This paper presents experimental measurements of masked thresholds of low frequency tones under background noises and application of loudness model to estimate the thresholds. The measurements of thresholds for tones at frequencies 20, 31.5, 40 and 50 Hz were conducted under three background noise conditions: one ambient noise and 60-100 Hz band-pass noises at two levels. The measurements were carried out in an uncontrolled environment in relatively quiet times. The perception thresholds of the same subjects were also measured for frequencies 31.5, 40 and 50 Hz inside a cabin with ambient noise levels well below the average hearing thresholds specified in ISO 389-7. Moore's loudness model has been used to estimate the masked thresholds. The estimated thresholds from the loudness model have been compared with the results obtained in the experiment. The results indicate that the noise above 50 Hz is effective in masking the low frequency tones at 50 Hz and below, and that Moore's loudness model can predict reasonably the average of the measured masked thresholds.