[Jim Pearson]

Hi Peter D,

My understanding is that, with the surface area of a hemisphere being twice that of its base circle, provided you use mesh with at least a 50% open area you would wind up with unrestricted flow.

Using flat mesh as you suggest, whilst easier to fabricate and fit, you will restrict the effective open area of your trumpet - and by a substantial amount if the mesh is only, say, 50-80% open area.

However, given that the trumpet is tapered, perhaps all you need to do is avoid restricting to less than the area at the narrowest point of the trumpet.....???

Regards,

Jim