If a pair of headphones is not loud enough for your listening needs, use an external device to further amplify the original headphone signal. A quality headphone amplifier is the best solution for making headphones louder. Headphone amplifiers provide a much broader control over the dynamic range of headphones, enabling the listener to experience audio at much higher decibel levels. There are many headphone amplifiers on the market that will be suitable for both amateur and audiophile listening needs.
Purchase a headphone amplifier. An inexpensive headphone amplifier is suitable for most casual listeners. You can find cheap headphone amplifiers for less than $30, while audiophile quality professional headphone amplifier models can cost several hundreds of dollars (see Resources below.)
Check the connector type on your headphones. Determine whether you have an eighth inch jack or a quarter inch jack on your headphones. If your headphones have an eighth inch jack, it will be necessary to buy an eighth to quarter inch converter. These converters are not expensive and will only cost one or two dollars at a music or electronics store.
Plug your headphones into the eighth inch to quarter inch converter if necessary. Plug your headphones into the input of the headphone amplifier.
Be sure that the master volume on the headphone amplifier is set to zero to protect both your headphones and your hearing from high volume levels before turning on the headphone amplifier unit.
Send a signal to the headphones from a source such as an iPod, MP3 player or a computer.
Turn the volume on the headphone amplifier up slowly until the desired volume level is reached.
Be careful. Headphone amplifiers have the ability to make volume levels extremely high. If turned up too loud, you may damage both your headphone speakers or your hearing.