The Modal Decomposition of an Impedance Tube
Abstract
Impedance tubes are commonly used for determining the acoustic impedance of a material. This process is accomplished by placing the material into the end of the tube, where it is subjected to acoustic energy. Additional uses for impedance tubes include the testing and calibration of microphones or instruments at a predetermined location inside the tube through insonification. Impedance tubes usually consist of long ducts, with a speaker mounted at one end or in the duct wall and with the material placed at the other end. Holes are drilled in the tube at various locations to allow pressure measurements with microphones. In the past, a steady-state continuous model was used to predict the response of an impedance tube for pressure excitation at one end and an unknown acoustic impedance at the other end. The work presented here extends the modeling of impedance tubes by developing an eigenvalue-based model of the tube in modal space that can incorporate the transient or steadystate response of velocity sources on the spatial domain and the pressure sources at the end of the tube. Experimental verification is included for several different test configurations. Finally, the inverse problem is solved, which allows the determination of acoustic impedance from the eigenvalues of the measured system response
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 08, 1994
- Accession Number
- ADA283591
Entities
People
- Andrew John Hull
Organizations
- Naval Undersea Warfare Center