Any old piece of wood you set under the front edge of a combo amp to tilt it up towards the guitar player’s head. It also works on a lot of monitor speakers, especially repurposed FOH PA speakers that have shapes that aren’t all that conducive to pointing to a person’s head.
A chair can work here too and a variety of stands that are specifically made to position a combo amp in a way that the guitar player’s can hear it better. Im amazed at the number of professional touring guitar players that come through our venue that plop these smaller combo amps on the floor and they arent hearing anything close to an accurate representation of their playing so the audience ends up getting blasted with ice pick because that high-end information is usually what you miss when your ears arent in the cone of dispersion.
So yeah…”sound wood”.