Development of an anechoic chamber

In the Institute of Mineral Industry Research at St. Hilaire, an anechoic chamber was constructed for the measurement of noise from light and medium hammer drills. The principle features of the chamber are its simplicity and cheapness. The general dimensions of the chamber are outside, 9 X 6 X 6 ft, and inside, 6 X 3 X 3 ft. It is lined with dihedral-shaped wedges manufactured from Eccodamp MG foam (density 35 kg/km2). The chamber is continuously ventilated and supported on rubber pads. It provides natural frequency under load of less than 7 Hz. The insulation against noise in the vicinity of the building is good according to our measurements. Brüel and Kjaer (B and K) equipment was used for all tests. Mention is also made of the microphone orientation system, the measurement cable installation, and the electrical installation. Finally, some measurements on the completed chamber, with regard to their free-field performances, are described. Calibration predicts cut-off frequency at 400 Hz. These measurements show that the chamber can be used for good measurements above 400 -Liz and under extreme outside conditions.