Table 1. Typical low frequency noise levels of electric devices in experimental rooms.

Electric devices	Noise levels (dB SPL) at 100 Hz
4°C freezers	65.3±4.8
−30°C freezers	66.1±4.5
−80°C freezers	69.9±2.9
Ice makers	61.8±1.0
Draft chambers	75.5±0.7

Noise levels (means ± SD) were measured by a noise level meter and calculated as an average of five repeated measurements. Noise levels were measured at a distance of approximately 20 cm from the devices shown in Table 1. Background level (mean ± SD) of low frequency noise at 100 Hz was 35.7±2.7 dB SPL in 5 experimental rooms without noise-generating devices shown in Table 1.