Tork X-Pro Motorcycle Helmet Speakers (with Volume Control) PLUS Booster Mini Amplifier (Headphone Amp) Superb Sound Quality // Great Bass Response Thin Bodied // High Volume Volume Control Included Booster - High quality sound amplifier for over 200% gain. Booster - Small and compact measuring 3.5" x 1.5" x 1/2" thick. Standard 3.5mm stereo music connector