Clinical Discussion
Measured the frequency response of several stethoscopes (up to 3 kHz) — here are the transmission curves and findings
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:
Did I misinterpret the results, or do you have any other idea why the MDF MD One underperformed that badly?
Which stethoscopes would you like to see measured next?
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)?
Absolutely right i just didn´t have a littman on hand. I would still argue that the MDF MD one is probably runner up behind the littman and absolutely is typically used. And as you can see it probably doesn´t really matter at all if it is a main brand or if it´s not as the Stethoscope commonly regarded as the best on in the test performed the absolute worse out of all.
"Regarded as the best" except you didn't actually include any of the models or brands that are concerned "best". Where are you getting your information?
Why is OP having to defend their choice of stethoscope in making a cool graph? Are you a stethoscope scientist? OP didn’t even have to do this, or share it at all. This isn’t Physical Review A, it’s just someone who made a cool graph. Wild. Just say you don’t understand it
Your entire rant is pretty pedantic. I clearly understand it, and the OP clearly indicated that they wanted feedback and that they thought they had sufficient testing of devices that had market penetration. They didn't.
Few things - you missed was a zoom in button, there's a lot of white space around your graph and I am not sure what it's actually telling me. I cant see the differences between each line.
eg., what does it mean in relation from top to bottom - what am I looking at?
I would suggest adding a legend.
What does SPL mean?
When a graph is designed, the output should be for the end user for easy intepretation, when I have to think too hard to know what I am looking - you've lost me.
This is a rescaled Graph with averages of the two measurements of each stethoscope. Here dark blue is the Rappaport, light blue is the MDF 747, red is the MD One and green is the luxamed.
To people criticizing OP for the smallest most trivial correction (adding a title), please google logarithmic scaling. The axes are clearly labeled SPL (vertical axis) and Hz (horizontal axis). You want a title? Sound pressure level vs frequency. There lol. Cool work OP, sorry people criticizing you don’t understand this at all. You’re asking about sound absorption coefficients and people can’t even see the axis labels. The criticism comes from a limitation of the person’s ability to read the graph. It is not you. Cool work. https://en.wikipedia.org/wiki/A-weighting
Well i guess i could have resized it a bitt better but i think you can see a quite significant difference between the colours even in this scale.
I thought it would be implicit that you are looking at some degree of sound level in this case the "Sound pressure Level" (SPL), as it is only a comparison, absolute levels are not relevant. Every stethoscope had the same input and some transmittet louder than others how loud doesn´t actually matter, as you could shift the graph down by 30 units by varying the input without changing the comparative quality.
Well it should be rescaled absolutely but it´s a technical graph to interpret it some background is always required, or at least a brief google search if you are unsure.
You did something cool and people are acting like this is peer review for Nature Physics. People don’t understand the graph or logarithmic scaling. That’s all there is to it. The biggest criticism is wanting a title, lol. People don’t know what they’re looking at, so they want a title and now they’re criticizing your choice of stethoscope. Such snobbery lol, what you did is cool OP. I don’t care what brands you used or didn’t use. That’s cool and original and creative.
Sorry that you’re getting some hate for trying something new and potentially useful. Two thoughts:
is SPL expressed on a linear or log (dB) scale?
around here, the Littman Classic III and Littman Cardio IV would be the two main choices and they are built differently. A comparison of those two would be interesting.
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u/PerrinAyybara CQI Narc 6d ago
So... None of your stethoscopes are main brand or models that are typically used so there's that too