Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: smokingwheels on 23/01/2011 14:17:15

Title: What would you call this effect with air?
Post by: smokingwheels on 23/01/2011 14:17:15

If I have 2 PVC tubes with tallyho papers taped over one end leaving about 50% open for the air to flow in and out I then placed them over the subwoofer port and then use my PC to generate some low frequency sounds from 10 to 40 Hz  thru my amplifier. note my subwoofer has 2 drivers.
See pic (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi231.photobucket.com%2Falbums%2Fee44%2Fsmokingwheels%2FJan%25202011%2Fsubbie.jpg&hash=c22bb1d677412ec81aa6cd148f4fb764)

The number 2 tube has a grooved surface inside done with a wirewheel of about 0.3mm.
The number 1 tube is untreated.
Anyway after some time I found that the untreated tube seem to bend the paper lower in the tube and it was more damaged see http://www.youtube.com/watch?v=JU6cjirpZTM  (http://www.youtube.com/watch?v=JU6cjirpZTM)
Part of the test can be seen here for more information to what I did http://www.youtube.com/watch?v=5CK_5KCKBUw (http://www.youtube.com/watch?v=5CK_5KCKBUw)

One guess is that it hetrodynes the air coming out of the port?
I am open to suggestions.
This effect on flowing air and fuel seems to improve the airflow as well when I ported my car engine it improve efficiency with some side effects.


PS: I will explane or draw pictures if you ask, my english is not very good.

Title: What would you call this effect with air?
Post by: Soul Surfer on 23/01/2011 23:31:05

I just do not understand the purpose of this experiment or see how it could possibly result in any sort of consistent observation.   As far as I can see all you are proving is that a speaker cone operating at a low frequency moves air backwards and forwards which when placed inside a ported enclosure can result in considerable air velocity in and out of he port.  This is a perfectly obvious observation.  The structure of the flaps is far too imprecise to enable any significant observations of differences in behaviour of the two tubes.  The nature of the differences of the internal surfaces of the tubes was also not observable in either of the videos.

If you wish to make reasonably accurate measurements of the amplitude of airflow like this a simple home made hot wire anemometer (QV) is probably the best instrument to use.