You can change how loud the bass is on the JBL Xtreme, by turning on and off its low frequency mode. When switched on, this super bass mode makes the passive bass radiators vibrate much more, and adds a low rumble quality to the playing program, that travels pretty far from the speaker.
JBL Xtreme Low Frequency Mode: How to Turn OFF
By default, the JBL Xtreme 1 has its bass mode turned on after a reset. This adds a bit of treble and lots of extra bass to the audio output as compared to when low frequency mode is OFF.
You can turn this extra bass mode off by pressing and holding in the Volume Down (-) and Bluetooth buttons for about ten seconds, until the Power and Connect buttons light up white, as shown in the next picture, pointed at by the green arrows. Find all these buttons on the top of the speaker, as shown in the picture above.
JBL Xtreme Low Frequency Mode: How to Turn ON
To turn low frequency mode back on, again, press and hold the Volume Down and Bluetooth buttons in until the Power and Connect buttons light white. Then release the buttons. When the buttons inside the circled oval above light white, the low frequency mode has resumed once again.
Warning
The drivers really thump when you enable low frequency mode. So use caution in how loudly you play this speaker with the resulting extra bass, to avoid damage to the speaker drivers inside. If the bass is crackling, tapping, or otherwise distorting, turn it down !