iPhone 14 in Firefox (still Safari under the hood of course) - no silent mode, no sleep/DND/etc., volume turned up (confirmed via other browser tab playing YT) - and still no sound from the app.

I’m guessing you may be using a JavaScript API which possibly doesn’t exist in whatever version of Safari (fuck Safari…fuck Apple’s control of browsers…etc).

My advice: Use the free tier of BrowserStack to test basic functionality on a wide range of devices (assuming they still have a free offering…). Also check “caniuse” to see if all the JS APIs you’re using are available on a wide range of devices.

Hey EdNutting - that's a good idea about Browserstack! Yeah my circle of friends only have android phones and/or iPads and we haven't encountered this issue yet.

If you get a chance, could you see if the Metronome works? It'll only play if you're in the middle of a game but it doesn't use the old soundfont-player, just direct web audio.