Abstract: Spurious cavity resonance effects in a cabinet housing electronics circuitry are suppressed by determining the maximum repetition rate or frequency for legitimate signals which can appear in the circuitry and then establishing the dimensions of each cavity within the cabinet such that each cavity's resonant frequency is higher than the critical repetition rate/frequency. Since a given cavity in a cabinet is typically block-shaped (such as the space between a cabinet door and the circuit panel facing the door), a special purpose formula may be employed to obtain a good approximation of the cavity's resonant frequency, and the cavity dimensions then adjusted to raise the cavity resonant frequency above the critical frequency. For the still more particular cavity configuration in which the length is greater than the width which is much greater than the depth, a further simplified formula can be employed to find an approximate cavity resonant frequency.