Guys i also had this problem for many years and as i just buyed an Jbl Charg speaker this was really getting on my nerve so i decided to check it up. Luckily the problem can easily be solved as you enter the settings on your Sony phone, go down to "about phone" and the click on the last "version" field about 5 times, This should unlock the "Developer mode". Once this is done go back one step to the "About phone" and look for the newly "Development alternative"-mode, enter this and go down to the "Deactivate-Absolute volume" alternative and click it. Tadaa! Your device will no longer interact directly with the speaker volume as you now can make changes both on your phone and on your speaker without the insane volume steps that always accured before. Hope this will help as im really glad i found the solution in another forum just a couple of minutes ago and became really happy when i turned out to be this simple.
... View more