Sound is very low in iPhone5/5s but not in iPad

I have little diffrent issue with sounds, I have few BG sounds on our game, all BG sound are 2D, "Compressed in Memory", 128 bit and not hardware decoding. Game is universal build (iPhone+iPad). When I install the game in iPad sounds work perfect with proper volume as soudn artist gave, but when we install same build in iPhone 5 or iPhone 5S, sound volume descre to 20-25%. We have also checked it using download same audio file in both device from mail and play from librery, it's works perfect with proper volume and sound effect in iPhone 5, iPhone 5S and iPad, but it's not working good with unity in iPhone 5 and iPhone 5s.