Bhashya
तथा दिशो मधु ।दिशां यद्यपि श्रोत्रमध्यात्मम्,शब्दप्रतिश्रवणवेलायां तु विशेषतः संनिहितो भवतीतिअध्यात्मं प्रातिश्रुत्कः- प्रतिश्रुत्कायां प्रतिश्रवणवेलायां भवःप्रातिश्रुत्कः ॥
In plain words
The same is true of the directions. Their inward counterpart is, in general, the ear — but at the very moment a sound comes echoing back, the ear is more present than at any other time. That is why, within you, it is named the echo: the echo is simply what arises the instant a sound returns.
Close to the Sanskrit
So too, the directions' honey: of the directions, although the ear is, in general, the inward correlate, since at the time of the resounding-back of sound it is especially present, therefore, with reference to the self, it is the echo — that which arises at the moment of the resounding-back is the echo.