Hi neojynx,
I had the Interphone F3XT system for a while, and provided the earphones were positioned
inside the helmet correctly, the volume seemed to be OK for me.
A few things you can try .....
( my apologies if these are stating the obvious, but it's possible to overlook one or more of them ) :
1. Volume turned uo to maximum on the Interphone F3 ( + button )
2. Volume turned up to maximum on the Trophy Audio system ( Handlebar controls )
( may not have an effect on the Bluetooth audio volume )
3. Volume turned uo on the Garmin - ( Menu / Volume / + for the GArmin 660 )
or volume + on other Sat Nav device
4. Interphone F3XT "Auto volume"
( I believe the F3 has a slightly different Volume feature - check the Manual ! )
I recall another Member having a similar problem where the Auto Volume feature ( which is supposed to
automatically set the volume to a pre-determined level depending on the background noise )
was causing the volume to be too low. The Auto volume feature can be turned off
by pressing and holding the Volume "-" button of the F3XT for 10 seconds,
until a "bi-tonal descending beep" is heard ! - See attached Chart.
Hope these help

Cheers

