This is an passive amplifier for mobile phone used at close range, that can make sound beautifully and be adjusted its tone. Continued use of earphones can lead to ear fatigue and hearing less. However, when you want to enjoy music without using earphones, the sound of mobile phone may not be enough, although it is not as necessary as the good sound of speakers. This passive amplifier brings the sound of your mobile phone in a beautiful and your preference of tone to you when you are doing a little work or resting. The superior sound effect of material paulownia wood, which has used for musical instruments since ancient times in Japan, and tightly closed containers made with Japanese technology of manufacturing paulownia boxes make the beautiful sound.