hi P,
My!, that helmet is way out.
[reminds me of a girl I used to date]
With a White LED, it has a drive voltage of ~3.3V, so that means at least a 4.5V battery.
That could be achieved by using 3*1,5V AAA's, which would mean a battery holder.
A quick alternative would be a 9V PP3 battery, which could drive two White/Tinted LED's in series for a better light distribution.
The 9V battery could power a electret mic and amplifier, located inside a free space within the helmet.
Do you have a mic' link or type you could post.?
E
BTW: have you considered a possible problem for the 'girl', due to internal light reflection within the helmet visor?