In anticipation of your kind replies, allow me to extend my gratitude. I have as of yet not been capable of securing a relaively definitive answer to this scenario; Evidently, magnetic fileds (such as those produced by an audio speaker) can produce irreparable damage to recording tape of many formats. Albeit that the formulation of digial video tape appears to be more resistant to its negative effects, my understanding is that traditional audio tape is necessarily not. As such, I may have inadvertanly done some harm to my reel to reel music collection. My wood speaker cabinet, which houses two 10 inch woofers, a midrange, and tweeter, sits approximately 1 feet from one of the shelves where the reel to reel music tapes are stored. Is this distance, coupled with the fact that the speakers are in an isolated structure (which would add another 12 inches of distance for a total of 2 feet) be collectively sufficient for shielding? I am most concerned. Thanx Very Much

I don't know how to calculate a safe distance, but that sounds way too close for speakers that size. I'd move 'em pronto.

If you keep the tapes inside something metal (as long as it is not itself magnetic) then the magnetic field cannot penetrate it so the tapes should be OK.

Actually, all of the tapes are in their original cardboard boxes. I wonder if lining the inside with aluminum foil would do the trick?

Aluminum is non-magnetic so it wouldn't help. Thin sheet iron or steel or something called mu-metal (a magnetic alloy) would. Easiest and cheapest - move the tapes to another shelf a little farther away.

You know, on the first reading of your post I missed that the total distance is more like 2 feet, rather than one foot. You might be okay with that. Magnetism drops off exponentially with distance. I'd probably just get a magnetic compass, hold it next to the tapes in their present location, and if the needle is unaffected by the speaker's magnet, call it a day and not worry about it, as the magnetic pull would seem to be less than that of the earth's.

Well, that actually is a good idea. The distance itself is approximately 1 foot + the distance of the driver in the cabinet is another 12 inches so, yes, it is more like 2 feet overall. Just how radically does the magnetic potency dimishes over distance?

Inverse square - double the distance, 1/4 the strength

Thanx Folks :) I searched the forum and read with interest an older thread from the Thin Black Line forum where a similar topic was discussed;Numerous memebers chimed in but, again, no definitive consensus was attained. I am certain that some empirically established criteria exists somewhere.

From my experience with commercial bulk tape degaussers and recorded 1/4, 1 and 2 inch magnetic tape, I'd say you'd have to literally drag your analogue tapes over your 10inch speaker coils to even partially erase them.

To *see* your speaker coils mag field, at the back slowly move a suitable small coin into range, take your watch off first.

I'd be more concerned with analogue tapes decomposing over time if they're the 'matt back' variety. Shiny Polyester backed tape doesn't decompose and carefully stored has a 30yr+ life. Either way if they're important I'd look at getting them xfered to CD.
Cheers.

In other words, if I take a dime and pass it along the rear panel of the speaker cabinet and it doesn't "tug" (feel the attractive force) would it be safe to assume that there will not be any negative impact on my tapes?

Not quite. To feel the 'tug' IMO you'd have to use a suitable coin and move it in close to the rear of an actual 10" woofers speaker coil, *inside* an average cabinet. And different coins would have different results depending on their composition.

One way to prove there's no effect on your tapes would be to take into consideration how long they've been stored in their present location as you described in post one. I'd guess at least a year or 2 before this thread and they play Ok? Magnetic recording tape erasure is instant if the mag field is large enough.

BTW do you regularly degauss your analogue tape players heads? They can build up residual magnetism through much use and can eventually partially erase tapes. You'd notice a lack of high frequencies developing. I don't mean to scare you but you say you're concerned. Please contact me if you need more info.
Cheers.

Back in my days of producing radio ads (for which I forever apologise) we were taught if we wanted to kill a tape and ruin a days work, store it on or near a speaker cabinet.

Six foot minimum was the go...

Years later I used to store VHS tapes about six foot from the TV. Yes... they are now dead tapes, as the degauss mechanism in the TV created such a strong field on startup.

The storage location depends on the strength of the magnetic field in the first place... then work with the inverse square law..

