The problems with plexi that no one has posted yet are definitely there. While some of you believe that it is strong, it is not as strong as wood or mdf in larger pieces. The larger the piece, the easier it can break. Plexiglass can bend much easier than wood can, thus if your box is flexing because the surface area is too large, you are losing energy that could be turned into sound. While it may be small it is still wasted energy. Plexiglass will flex much easier than mdf does, especially in a larger surface area when compared to the same thickness of mdf. This is why most people use a thicker plexi material.
The other side of an issue to plexiglass is it's reflectivity. Plexiglass and glass in general is a highly reflective surface as compared to mdf, wood or a painted surface. Reflected waves on the inside of a sub box eat up output, especially in a box that has parallel surfaces. When using plexiglass it is also recommended to use a material that will help to scatter the reflected wave on the inside of the sub box.
The other side of an issue to plexiglass is it's reflectivity. Plexiglass and glass in general is a highly reflective surface as compared to mdf, wood or a painted surface. Reflected waves on the inside of a sub box eat up output, especially in a box that has parallel surfaces. When using plexiglass it is also recommended to use a material that will help to scatter the reflected wave on the inside of the sub box.
