Chosen Solution

Marshall Kilburn speaker volume is low, and the volume control knob does not change the volume in any way. Bluetooth and line in is all the same. I have tried this on three different devices and they are all the same.

Hi from what your question has told me it sounds like time for a new battery in your speaker! im not quite sure how to replace it on this model but im pretty sure that YouTube will have a tutorial and eBay will have a battery for you if you need any help along the way I can try my best to assist you! Thanks:-)