Ben

In other words, if I take a dime and pass it along the rear panel of the speaker cabinet and it doesn't "tug" (feel the attractive force) would it be safe to assume that there will not be any negative impact on my tapes?

If you have a dime that gets attracted by a magnet, then you have a very rare collector's item.

dimes are made of non-ferrous metals. If you have one that's made of a ferrous metal then you either have a dime that's one in a billion or a counterfeit coin! :-)

Greetings to All & Thanx Much for your insights to date, I do appreciate them :) In direct response to Allan, yes i do degauss the heads on both my players as was outlined in he original owner's manuals which accompanied the recorders; I use a standard wand type device to accomplish this task. I;m just wondering if using the "safe better than sorry" approach now wold save me a whole lot of trouble - Just move everything away 6 feet like Ben adopted and be done with it. My biggest issue is space and reconfiguring the layout is going to be next to impossible. And, good point about the dime Dean! I guess I could always just try to use a small nail of something of that nature. I think I'm going to run out right now and buy a cheap compass and attempt the compass experiemnt as was suggested by Marco. I'll report back as to what develops. Can anyone recommend if there is a cheap way with which to measure the actual field (a Radio Shack meter for instance)?

Okay, here it goes...... I don't know how scientific this experiment was but I did want to duly report back my observations. I purchased an orienteering compass and basically set it on the ground. What I was able to assess is that at a 5 foot distance (having used 3 different sets of speakers) I was not able to affect the needle of the compass; However, at 4 feet I was able to influence the movement of the needle moderately by simply rotating the speaker cabinet; Now at 3 feet I was able to more readily control the needle's movement by rotating either of the cabinets which I used for testing purposes. So, I need to decipher what all this means. How much damage have I done to my beloved reel to reel tape collection? Have only the "highs" been compromised? Damn!!!!! I going to go and test a few tapes by listening and report back.

If you have a dime that gets attracted by a magnet, then you have a very rare collector's item.

dimes are made of non-ferrous metals. If you have one that's made of a ferrous metal then you either have a dime that's one in a billion or a counterfeit coin! :-)Actually, our poster is from Quebec and Canadian coins are attracted by a magnet. Since 2000, the Canadian dime has been made from 92% steel, and is therefore quite magnetic.

Thanx for the information Chris, I did not know that :) I took a random sampling of some of the reel to reel music tapes and they seemed to play fine. I have no idea what's going on; My compass experiment demonstrated that as close as four feet the speaker cabinet could effectively influence the needle. Question is, is the force being emitted at 4, 3, & 2 feet from the magnet in the speaker cabinet enough to adversely affect the recordings?

Benny, any compass is extremely sensitive and yours could be reacting to the screws or metal frame of your speaker cabinet. Playing your tapes was the right test.

Cheers.

Thanx for having taken the time to reply Allan :) I do not know how much merit the validity of this test was since you are indeed correct that it could have been any number of elements in the cabinet that would have influenced the needle to fluctuate. However, I also cannot be certain as to what degree my tapes were adversely affected (if any.....) because they did play; This is exactly why I had inquired as to whether anyone knew of an economical device that could help me to render a concrete reading of how strong a magnetic field was being emitted from the speakers. I am uncertain as to what to do next.

Ok try this. On a piece of new tape at the end of a reel, record a minute of music with high frequencies in it, at 7.5 IPS.

Play it back and memorise what it sounds like, then cut it out of the reel and wind it onto a small reel. Now move that in very close to the back of your speaker cabinet, wave it around and play it again. If there's no difference to the sound, take the back off your speaker box and wave that tape around a foot from the rear of your woofer coil, Play it.. no difference? wave it *right up against/across/around that speaker coil for 10secs* and play it.

Now I think you might hear something, a lack of highs or just maybe, nothing at all.

Dang Benny, you're clearly concerned about this. I think it's time to move either the tapes or the speakers. It doesn't sound like this is something you want to take a chance with.

