How to record the sound from a stethoscope

Introduction

On this page, I will explain a reasonably cheap way to (destructively) alter a stethoscope so you can record what it hears. All you need is an old stethoscope (or just the chestpiece and tubing) and a lavalier condenser microphone. The result will produce sound only through the microphone - you won't be able to listen to it otherwise. Basically, you just cut the tubing a few inches from the chestpiece and shove a microphone into the hole. The only difficult part is widening the hole so that the microphone will fit. Do all of this at your own risk.

What you need

• A stethoscope chestpiece (the head part) connected to some stethoscope tubing. The easiest and cheapest way to get hold of these is to sacrifice a cheap stethoscope or a second-hand stethoscope. As of 2025, you can buy a perfectly good new Spirit Lightweight stethoscope for £15 or less, and you can find second-hand stethoscopes on eBay (some of which are more expensive than if they were new). If you don't want to ruin a good stethoscope, you could pull the chestpiece off a stethoscope and plug it into some new tubing. If you do this, you will need to use proper stethoscope tubing because other types won't carry the sound as well.
  
  
  
• A lavalier condenser microphone with a plug or USB socket on the end. The word "lavalier" is just a fancy term for "lapel mic" - it's the sort of small microphone that could be fitted to a shirt lapel, and that a newsreader might wear. A condenser microphone (where condenser is the old term for capacitor) has better sensitivity than a dynamic microphone, but it requires an external power source such as a battery. The term "condenser" refers to the technology used within the microphone, while the term "lavalier" refers to the intended purpose of the microphone. If I were in charge, a "lavalier condenser microphone" would be called a "shirt-lapel capacitor microphone". I used an Audio-technica ATR3350x microphone with a 3.5mm plug, but anything similar would probably work. The microphone part of the ATR3350x has a diameter of 8.25mm. This is much larger than the hole in the tubing, so the hole needs to be widened. In the following picture, the black cylinder contains electronics and the little battery.
  
  
  
• A heat source to heat the tubing to make the hole bigger. I used a hot air solder rework station set to about 250°C. It might also be possible to hold the end of the tubing near to a soldering iron. Holding it near to a kitchen hob might work too, as might a hairdryer.
  
  
  
• Some needle nose pliers with a point narrow enough to fit into the hole in the tubing. These will be used to stretch the hole when the tubing has softened in the heat.
  
  
  
• Any cylindrical object that has roughly the same diameter as the microphone. This should be made of something that won't melt. For the ATR3350x microphone, we need anything that has a diameter of about 8.25mm. We will put this into the widened hole while the tubing is still hot. When the tubing cools around it, the hole will stay large enough for the microphone to fit in without forcing it. (You might not need this at all, but it will make sure the microphone doesn't get hot, and it makes things easier.) I used a small socket from a socket set that happened to be the right size. You could also try using the flat end of a pencil, a thick knitting needle, a drumstick, a piece of doweling etc. Only a small part of the object needs to match the diameter.
  
  
  
• Safety gear: gloves so you don't accidentally burn your hands, goggles so you don't accidentally burn your eyes, water to put out fires.

The process

(Practise this first on a separate section of tubing, so you can become accustomed to the behaviour of the tubing.)

Most of this is concerned with widening the hole, which can be tricky if you haven't done something like this before.

• It's easiest to keep the tubing attached to the chestpiece throughout the process.
  
  
• Cut the tubing about 10 cm (four inches) from the chestpiece with a Stanley knife (utility knife, craft knife). If you think you might mess this up, cut it further away so you can have another go if it goes wrong.
  
  
• Push the end of the needle-nosed pliers into the open hole of the tubing.
  
  
• Heat the open end of the tubing, while gently trying to open the pliers.
  
  
  
• Eventually, the tubing will soften slightly, and you can widen the hole with the pliers just a bit. Ideally, rotate the pliers in the tubing to get an even expansion. The tubing is very heat resistant and it might take a while for it to soften. You can feel the change when it does.
  
  
• When the tubing softens and the hole becomes bigger, remove the heat source, and wiggle the cylindrical object (of the same diameter as the microphone) into the hole. If you don't do this, you would need to put the microphone into the hot tubing, and the heat might damage it. It might not matter though.
  
  
  
• Let the tubing cool for thirty seconds or so.
  
  
• Remove the cylindrical object, and wiggle the microphone into the tubing hole.
  
