These KitSound muffs are more than just earmuffs. These super-warm earmuffs have a cunning trick up their sleeves - you can connect them to your iPod/iPhone/music phone/mp3 player or anything with a (3.5mm) headphone jack. Enjoy an excellent sound experience whilst keeping your ears nice and toasty. The back band is fully adjustable to fit most head shapes (just gently pull apart to adjust). The 40mm drivers and the latest back band design hot off the catwalks of Milan and NYC ensure that you are just as banging as the beats are. Take either the quilted or knitted styles to the streets. Technical specification 40mm drivers 40hz - 20khz frequency response.