Because X-Desk uses SSL's proprietary Superanalogue technology, proper procedure must be followed when powering down.
Superanalogue circuitry does not use captivators, therefore a build up of DC voltage can manifest in the X-Desk. Upon powering down this DC voltage is discharged which causes a low frequency burst of sound through the output of the desk.
1 - Switch off monitors and sub woofer if applicable, remove headphones
2 - Switch off X-Desk
To power the desk back up the reverse procedure should be carried out, switching the X-Desk on first followed by monitors and headphones.
Failure to adhere to the recommend power down procedure may cause damage to your studio monitors!