Estimation of the speed of sound waves using a modular 3D printed Helmholtz resonator

This work shows the redesign of an elemental experience based on the Helmholtz resonator using 3D printing. A Helmholtz resonator is based on a volume and at least one opening that can include a tube or not. The air column inside the tube can be considered the mass of the system, whereas the volume represents the system's stiffness. Due to these analogies between acoustics and mechanics, the Helmholtz resonator is an interesting example of a harmonic oscillator. The relevance of harmonic motions is well known, and this topic is present in the syllabus of many technical and scientific education degrees. In this work, a bottle has been designed and fabricated using 3D printer technology. The design aimed to create a Helmholtz resonator with a variable frequency of resonance. Different mouthpieces have also been designed. The bottle is composed of a set of cylindrical sections that can be attached, enlarging the length of the container. For ensuring that the different parts set a tight enclosure, an O-ring seal has also been designed and fabricated. As more rings and O-seal junctions are attached, the volume of the resonator grows. By blowing the mouth of the Helmholtz resonator with different sections, different resonance frequencies can be measured. From these measurements, several parameters can be estimated indirectly, such as the speed of sound waves, the room temperature, and air density. 3D printing permits to analyse several scenarios without using uncomfortablestrategies to vary the bottle's volume, such as water, reducing the hazard in a laboratory with electronic instrumentation. This research was funded by the Ministerio de Ciencia e Innovación (Spain) under Projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and PID2019-106601RB-I00, by the ‘Redes-I3CE Research Program in university education of the Institute of Education Sciences of the University of Alicante (2020–21 call)’. Reference: 5310.