Change how much rumble you get on the JBL Xtreme, by turning on and off its Extra Bass mode. When ON, this mode makes the passive bass radiators vibrate much more. And many of you would enjoy this. It indeed adds a low rumble quality to the playing program, that travels pretty far from the speaker.
JBL Xtreme Extra Bass Mode: How to Turn OFF
By default, the JBL Xtreme has this mode ON after a reset. This adds a bit of treble and lots more bass to the audio output.

You can turn this mode off by pressing the Volume Down (-) and Bluetooth buttons. Then hold them in for about ten seconds, until the Power and Connect buttons light up white. Find all these buttons on the top of the speaker.

JBL Xtreme Extra Bass Mode: How to Turn ON
To turn Extra Bass mode back on, again, press the Volume Down and Bluetooth buttons in. Then hold them in until the Power and Connect buttons light white. Then release the buttons. When the buttons inside the oval above light white, the Extra Bass mode is active once again.
Warning
The drivers really thump when you switch ON extra bass mode. So use caution in how loudly you play this speaker with the resulting bass. That way, you’ll avoid damage to the speaker drivers. So if the sound crackles, taps, or otherwise distorts, then turn it down ! Not only will this save the speaker itself, but it also conserves battery power. Of course, saving battery juice is particularly important if you’re taking the Xtreme outdoors. So you might be away away from a charger for a long time. Plus, you don’t want to risk losing your music before the party’s over.