ResoSearch, Acoustic resonance &spectrum measuring

It is an application that performs acoustic measurement using the attached earphone with a microphone.
When placing the L side earphone and the microphone on the object to be measured and pressing the Start button, a sound of a specific frequency is output from the L side　earphone and the volume in the measurement object is measured with the microphone.
The specific frequency is swept from the start frequency shown in the upper left of the screen to the end frequency shown in the upper right. The measurement takes 2 to 3 minutes. Please measure in a quiet room. If there is a resonance phenomenon, peaks or dips appear on the frequency characteristic graph at the bottom of the screen.
Put the L side earphone and microphone in a milk bottle or a wine bottle, then push Start button, you can measure the Helmholtz Resonance of the narrow mouth bottle.
Wrap a magazine or a poster in a cylindrical shape, put the L earphone on one side of the cylinder and the microphone on the other side, then press Start button, you can measure the Air Column Resonance.
You can adjust the volume with the volume button of the iPhone　before measurement.
After the measurement is completed, the circle cursor is displayed. It moves by the screen drag operation with left or right moving, then the Hz value and the dB value of the cursor position are displayed.
Measurement can be performed using the built-in speaker and the built-in microphone, but iPhone body itself has an acoustic characteristics and it can not measure well.
Measurement can also be performed using the external speaker and the built-in microphone, but there is a possibility that a big sound may come out, which is dangerous.
Demonstration Videos
Helmholtz Resonance, https://youtu.be/IJ5lT08aEkM
Air Column Resonance, https://youtu.be/wv1PsR0SS7k
Caution!!
Because there of a loud noise, please never put your earphones in your ear. Do not place your ears close to external speakers.