No, copper edges out aluminum in that regard.
An externally hosted image should be here but it was not working when we last tested it.
se
But not necessarily at the same time.
If the interference is largely E field, then permeability and thickness doesn't really matter so much as conductivity. If the interference is largely H field, then conductivity doesn't really matter so much as permeability and thickness.
So it depends on what type of interference you're trying to shield from.
Michael Percy sells TI-Shield which is a sandwich of copper/Permalloy/copper which provides both E and H field shielding.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
I've always wondered why not castings? - I know Al casting porosity may give poorer finish even after machining but the material savings would be huge even with a crude sand casting - Cu or Bronzes would likely look better, investment casting could give finer detail at "reasonable" cost compared to machining a billet
Last edited:
Nice, the janitor is late again, i suppose the Orion just went in production ?
The hanging "raft" subchassis idea doesn't look half bad (photos section, second image).
The Orion has variable gain, or separate stages for MM and MC ? (guesstipating the latter, with 20 DPDT's)
Wowza, impressive team list.
You guys are novices in metal work. We have discussed this to death in part one of this thread. PLEASE learn from those with experience, or a knowledge metal worker of your acquaintance, but your questions are elementary and time consuming. This includes: type of materials, finish quality, practical seam concealment, etc. We have experts who do this for us, and they do a pretty good job, even though it can be rather expensive.
sand casting is about as cheap as dirt - the patterns are often wood
investment cores can be hand built/machined out of wax slabs/forms themselves cast in plasitic moulds - at even a dozen pieces you have a few US$K to work with if you can save many hours of CNC per part (if made in the US)
investment cores can be hand built/machined out of wax slabs/forms themselves cast in plasitic moulds - at even a dozen pieces you have a few US$K to work with if you can save many hours of CNC per part (if made in the US)
Last edited:
Sand casting does not yield a high quality aluminum product. Aluminum shrinks a lot as it cools. It is great for iron and works for bronze. There are ways to cast aluminum to get a useful product but thick walls are also a problem.
The alloys that work for casting are different than the ones you would normally machine. I have seen aluminum castings of such poor quality the would not hold water!
Up to 1/4" thick is still considered sheet metal and can be bent and welded. My tools in theory can bend 1/2" thick by 8 feet long, but for quality 1/8" thick is my limit and getting 8 feet to be all at the same angle requires a bit of set up and adjustment. 4 feet is about all I try.
Casting aluminum was a real pain and gave very poor results, so we bend and weld when needed. But I prefer bolts to welding.
The method that would be best in cost for a thick walled case is extrusion and then machining. A "U" shaped channel could have front and back panels to form 5 sides of the box. Standard channel is actually available that would work for cases smaller than a foot wide.
But as mentioned before Boeing finds carving things as large as wings to be economical!
where was I critical? - I aknowleged the porosity and finish issues from the start
where I last worked my instrumentation/control electronics was in welded corner bent sheet steel boxes with RF gasketing, the mechanical parts started with a few hundred lb of 3" thick MIC 6® plate "table top" - some parts machined in house from 6" thick stock
everyone in the company used the shop after hours for hobby projects - I'm not claiming to be a machinist but I have had college level hands on labs in manufacturing processes and machined my own hobby electronics housings (from heavy wall Al U channel stock in fact)
I would venture the current practice owes much to the "conceptual art" meme in marketing - where the claimed process is as much or more of a selling factor as the exact same function/appearance achieved by "lessor" means (and admit some "lessor means" may mean lessor finish quality at the highest levels)
where I last worked my instrumentation/control electronics was in welded corner bent sheet steel boxes with RF gasketing, the mechanical parts started with a few hundred lb of 3" thick MIC 6® plate "table top" - some parts machined in house from 6" thick stock
everyone in the company used the shop after hours for hobby projects - I'm not claiming to be a machinist but I have had college level hands on labs in manufacturing processes and machined my own hobby electronics housings (from heavy wall Al U channel stock in fact)
I would venture the current practice owes much to the "conceptual art" meme in marketing - where the claimed process is as much or more of a selling factor as the exact same function/appearance achieved by "lessor" means (and admit some "lessor means" may mean lessor finish quality at the highest levels)
I can't believe you said this. Where did you say you were taught physics again? What do you do, just say anything that pops into your head and expect people to believe you because you said it?
Classifications of Magnetic Materials - Succeed in Understanding Physics: School for Champions
"Paramagnetic materials are metals that are weakly attracted to magnets. Aluminum and copper are such metals. These materials can become very weak magnets, but their attractive force can only be measured with sensitive instruments.
Temperature can affect the magnetic properties of a material. Paramagnetic materials like aluminum, uranium and platinum become more magnetic when they are very cold.
The force of a ferromagnetic magnet is about a million times that of a magnet made with a paramagnetic material. Since the attractive force is so small, paramagnetic materials are typically considered nonmagnetic."
