(10-04-2021, 09:43 AM)Jens Noritzsch Wrote: Dear Eric,

there is an alternative with just one smartphone and earbuds suggested by the NPL, https://www.npl.co.uk/measurement-at-home/measuring-sound-using-toilet-rolls, and utilised by Physics in Advent on December 3, 2020, see https://youtu.be/wUAFem8eEKI and https://youtu.be/-8MO0Uacn5w

Would this work for you?

Best regards,
Jens

(10-04-2021, 05:43 PM)solid Wrote: Hello

Thank you for the references, Jens .

I tried the toilet paper NPL experiment and I found it not very precise.. I got the wavelength 10 cm and the sound speed 400 m/s for the frequency of 4 kHz.

Then I took one smartphone with phyphox sound generator at 4 kHz. I put its headphones 50 cm apart and took another smartphone with audio amplitude of phyphox and moved it slowly at a distance of 1 m over about 1 m. I tried to keep a constant speed of the motion. The result is here, could be better... Probably some things around including me interfere also.





Best

Mikhail

(10-05-2021, 02:52 AM)solid Wrote: Two phones maybe are not correlated well as two headphones of the same phone and the interference will be absent. . .
By the way I did not use the toilet rolles, I used a tube. The tube length is limited by the distance between the headphones.

• 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
  

(10-05-2021, 12:03 AM)Erik Josefsson Wrote: Further to solid's response in this thread, has anyone seen device-specific calibration data for the Audio Amplitude experiment? My Galaxy III has a "Reference SPL" default setting 60 dB (not sure what the "offset" below does?), but maybe that's a default value set for all phones?

(10-05-2021, 10:17 PM)Jens Noritzsch Wrote:

(10-05-2021, 12:03 AM)Erik Josefsson Wrote: Further to solid's response in this thread, has anyone seen device-specific calibration data for the Audio Amplitude experiment? My Galaxy III has a "Reference SPL" default setting 60 dB (not sure what the "offset" below does?), but maybe that's a default value set for all phones?

The calibration tab could be used for a rather vague calibration of the audio amplitude, either by a reference sound of known SPL or by remembering a previously measured offset. Sebastian has tried to explain the limitations in the FAQ tab.

This gets particularly difficult now that we know about hardware variations in a device's lifetime, see https://phyphox.org/sensordb/ (Samsung Galaxy III could be any of the four –err, at least six different– GT-I930… or a SGH-I747M, tbc?).

(10-05-2021, 08:06 PM)solid Wrote: 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