The chest is a significant collector of ambient noise in heart sound recordings

Weak murmurs related to coronary artery disease might be masked in ambient noise when heart sounds are recorded in clinical settings. The aim of the current study was to characterize the influx of ambient noise through the chest and through the microphone´s coupler house. To estimate the transmission through the coupler house the coupler was placed in contact with a heavy block of steel in an anechoic chamber while 100 dB(A) SPL pink noise was played as ambient noise. The transmission through the chest pathway was measured for three males and two females. 45 seconds of heart sounds were recorded in silence in the anechoic chamber and under the presence of 100 dB pink noise. The spectrum of the noise entering the recordings was estimated by subtracting the spectrum of the heart sounds recorded in silence from the spectrum of the heart sounds recorded during 100 dB noise. In the frequency band of interest (200-1000 Hz) the noise was attenuated 53.5 dB by the coupler house. The chest pathway amplified the noise by 6.6 dB (Std.0.9). In conclusion the ambient noise is conducted via the chest path to the microphone with a slight amplification.