Science Buddies: "Ask an Expert"

Hi,
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 posted this question in the Human Biology section, and they suggested that I post here for an answer.

I look forward to your insight.
Thank you.

Hello:

It seems to me that the 1st stethoscope should have been the best one because the volume of air in the tube was the smallest. Since you are posting in the K-5 forum, I'm assuming your ears are smaller than an adult's. Is it possible that the cardboard tube fit the best over your ear and against your head? If so it could be that the cardboard tube isolated your ear from the noise around you the best and made the best seal.

It would be good to remove this variable from the experiment. Do you have another small funnel that you could stick into the cardboard tube and use to listen to the output of the stethoscope? Then all 3 will have the same "earpiece." Alternatively, would it be possible to somehow fit a piece of cardboard tube to the end of the other 3 hoses (in an air tight fitting)?

Another thing to try to make the 3 stethoscopes more alike would be to get another cardboard tube and extend the 3rd one to 15 inches like the other 2.

If you have reduced your variables to just the tube size, then this is a better experiment. Science fair judges will like hearing how you investigated this problem.

Good luck and let us know what you find out.
Keith

Hello again:

I had one more thought on this experiment. If you make the changes I suggested, and the cardboard tube is still the best, it could be because the sound of the heartbeat is transferred through the stiff tube as well as through the air in the tube. I noticed that the 3 tubes in this experiment, besides getting larger, also get stiffer. Sound transmission through the walls of the tube will possibly be better than through the air in the tube.

Keith

kgudger wrote:Hello again:

I had one more thought on this experiment. If you make the changes I suggested, and the cardboard tube is still the best, it could be because the sound of the heartbeat is transferred through the stiff tube as well as through the air in the tube. I noticed that the 3 tubes in this experiment, besides getting larger, also get stiffer. Sound transmission through the walls of the tube will possibly be better than through the air in the tube.

Keith

Thank you for your response. We were surprised too by the results. Will try to modify the experiment to reduce the variables.