The walnut mantle with a custom heat shield was a project for a customer we have done multiple projects for. The homeowners were having an issue with the heat rising off of the gas fireplace and overheating their sound bar. They wanted a sleek minimalist look, functional, and they wanted it to contrast with the white oak floating shelves we built for them in the adjacent alcove. This is what we came up with and it was definitely a winner!
For the heat shield we had our local meta shop cut a piece of steel and bend it on their brake at a slight angle about one inch from the end; this is to deflect the heat away from the mantle. Then we cut one inch steel tube into one inch standoffs, coated the metal with a high temp paint and attached it to the bottom with screws countersunk into the bottom of the heat shield. Bam!