Change how much rumble you get on the JBL Boombox 1, by turning on and off its low frequency mode. When ON, this mode makes the passive bass radiators vibrate much more. Plus it adds a low rumble quality to the playing program, that carries pretty far from the speaker.
JBL Boombox 1 Low Frequency Mode: How to Turn OFF
By default, the JBL Boombox 1 has its bass mode turned on after a factory reset. This adds a bit of treble and lots of extra bass to the sound.
You can turn this low frequency mode off by pressing the Volume Down (-) and Bluetooth buttons. Then hold them in for about ten seconds.
Hold until the Power and Connect buttons light up together. Find all these buttons on the top of the speaker.
JBL Boombox 1 Low Frequency Mode: How to Turn ON
To turn low frequency mode back on, then again, press the Volume Down and Bluetooth buttons. Hold them in until the Power and Connect buttons light up. Then release them. When the buttons inside the oval island light up, the low frequency mode resumes once more.
Warning
The drivers really rock when you activate this mode. So use caution in how loudly you play this speaker when LFM is active. Doing so avoids damage to the speaker drivers inside. So if the bass is crackling, tapping, or otherwise distorting, turn it down !