Adjust Siri’s Volume Level Independently from iOS System Volume

The volume level of Siri can be independently adjusted from the rest of the system volume of an iPhone or iPad, and it’s really easy to do:

• Hold the home button as usual to summon Siri
• While Siri is visible, use the volume buttons on the side of the iPhone or iPad to adjust only Siri’s volume

This impacts the sound level of Siri both when initially querying with the double-ping sound, as well as the volume of Siri’s responses to queries. The sound effect of hitting the Dictation button will also be impacted by this adjustment, but general system volume will stay where ever it’s set.

This great little trick comes from Lifehacker

Source : http://osxdaily.com/2012/10/26/adjust-siri-volume-level/