Google Now voice too loud compared to media

A

AC Question

I ride a motorbike with a Bluetooth headset. I listen to music a lot and sometimes I need to use the Google Now feature to change a navigation destination or make a call.
Mostly the music is from spotify and the media volume is up full as I have a separate volume control on the Bluetooth headset.
My problem is that when I activate google now, the google voice responses and 'speak now' notification nearly deafens me. Is there any way to change this? I have already tried turning down the ringer and notification volumes.