Williams is a brand, like Lionel and MTH. They have a "True Blast" sound board that is decent and easy to install. There are several versions with different sound quality. The latest, True Blast Plus, costs about $70, includes the prime mover sound in addition to the horn and bell. Many of the forum sponsors sell them or you can just google for it. You can find the previous version, True Blast II, without the prime mover sound for less but you get what you pay for. The difference in sound quality of the horn and bell between the two products is significant.