Aftr installing ios 7 the output of earphones decreases what is the problem on iphone5?

Hello Karman,

You may have a volume limit set. This can be checked in Settings > Music > Volume Limit.

Otherwise, the following steps may help get your audio restored to its prior state.

No sound through stereo headset

1. Inspect the headset jack for debris and clean if necessary.
2. Connect the headset and make sure the connector is pushed in all the way.
3. Check the volume setting. Adjust the volume by pressing the volume up and down button on the left side of the iPhone.
4. If you are trying to listen to music and cannot hear any audio, make sure that the music on iPhone is not paused. Try squeezing the headset microphone to resume playback. Additionally, from the Home screen you can choose iPod > Now Playing, then tap Play.
5. Make sure the latest version of iTunes is installed on the computer that you are syncing the iPhone with (songs purchased from the iTunes Store using earlier versions of iTunes won't play).
6. Try another Apple headset (some third-party headsets require an adapter to be used with original iPhone).
7. Try a different song or video.
8. Check to see if the iPhone alert sounds or other iPhone sound effects exhibit the same audio issues.
9. Disconnect the headset from the iPhone and see if sound comes from the built-in speaker.

iPhone User Guide - Volume controls

http://help.apple.com/iphone/7/

iPhone: Hardware troubleshooting

http://support.apple.com/kb/TS2802

Cheers,

Allen