Went to a studio room for the first time since january , and there was a trash metal band next door, I think he mic'd is double bass pedal up, we could hear it over our full band, really ruined the session
Good luck with the studio build, as others have said, build stud internal walls just off what you have already with cavitys filled with the most dense rockwall or similar you can stuff in will reduce, unless you want to go down a more expensive professional build, but that may be over the top
I did my garage like this in my old house and I could get very loud before it travelled into the other rooms , louder than i needed it to be