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In Reply to: RE: Pardon me posted by unclestu52 on August 04, 2007 at 14:47:53
i could think of a couple of areas:
1) around any transformer to remove EMI field
2) inside any signal generating equipment to help create an EMI-free field
3) around signal paths where parts used are metallic (would need to use small magnets obviously, but if i recall correctly, EMI fields operate in the inaudible-but-really-is-audible upper treble region)
4) on select AC cables (the z-shield which was a degaussian tube has got to have some magnetic elements to it)
best
rc
Follow Ups:
In general magnets make lousy shields, there are better ways to do it.
First lets break the "fields" down into two categories, magnetic fields and electric fields (I know this is a simplification and not really true, but it useful for most gross uses). The field coming out of a power transformer is primarily low frequency magnetic field. High frequency "RFI" is primarily electric field. These two take differing types of shielding.
The electric field can be shielded with a thin sheet of electricaly conductive material. Aluminum, copper etc. Good old household aluminum foil is perfectly sufficient. It does NOT need to be "grounded" to be effective. This does very little to stop low frequency magnetic fields.
There are two ways to stop the magnetic fields, THICK conductive material (say 1/4" or thicker aluminum plate, those thick aluminum face plates are not just for looks) or high permeability magnetic material. This is NOT magnets! magnetic material is composed of microscopic "domains", in a magnet the domains are all aligned so their magnetic fields add up, producing a strong external field. To be useful as a shield the domains need to go all which way (ie not aligned), but can easily be aligned when an external field is applied. These domains aligning with the field cancel it out preventing it from passing through. The domains in a magnet stay aligned, thus they cannot change based on the external field, thus they don't shield.
Once all the domains are completely aligned it cannot shield any more, the material is said to be saturated. Its important to use shield material that will not be saturated by the field you are trying to stop. There are a class of material commonly called "mu-metal" which are used for magnetic shielding. The domains in this material will will allign with a very weak external field, this is great for shielding detectors and such, but lousy for shielding say a power transformer. The field from the transformer is too strong and will saturate the material.
Given the above I prefer to use the thick aluminum approach, it can shield both types with one material and never saturates. Its magnetic shielding works by electric currents being induced inside the aluminum, the magnetic field from these currents blocks the external field. The lower the resistance of the material the better it works (hence thick material). Superconductors are the best, no magnetic field can get through a superconductor, just slightly impractical for home audio use.
A magnet near an audio transformer CAN change the sound of the transformer because it partially alligns the domains to begin with. This usually makes the sound worse rather than better. But it can for sure change it.
I hope this helps understand a little bit about shielding.
John S.
At the risk of becoming a bore, I would add a few more.
Magnetism and electricity are forever interlinked. A lot of time I find it more useful to simply convert that field into other forms and to vent the converted energy.
In the case of transformers, the fluctuating AC field generates a fluctuating magnetic field, and, as you sometimes experience, the transformer cores can hum and buzz. You can convert part of that energy into heat by simply shock mounting the power transformers. I use simple rubber grommets and longer bolts to fasten my transformers and this allows the transformers to convert those fields into movement and thus convert that energy into heat.
Likewise, those bolts, usually steel, which hold the laminations together can be changed to brass or other non magnetic material to audible sonic benefit. For toroidal transformers, there is usually a steel bolt down the center to anchor them, and a change out to a non ferrous material or even better a non conductive material adds to the sonic benefit. Typically in this kind of 'mods' there is a significant increase in midrange energy and warmth. The music takes on a more 'relaxed' feel.
Some EI transformers are mounted with the laminations bolted against a chassis. This economically saves on the cost for an additional bell end, but it couples the transformer to the larger surface of the chassis, spreading the effects of the magnetic field. Using the inverse square law, where you can achieve effective shielding simply from distance, try raising the laminations, say, a quarter inch above the chassis using a simple spacer and longer bolts. You will get a subtle but audible sonic shift in obtaining better high frequencies.
I have not played around with using magnets to counter magnetic sources, but effective shielding was a bit difficult to achieve in my experience. I simply found it easier and cheaper to sort of direct the magnetic fields. Pieces of ferrous material (sheet iron or mu metal) work very well in accomplishing this. I bought a roll (100 feet) of mu metal foil for experimentation, and while the shielding worked to a degree, I found it easier to simply place small doubled up pieces between the magnetic source and the component I wanted to shield.
Other people use this principle to good effect also. The "power wraps" by the High Wire people is essentially that, a magnetically permeable material that you coil around the wire. It basically takes the "rule of the right hand" and exploits it. That's the rule of physics where if the current flows in the direction of the thumb of your right hand, the magnetic field curls around like the fingers of that hand. The wraps take that magnetic field and since magnetism would rather go through a permeable object rather than air, it literally 'speeds' up the magnetic flow. It does induce a current in the wrap, so if you ground the end of the wrap you get even better performance. Incidentally the Cable Jackets from Shun Mook work on the same principle, but they reverse the twist to slow down the signal propagation in order to achieve a more 'laid back'
sound. If you want a 'faster' sound, simply reverse the wrap and attach the ground wire.
