When you are working in silent office environment or in a study room then you may want to turn off startup sound of Mac. So, here we are writing the process which you may follow to control or completely turn off startup sound.
Control startup sound on Mac OS X
Download and install StartupSound.prefPane
Now click on Apple logo > System Preferences
Under Other section click on Startup Sound icon
You can controls or mute Mac startup sound using volume slider or you can turn the startup sound off by clicking on Mute checkbox
Just for prevention measure always Click the lock to prevent further changes on above screen.
You can use this guide on any Apple MacBook, MacBook Pro, iMac, MacMini or computer that using Apple Mac OS X.