^^ i think those boards are used inside the rooms to dampen echoing and prevent noise/sound to escape outside.
what you need is some clever solution to let the air in but block the noise. sound travels in waves in bounces away from obstacles. so, you can install louvres outside your windows in such a manner that it deflects the sound waves. or create a sound generator that cancels out the incoming noise. it's easy to make but i've heard that it's difficult to up-scale such devices. and even an air flow can block/deflect sounds upto some extent.
i think some kind of sound dam in the form of louvres, bamboo curtains etc will help in blocking the noise thru a window. you'll need to adjust the direction your contraption to block maximum noise.
