John Gill Commentary 2 Chronicles 15:14

"And they sware unto Jehovah with a loud voice, and with shouting, and with trumpets, and with cornets." — 2 Chronicles 15:14 (ASV)

And they swore to the Lord with a loud voice
As not being ashamed of the oath they took, and that there might be witnesses of it, and that it might be clear they did not equivocate but expressed themselves in plain words:

and with shouting, and with trumpets, and with cornets ;
showing that the oath was not extorted from them unwillingly, but that they took it with the utmost cheerfulness, and with all the demonstrations of joy and gladness imaginable.