Combining a European design team and American engineers, we endeavored to integrate the familiar form of the stethoscope with advanced technology, to produce a result that works eginomically, technically, and clinically. We take you inside some of the decision-making processes.

Probe

The Probe is critical to the feel of the stethoscope. Users have developed their favorite way to hold a stethoscope – fingers parted in a V, gripping between thumb and forefinger, or some personal variation on these. We didn’t want users to have to change their personal grip or handling of the stethoscope.

And so the Probe of a Thinklabs stethoscope is reminiscent of a conventional 2-sided stethoscope (Bell/Diaphragm). It is the same size, and feels naturally familiar in the hands of the user. Machined aluminum alloy with (environmentally friendly lead-free)  hard chrome plating maintained the solid metallic quality of a conventional chestpiece, while adding to the acoustic performance. The Probe housing would be the most expensive mechanical part of the stethoscope, but the sense of quality is unmistakeable.

Primary color LEDs and the intuitive design of an analog watch-face were selected to display operating modes. Glance at the display and you immediately know whether you’re in Bell, Diaphragm, Amplify or Acoustic Modes.

Digital Control System (DCS)

The DCS houses the 2 AAA batteries, the control and signal processing electronics, and the Control Keys and Volume Control. At first glance, it seems that controls should be on the Probe, facilitating one-handed operation. We tried this on early prototypes. The problem we encountered was two-fold. First, the controls then dictate that there is only one way to hold the Probe, and it’s not like any method currently used by any practitioner. Second, adjusting the controls cause the user to move the Probe around on the patient’s skin, press against the patient to activate a key, and so on. Both these problems were anathema to our design priorities on user comfort and audio unadulterated by motion artifact.

AAA batteries were selected for their convenience. Two are used to provide the wattage to drive the headphones with sufficient power to provide undistorted bass. The internal battery voltage is boosted and regulated to ensure the same power regardless of battery voltage (until replacement levels, of course).

Headphones

Like the metallic Probe, stethoscopes derive their sense of quality from the solid metallic feel of the binaural headphones. This, and the need for durability, dictated the use of stainless steel for the headphone tubing.

Eartips are critical to stethoscope comfort. We’d like to say that we used complex anatomical models to design the eartips. Truth be told, we drew the design on our 3-D computer-aided design system, and got them right the first time! Design doesn’t usually work that way. We got lucky. We’ve found that for 99% of users, the eartips are perfect. For some users, a slightly larger design is would be helpful. Stay tuned or write to us, if you’re one of the 1%. The eartips are soft silicone, which is latex-free.

We then discovered that due to the combination of amplification level and eartip softness, it was no longer necessary to use severe force on the spring to push the eartips into the ears, as is done with conventional stethoscopes. All we needed was a light spring, and the eartips sealed correctly. This was a major advance in stethoscope comfort! One doesn’t think of electronics as providing physical comfort, but this is exactly what happened.

As we discussed in the section on 100% End-to-End Electronics (EEE), our tests showed that the loudspeaker drivers have to be right at the eartips. The loudspeakers also needed to be designed as essentially sub-woofers to reproduce heart murmurs which have significant low frequency content. This required specific tuning of the loudspeaker cavity, and the use of Neodymium magnets, which are used on most audiophile loudspeakers.

Attention to Detail

We started out by explaining that we had to maintain Form while achieving much more Function. We discovered that perfection means attention to every last detail, literally from Probe to eartip. The goal is that when you hold a Thinklabs stethoscope, you intuitively enjoy the result, without having to think about why.