You can adjust the bass response of the JBL Charge 4 speaker by turning on and off its bass boost mode.
How to Bass Boost the JBL Charge 4 Speaker
Firstly, by default, this BT speaker has bass boost mode turned on. So this mode adds a bit of extra treble and lots of extra bass to the audio output. It makes the passive bass radiators vibrate a lot more, and adds a decidedly “thumpy” quality to the content playing. But when OFF, you get a more flat sounding, less bassy response.

How to Toggle JBL Charge 4 Bass Boost Mode Off and On
You can turn this bass boost mode OFF by pressing and holding in the Volume Down (-) and Bluetooth buttons for about ten seconds, until the oval ring around the buttons lights up, as shown in the next picture. Find these buttons on the top of the speaker, as shown in the picture above.

To turn bass boost back on, again, press and hold the Volume Down and Bluetooth buttons in until the oval button ring lights up again. Release the buttons when you see that. Then, when the ring goes off, bass boost mode has been enabled once again.
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References
Revision History
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- 2020-12-06: First published.