Development of a Low-Cost Impedance Tube to Measure Acoustic Absorption and Transmission Loss of Materials

Traditional methods of measuring sound absorption coefficient and sound transmission loss of acoustic materials and treatments are time-consuming and expensive. To overcome this limitation, normal incidence sound absorption and transmission loss measurement technique using an impedance tube was developed. Unfortunately this equipment is equally expensive. This paper presents an effort made to develop a cost-effective impedance tube for wider use especially for educational use in emerging countries. An impedance tube capable of measuring absorption coefficient and transmission loss is designed and built under a budget of $1500 suitable for educational institutions in developing countries. The design, development and fabrication of the low-cost impedance tube along with measurement results demonstrating its accuracy is presented. Using a calibrated acoustic sample, data obtained from the low-cost impedance tube were compared with those from a standard commercial tube with encouraging results. A parametric study was conducted showing the effects of various parameters on the accuracy of the measured results. These include tube material, tube dimensions, frequency range, source transducer, pressure-microphones, sample and microphone holder, data acquisition and reduction technique. Based on these, design options were generated to meet the cost and functionality targets pre-assigned. A list of suggested parts and vendors is also included for anyone interested to custom-build the tube.