Not sure if there is any steel. I know my Z uses a lot of aluminum. I read somewhere that the column-style motors like this do not use a steel top plate because of their magnet orientation. I am not 100% sure this is accurate. I know looks don't mean everything, but its a solid design. Thanks
Of course they're steel. That's how they make the N and S pole of the magnet wrap around and create the gap... it needs to be as conductive as possible for magnetic flux, this is why the grade of steel is important. Think of it as a big horseshoe magnet with the two ends turned inwards, that's what a loudspeaker motor is.
I can't recall the specifics, I was told by someone at Atomic had it written down somewhere. The point isn't so much what you want it to be or don't want it to be, it's the fact that you will NEVER KNOW for sure unless you are the manufacturer or trust the manufacturer is actually building with the materials they promise. I've heard more than one story about the Chinese factories promising certain materials or building a nice prototype then cheaping out to save a buck once they have your money. Without some very advanced and expensive test equipment you'd likely never know what you're getting.
One story in particular I've heard about is some old 21" Pyle PA woofers where the buildhouse did a switcheroo with the magnetic materials in a later production run. There was over 2dB difference (audible). The person who got them thought that the motors might not have been charged fully so he went to have them charged and they exploded.