Hmmmmmmm, now I don't know what to think. This procedure took awhile because I wanted to do it right. I decided to take heed to Allan's suggestion and duly recorded a 60 second passage at 7.5 i.p.s. with several high frequency sequences. I repeatly played it until I had a firm grasp of the actual sound. My first test entailed moving the reel around directly on the rear wood panel of the speaker cabinet for appoximately 30 seconds - I played back the tape and noted no change in sound. Next, I removed the rear wood panel of the cabinet and waved the reel 5 to 6 inches away from the magnet of the woofer for approximately 30 seconds - I played it back and was not able to hear any difference. The next incremental step was to place the reel directly on the surface of the magnet (3 inches in diameter) and moving it around for approximately 30 seconds - I played it back several times with scrutiny and was not able to hear any difference. I was completely disarmed with the results. Almost wanting to dispel these unanticipated results I proceeded to remove the rear panel of my largest speaker cabinet; The woofer's magnet is 5 inches in diameter and almost 1 inch thick. I placed the same reel directly on this large magnet and moved it around for over 1 minute - I played it back and much to my surprise, I was not able to hear any discernable difference in the sound. What is going on? I was absolutely certain that "something" was going to happen. What is going on? I have no reason to doubt Ben, for instance, when he states than during his radio days they were taught that a sure way to ruin a days work was to store a tape near or on a speaker cabinet. I am very much looking forward to your opinions. Thanx

Benny, hope that answers your question, shows your tapes are safe stored where they are and hopefully puts your mind at rest, although I did think you may hear a very slight loss of high frequencies with the last test. So it shows what a low strength magnetic field your biggest speaker puts out.

To erase recorded audio tapes the magnetic field strength of your speaker would have to be 2 to 3 times higher than the coercivity (magnetic field strength Oe) of your tapes. The average audiotape has a rating of 330 Oe and consumer videotape 650 Oe, in line with that videotape needing a bigger degaussing current to erase it.

So you'd need something with a rating of 660-1000 Oe to erase your tapes and 1300-1950 Oe to erase consumer video tape. And that's running the tape over the degaussing rig with no masking medium like a tape box. That's one big degausser.

I've still got one of the small AC powered degaussers we used in our studios. When you put a large pair of metal scissors on it and turn it on, they clamp down so tight to it I've got to prize them off with both hands. 8 inches away there's no magnetic attraction at all. Yet a full 7" reel of 1/4" analogue audio tape needs a slow revolve on the platen to make sure it's fully erased.

When we were training newbies at 2UE, we'd use warnings like .. 'leave your wrist watch out here before you go in there, the degausser could drag the hands off it' Frighten the bejeezes outa them to hopefully save a valuable master tape in the future.

Cheers.

Hello again. And, Thanx Very Much Allan. This experiment was indeed enligtening. What really intriques me is why all of the dire warnings that are floating around with regards to just how sensitive these tapes really are when in reality it takes quite a significant bit of juice to get them compromised. Is most of the information that's exchanged on his matter moreover based on urban legends?

Is most of the information that's exchanged on his matter moreover based on urban legends?

Others might disagree but basically yes! It builds up over the years like a lot of other things. Some businesses make their livlehood with it, drinking bottled water is one. We all grew up with domestic tap water so what's that about lol.

When you put your tape recorder into rec. mode you can imagine the current the erase head puts out to erase the tape passing over it. But that head is only a few inches from the record head itself and it's not affected by the erase head current.

O/T But magnetic underlay sleep mattresses work, get a good brand, it takes about 6months but they do work. :)

Cheers.

How interesting. Thanx Very Much for all of your insights Allan, they are indeed all greatly appreciated. I was under the distinct impression, as it appears that other members here also were, that this issue of proper distance to a tape recording medium was of imperaive importance. Can anyone here give me an estimated idea as to just how much coercivity an "average" speaker magenet has in terms of Oe force?

Greetings to All :) Surely some enlightened soul here on the forum can entertain my last query; I have had the privilege as a new member to come across many genuinely kind and insightful people. Thanx

Hi Alan,

Speaking of others in a radio studio, I used to put the bulk eraser to the side of my head (in line with the eyes) and press the button. No matter how safe I proclaimed it was, I could never get any of the others to do it as well.

