In this paper, a three-dimensional optimal higher-order Ambisonics encoding (3-D HOA) method, which offers the possibility to impose spatial stop-bands in the directivity patterns of all the spherical harmonics while keeping the transformed audio channels still compatible with the 3-D HOA reproduction sound format, is introduced. This might be useful as a post-processing technique for suppressing interfering signals from specific directions in a 3-D HOA recording. The method is adapted from recent work on the optimization of spherical microphone array beamforming. The new spherical harmonics decomposition approach also exhibits its advantage in improving the resolution of audio source localization. Numerical simulations and experimental results are used to evaluate the proposed method.