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Comment by anfractuosity | Hacker News Reader

I'm just wondering regarding the stethoscope, I was looking at - https://en.wikipedia.org/wiki/Stethoscope#Acoustic which mentions there are seem to be two types of acoustic pickup, bell or diaphragm. The Glia one appears to be the bell type I think?

It says that the "bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds". Is there an advantage of one type over the other, or are they used in different scenarios?

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Hey, I made the prototype for it. I reverse engineered a Littmann cardiology 3 and used a similar diaphragm setup. For the early prototypes I used the one that came with the Littmann stethoscope; later on we got the same result with different approaches, such as cutting out one out of transparent plastic sheet or using shrinkwrap around it.

Cheers, that's very interesting!

They're used to listen to different things. The diaphragm is in my experience much more important. TBH I never even use the bell. Some pediatricians like it for infants because it is physically smaller (but they put a smaller diaphragm over it). Lots of stethoscopes don't even have one.

Funny article about the bell: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1790765/

The usual answer to such question is "it depends".

That being said, heart related sounds are generally low-frequency while breathing/lung related sounds are broadband so they do contain a significant higher frequency part.

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