Physical demonstrations using vocal-tract models have been shown to be a quite intuitive way to teach acoustic phenomena on speech production for acoustic phonetics and speech science classes. Several models for different purposes have been developed by Arai within the last 20 + years, including vocal-tract models, sound sources, and lung models [e.g., T. Arai, J. Acoust. Soc. Am.131(3), 2444–2454 (2012)]. By combining them, the following topics can be effectively taught in virtual and in-person classrooms: visualizing the sound propagation, the relationship between vocal-tract configuration and sound quality; the source-filter theory of speech production; the quantal theory; many-to-one mapping between articulation and sound; many-to-one mapping between sounds and phoneme; and source-filter interactions. Because such demonstrations are highly demanded, the Acoustic-Phonetics Demonstrations (APD) website has been made public ( to make videos and sound demonstrations available for academic use. The same website contains files of subsets of the vocal-tract models for 3D-printers, so users can download and 3D-print them to have their own models. In addition, some of the models are being used for workshops and exhibitions at museums. The applications of the models are now expanding to multiple areas, such as language learning and clinical situations like speech therapy.