I had a conversation with Eddie Kramer at AES last month about this, since he was there promoting his endorsed 'Waves' plug-ins. None for Pre-echo print-through though. (laugh)
At that time, Eddie used higher than normal alignment levels, i.e: ('nanowebers' a unit of magnetic flux) which became a some-what common practice in the 70's & 80's. For instance: not uncommon to see notation on tape box:+6dB over 185 N/Wbs... as I recall.
Sorry about ranting off topic.

Good Morning to All. Andrew - I humbly believe that this really is more than just "taking the easy approach and not storing tapes near a speaker". Unless I'm mistaken, there really hasn't been a definitive consensus on this matter. As a matter of fact, based on the limited experiment which I perfomed based on Allan's suggestion, the results seem to indicate the opposite of what the established norm actually is. I am not an expert by any means and as such choose to kindly seek the helps of members on this forum. Despite no having a echnical background, I am certain that magnetism plays a role on directly influencing particles on a tape. However, if the adopted convention (based on precautionary measures) is not necessarily valid why finally serve to dispell the myth? If the information provided here is accurate in that a typical audio tape possesses 330 Oe yet a "powerful" speaker magnet (200 watt driver +) only has 100 Oe then we can safely assume that there is no possible way that it will have a negative effect on the medium since it needs to be at least double the value before undesirable ramifications begin to transpire. I for one would very much like a definitive resolution. No need for anyone to apologize for anything "off topic" because I am learning alot from you all and i still need to get to the bottom of a few considerations....... Thanx :)

Hi Benny, a conclusion you could draw and be satisfied with is, a degausser will erase magnetic analogue tape *if it's big enough and if it's close enough to it*. But any magnets (or regular degaussers) magnetic field falls off very rapidly and only exists a few inches from the unit itself.

The worlds zillions of smaller *undersize* magnets don't have Oe ratings because they're so low, vary so much, and they're just not needed for common everyday or industrial use. HTH.
Cheers.

Hi Benny,

I'm not a boffin in this area of science, but ....

I think the issue of print through was worse in the "old days" of reel to reel audio recordings (quarter inch tape) because the oxide layer didn't require as much magnetism 'force' to record a signal as our modern day tape formulations do/would. This allowed print through to occur more easily as the threshold was lower.

There was also the problem of oxide shedding - particularly from older and/or cheaper tapes. Usually this just served to gum up the playback head.

Modern tape technologies (such as those used in DV tapes) have formulations that enable a much higher density of information to be stored on the same surface area. Hand in hand with that, you would need the formulation to require a greater magnetic signal strength in order to 'write'; so that the accuracy or recording bits of information can be controlled to the required higher tolerances and recording density.

As a result, our DV tapes aren't as vulnerable to accidental degaussing as ye olde cassette or quarter inch tapes were.

Still, I'd keep them away from the speakers just for the sake of being 'safe' rather than being 'sorry'.

On the other hand, this really is at the extent (and then some) of my knowledge in this area and I could easily be "full of it". Hope this helps, and I don't mind receiving knowledgeable correction.

Andrew

PS. Thanks for making me do so much typing! ;-)

Thanx for contributing again to this topic Allan, I've appreciated all of your very kind collaboration. And Andrew, not unlike you, I neither am an expert in the domain of science by any means; As such, I have eagerly looked forward to the education which I have been able to embrace here. In my opinion, wanting to adopt the "better safe than sorry" approach is ultimately futile because no one is provided with a tangible answer based on some facts. My simple assumption was that with all of the collective knowledge on this forum a concrete consensus could be attained. To date there have been relatively few insights proferred that are resolute in nature; I respectfully believe that this is due to the majority of people simply adopting the familiar convention - Beter safe than sorry. In my case, the tapes are all of the vintage era; In other words, older 1/4 inch reel to reel audio tape. However, these are also essentially all factory recordings (primarily by Ampex). Given what I've managed to discover to date, a speaker cabinet's inherent magnetism from a driver has utterly harmful impact on the reels. Despite this sounding like a contradiction to the physics involved in the matter, it stands because the details are what ultimately reatin the greatest degree of relevance. The Oe factor of the magnet in question has to not only be strong enough to manipulate the magnetic particles on an audio recording but be in tight proximity as well. My objective now is the render a detrmination of these threshold variables; What is the approximate force that an "average" speaker driver possesses and how close is too close?

Ha! Good one!

Ask 20 DVInfoers their opinion and you'll get 40 different answers. That's what makes this place great.

:) Good one! A man with a watch knows the time, one with two is never sure........

Okay folks, it's time for the engineers/scientists to pipe in; Just how strong are speaker magnets?

Speaker mag fields
 

Many of the more recent speakers made for table-top (or "computer") use were "magnetically shielded" because the mag field would affect CRT monitors. Now that CRT monitors are dying off in favor of flatscreen monitors, its not as much an issue anymore. Much of the "shielding" came from simply gluing a second magnet on the back of the speaker in the opposite direction (to cancel out external magnetic fields.)

If I had a bunch of reel-to-reel (or cassette) analog tapes 2 ft away from an unshielded speaker, I would not be worried about the effect on the recordings. I might move them to the other wall (or another room) for future reference, but nothing to freak out about. Remember that it takes a MOVING magnetic field to achieve any significant erasure.

Anyone who remembers early days of color TV CRTs knows that the earth's own magnetic field is a significant force, and it is the reason most CRT color TVs have automatic degaussing coils (the loud buzz when you first turn them on.) Nobody worries about the DC (constant) magnetic field of the earth erasing mag tape, and a 10-inch speaker 2 feet away is not significantly more powerful than the earth's own magnetic field. Now if you were waving the reel back and forth in front of the speaker for hours at a time, THEN you might have something to worry about.

Note that simple metal boxes, even ferrous metal (steel, etc.) offer no significant magnetic shielding because magnetic fields pass through them, mostly undiminished. Special materials (such as "mu-metal") are required for significant magnetic shielding, and it is very expensive and very difficult to make things out of mu-metal because merely bending or cutting it greatly reduces its magnetic shielding properties. Mu-metal is typically used only in very special cases where the advantages warrant the difficulty and expense. (For example, shielding tape playback heads, etc.)

Degaussing (erasing) magnets are AC (alternating current like from the power mains) and are quite strong. Many people have lost their old-fashioned mechanical wrist-watches to the strong magnetic field of these things. But that is what it takes to throughly erase a mag analog tape. Digital tapes (both audio and video) are much more difficult to degauss and most of the time it is cheaper to buy new tape than it is to try to completely erase a digital mag tape. This is also the reason that 99.9999% of all this planet's most valuable data is archived on digital mag tapes.

Reel to reel tapes in cardboard boxes 2 ft from the speaker magnet would not be a great concern, IMHO. If you haven't moved them away already (WHY?), then do it today for peace of mind, and get on with your life.