This is down to a lot of factors like:

• The impedance of the headphones, measured in Ohms. Lower values normally mean louder headphones. Some cheap headphones can sound much louder than more expensive ones.
• The quality and power of the amplifier in the audio player
• The frequency response curve of both the headphones and the audio player can vary (depending on quality of the hardware) and may not match up well.
• If you are from the EU then there are legal restrictions introduced a few years ago that limit how loud MP3 players can be. These limitations can sometimes be removed by setting your location to the US but that probably won't work with iPods.

For best results, use brands that gets consistently good ratings, e.g. Cowon. You could also try an external headphone amplifier.

This is down to a lot of factors like:

• The impedance of the headphones, measured in Ohms. Lower values normally mean louder headphones. Some cheap headphones can sound much louder than more expensive ones.
• The quality and power of the amplifier in the audio player
• The frequency response curve of both the headphones and the audio player can vary (depending on quality of the hardware) and may not match up well.
• If you are from the EU then there are legal restrictions introduced a few years ago that limit how loud MP3 players can be. These limitations can sometimes be removed by setting your location to the US but that probably won't work with iPods.

For best results, use brands that gets consistently good ratings, e.g. Cowon. You could also try an external headphone amplifier. You connect your device as the input and your headphones as the output and it will boost the sound level (good for high impedance headphones). I believe some headphone amplifiers can use the line-level output from the ipod dock connector to bypass some of the ipod's own circuitry and provide better quality.

This is down to a lot of factors like:

• The impedance of the headphones, measured in Ohms. Lower values normally mean louder headphones. Some cheap headphones can sound much louder than more expensive ones.
• The quality and power of the amplifier in the audio player
• The frequency response curve of both the headphones and the audio player can vary (depending on quality of the hardware) and may not match up well.
• Some players (e.g. the Sansa Fuze) have an artificial restriction on how loud they can be because of EU laws/guidelines but these can sometimes be lifted. I don't think the iPod has this though

For best results, use brands that gets consistently good ratings, e.g. Cowon. You could also try an external headphone amplifier.

This is down to a lot of factors like:

• The impedance of the headphones, measured in Ohms. Lower values normally mean louder headphones. Some cheap headphones can sound much louder than more expensive ones.
• The quality and power of the amplifier in the audio player
• The frequency response curve of both the headphones and the audio player can vary (depending on quality of the hardware) and may not match up well.
• If you are from the EU then there are legal restrictions introduced a few years ago that limit how loud MP3 players can be. These limitations can sometimes be removed by setting your location to the US but that probably won't work with iPods.

For best results, use brands that gets consistently good ratings, e.g. Cowon. You could also try an external headphone amplifier.