There are at the present time two types of loud speakers generally available for use in theaters, the horn type and the free radiator baffle type. Although these two types as usually used in theaters are similar in that they employ moving coil driving elements, they differ materially in their performance characteristics, and for theater purposes where large sound powers are required these differences become very important. Some of the inherent characteristics of these two types of loud speakers are discussed in a general way in the following paragraphs and the effects of these characteristics upon the requirements of theater systems are illustrated.