Case studies of acoustics outreach: Craft kits for children’s workshops and a 2-km giant megaphone experiment

We developed two hands-on craft kits for children’s acoustics workshops. The first kit is a paper craft smartphone stand designed as an acoustic horn. When a smartphone is placed in the completed model and music is played, the horn structure amplifies the sound. In the workshop, participants first learn about the principles and characteristics of acoustic horns in a short lecture, and then practice basic crafting skills such as cutting with a craft knife and gluing. The second kit is a vocal-tract model constructed from everyday materials such as condiment bottles, straws, and rubber sponges. Based on the principle of Kempelen’s speaking machine, participants can deform the bottle to produce vowel-like sounds, thereby learning the mechanism of voice production. We also collaborated with a television program to conduct an outdoor experiment using a giant megaphone designed to project the human voice over a distance of 2 km. Theoretical calculations predicted approximately 60% syllable intelligibility at 2 km under calm conditions, and the experiments generally confirmed this result. I experienced a 6-s delay between speech and reception, showing potential as a museum attraction. For outreach use, 500 m–1 km is more practical, and visual confirmation of the speaker is recommended.