> I see occasionally in tv sets and the like aluminum (?) shields or
> screens covering a particularly sensitive (or radiating!) sections of
> circuitry.  My question is ... are these available anywhere?  Or are
> they typically something that is made in a metal shop along with
> whatever chassy metalwork that needs to be done?

These are probably designed for the project rather than a standard item
bought in.

> If I have them made, is any particular types of metal better or worse
> than others?  Right now I'm thinking of just a vertically mounted
> "strip" or "wall", kind of like a tennis net, say, between the two board
> sections.

I suspect all you will need is a "wall" made from a piece of un-etched PCB,
suitably grounded along one edge. That is if you need anything at all.

> I'm not 100% sure its necessary, this design is a radical reworking of
> an (aging) existing product, which used two layers, and I'm using four,
> and am getting significantly better performance already.  But if a 25c
> piece of metal can get me another 2db, I'll take it!  Also I have seen
> these screens over crystals/clock gen circuits in other audio A/D
> products and maybe it would help this one too.

Well sorting out grounding separation and using flood planes in the inner
layers will help a lot to keep the signals where they should stay. However I
would be tempted to run an un-attached trace between the two halves of the
board which will get grounded to the metal box. If there are a couple of
screw holes in it then a piece of metal can also be secured to test if this
will help your performance. Even a piece of cooking foil will allow you to
see if a difference will occur.

> I have access to an audio precision 2 (amazing piece of equipment) so a
> does-it-improve-things yes/no test is easy to do.

having suitable test equipment to see the small differences is a big step
forward :)

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