How loud can music be played?
There is no set level. It will depend whether anyone is likely to be disturbed by the noise. Daytime noise is more likely to be tolerated than night-time noise.
As a guide if you close the door to the room where the music is playing and the music can still be heard in the adjacent rooms then it is likely that your neighbour can hear it too.
If you are going to have a party you should let your neighbours (including the ones behind you) know well in advance.
If the party goes on late make sure the music is kept inside the house and the windows and doors are kept shut (do not erect sound systems inside marquees at night), keep the music down especially late at night and keep people inside the house.
Environmental Services will serve a noise abatement notice if they witness nuisance and consider further action if the noise is not abated (especially if there is a history of parties).