Magnetic Field - Any Insights (Please)

Benny Sampson · November 5th, 2009, 10:06 PM

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.

Allan Black · November 6th, 2009, 01:52 AM

Quote:

Originally Posted by Andrew Smith

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.

Benny Sampson · November 6th, 2009, 09:21 AM

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

Don Xaliman · November 6th, 2009, 03:15 PM

A curious thought

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

Benny Sampson · November 6th, 2009, 03:38 PM

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).

Rick Reineke · November 6th, 2009, 05:00 PM

"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.

Benny Sampson · November 6th, 2009, 09:34 PM

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......... ?

Andrew Smith · November 7th, 2009, 12:16 AM

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)

Paul R Johnson · November 7th, 2009, 02:25 AM

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.

Jon Fairhurst · November 7th, 2009, 02:38 AM

Yep. Tails out.

Rick Reineke · November 7th, 2009, 09:22 AM

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.

Benny Sampson · November 7th, 2009, 11:08 AM

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 :)

Allan Black · November 7th, 2009, 06:27 PM

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.

Andrew Smith · November 8th, 2009, 08:25 AM

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! ;-)

Benny Sampson · November 8th, 2009, 09:52 AM

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?

November 7th, 2009, 02:38 AM	#40
Jon Fairhurst Inner Circle Join Date: May 2006 Location: Camas, WA, USA Posts: 5,513	Yep. Tails out. __________________ Jon Fairhurst

November 7th, 2009, 06:27 PM	#43
Allan Black Inner Circle Join Date: Sep 2006 Location: Sydney. Posts: 2,930	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. __________________ Drink more tap water. On admission at Sydney hospitals more than 5% of day patients are de-hydrated.

November 5th, 2009, 10:06 PM	#31
Benny Sampson New Boot Join Date: Oct 2009 Location: Quebec Posts: 22	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.

November 6th, 2009, 09:21 AM	#33
Benny Sampson New Boot Join Date: Oct 2009 Location: Quebec Posts: 22	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

November 6th, 2009, 03:15 PM	#34
Don Xaliman Regular Crew Join Date: Sep 2008 Location: Vancouver BC Posts: 96	A curious thought The tape is also a magnet. It is probably, also affecting the speaker magnet.... to some minute degree.

November 6th, 2009, 03:38 PM	#35
Benny Sampson New Boot Join Date: Oct 2009 Location: Quebec Posts: 22	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).

November 6th, 2009, 05:00 PM	#36
Rick Reineke Inner Circle Join Date: Aug 2008 Location: New York Posts: 2,039	"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.

November 6th, 2009, 09:34 PM	#37
Benny Sampson New Boot Join Date: Oct 2009 Location: Quebec Posts: 22	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......... ?

November 7th, 2009, 12:16 AM	#38
Andrew Smith Equal Opportunity Offender Join Date: Feb 2009 Location: Brisbane, Australia Posts: 3,065	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)

November 7th, 2009, 02:25 AM	#39
Paul R Johnson Inner Circle Join Date: Nov 2005 Location: Lowestoft - UK Posts: 4,045	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.

November 7th, 2009, 09:22 AM	#41
Rick Reineke Inner Circle Join Date: Aug 2008 Location: New York Posts: 2,039	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.

November 7th, 2009, 11:08 AM	#42
Benny Sampson New Boot Join Date: Oct 2009 Location: Quebec Posts: 22	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 :)

November 8th, 2009, 08:25 AM	#44
Andrew Smith Equal Opportunity Offender Join Date: Feb 2009 Location: Brisbane, Australia Posts: 3,065	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! ;-)

November 8th, 2009, 09:52 AM	#45
Benny Sampson New Boot Join Date: Oct 2009 Location: Quebec Posts: 22	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?