An impedance tube is a piece of test equipment which can be used to measure the absorption coefficient of a material and the transmission loss through a test material. As of when I started, the acoustics team was relying on manufacturer's data for any noise specifications of materials, like foams, we needed. Oftentimes the manufacturers who provide noise data such as absorption coefficient are those who manufacturer sound specific materials - These manufacturers are typically more expensive than those who mass produce general purpose foams. Building a custom impedance tube to use in house would allow our team to characterize cheaper materials for more informed use in our products.
To build this project I followed various published papers describing the theory, construction, and use of custom built impedance tubes. Following the papers as a guide and working with other members of the acoustics team, a fully working set up with a user guide was made and various materials were tested for their absorption coefficient and transmission loss characteristics. The results of these tests were verified against manufacturer data and theoretical models.