Table 1: Relative peak-to-peak amplitude of the 1000 Hz signal obtained for four stethoscope assemblies (Fig. 1), scaled relative to the diaphragm side of the Littman Classic II SE unit (reference unit). The absolute sound intensity at the vibration plate was measured at 79.1 dB SPL (A-weighted) using an EXTECH Model 407750 Digital Sound Level Meter, while the relative sound intensity obtained at the stethoscope under test was measured using a RadioShack 33-3013 miniature omnidirectional electret microphone connected to the stethoscope head through a short piece of tubing and amplified using a RadioShack miniature audio amplifier (Catalog # 2771008) for display on a USB oscilloscope (Picoscope 2205). All assemblies were placed on the test surface and held in position by their weight except the disposable unit (test assembly 5), which on account of its lightweight had to be secured with a double-sided adhesive disk specifically designed for the use of stethoscope (3M Model 2181).

Stethoscope Assembly Under Test	Figure Reference	Voltage Ratio
Test assembly 1 Littman Classic II SE – diaphragm side	Figure 1 Bottom left	1.0 (reference)
Test assembly 2 Littman Classic II SE – bell side	Figure 1 Bottom left	0.55
Test assembly 3 Generic stethoscope – diaphragm side	Figure 1 Upper left	0.79
Test assembly 4 Generic stethoscope – bell side	Figure 1 Upper left	0.16
Test assembly 5 Diaphragm only disposable stethoscope	Figure 1 Bottom right	0.25
Test assembly 6 Weighted chest piece	Figure 1 Upper right	0.24