The delayed resonator, as a tunable active vibration absorber with an emphasis on the design features. This technique uses a control that has a time-delayed feedback of the absorber mass displacement. The substance of this process is in that the absorber completely removes oscillations from the harmonically excited primary structure. Seminal features of this method are the excitation frequency range can vary over a semi-infinite interval, and the absorber can be tuned in real time. These characteristics uniquely distinguish it from the other techniques. Stability issues of the primary system combined with the delayed resonator are addressed following Nyquist and root locus methods. In particular, the absorption performance for cases with time-varying excitation frequency is studied. An analysis of transient absorption behavior of the delayed resonator during the tuning phase is presented. An example case is taken that considers a step change in the excitation frequency. The superiority of the delayed-resonator absorber over the conventional a priori tuned absorbers is also demonstrated. The highlight of the paper is at the design aspect of this novel absorber. A selection template is proposed for the designer to achieve a desirable frequency-tuning property for the absorption. A set of simulation verifications is included in the text.