Is it necessary to have a sound trigger on high speed photography?

Is it necessary to have a sound trigger while doing a high speed photography? And what is the sound trigger for? And lastly, is 1/4000 second enough to do a high speed photography? BTW, my dslr is nikon 3100…

Added (1). And lastly( i swear this is the last), what mode should I use while doing a high speed photography, is it the S(for shutter speed) mode or manual?

Added (2). And this is for next week Tuesday.

It depends on what you want to shoot.

Water drops - no need for high speed photography at all - just use off camera flash to freeze motion.

Bullets bursting balloons - a sound trigger is used to activate an off camera flash (not usually the camera itself). The sound of the gun firing fires the flash (usually after a millisecond delay). The camera does not need to be set to high shutter speed as again it's the fast burst of flash that freezes motion.

1/4000 shutter speed is generally not fast enough for very fast events - a flash fires at around 1/10, 000 sec and it's this that freezes the motion.

For high speed work using flash, you shoot in manual (incl.manual focus - the AF is too slow, so you need to pre-focus manually on where the action will be). You can either shoot at the max sync speed for the flash (usually around 1/200), in which case you can use normal ambient light. OR you can use bulb mode & a flash - open the shutter, trigger the event (& flash) then close shutter. To do this method though you need to be in a very dark room (almost black).

These are examples from my photostream where flash is used in ambient light;