Other ramifications of this rule can be utilized in how you arrange the twist of a twin lead pair. When twisting a pair of wires together, the natural tendency is to make a left handed twist (I'm right handed). That goes against the rule of the right hand, and it warms up the sound by slowing things down. Give the pair a right hand twist (like most ordinary screw thread) and things speed up as you are now harnessing the magnetic field to sort of being self propagating.
An interesting cable to play around with this is the Kimber speaker cables. If you sort of puff them up you will notice that their braid is a double helix with the negatives going in one spiral direction and the positives in the other direction. Again if you make the positives take the right hand twist group, you get a 'faster' sounding cable. If you reverse the set up, and make the positive wires take the left hand twist group you get a 'slower', more laid back sound.
I do not mean to discourage experimentation, because we all learn from it, even from 'mistakes' (and boy have I barked up many incorrect paths!). Everyone has different ideas and implementations so please do not take this as being negative. I simply find that it pays to harness the magnetic interactions rather than simply to quell them.
Looking forward to reading about your own experimentation.
Stu
I've pondered about some of those effects, but then I ain't no great thinker. 8^)While I have a fairly large number of magnets lying about, I've actually been more worried about limiting the magnetic field, for the most part.
The Z-sleeve which you refer to was described by Mark Hampton, it's designer, as a modified zero gauss chamber, but it uses shielding to reduce fields, but not any actual magnets, IIRC. It is fabulously effective, IMHO.
Certain other products, like Purist Audio break in disc, claim to have degaussing tones (this from Jim Aud himself).
With the experiences of those two products I have been relatively reluctant to introduce additional magnetic fields into the system. Since most signals are AC, the resulting EMI field is likewise fluctuating and I have never really thought about the effect of placing a fixed magnetic field in close proximity to the fluctuating one.
A 'White' paper by Counterpoint years ago, while they were still in business explained their selection of EI core transformers as being preferable, because they thought the generated magnetic fields could fluctuate faster with shifting load demands (or something to that effect, it's been a while).
I am fascinated by your proposals and inquiries, and certainly would appreciate a report on any results when you try them.
I have done a little experimentation myself and have posted it before, and perhaps in other forums. These are a couple:
Had a chance to peer inside a VdH Grasshopper cartridge and while it is a Benz in different anodizing, one of the chief differences is that there is an additional magnet placed on the front pole piece of the cartridge. In trying this myself, using simple refrigerator magnets cut to shape, I achieved a very nice increase in sonic retrieval, but then the application here is quite obvious: a strengthening of the magnetic field on the coil structure.
Elsewhere I had posted (Isolation forum, IIRC) that I place magnets on the crossbars of my steel equipment rack (a ladder type assembly solidly welded) This, I believe, restricts the magnetic field induced by the power transformers of the equipment. Do not use this on a TT stand, BTW, it really screws up the sound! Here I believe the magnetic induction actually generates a current in the adjacent steel rails and the magnets restrict that field generated.
I have never placed magnets adjacent to a transformer thinking that the field of the magnet could compound the issue. I would guess if it is slightly weaker than the generated field it could be of benefit, though.
At any rate, it would be greatly appreciated if you report on the progress of your experimentation.
Stu
I have been using a Hammond F 21 tape eraser on my cds, dvds and lps to great effect, so much so that all my audio friends are trying to find a similar device.I know there are the Furutech and Walker units, but this is a large industrial unit used in recording studios from the past.I have tried the various demagging cds and all manner of cd tweeks from having them cut,washed and coloured .There were some slight sonic changes,but no flat out sonic winners.Then on a lark and reading about the Talisman et al I sourced the above mentioned Hammond.All you do is place the cd on the flat plate turn on the switch for 30 sec, then repeat on the other side.For albums I leave them in their sleeves and slowly rotate the lp over the plate and then do the other side.The first response from audiophiles is "did you just turn up the volume?"The increase in separation,tone, information and the level of relaxation is enormous.It's the most beneficial component I have added to my system which includeds a dedicated 30 amp line, a Furman IT 1220 balanced power conditioner, Shunyata Hydra 2 and Annaconda power cords.They all made a difference, but not as night and day an improvement as demagging with the Hammond.
The how or why, I will leave to those with an electrical background to figure out.But you don't need an engineering degree(although one of my audio friends has one)to hear the difference.Nor does your system have to cost more than your car to demonstrate the difference.The change on lps is like the the difference in relaxation you feel when you put on some vinyl after a listening session with cds.
I use a Geneva brand degausser myself: it was advertised as being the strongest hand held unit and puts out 2800 gauss. Table models can put out even more.
I had, but had to dump, some military units which weighed in at 350 pounds. Never got a chance to use them because they required 240 VAC and the warning labels on them stated personnel with pacemakers had to be 10 feet away (not that I have one). They were so big I simply couldn't find a place for them.
The biggest benefit of degaussing the LP's is that it lowers surface noise when you find that rare but very well used disc.
Stu
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