This post will show you how to change the volume of siri.
ie change how loud siri’s beeps and voice is.

the iphone and ipad have 3 volume settings:
ringer
media
siri

the media volume is the volume for your music, etc.
the ringer volume is for the volume of your ringtone.

the volume that siri is set to can be set quite easily:

open siri ( press and hold your home button)
instead of saying anything while siri is open, adjust the volume buttons instead.

the volume of siri will now be changed, rather than the overall system volume :)