I'll bet if you hunted around real hard, you just might find volume II of Resnick and Halliday. That's the volume you said you lost and the one with the chapter about magnetism in it.
I believe we usually worry about AC magnetic fields – DC Hall effect may be one of the few physical effects not yet seized on by audiophile tweakers as being ignored by cloth eared engineers
for the most prevalent line frequency and harmonics AC currents causing interfering AC magnetic fields really thick conductors do "shield" magnetic fields – as already mentioned
for the most prevalent line frequency and harmonics AC currents causing interfering AC magnetic fields really thick conductors do "shield" magnetic fields – as already mentioned
Only materials which form a low magnetic flux path surrounding a source of a magentic field or a target to be protectect can shield magnetic fields. Generally this means an enclosure of that material of nearly 360 degrees in all planes. Mu metal is one such material. Copper, aluminum, tin (so called tin foil is mostly aluminium) won't work. Effective magnetic shielding is expensive and difficult. It is also usually unnecessary unless you live near a large transformer or a power line carrying high current (not necessarily high voltage.)
Here's a company that specializes in designing and fabricating magnetic shielding materials and devices;
Definitions | Amuneal
Extreme care must be exercized in designing magnetic shielding of electrical components. Many components such as wire which carry power depend on the flow of ambient air to cool it even when it is installed in conduit. Its safe ampacity rating depends on it and restricting air flow can sharply reduce the amount of current it can safely handle by reducing its ability to radiate resistive heating. A $100,000 magnetic shield installed around a 4000 amp 480 volt bus in a transformer vault I saw in an industrial facility some years ago virtually nullified its UL rating. And it didn't solve the magnetic field problem in nearby offices either. In another case, someone tried a large piece of sheet metal (steel) between a transformer on one side of a wall and an office on the other side. It had no effect.
The principles of magnetic fields and how to shield them have been known since the 19th century when Maxwell's laws were published. Volume II John, the one with the blue cover you misplaced.
Here's a company that specializes in designing and fabricating magnetic shielding materials and devices;
Definitions | Amuneal
Extreme care must be exercized in designing magnetic shielding of electrical components. Many components such as wire which carry power depend on the flow of ambient air to cool it even when it is installed in conduit. Its safe ampacity rating depends on it and restricting air flow can sharply reduce the amount of current it can safely handle by reducing its ability to radiate resistive heating. A $100,000 magnetic shield installed around a 4000 amp 480 volt bus in a transformer vault I saw in an industrial facility some years ago virtually nullified its UL rating. And it didn't solve the magnetic field problem in nearby offices either. In another case, someone tried a large piece of sheet metal (steel) between a transformer on one side of a wall and an office on the other side. It had no effect.
The principles of magnetic fields and how to shield them have been known since the 19th century when Maxwell's laws were published. Volume II John, the one with the blue cover you misplaced.
Paramagnetic and diamagnetic phenomena are interesting to study in a laboratory but they are of no value to engineering solutions to magnetic field problems in the real world, at least not in the audio world. People use the terms electrical and magnetic fields interchangeably but they are quite different even though they are often found together. The term electromagnetic field only helps confuse the situation.
A typical magnetic field problem in offices was the experience of CRT images that were unstable in fields of around 20 milligauss at 60 hz. Particularly sensitive were Sun workstations in the mid 1990s. The solution was to either move away from the source of the field or to purchase and install magnetically shielded boxes made for the workstations. The price was around $1000 each. Interference in audio systems is usually due to electrical fields, not magnetic fields. The sole exceptions may be from poorly shielded turntable motors near poorly shielded magnetic cartridges and power transformers. One other was deflection of the image of my CRT television set by powerful unshielded woofer magnets not far away from it. How forutunate that CRTs have gone the way of the dinosaur, the dodo bird, and phonograph records.
A typical magnetic field problem in offices was the experience of CRT images that were unstable in fields of around 20 milligauss at 60 hz. Particularly sensitive were Sun workstations in the mid 1990s. The solution was to either move away from the source of the field or to purchase and install magnetically shielded boxes made for the workstations. The price was around $1000 each. Interference in audio systems is usually due to electrical fields, not magnetic fields. The sole exceptions may be from poorly shielded turntable motors near poorly shielded magnetic cartridges and power transformers. One other was deflection of the image of my CRT television set by powerful unshielded woofer magnets not far away from it. How forutunate that CRTs have gone the way of the dinosaur, the dodo bird, and phonograph records.
Sleep through that lecture John?
Well if you did and you can't find the book.....
Maxwell's equations - Wikipedia, the free encyclopedia
Where I went to school we never used the del notation for the differential form, they were always written as full partial differential equations. The shortcuts were for the physics students.
- Status
- Not open for further replies.