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Three phyphoxphones and superposition - Printable Version

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Three phyphoxphones and superposition - Erik Josefsson - 10-04-2021

Hello!

If two phyphoxphones at some distance from each other is set to generate a 1000 Hz sound wave (it's uncomfortable but not dangerous I think) then you should get interference/superposition at the same distance (0.34 m) as the local speed of sound (340 m/s).

Is there a way to use a third phyphoxphone to manually find two or three of these maxima/minima? Exact measurement not needed, but a distance that students could confirm looks like about 30 cm would be great.

Anyone tried to do it with "Audio Amplitude"?

I hope it is possible to do with less gear than anno dazumal (see attached png)!

Best regards.

//Erik


RE: Three phyphoxphones and superposition - Jens Noritzsch - 10-04-2021

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


RE: Three phyphoxphones and superposition - solid - 10-04-2021

Hello

Thank you for the references, Jens Smile .

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. Big Grin


   


Best

Mikhail


RE: Three phyphoxphones and superposition - Erik Josefsson - 10-05-2021

(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

That's a very nice setup! Thank you!! //Erik

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

Thank you for the references, Jens Smile .

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. Big Grin





Best

Mikhail

Well, one pair of headphones is actually two speakers, so we did more or less the same experiment :-) I was also trying to move the phyphoxphone/Audio Amplitude with constant speed, but your result is much better than mine!

Thank you solid.

//Erik

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?

Anyway, I will try again tomorrow with a larger tube than stacked toilet paper rolls. Turns out a transparent plastic curtain box from IKEA (FRIDANS) works perfectly as running tracks for their toy cars (LILLABO). Maybe I can pull a phyphoxphone on a string through it and get the Audio Amplitude to clearly detect sound wave interference peaks.

//Erik


RE: Three phyphoxphones and superposition - solid - 10-05-2021

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.


RE: Three phyphoxphones and superposition - Erik Josefsson - 10-05-2021

(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.

Two phones on 440 Hz sounds perfectly in tune to me. If the frequency would differ the slightest I think you would hear it, no? If you listen to 440 Hz from one and 441 Hz from the other you clearly hear a 1 Hz "pulse" (or "beat") from the interference. But volumes could differ of course!


RE: Three phyphoxphones and superposition - solid - 10-05-2021

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


RE: Three phyphoxphones and superposition - Jens Noritzsch - 10-05-2021

(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?).


RE: Three phyphoxphones and superposition - Erik Josefsson - 10-08-2021

(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?).

Thank you Jens, this brings me back to my "old phones" question since I just broke all the screens on all my Galaxy III phones. I see 52 Galaxy S5 (SM-G900F) in the sensor db and that DivestOS works on that model: https://divestos.org/index.php?page=faq

Would you buy five of those for student's experimenting? Or would you prefer any other model?

Best regards.

//Erik

(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

That's really beautiful!

Hey, wouldn't it be possible to compare "distance between minima" in time from the "Audio Amplitude" graph with actual location in space of the phyphoxphone if you'd have a magnet ruler? (I'm trying to figure out other uses of the magnet rulers I made for determining g since resolution at dropping speed wasn't good enough)

Best regards.

//Erik


RE: Three phyphoxphones and superposition - Jens Noritzsch - 10-08-2021

Dear Erik,

we do not have that much experience with the plethora of smartphones out there. I cannot perhaps read more information from our sensor database than you. From what I can see, it does look quite ok sensor wise, all “relevant“ on board including a barometer, which is great. I cannot judge their performance in smoothly running phyphox…

Have a nice weekend.