This report describes the project of designing an interactive exhibit for children in the context of Science Centre Delft to actively explore, and thereby learn about, the interactions of light and sound beams with materials. It involves the application of a directional speaker in a totally new and dynamic way to trigger sound and light effects. The project is an example of a design project which is not about problem solving. It involves children as target group, which do not have urgent problems with current exhibits about light and sound interactions and do not have a specific need to learn about it. A solution space can thus not be defined by the needs of the target group. Therefore the context, the target group and the subjects of sound and light are thoroughly researched first. Then three iterations of experimentation, ideation, prototyping and evaluation are performed to gain a design vision. A final concept is developed which is evaluated with children in the context by means of a working prototype. The final concept, Sonolum, demonstrates a totally new dynamic application of a directional speaker to actively explore multi-sensory interactions with materials. With the Sonolum children can aim directional sound at modules to trigger sound and light effects. The children are invited to configure and explore patterns of modules with different materials on a magnetic wall. By doing so they can explore and learn more about different sound-light-material interactions. For example a module with a mirror reflects the sound and light in a specular and directed way, while a module with black foam will absorb the sound and light. The final prototype of Sonolum is evaluated upon enjoyment, stimulation of exploratory behaviour and bringing across the subjects of sound and light interactions with materials. The study was performed with 48 children over 2 days in the context of ‘Gamelab’ inside Science Centre Delft. The results show that children enjoy the exhibit, that the exhibit shows promise in supporting exploratory behaviour, but unfortunately does not yet bring across sound and light interactions with materials, although the children do indicate that the subject of the exhibit is light, sound and music. This may be due to some limitations of the prototype. Future development and investigation is needed to improve the perceivability of the sound-material effects in the exhibit.