1 watt at 86 db,2 watts for 89db,4 watts for 92, 8 watts for 95, 16 for 98db, 32 watts for 101, 64 watts for 104 and so on. So yes,40 is usually sufficient but keep in mind that thx is 110db and ultra thx is 112db.
Extra wattage is always a good thing with transient peaks (symbol crashed or bass drums).
Finally, you should have a "perceived" doubling of volume for every 10db increase.
Extra wattage is always a good thing with transient peaks (symbol crashed or bass drums).
Finally, you should have a "perceived" doubling of volume for every 10db increase.