Impact noise is walking around type noise that travels through the floor. The very best way to reduce this problem is to soundproof the floor above rather than try to deal with it just by soundproofing the ceiling below. If this is not possible then to soundproof the ceiling you must use some form of soundproofing isolation system. Just adding extra boards will not be worth the effort. Hoever if installed correctly a soundproofed ceiling system can often provide at least a halving of the perceived noise before the soundproofing was installed.