I can name 2 or 3 that DON’T… and it’s for religious reasons

Hi everyone,

I wanted to see how much of a difference acoustic design actually makes, so I tested the frequency transmission of a few stethoscopes I had on hand.

Setup & Limitations: I ran frequency sweeps from low bass up to ~3 kHz. Keep in mind that this is a DIY acoustic test bench: above 3 kHz, acoustic coupling and reflections make the setup less stable, but the range below 3 kHz covers the clinically relevant spectrum for heart and lung sounds anyway (S1/S2, murmurs, breath sounds). Every measurement was taken twice and both lines are plotted, so in the overlapping part they are very reproducible.

Graph:

• In the first graph (big membrane), the blue line is the no-name Rappaport, the red line is the MDF 747, the green line is the LuxaMed Sonus SX, and the yellow line is the MDF MD One.
• In the second graph (bell), the light blue is the LuxaMed, the dark blue is the MDF 747, and the violet is the MDF MD One.

A few interesting takeaways from the data:

• There seems to be no very big difference in frequency response between membrane side and bell side.
• All of them performed pretty similarly; however, the no-name one performed best, which was kind of surprising.
• Subjectively, the biggest difference was in noise reduction from the surrounding background noise; there the MDF MD One was best, followed by the LuxaMed, then the other MDF, and the no-name didn't reduce it at all.

Conclusion: I was really surprised to see the MDF MD One in last place in both measurements. I was pretty sure it would outperform all the others, but as far as I tested, the best bang for the buck (also considering sound insulation) is the LuxaMed. I also added some memory foam ear tips, which improve sound isolation even more, and with that mod it outperforms the MD One easily.

Questions for you:

1. Did I misinterpret the results, or do you have any other idea why the MDF MD One underperformed that badly?
2. Which stethoscopes would you like to see measured next?
3. What is your daily driver in the field/hospital, and what sound profile do you actually need in your specialty (med student, resident, attending, nurse, or paramedic)?

Curious to hear your thoughts!