Box plan is the full-fledged back loaded horn enclosure for FE168Esigma. The box realizes no stress reproduction from 50Hz to 20kHz with single FE168Esigma. Well-tuned low frequency realizes tight and massive sound with perceptible fast response. Effectively downscaled baffle size realizes prior sound field and image localization and ensures FE168Esigma’s dynamic sound with abundance of energy.