  
  
• And that's it really. To make it more secure, you could use tape or heat-shrink tubing to fix the microphone in place, but it's probably unnecessary.
  
  

Notes:

• If your heat source covers a large area, maybe remove the chestpiece (or just the membrane and any rubber parts from the chestpiece) so you don't damage it.
  
  
• A wider microphone will require more stretching.
  
  
• If the microphone is completely covered by the tubing, it will record less outside noise than if it is just sitting on the outside. On the other hand, it will be harder to remove.
  
  
• A better microphone and a better stethoscope will achieve better results, but will be more expensive.
  
  
• On the stethoscope I used, the tubing tightened slightly during the few hours afterwards, so you might have to re-heat the tubing if you remove and refit the microphone.
  
  
• More expensive stethoscopes (e.g. 3M Littman ones) have two holes ("lumens" as medical folk like to call them) through the tubing - one for each ear. I've only put a microphone into single-hole tubing, but I imagine that you just need to pick one of the two holes, and everything would work the same.
  
  
• Some stethoscopes have parallel tubes - one for each ear. Again, you would need to pick one of the tubes for the microphone. You might be able to use this type of stethoscope to make a hybrid "microphone and one ear" stethoscope.
  
  
• If you buy a second-hand stethoscope, make sure you clean it properly. Otherwise, you might catch whatever the last person to use it had.
  
  
• The only parts you need are the chestpiece and the tubing, so you could buy a broken stethoscope if you can find one.
  
  
• Tubing that isn't intended for stethoscopes is unlikely to be good at carrying the sound while keeping out external sounds.
  
  
• If you put joints into the tubing, you will probably lose a lot of the sound.
  
  
• Cheaper stethoscopes will be less sensitive than expensive ones, and are more likely to introduce outside noise. Having said that, the Spirit brand stethoscope that I used seemed perfectly fine.
  
  
• (For non-USB microphones): Remember that the output of the microphone is still a microphone output and not a line-out, despite the battery and electronics. You can't plug it directly into headphones or into the line-in socket on things because you won't hear anything. Instead, you will need to plug it into the microphone socket on a recorder, computer or speaker. You can then use headphones (if you want) that are plugged into that recorder, computer or speaker.
  
  
• As the microphone uses batteries to run, remember to switch it off when you aren't using it.
  
  

Why would you want to do this?

A stethoscope is a very individual tool - only one person can listen at a time, and it is difficult to convey to other people what you are hearing. Unlike repeating what a rhythmic drummer is doing, a heartbeat isn't necessarily regular, and it's difficult to tap out the beats you hear without getting confused by your own tapping. Unless you are good at musical notation, you can't easily tell someone later what you heard. The solution to these problems is to put a microphone into a stethoscope and either amplify the sound on a loud speaker, or record it for later.

If you are wearing a stethoscope, it is easy to hear the sound being amplified (obviously), but if you put a microphone against the earpieces, it's unlikely the microphone will pick up anything at all. It seems to be nearly impossible to record the sound that the stethoscope hears with an external microphone.

If you like spending money, you can buy stethoscopes that can record sound, but the ones I have seen don't have a line out or a microphone plug. Instead, they use Bluetooth to communicate with an app on your phone. They use electronics to amplify and level the signal, and the app provides graphs and analysis. At least one company requires you to register an account before you can use the app, and then you have to pay a subscription to actually get any recordings (which are stored on the cloud). This is for a stethoscope that you have already paid for. Not only is this totally unnecessary, mercenary and convoluted, but it also means your private recordings are held by a third party, you need the internet to use the stethoscope, and the stethoscope will only work for as long as the company's servers work. You are essentially hiring the stethoscope after you've already paid for it. Also, any Bluetooth stethoscope requires a phone with that particular app installed, so you have to have your phone with you, which often isn't allowed or possible, and no one without the app can borrow your stethoscope. Bluetooth apps that connect to hardware are generally awful anyway.

[Examples of internet-of-things companies shutting down their servers: Hackaday reporting on Insteon, a discussion on Reddit. Examples of Bluetooth apps that are supposed to communicate with hardware, but don't work particularly well: Literally any review of literally anything anywhere on Google Play.]

Sticking a microphone into the stethoscope's tubing, as we do here, will produce something that will last until the stethoscope tubing degrades or the microphone fails, and even then, those parts can be replaced. This method allows you to record the audio, and what's more, possess the audio. It's the minimum any reasonable person would expect from the term "digital stethoscope", but the opposite of what is currently being manufactured.