While HDB window restrictors are primarily designed for safety reasons, they can also have some benefits for sound control. The restrictors can help to reduce the amount of external noise that enters a building through windows, which can be particularly important in noisy urban environments.

By limiting the opening angle of the window, window restrictors can help to reduce the amount of noise that enters a room from outside. This is because the smaller opening reduces the amount of air that can flow through the window, which can reduce the amount of sound that is transmitted. Additionally, the rubber or silicone gaskets that are used to secure the glass in the frame can also provide a barrier to sound.

However, it is important to note that window restrictors are not specifically designed for sound control, and their effectiveness in reducing noise will depend on various factors, such as the type of window, the location of the building, and the type of noise. Other sound control measures, such as double-glazing, sound insulation, or sound-absorbing materials, may also be necessary for more effective noise reduction.

Overall, while HDB window restrictors are primarily installed for safety reasons, they can also have some benefits for sound control. However, it is important to remember that they are not specifically designed for this purpose and that other sound control measures may be necessary for more effective noise reduction.