magnetism and "safe zones"

[Wil816]

Ill have no troubles keeping my tapes a long way from speakers, but the my CRT monitor worries me. Do they have a magnetic field when turned off?

Why not just experiment? Record some tones (and music, if you wish) on a tape that's ok to erase, and then put it right next to the monitor-- even leave it for a few months if you like-- and see if it loses anything. For an experiment I'm running now after the exchange above, I recorded tones at 1kHz and 10kHz alternately, and I'm leaving it on the unshielded speaker (which I think was 4-watt) of the Marantz CD-320 portable cassette, less than an inch from the magnet, picking it up and putting it back down there and turning it over a couple of times a day, to see if the 10kHz loses anything over time. (It has only been about three days so far, but there's no loss at all yet.) I may do another one now and keep it on the monitor, which gets turned on and off several times a day. As in many fields, some superstition has been added to science, and I want to find out how much is which.

 

[MCI2424]

Why not just experiment? Record some tones (and music, if you wish) on a tape that's ok to erase, and then put it right next to the monitor-- even leave it for a few months if you like-- and see if it loses anything. For an experiment I'm running now after the exchange above, I recorded tones at 1kHz and 10kHz alternately, and I'm leaving it on the unshielded speaker (which I think was 4-watt) of the Marantz CD-320 portable cassette, less than an inch from the magnet, picking it up and putting it back down there and turning it over a couple of times a day, to see if the 10kHz loses anything over time. (It has only been about three days so far, but there's no loss at all yet.) I may do another one now and keep in on the monitor, which gets turned on and off several times a day. As in many fields, some superstition has been added to science, and I want to find out how much is which.

keep it up!

I had fun a while ago finding out if a demagnatizer is as dangerous as it is proposed in history. I had an old 2 track R -R deck and experimented. I did everything you are not supposed to do. I even switched it on/off while touching the heads directly. I could not get those damn things magnatized at all. Who knows the truth anymore. So many people have told us about such things and there is some truth to all of it. I would not do these things to my good tape equipment, but when you don't care, everthing seems to go opposite from empherical wisdom and when you do care, the very things go right in the wrong direction!

 

[Beck]

Thanks Beck, for moving the thread back into topic, and rounding it off in such a convincing way.

Ill have no troubles keeping my tapes a long way from speakers, but the my CRT monitor worries me. Do they have a magnetic field when turned off?

I thought that the magnet in CRTs was the degausser, which is activated when the screen is turned on (and when you press the degaussbutton). Bet theese things could be a real tapekiller.

Baard

Tapes should be kept away from monitors and TVs as well. Yeah, the degausser comes on during power up and that goes back to ancient TV sets.

You don't have to paint Lamb's blood over your studio door or anything so the angel of stray magnetism passes over ... Just use common sense habits around your studio and you'll be fine. Never lay or lean tapes on speakers or CRTs, and degauss your tape path on a regular schedule. There should be no reason you would have to lean a tape against a monitor, whether off or on.

I store my tapes well away form everything else on a top closet shelf.

 

[the cool one]

I had a home-made cassette tape with some good stuff I wanted to save on it. The leader broke so I set it aside for awhile. It sat a few inches away from a 110 volt ac air-conditioning power cable. By the time I got around to fixing the leader…

 

[Rodrev]

You don't have to paint Lamb's blood over your studio door or anything so the angel of stray magnetism passes over

Maybe that technique would keep bad recordings away?

 

[rayc]

Let me rephrase Light's salient points, (which I conincidentaly agree with but that means nothing as I'm a Gumby), in a more easily digestible form:
Magnet = earth magic
Tape = people science.
In scissors (time), paper (people science), rock (elemental earth), magnets gets revenge on tape, magic beats science and your hard work can be stuffed up badly.
Don't leave tape on the machine too long;
Don't leave tape near fridges as fridges are magnet magnets;
Don't wave your demag wand over your tapes unless you want to do what the package says it will do
&
Keep your tapes in an even temp with low humidity away from electrical circuits, wires, North Magnetic Poles (ie Santa's Place), transformer plugs AND ESPECIALLY speakers.
OR
Gandalf will come out of your pirated Video Cassette of TLOTRings and, having consumed too much Elven curry the previous evening, pass a 13000 gauss gas over your work rendering it uninhobbitable.

 

[cjacek]

OR...Gandalf will come out of your pirated Video Cassette of TLOTRings and, having consumed too much Elven curry the previous evening, pass a 13000 gauss gas over your work rendering it uninhobbitable.

