Recommended for medium-to-large areas, such as concert halls, gymnasiums and churches, those rooms with pronounced low-frequency problems and for those rooms where sonic accuracy is mandatory and maximum absorption is required. 4" Studiofoam provides excellent low-frequency control (3x that of 2" Studiofoam) and can make rooms very dry. In some instances, using 4" on your walls can negate the need for significant bass trapping.