Some different versions added up in the original post to give options - including the Optimus Lite 2gb/16gb version
Also - here is a tip for helping people with low speaker volume issue. People who do not have the little pressure relief valve hole on the rear cover of the watch.
I have tested and I am sure that this will help those people who are having low speaker volume issues. As always - YOU DO THIS AT YOUR OWN RISK!!!
It’s actually very simple to do - very carefully remove the rear cover of the watch. Take out the 4 little screws holding it down and VERY gently pry open the case at the rear with a plastic tool or tooth pick. It is a VERY tight fit - so be very careful!!
Gently lift the cover but do not try to pull it away from the watch. It is not necessary.
Then just replace the cover and replace the 4 screws. That’s it
I have tested this and I can confirm that once the cover is replaced the speaker functions normally.
I guess the seal must be creating a vacuum and it affects the sound. You can try this if you want to.