來自Why are high frequency sounds more directional than lower frequencies? Jørgen Dal的回答
A high frequency wave will pass right through the gap - while the low frequency wave will be diffracted going through the same gap.
The wavelength/gap ratio is the deciding factor for diffraction.
總之, 指向性是和信號的頻率還有孔徑有關係的.
Also remember that a high frequency wave has more energy than a low frequency wave of similar amplitude.
(這裏個人推測因爲power是按一段時間內的信號來算的, 高頻的power會比低頻大.)