Why you did it? because I think it's a weak point in the wall that let's the sound getting outside.
It is not a weak point when proper sound isolation techniques and methods are utilized.
What's the method to eliminate the sound that go through your air-condition tube in the ceiling?
Again, accepted sound isolation techniques and materials were used to reduce noise transmission by way of HVAC ducts.
NOTE: The primary purpose of sound isolation in a sound playback space is to reduce noise penetration into the room to a level of NR20 or NC20. The secondary, more expensive, and only sometimes requested requirement to reduce sound transmission out of the room. In this case, the generally accepted practice is to not increase the noise floor of adjacent spaces by more than 3dB. Contrary to common layperson belief, the purpose of sound isolation in sound playback spaces is to reduce sound entering the space not the other way around. The softest sound recorded on a sound track is 22dB, therefore, the in room noise floor must be below that level.