Gemini GTR300: Bluetooth Stereo Speaker & Guitar Amp Stylish and efficient, the GTR series of Portable Bluetooth Speakers are sure to liven up any aspect of your life. Whether it be a party or just relaxing at home, the sound quality from a GTR speaker will set any mood. Each speaker comes with the ability to play music via Bluetooth or plug it in through an AUX input so you can truly listen to music any way you want. Each speaker also comes with full control over the bass and treble for the ultimate customizable music listening experience.