**Abstract**

Heat exchangers and boilers are widely used in various plants such as power plants and chemical plants. In the heat exchanger and the boiler, a high level sound is sometimes generated from the tube bank installed in a duct. In tube banks, warm gas flows outside of the tube, and due to the external flow around tube banks, the Karman vortex shedding occurs. At a certain frequency of the Karman vortex shedding that depends on the flow velocity, the resonance phenomenon called the self-sustained tone occurs. The self-sustained tone might cause noise problems in the surroundings, losses due to plant shutdown, etc. For suppression of the self-sustained tone, insertion of baffle plates in the tube bank is generally used. Although the insertion of baffle plates has been adopted for a long time, it is difficult to decide the effective insertion positions. On the other hand, a method using perforated plates has been proposed for the suppression of the self-sustained tones. In this chapter, we review the generation mechanism of the self-sustained tone clarified experimentally and numerically, and the methods for suppressing a self-sustained tone using baffle plates and perforated plates.

**Keywords:** self-sustained tone, high level sound, acoustic resonance, lock-in phenomenon, countermeasure, baffle plate, perforated plate
