Homemade stethoscope

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Homemade stethoscope

Postby karbassi2 » Tue Jun 17, 2014 12:48 pm

I am teaching a science class for 4th-5th graders and am planning the homemade stethoscope experiment on the science buddies website. Can someone please explain to me the factors that affect sound transmission in a stethoscope? I am using cardboard, quartz, glass, rubber, and PVC tubing - but know very little about the physics behind how these materials affect the sound transmission. Also, how does diameter affect sound transmission? I would think that the smaller diameter tubes would transmit sound better because of less turbulence, and knowing that stethoscope tube diameters are not very big. I would like to be able to explain to the students what is "supposed" to happen based on the theory behind the experiment, but I'm personally not able to say why one works better than the other. I have searched for useful information but cannot find answers to my questions - please help!
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Project Question: "Make a Stethoscope" experiment on sciencebuddies - Need more info on the science behind it and which equipment should be most effective (plastic tubing vs cardboard vs glass?)
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Re: Homemade stethoscope

Postby jkim77 » Thu Jun 19, 2014 6:02 pm

Hi, I did some research on quartz and I found out that.The piezoelectric property of quartz crystals enables them to receive energy, process it, and transmit the oscillations outward in precise patterns of vibrations. Piezoelectricity, a word derived from the Greek word piezo which means pressure or push, is electricity resulting from pressure. Quartz acquires a charge when pressure is applied to it. Scientists found that the vibration patterns quartz crystals receive and transmit could be manipulated to store, amplify, transfer, transform and focus other vibrational frequencies of energy, including sound, electricity and even information in the form of precise periodic pulses. Also, the tube should be made from thick material; this improves sound transmission and isolates external noise. Hope this helps!
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Re: Homemade stethoscope

Postby rmarz » Thu Jun 19, 2014 11:01 pm

karbassi2 - The passive stethoscope is very effective because of the ratio of the area of the sensing element (part that is placed against the chest) and the area of the earpiece conduit. The Science Buddies experiment uses two funnels to achieve this transformation. I would argue that the earpiece funnel is too large for efficient amplification. In a professional stethoscope, the sensing element may be approximately 2" in diameter, or having an area of 6.28 square inches. The earpiece is typically connected thru rubber tubing with a cross section of about 0.125", ending in a plastic earpiece, that has an effective area of 0.393 square inches. Therefore the pressure amplification factor of this system is 6.28/.393, or 16. If you account that it feeds two earpieces, call it an amplification factor of 8. That said, the stethoscope has a fairly large amplification factor from sensor to receiver. The displacement of the chest cavity, or major arterial source, is enhanced by this ratio, and made very audible in the receiving apparatus, funnel or earpiece. The actual orifice of the ear canal and the eardrum is closer to the 0.125 diameter of the tubing of the professional stethoscope, so is an efficient medium to transfer the acoustic wave from the sensor. I hope these thoughts help you better understand this simple, but very effective instrument.

Rick Marz
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