Low frequency acoustic method to measure the complex density of porous materials.

In this paper, a new acoustic lumped element-based method to measure the complex density of porous materials at low frequency is provided. Based on the electroacoustic analogy of wave propagation inside a porous medium, an analytical derivation of the measurement method is given. Measurements can be performed in a short open tube and by placing the tested sample between an acoustic source (i.

Low frequency acoustic method to measure the complex bulk modulus of porous materials.

In this work, an acoustic lumped element technique has been developed to measure the dynamic bulk modulus of porous materials in the low frequency range ( f<500 Hz). Based on the electroacoustic analogy of wave propagation inside a porous medium, an analytical derivation of the measurement method is given. Unlike other techniques, it requires the use of only two microphones placed in the cavity containing the sample being tested and in the loudspeaker box.

Acoustic and thermoacoustic properties of an additive manufactured lattice structure.

With the advent of additive manufacturing, lattice structures can be printed with precisely controlled geometries. In this way, it is possible to realize porous samples with specific acoustic and thermoacoustic characteristics. However, to this aim and prior to the manufacturing process, it is fundamental to have a design tool that can predict the behaviour of the lattices.

A study on the energy and the reflection angle of the sound reflected by a porous material.

Many noise control applications are based on the use of porous materials; therefore, it is important to have a tool to simulate acoustic behaviours. Plane-wave acoustic properties such as the sound absorption or reflection coefficient at normal incidence can be quickly obtained using standing wave tube or theoretical models and can be used to select the type of porous material and its dimensions. However, in real situations, no plane wave exists, and the sound field is more complex.

Measurement of the resistivity of porous materials with an alternating air-flow method.

Air-flow resistivity is a main parameter governing the acoustic behavior of porous materials for sound absorption. The international standard ISO 9053 specifies two different methods to measure the air-flow resistivity, namely a steady-state air-flow method and an alternating air-flow method. The latter is realized by the measurement of the sound pressure at 2 Hz in a small rigid volume closed partially by the test sample.