If you are not satisfied and having problem on Samsung Galaxy S II speaker volume like its very low even you've already set to its maximum volume. Many users experiencing and been complaining about speaker volume like a very low on phone calls,earphone, headset and in the car using AUX.
This tips might help you solve the problem, give these a try just send us a feedback whether it works for you or not:
A) Enter service mode by typing below code on your dialer :
click the following:
 NB (VOICE CALL)
Choose Handset, headset, Speaker (which ever you want higher volume)
 SRC Speech RX Volume
Change default values and higher the values any number of your choosing, here is an example:
0_lvl : 68
1_lvl : 72
2_lvl : 76
3_lvl : 80
4_lvl : 84
5_lvl : 88 Higher these values to until hear volume improvement.
Can also edit the values from:
DST I2S1 TX Volume
SRC I2S1 RX Volume: 100
DST Speech TX Volume: 94
This Samsung volume setting, worked for several people but sadly only worked 2 times for me and values keep resetting for me (doesn't mean for you, so give it a try) Also this is based on STOCK firmware.
B) the second thing you might to try is app called Volume+:
This app guarantees it higher the volume without the need of touching its default settings, BUT huge drawback it highers everything: Headset, speaker and Bluetooth EXCEPT HANDSET which is the most important
(I also downloaded many volume increase apps, but Volume+ was the only one got the job done for everything but handset)
C) Lastly get GOOGLE VOICE app (create a GV account if you don't have one)
just by installing Google and logging on, every time you make a call, your calls get forwarded through Google voice and volume levels become acceptable in ALL HANDSET, HEADSET, SPEAKER, BLUETOOTH (just like phone should of have been) (this what i personally use fix my volume issues)
If the above tips doesn't work for you, the best way is to complain it to your Samsung Galaxy S II provider.