What Yamaha say:
Every element of these high-resolution monitor headphones has been designed to suit professional monitoring applications. They feature 45mm custom drivers equipped with CCAW voice coils and powerful magnets to achieve precise definition and control. Made from aluminium wire coated in highly conductive copper, these lightweight voice coils give the HPH-MT220 a broad frequency response of 15Hz-28kHz and deliver flat, ultra high-resolution sound with precise stereo imaging. These headphones are ideal for recording and monitoring during mixing and mastering at studios.