Denon HEOS AH-C820 In Ear Headphone Dual 11.5MM Die Cast AlluminumHeos by Denon AH C820 In Ear Headphone Dual 11. 5MM Die Cast Alluminum Drawing on half a century of Denon headphone engineering experience, the new 2016 models are designed to combine comfort with no compromise sound. Aimed at those who want the very best sound whether traveling, working or relaxing, the new in ear models are packed with advanced Denon technologies, designed to deliver the best possible performance from compact, lightweight earphones.