LOL!!

 

[Wil816]

Originally Posted by Wil816
Why not just experiment? Record some tones (and music, if you wish) on a tape that's ok to erase, and then put it right next to the monitor-- even leave it for a few months if you like-- and see if it loses anything. For an experiment I'm running now after the exchange above, I recorded tones at 1kHz and 10kHz alternately, and I'm leaving it on the unshielded speaker (which I think was 4-watt) of the Marantz CD-320 portable cassette, less than an inch from the magnet, picking it up and putting it back down there and turning it over a couple of times a day, to see if the 10kHz loses anything over time. (It has only been about three days so far, but there's no loss at all yet.) I may do another one now and keep in on the monitor, which gets turned on and off several times a day. As in many fields, some superstition has been added to science, and I want to find out how much is which.

keep it up!

I had fun a while ago finding out if a demagnatizer is as dangerous as it is proposed in history. I had an old 2 track R -R deck and experimented. I did everything you are not supposed to do. I even switched it on/off while touching the heads directly. I could not get those damn things magnatized at all. Who knows the truth anymore. So many people have told us about such things and there is some truth to all of it. I would not do these things to my good tape equipment, but when you don't care, everthing seems to go opposite from empherical wisdom and when you do care, the very things go right in the wrong direction!

Well, it has been about a month. I have kept the cassette on top of the machine's speaker, less than an inch from the magnet, turning the tape over occasionally and moving it around on the speaker, playing it several times on an almost 30-year-old machine that has never seen a demagnetizer, and the 10kHz is just as strong still as the 1kHz, and just as strong as it was the night I recorded it.

I have not done the same experiment leaving the tape on the monitor all that time, but I did put the tape right up to the screen, and on the sides, around the back, underneath, etc, all flat against the monitor's surfaces, turning the monitor off and on several times, and played the tape again. Same thing. No high-frequency loss.

 

[Beck]

Interesting. However, you'll have to test 15kHz or above for high frequency loss. 15k and up are most vulnerable to even minuscule residual magnetism as would be found on a neglected tape path. I mentioned this in an earlier post.

What type of cassette are you using… Normal, Type II or metal? Are the speakers shielded? What is the flux power of the magnet @ ¼”?

~Tim

 

[Wil816]

I didn't do it at 15kHz because this little 2-head machine is practically incapable of 15kHz. Tape is type II. Speakers are not shielded. I have no way to measure the flux density, but at that distance, one end of a magnetic compass's needle is stuck hard to the bottom of the compass and will not rotate, or budge at all for that matter. (I know that doesn't tell you much, but it's all I can do for now.)

 

[Beck]

Here are a couple things to keep in mind:

1. Type II tape, whether cassette or EE reel-to-reel is harder to erase than standard oxide tapes typically used for professional open reel applications, such as 456, 911, etc. Metal tape is even harder. Many consumer degaussers won’t even do the job with metal cassette or DAT. You can erase a ¼" reel-to-reel normal bias tape with less power than would be needed for CrO2 or metal 1/8” cassette.

2. The high frequencies of most concern when it comes to accidental erasure through proximity or residual tape path magnetism are 15k and above. Even a good consumer quarter-track stereo tape recorded at 7-1/2 ips can have frequency content above 25k.

3. The two main concerns in a professional environment (including a home studio) are 1) loss of high frequency content from an important multi-track or master, and 2) gradual erasure of the high frequency tone from your MRL or other calibration tape. This is usually 16k or 20K. As that tone becomes weaker relative to the 1K reference your equalization curve (NAB or IEC) will be skewed. That is, it will no longer conform to the standard curve… meaning your calibration tape is useless for checking or setting the EQ curve on your machine.

As far as erasure in day-to-day, I’ve experienced both proximity and residual tape degradation over the years that is audible. Residual magnetism from a neglected tape path (not regularly degaussed) is more uniform in dulling the highs on a commercial ferric oxide tape. Proximity erasure from nearby speakers, motors or TVs often affects one area of the tape.

This will manifest itself as a rhythmic series of dropouts, which is worse on songs near the outer layer of the spool. For example, a fully rewound cassette that has been stored lying flat near a magnetic field will have audible erasure only on one side of the spool. When you play it the highs drop out every time that area passes the play head. Many people have experienced this with cassettes, but didn’t know what it was.

~Tim