A conventional stethoscope transmits sound via pressure waves traveling in the hollow tubing. A tube or pipe is a natural acoustic filter – talk through a tube, and the sound at the other end is significantly modified.

It is therefore apparent that to achieve perfect transmission, electronics and wiring has to replace air. Replace pressure waves at the speed of sound with electrical signals at the speed of light.

During our research, we wondered if some air tubing transmission would be acceptable. Could we, for convenience, use the binaural heapdhones of a conventional stethoscope? The sound would be electronic for most if the distance, but the last 10-12 inches (25-30cm) would be acoustic tubing. It would certainly make for a simpler headphone design, and almost every other electronic stethoscope today uses air tubing for sound tranmission, even if there is some electronic portion in, say, the chestpiece.

What we found was that the maximum distance beyond which clarity was compromised was just a few inches! If we weren’t going to compromise sound, the loudspeakers had to be right at the eartips. Hence the design of Thinklabs stethoscope headphones.

A One-Minute Experiment to Validate End-to-End Electronics

Play music through iPod-style earbud headphones, place them in your ears normally, and listen to the detail in the music. Now take a conventional stethoscope, set it to Bell position, and hold an earbud heapdhone up against the hole in the Bell. Ideally, seal the earbud so it is airtight against the Bell opening, using a soft material such as foam or even playdough. Now listen to the music through your stethoscope. Notice the loss of high frequencies and the dispersion of bass notes? Sound becomes "smeared" and dulled by the trip through the tubes.

Now you also know what you're missing when you listen to your patients with a conventional stethoscope. An "elegant proof", as we say in mathematics.