Specific MP3 plays over headphones only I am out of ideas. The following MP3 does not play correctly on many Android-devices:
https://www.heimatmuseum-zinnowitz.de/app/download/12553824899/Kino%20Audiodatei%20Deutsch.mp3?t=1590484494

It contains a German female voice. But on several devices, it does only play over the headphones. If I use the normal speaker, I do only get some noise.

I tried many different things:


Used different devices (works fine on a Samsung-tablet (Android 8.1), but does only work over headphones on my Huawei P20 Pro (Android 9) and another older phone (Android 7)).
On Windows, it works just fine.
I converted the file a different format (OGG and WAV)
I changed the sampling-rate from 48.0 kHz to 44.1 kHz
I switched between constant and variable bitrate
I tried the default-player and a different app (MusicFolderPlayer)
I used different converters (Audacity and several online-converters)


The problem is always the same: I hear everything using headphones, I do only get noise with the speaker.
How can I get this to work?

Needless to say that all devices used for testing are working fine with other files.
This is due to the audio having stereo (left and right) channels being out-of-phase.

To put it very simply, when the audio waveform on the left channel is out-of-phase with the right channel, the resulting mono mix (basically (left+right)/2) may reduce the volume or even mute it (further reading: destructive interference &amp; dead spot).

When playing with headphones or stereo speakers, there should be no issue hearing the audio because each channel is played through each speaker respectively. However, on some Android devices (e.g. Nexus 5) that only supports mono playback, the issue appears due to the previously mentioned phenomenon.

Depending on the model, there might be a true stereo (left-right channel separation) mod that can be applied/flashed. E.g. a detailed post by user "chdloc" on XDA Forum to apply true stereo on Nexus 5.

The alternative workaround is to fix the audio source by inverting the waveform on one of the channels. Example using Audacity (reference: https://forum.audacityteam.org/viewtopic.php?t=71779):


Open the audio file
(Optional) Select the track, then open the menu bar: Tracks - Mix - Mix Stereo Down to Mono to see the effect of destructive interference, then undo the operation to continue to the next step
Select the track
Open menu (press Shift + M, or click the dropdown menu above the "Mute" and "Solo" button)
Select "Split Stereo Track"
Select one of the channels (either left or right)
Select all region of the track (double-clicking the waveform, or from the menu bar: Select - Region - Track Start to End)
On the menu bar, select Effect - Invert
Open menu on the first track (follow step 4)
Select "Make Stereo Track"
(Optional) Select the track again, then open the menu bar: Tracks - Mix - Mix Stereo Down to Mono to see if it is still affected by the destructive interference, then undo the operation to continue to the next step
Export the resulting audio from File - Export - ...