11-03-2021, 09:40 AM
(10-30-2021, 01:07 PM)solid Wrote: Dear Erik,
the measurements have to be done not between the speakers (it should work but it is not the classical geometry of the interference pattern from two sources), but along a line parallel to the line connecting the speakers. Distance from the sources to the measurement line is d. d can be much bigger than the distance between speakers L, which should be larger than the wavelength.
The sound level was not so high in my case and no protection was needed, but 4 kHz is not very pleasant to hear if you do not know that this is for a scientific reason...
Regards
Mikhail
Thank you Mikhail. I'm starting to get results that look almost like yours and will try to find a frequency (and volume!) that is bearable for students with much better hearing than mine. Hope to post that soon.
Meanwhile, can I ask about the HiFi headphone amplifier you used? This is a bit beyond where my learning curve ended when I studied (basic) circuits, but I wonder 1) if that amplifier would be powerful enough to pull a 35 gram neodym magnet (see picture) hanging in a spring into a forced oscillation? and 2) Do you think you could force a spring to oscillate with frequencies as a low as 1-2 Hz if you used phyphox's MULTI TONE GENERATOR (e.g. 440 and 441 Hz)? Obviously you would have to connect an iron core electromagnetic coil of reasonable size to the headphone amplifier instead of headphones. And be careful with distance etc.
I'd really like my students to work with resonance and use the phyphox Spring experiment which has a very nice graph where relative amplitude is plotted against frequency. The video is great https://www.youtube.com/watch?v=VbL4IInVAO4 but as you can see from the snapshot at 3m44s, the whole setup with an electrical motor generating the vertical oscillation is quite elaborate and, I guess, could require time consuming maintenance. In particular if you'd have five setups for five groups of students and not only one for me.
I believe that the neodym magnets and iron core electromagnetic coils could be used in other experiments and should be "standard shelf equipment" anyway. Adding five small amplifiers to the shelf doesn't feel like a stretch.
What do you think?
Best regards.
//Erik