Currently we know of no way to boost bass output the JBL Go 3 Bluetooth speaker via the speaker controls themselves. But if this were possible, it would make the speaker vibrate much more. It would also add a louder bass quality to the playing content. Thus if JBL ever added this, it could work something like the following…
How to Bass Boost the JBL Go 3
First of all, by default, the Go 3 would have its bass boost mode turned ON. This is like many of the other speakers in the JBL line. This mode would add more treble and notably more bass to the audio output, like switching on the Loudness control on vintage stereo systems.
How to Turn Bass Boost OFF on the JBL Go 3 Speaker — Proposal
For example, find the Bluetooth and Volume Down buttons on the top and right side of the speaker, as pointed out in the picture above.
Then, you could turn bass boost mode OFF by pressing and holding in these buttons for about ten seconds, until the pilot lamp on the right side blinks a few times, as shown in the next picture.
Finally, to turn bass boost mode back on, you would press and hold the Volume Down and Bluetooth buttons in, as before. Then, keep holding until the light again flashes a few times. You would release the buttons after that and bass boost mode would once again be activated.