Many factors affect stethoscope sound transmission. Although bench measurements with an artificial pure tone make for a straightforward measurement, chest sounds have many different simultaneous frequencies. We compared stethoscope output using a 50-3000 Hz pure tone sweep and pink noise (50-10K Hz).
The sound transmission characteristics of a pure tone sweep and pink noise through a double-tubed diagnostic stethoscope were measured in an anechoic chamber using a computerized signal analysis system (CoolEdit™ and MATLAB®). The reference signal was measured at the chest piece and the earpiece (other earpiece occluded). A plot of frequency vs. decibel change is given below.
The plot shows a difference between the shape of the pure tone sweep output and the pink noise output. The sweep output appears to develop periodic additive and subtractive nodes that would create signal distortion.
Real use conditions would involve listening to multiple frequencies simultaneously. Using concurrent, multiple frequencies during bench testing appeared to limit confounding variables that are more likely to occur with pure tones.
Clinicians using stethoscope comparisons for selection of a stethoscope should pay careful attention to the methodology employed and seek comparisons that use simultaneous multi-frequency analysis (natural or artificial).
J.B. Waugh, None.