A sensitivity of 90 db, is 90 db at 1 meter with 1 watt, so 1 meter basically listening position in a car, going 10 x to 10 watts gives you a 100 db, going 10 x again a 100 watts equals 110 db, can't really go up another 10x's and doubling to 180 watts only gives you a just noticeable change in volume.