### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 5aPAa5. A model for sound absorption by and sound transmission through limp
fibrous layers.

**Srinivas Katragadda
**

**
Heng-Yi Lai
**

**
J. Stuart Bolton
**

**
**
*1077 Ray W. Herrick Labs., School of Mech. Eng., Purdue Univ., West
Lafayette, IN 47907-1077
*

*
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In recent tests it was found that the measured surface normal impedance and
transmission loss of limp, fibrous materials could be predicted more accurately
when using an elastic porous material model rather than a rigid porous material
model: i.e., the motion of the solid phase was found to be acoustically
significant. However, it was noted that if the frame stiffness was set to too
small a value in the elastic porous model, the boundary value problem that must
be solved to yield the surface impedance or transmission coefficient becomes
singular. Thus it was of interest to develop a porous material model in which it
is assumed from the beginning that the solid phase may move, but that it has no
bulk stiffness. Under these circumstances, the Biot model for elastic porous
materials may be simplified to yield a single second-order wave equation
governing the propagation of a single wave type in the limp porous material. The
solutions to that wave equation in combination with appropriate boundary
conditions may then be used to predict either the sound absorption by or sound
transmission through layers of limp fibrous material without concerns regarding
the numerical stability of the predictions.