Legendary akg sound. all wms 40 pro vocal systems share the same brilliant sound and ease of use. unique hdap (high definition audio performance) technology ensures the best possible, realistic sound at any time. the rugged handheld transmitter with its soft-touch finish is extremely easy to use and fulfills the highest esthetic requirements. the transmitters operate for 30 hours off a single aa size battery, saving frequent battery replacements and thus money. if you need two transmitters, consider the cost efficient dual set systems.