An adjustable equipment curb has upper and lower frames, each having opposed first and second length-adjustable sides and opposed length-adjustable first and second ends interconnectable to form a rigid frame and height-adjustable mounting legs. The lower frame may be used alone, or may support the upper frame through a shock mount system having mounts affixed to both the upper and lower frames and shock absorbing springs between the mounts. The frames may be formed of interconnecting channel members, and the lower frame channel members may be of a perforated construction that, in conjunction with applied sheathing, provides acoustic damping. Seismic brackets may be affixed to the either of the frames to provide resist seismic shock and developed moment resistance.