Thank you for the kind words! Yeah, I think it gets a lot more complicated once you start dealing with speaker hardware. It pretty much only works for the device's native speaker at the moment.
The instant you start having wireless speakers (eg. bluetooth) or any sort of significant delay between commanding playback and the actual sound coming out, the latency becomes audible.
Bluetooth audio devices that I use tend to change the protocol as soon as it switches to headset mode (with microphone enabled), which works terribly for music. I imagine the protocol used when the microphone is enabled might have completely different latency characteristics than the one used purely for audio, so a chirp might be measuring completely different thing
You could use a different device in the swarm for measurement, but yeah it seems pretty quickly complicated! I have no idea as well how stable the latency is
If you support mic input, you can allow the user to select a device as the "nexus" with mic recording on. Then you tell each device in your setup to "chirp" at the same exact time, but at different frequencies. Then you can derive the individual device's "local delay" and compensate.
This allows you to tune the surround setup to full accuracy for a given point in space, and it will take care of ring buffer differences, wireless transfers of non-teathered speakers, etc.
The instant you start having wireless speakers (eg. bluetooth) or any sort of significant delay between commanding playback and the actual sound coming out, the latency becomes audible.