Drive Units are delicate, expensive electrical components and, especially in the case of the tweeters, are sensitive to contamination with dust and dirt. There is also a danger of inquisitive small children and pets in my household, which can be even more detrimental to driver performance! Protection from these elements should be via an acoustically transparent grille. This could either be a cloth grille mounted over the whole front baffle, or round metal grilles clamped over the front of each individual drive unit.