There was this issue of one's vision wibbeling while the bulk eraser was on, but that's about it. :-)

Andrew

Ha! Degaussing body parts too :)

Just for everyone's edification, I choose to do this to confirm that all that I had attempted to date had some merit; That same tape which I had used in all of the previous experiments recorded at 7.5 ips with several passages of high frequencies was left sitting directly on a 3 inch diameter magnet for almost 40 hours. Well, I played it and in all sincerity was not able to hear that there was any impact on the sound.

Hi Alan,

Speaking of others in a radio studio, I used to put the bulk eraser to the side of my head (in line with the eyes) and press the button. No matter how safe I proclaimed it was, I could never get any of the others to do it as well.

There was this issue of one's vision wibbeling while the bulk eraser was on, but that's about it. :-)

Andrew

Hi Andrew, yep magnets rock! I've slept on magnetic mattresses for the last 20yrs, they're popular cause they work.

Not to run ads here (mods please note) but it takes about 6 months to assist any rheumatic problems. I started (hopefully) before they start.

Nice to see Benny can now sleep well too :) Cheers.

I'm going to seriously look into the matress :) I'd still really like to know from anyone out there whether they could give me a rough idea of how much magnetic field strength (Oe) and average or even above avergae speaker magnet possess; Based on this information I can make a much more empirical assessment given the data that Allan kindly outlined here in one of his responses - i.e. If the average Oe of an audio tape is approximately 330 and a "strong" speaker magnet (like from a 150/200 watt driver) is only 100 Oe then the coercivity is not nearly enough to have an adverse affect but I have no idea what that numerical value typically is. Unless I'm mistaken, it would have to be at least double (660Oe) before any damage can occur. Thanx

A curious thought

The tape is also a magnet. It is probably, also affecting the speaker magnet.... to some minute degree.

Hmmmm, Very interesting observation. In fact, I've moved the magnet so close to the tape that it actually attracts itself to the tape (you can see the strand moving).

"The tape is also a magnet."
I'm sure the "Old School" folks among us recall "print though".. One of the reasons for "library spooling" and storing R/R tapes "tails out" so any print-though would be post echo, not pre-echo, like on LZ's Whole Lotta Love.
More analog fun: How about the joys of transport & head alignments and repro/rec calibration on a A-800 or MTR-90. The 90 was a bit easier. We have it so easy now.

Rick - Please do not torment me like this. Please do elaborate on these issues: What exactly is "print through", "library spooling", and "tails out" ? I'd really like to know since I may need to put some of these into practice for my own collection; What's up with Led Zeppelin's "Whole Lotta Love" with post and pre echo? Also, if anyone can provide any other essential recommendations, please do not hesitate to volunteer them. Why can't I find any information on how much Oe an average speaker magnet has anywhere online......... ?

Most of us take the easy approach and don't store tapes near the speaker. Just saying.

Andrew
(who just glanced over to his Sony CRT professional video monitor and spotted a few tapes left on top)

Print through is a very annoying thing. Imagine a track that is very quiet, and then suddenly goes BOOM BOOM - the bit of tape with the very loud boom boom is perhaps a single turn of tape under a really quiet bit of tape. The print through effect means that the loud bit - more magnetism literally 'leak's through the tape backing and imprints itself on the layers either side. So when you play the tape, during the quiet bit, you hear a quieter version of the BOOM BOOM bit a short time before you should. This is a well know phenomena, and some studios used to have a rewind and restore policy - sticking the tape in, and winding it end to end so the physical 'lay' would be slightly different. If you store your tapes at the end of the tape, not the beginning, then the pre-echo becomes a post echo - and isn't so noticeable at the start of a track, because the music is already playing. Print through before the track starts is very, very, obvious.

Yep. Tails out.

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?

My simple assumption was that with all of the collective knowledge on this forum a concrete consensus could be attained. 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?

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.