This paper intends to set forth some of the more important facts about sound‐absorbing structures of the kind whose absorption may be explained as primarily due to resonance phenomena of the same kind as that occurring in Helmholtz resonators. It is believed that this kind of absorption has not been met with the general interest which it deserves, neither from the theoretical nor from the practical point of view. The theory is developed here only for the simple case of a single resonator. Special attention has been given to the question of the resistance of the resonator. It is pointed out, that the formula commonly used for the resistance of an aperture is not applicable in the case of resonance absorption, the actual values of the resistance being 3–6 times higher than the calculation predicts in the cases considered. Some examples of the practical applications of resonance‐absorbing structures are mentioned.