A sound cartridge is not necessary and is not included in the Crayola Color Wonder Sound Studio. The Color Wonder Sound Studio is an interactive coloring pad that lets you choose from 60 sound effects and place them anywhere on the Color Wonder coloring page. It includes 6 sound cards, 5 Mini Markers, 12 coloring sheets and 6 blank sheets. The sounds are "built into" the unit, and are activated by using one of the 6 sound cards. Color Wonder Sound Studio Expansion Packs can be purchased separately to extend the Sound Studio experience! Themed Expansion Packs, like Disney Princess and Toy Story, include 1 sound cartridge, 4 sound cards, 4 Mini Markers and 12 coloring pages. For additional information, visit
http://www.crayola.com/products/splash/color_wonder/sound-studio/.