Without having an SPL meter. Run your receiver's auto room correction (Audyssey, YPAO, MCACC) If you leave all levels set where that software puts them then 0db on your master volume control is reference level. That's why its 0 and anything lower has a - number because you are below reference. However I use Audyssey then use an SPL meter to get 75db from each speaker to my MLP. For what ever reason there is quite a big difference in how Audyssey sets it and the SPL meter ( I think its like 3 or 4 db difference).