Thank you for your kind words. There are two elements to transmitted noise – one is the sound insulation or lack of it, the other is the behaviour of the people creating the noise.
You are right in assuming that it will be trickier to prove a “nuisance” case, but not impossible. You need to gather evidence of what the noise sounds like, when it occurs and how frequently. This could be recordings and stat decs from friends and neighbours.
Then you can approach the neighbour and ask them what it is that they are doing that creates the thumping sound. It’s worth them cooperating on this as the next step is messy for both of you – mediation and maybe the tribunal.
I have an upstairs neighbour whose original owner put in a cheap floor then buggered off overseas and sold. The floor has never been brought up to the building’s now stringent standards but the occupants don’t make much noise … except when the owner’s teenage son is visiting; he can’t move from one room to the other without running.
If it ever became unbearable, I too would be looking down the barrel of a trip to Fair Trading and NCAT, so I sympathise.
By the way, you could get a different acoustic consultant to give you another interpretation of the test results. If the limit is 50, then 52 is a breach.