Experimental Study of the Low-Frequency Noise Characteristics of Empty and Fitted Workshops

In order to investigate the temporal and steady-state low-frequency characteristics of sound in industrial workshops, measurements were made of reverberation times and sound-pressure levels in a machine shop and in a 1/8-scale-model workshop when empty and fitted. Low-frequency pure tones and octave-band noise were used as the source excitation. Fittings generally reduced reverberation times. In the empty machine shop, levels showed strong spatial variations due to modal effects, as expected. When fitted with machine tools, levels changed by up to 20 dB, and local variations increased, despite the fittings being small compared to the sound wavelengths. In the scale model, smaller and larger fittings were tested. Results for the model when empty and when fitted with the larger fittings were similar to those in the machine shop. With the smaller fittings, the results suggested that fittings can act to diffuse sound, reducing spatial variations. Tests were also done in an empty and fitted hemi-anechoic chamber to study the effect of fittings in the absence of the room. Fittings alone only slightly affected the sound field, demonstrating that modal effects are predominantly due to the room, possible modified by the presence of fittings.