Yeah I think so, I guess I tried it with a 9v and it wasn't enough for my 555s. If you want to use just a 9v you can probably find low power 555s, you'll have to look at some data sheets.Cheers
Hello4 AA batteries in series is 4*1.5v=6v and this is what goes into both 555s as they're connected in parallel. You should look up how voltages work in series and parallel circuits. Best.
To allow it to be a bit tunable and increase the range of pitches it could play