Re: FYI: "alnico" magnet types defined
I'm researching what the tech specs mean to us. I'll re-post when I know more
-jbb
'k, so here's the scoop: (see original post for link to table of alnico properties)
1. The table shows that alnico magnets are various mixtures of aluminum, nickel, cobalt, copper, titanium, and mostly iron.
2. The "strength" of the magnet is given by the "Br" value; called resonance or residual induction. This roughly defines how heavy an object it can pick up.
3. The "energy product", "Bh" relates to the density of the magnetic energy. Think of those diagrams of a bar magnet with flow lines drawn showing an arcing path from one pole of a magnet to the other (or the flow lines from the Earth's north pole to the south pole). The Bh is a measure of how many flow lines there are, or how densely the flow lines are packed. Another way to think about it: Suppose you have two steel plates, each 1 ft X 1 ft and weighing 100 lbs. On the first plate attach 1 strap to each corner. So 4 straps per 1 square foot or 100 lbs. Hook the 4 straps to one hook on a crane and lift it. Now take the other plate and attach straps on the plate on a 10 x 10 grid, so 100 straps per square foot or 100 lbs., and lift it with the same crane. so the Br is the same but the Bh varies by a factor of 25.
So if Br is a measure of a magnet's strength (force), Bh is a measure of how densely the force is applied (i.e. does the object feel 10 flow lines per square inch, or 1,000 flow lines per square inch?)
4. Electrical resistivity is another property that may have meaning to us, but it doesn't change much and I don't know just how it affects the sound. I don't think the other properties affect us either (unless you're playing a really hot room, say 850 degrees C).
So, by measures of Br and Bh, alnico 5 magnets are "stronger" than alnico 2 magnets.
Cast magnets are made by pouring molten alloy into a mold. Sintered magnets are formed by heating small, solid alloy grains under pressure, but not to the melting point.
Isotropic magnets have the same physical properties in all directions. In anisotropic magnets, the physical properties differ in different directions, and are usually set up to have the strongest properties aligned through the poles of the magnet.
But then, don't forget rare earth magnets. They are used extensively in computer hard drives, microphones, head phones, speakers, &tc. I don't know why they haven't made it into pups yet. Look here and compare to alnico magnets:
https://en.wikipedia.org/wiki/Rare-earth_magnet
Thanks a heap,
-jbb
PS: I made all that stuff up.
