Rod and beam with fuzzy structures is modeled using sprung mass system to analyze vibro-acoustic responses of complex structures. Energy density is used as response method to simulate the structural vibration, and the simulation indicates that the fuzzy structures affect the master structure maximally around the natural frequency of the fuzzy structures. The effect acts as a frequency dependent equivalent mass. The equivalent mass is positive under the natural frequency of the fuzzy structure and negative over the frequency. The positive equivalent mass decreases, while the negative one increases the vibration energy density responses.