Sound waves travel through air. If your boards managed to block the sound then the slightest gap would allow sound through.
When jointing boards in studios some people use a sealant which always stops flexible. They would also use insulation which absorbs the sound.
Sound will also travel through some materials. So if your boards are connected to the wall then sound could travel because they are fixed to the wall.
If acoustic insulation was put on your wall then a studded wall. There would be a break between your noisy house and the joining wall of you and your neighbors. This way you may lose up to 6"/150mm of room space.