Saw a design similar to this on the internet (can't remember where) and thought I like that I will do my own version.
So here it is, I have done four versions depending on where your speaker is on your phone (mine is near the top on the back) so The one shown printed is 'Speaker Left'. choose the one that suits your phone and print.Supports will be needed but will be very easy to remove and it works really well, sound is nice, try with high infill for better sound.
either use full or split files and glue the split files together
thanks and enjoy.