for my SD 302 mixer and G2 wireless systems. I made it from an old handbag. The bag has several magnets to help with the closure of the compartments. Could this lead to interference with the audio equipment? Should I get them out? Thanks.
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Old August 15th, 2008, 06:40 PM   #2
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I would would be more worried about the magnets introducing noise, or even partially erasing video/audio tapes that just might come near to them in just carrying it with all your gear.

I would defineatly get rid of them.

R.C.
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Old August 15th, 2008, 07:32 PM   #3
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A steady magnetic field should have no influence of any kind on an electronic circuit. A changing magnetic field, however, can induce noise or a signal in any nearby conductor. That's how transformers work.

Having a small, fixed, permanent magnet near an audio circuit won't have a noticeable effect. If you move the circuit back and forth over the magnet rapidly, then you'll introduce a signal, though way below the threshold of hearing. There are circumstances where you could --possibly-- have audio problems, though I'd say getting struck by a car is more likely. And you sure don't want magnets around magnetic tape. The safe bet is, get rid of the magnets and replace them with velcro.

Martin
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Old August 16th, 2008, 01:24 AM   #4
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I suppose you're right. Better not take any risks. Thanks guys.
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Old August 16th, 2008, 05:37 AM   #5
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Quote:
Originally Posted by Martin Catt View Post
... There are circumstances where you could --possibly-- have audio problems, though I'd say getting struck by a car is more likely.
You mean, the magnets will attract cars?

:-)
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Old August 16th, 2008, 08:40 AM   #6
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quote "A steady magnetic field should have no influence of any kind .."

nope, 101 physic teach that current flowing in a solid conductor generates a magnetic field.
and the reverse is true too... A magnetic field generate a current .
so if you got a wire crossing a magnetic field (even steady) you could get some disturbance, especially if you got an amplifier in between.
For sure you got more chance to win the lottery than to have an audible disturbance from a little magnet.
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Old August 16th, 2008, 10:35 AM   #7
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Quote:
Originally Posted by Giroud Francois View Post
quote "A steady magnetic field should have no influence of any kind .."

nope, 101 physic teach that current flowing in a solid conductor generates a magnetic field.
and the reverse is true too... A magnetic field generate a current .
so if you got a wire crossing a magnetic field (even steady) you could get some disturbance, especially if you got an amplifier in between.
For sure you got more chance to win the lottery than to have an audible disturbance from a little magnet.

While a steady current generates a magnetic field, it doen't work the other way around with a steady field generating a current. It's a classic demonstration in Physics 101 class ... hold a wire carrying a direct current over a compass and the needle deflects in an amount proportional to the current. But hook up a coil of wire to a meter and move a bar magnet through the centre of the coil. The meter deflects only when the magnet is moving. When the magnet is motionless, the current flowing through the coil drops to zero. The magnetic field is still there but that in itself does not generate current. It is the energy of the mechanical motion of the magnet converted into motion of electrons within the conductor that causes the current to flow. The magnetic field doesn't generate the electrical energy per se but rather acts as the vehicle for the energy transfer.
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Old August 16th, 2008, 10:45 AM   #8
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Quote:
Originally Posted by Giroud Francois View Post
quote "A steady magnetic field should have no influence of any kind .."

nope, 101 physic teach that current flowing in a solid conductor generates a magnetic field.
and the reverse is true too... A magnetic field generate a current .
so if you got a wire crossing a magnetic field (even steady) you could get some disturbance, especially if you got an amplifier in between.
For sure you got more chance to win the lottery than to have an audible disturbance from a little magnet.
Actually, it is the CHANGE in magnetic flux that induces the voltage in a conductor. Lay a conductor alongside a permanent magnet, and once it is in position -- AND NOT MOVING -- you won't see any voltage generated. Move the wire in the magnetic field, then you will see an induced voltage in the conductor as it cuts through the lines of magnetic force. That's how generators work.

Of course, it can't be quite that simple, as there is the Hall Effect, where a magnetic field produces a voltage ACROSS (not along) a conductor when the magnetic field is oriented perpendicular to the current. But this is in the order of microvolts and is used primarily for sensing magnetic fields with Hall Effect sensors.

(My company spent a ridiculous amount of money recently to have me trained in alternating-current theory, including inductance and transformers, which quite frankly has no practical impact on my job, which is primarily diagnosing and correcting problems with mechanical gear trains. However, the training was mandated by the FAA, and I was paid to take the classes, so I can now do things like calculate phase angles, resonant frequencies, and voltages across capacitors and inductors in various circuits.)

Martin
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Old August 16th, 2008, 05:07 PM   #9
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Quote:
Originally Posted by Giroud Francois View Post
quote "A steady magnetic field should have no influence of any kind .."

nope, 101 physic teach that current flowing in a solid conductor generates a magnetic field.
and the reverse is true too... A magnetic field generate a current .
so if you got a wire crossing a magnetic field (even steady) you could get some disturbance, especially if you got an amplifier in between.
For sure you got more chance to win the lottery than to have an audible disturbance from a little magnet.
So are you saying if I get some magnets I will win the lottery... this SAG shit is killin me!
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Old August 20th, 2008, 09:20 AM   #10
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Magnets on a bag???

Velcro, son, velcro.....
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Old August 20th, 2008, 11:36 AM   #11
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Quote:
Originally Posted by Martin Catt View Post
Actually, it is the CHANGE in magnetic flux that induces the voltage in a conductor. Lay a conductor alongside a permanent magnet, and once it is in position -- AND NOT MOVING -- you won't see any voltage generated. Move the wire in the magnetic field, then you will see an induced voltage in the conductor as it cuts through the lines of magnetic force. That's how generators work.

Of course, it can't be quite that simple, as there is the Hall Effect, where a magnetic field produces a voltage ACROSS (not along) a conductor when the magnetic field is oriented perpendicular to the current. But this is in the order of microvolts and is used primarily for sensing magnetic fields with Hall Effect sensors.
Martin
Martin's correct. Pretty much, no motion, no current. There's the right hand rule. (or was it left hand rule). Curl the fingers of the right hand and extend the thumb. The fingers indicate the field flow and the thumb indicate the current flow in the wire. I think it works that way both above and below the equator, but I could be wrong. :)

Regards,

Ty Ford
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Old August 21st, 2008, 10:33 AM   #12
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Quote:
Originally Posted by Tim OBrien View Post
Magnets on a bag???

Velcro, son, velcro.....
Well, I got the magnets out, but I have some doubts about putting Velcro on the soundbag. Isn't there a noise issue with Velcro? 'krrr'.
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