First, check what the volume of your NVDA voice is in NVDA preferences under speech, sometimes it can get turned down if your using different voices.
If your NVDA volume is okay, another problem might be NVDA's volume vs other programs. , If your using windows ten, go to the volume mixer and check what your NVDA volume is as compared to your system volume.
You can do this by right clicking in the "speakers" button in the notification area, or going into Pc settings/system/sound and looking for ap volume preferences.
this will give you both a main volume for your speakers/headphones, and relative volume for any other aps and things that are running, including system sounds. Make sure NVDA isn't set too low.
Again, what volume you want might depend upon what voice your using (I had to turn my NVDA up when using windows core George).
hth.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)