Help with Homemade Stethoscopes

[jackstill]

I chose a project in your Human Biology & Health list entitled "Make Your Own Stethoscope." I made three stethoscopes, the first from a 15"-long plastic tube, 3/8" diameter, with two plastic funnels (one large, one small); the second was made of a 15"-long rubber garden hose, 5/8" diameter, with two plastic funnels (one large, one small); and the third was made from a 12"-long, 1.24" diameter cardboard paper towel tube with only one large funnel on the end. After conducting the study to find out which of these three stethoscopes best amplified the heartbeat, it was clear that stethoscope #3 best amplified the sound, with the second best being stethoscope #2, and the least effective being stethoscope #1.

My question is, why was the paper towel tube the best amplifier of the sound? Was it that the length of the tube was shorter so the sound had to travel a shorter distance? Was it the diameter of the tube - the larger space allowed a greater volume of sound? Was it the materials? I had anticipated that stethoscope #3 would have been more effective as there was less air volume in the smallest diameter tube. But that was clearly not the case.

I look forward to your insight.
Thank you.

[cbrambley]

I love that you're asking all these questions after collecting your data. This is what science is all about!

So now that you know which stethoscope works the best, you have a new question. WHY does it work the best? Personally, I don't know. Maybe someone else with a better knowledge of sound waves and physics could chime in on this one. Since you're finished with your experiment, you probably don't have the time, BUT one could always take the experiment even further to find out. To give an example, one suggestion you made was that the length of the tube might explain the difference. This is a testable hypothesis! Create another identical stethoscope(s), except with longer and/or shorter tubes, and rerun the experiment to see if there's any notable differences. And of course the same can be done with the other variables you mentioned. Tube diameter/materials/etc.

[connief]

Hello there,

cbrambley already gave you some excellent advice, and I totally agree. One thing I would add is that if you want to seek advice from someone who knows more about the physics of sound waves, I would suggest posting in the physical sciences thread, for there could be physicists there who probably know more about this topic.

Let us know if you have anymore questions!

Best,
connie

[jackstill]

I love that you're asking all these questions after collecting your data. This is what science is all about!

So now that you know which stethoscope works the best, you have a new question. WHY does it work the best? Personally, I don't know. Maybe someone else with a better knowledge of sound waves and physics could chime in on this one. Since you're finished with your experiment, you probably don't have the time, BUT one could always take the experiment even further to find out. To give an example, one suggestion you made was that the length of the tube might explain the difference. This is a testable hypothesis! Create another identical stethoscope(s), except with longer and/or shorter tubes, and rerun the experiment to see if there's any notable differences. And of course the same can be done with the other variables you mentioned. Tube diameter/materials/etc.

Thank you for your comment and guidance. I wish we did have the time to conduct further research - and may do so on our own after the science fair - but for now I will seek further input from the physics group. Thanks again.