Dual excitation shaker systems are commonly used to test long or heavy devices under test (DUT). When the device under test is very long or too heavy, a single shaker cannot perform the test because of oversized dimensions or a large driving force. Thus a dual excitation shaker system is arranged as the solution. Users can fix the longer sized or heavy DUT horizontally or vertically on top of a dual excitation shaker system. Common arrangements are horizontal push-push, push-pull, and vertical.

Head expanders are commonly used for vertical environmental testing. The purpose of the head expander is to extend the surface area of the shaker top to accommodate units under test (UUTs) with large dimensions for mounting and testing. One of the key parameters is the working frequency range associated with each head expander. The upper frequency is often used instead of the first resonance frequency of the head expander in vibration control tests.