auEQ!

If you are using your iPhone together with external loudspeaker or even a HiFi-System then this app provides the next level of sound quality by applying a smart room frequency response equalization technology. Your loudspeaker and amplifier combination may have a perfect frequency response within limits of +/- 1 dB over the whole frequency range but the listening room is the most critical component in the HiFi audio chain, causing amplitude peaks and dips of more than +/- 10 dB. Use the auEQ internal audio player to playback music through your HiFi-System via dock-connector, cable or AirPlay.