Big on sound – precise in design The JBL Synchros S300 is a tough act to follow when it comes to precision listening. With its portable, conveniently collapsible steel headband design, leather earcushions, the S300 goes above and beyond in craftsmanship both inside and out. Available in 6 different color combinations, it not only feels good and looks good, it brings you all the sonic power, richness, and depth of JBL PureBass performance.