The test platform used to compare the various stethoscope assemblies. The platform consists of a small loudspeaker coupled to a plastic vibration test surface (light blue color) and driven by an audio amplifier, the amplifier in turn being driven by a signal source such as a function generator (upper left). The signal generator used is an inexpensive DDS (direct digital synthesis) model FG-100 readily available on eBay and operating in sinusoidal waveform mode at 1000 Hz. A RadioShack 33-3013 miniature omnidirectional electret microphone is connected to the stethoscope head under test through a short piece of tubing and amplified using a RadioShack miniature audio amplifier (Catalog # 2771008) for display on a USB oscilloscope (upper left). Table 1 shows the obtained results with a 1000 Hz test signal. Note that the system used two audio amplifiers, the first (located at the bottom right of Fig. 2) to drive the loudspeaker and the second (the RadioShack amplifier) to amplify the microphone signal for presentation to the USB oscilloscope.