Besides closing it very slowly, any good tricks / gadgets that will slow down the door so it doesn't close with a thud?
There are a few things you can do:
Check the hinges and use a level to see that the door is square. A heavy door hung incorrectly can slam heavily. Check this guide at national contractors for how to level a door. Some tips from it: check that the hinges are tight, not too heavily greased, and the same distance from the frame.
Install a closer arm (can be expensive)
- If the door isn't closing too hard, but makes a fair amount of noise, try putting some small felt pads on the inside of the jamb to soften the closure.
You could also install from 2-> several dampers like these ones depending how heavy the door is or how well you want to dampen it - for example you have a heavy draft that SLAMS the door shut several will be recomeneded to adsorb the doors speed. These work well if installed fairly well.
Either into the frame somehow- slighlty countersinking it so it hides nicely, or not- its up to you and your skills.
Or just using a provided housing the will mount flush onto the frame of your door in any position that is best for you.
An other couple of possible hardware solutions to look into (exact size & weight of the door will determine if they are appropriate or not)...
Cheaper end of the market, Chain Spring Door Closer:
High end of the market, Concealed (Automatic) Door Closer: