Three phyphoxphones and superposition

[Erik Josefsson]

Hi Erik,

I realized some measurements of the classical interference of (sound) waves from two "point" sources (headphones) from a smartphone using "Tone generator" of phyphox. In order to have a stronger sound I have added a small HiFi headphone amplifier as you can see on the given photo.  The result of the interference measurements by a second smartphone with "Audio amplitude" of phyphox is not so bad. It could be better but somebody from a nearby laboratory was not too much happy hearing (reasonably) amplified 4000 Hz. For comparison I have calculated the expected interference pattern for exactly the same parameters:

• Speed of sound Cair = 344 m/s
  
• Frequency f = 4000 Hz
  
• Wavelength (from previous two) = 8.6 cm
  
• Distance between sources L = 54 cm
  
• Distance from the sources to the measurement line d = 69.5 cm
  
• Interval of measurements (second phone scan) x from -50 cm to + 50 cm
  

Knowing the time interval of measurements (with constant speed of the phone) one can recalculate time to x.
Additionally a small modification of the "Audio amplitude" was done to see the sound intensity in the direct scale (also attached here). Unfortunately, I had to keep only French and German translations because somewhere in many others an error existed and I could not find it.

Enjoy
Mikhail

Dear Mikhail,

I'm trying to reproduce your experiment. Turns out I don't understand if "the measurement line d" is parallel or perpendicular to  L (the line marked added to the photo).

I attach my setup and first result. It's not even close to yours. Speakers are facing upwards and I'm moving the Audio Amplitude phone along a straight equidistant vertical line downwards.

Should I turn the faces of the speakers towards each other and move the Audio Amplitude phone along a straight line from the speaker to the left to the speaker to the right instead?

Was your sine wave sound really loud? Did you wear hearing protection (ear plugs or similar)? I'm asking not only for me reproducing this at home, but also whether you think this experiment can be reproduced in a classroom with students.

Best regards.

//Erik