cut and paste from the website
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THE REFERENCE HEADPHONES FOR RADIO STATIONS
Semi-open headphones meeting the Institute of Radio Technology standards.
The K 240 DF follows the criteria specified by the Institute of Radio Technology (IRT) in Munich for a "diffuse field" equalization curve that provides headphone listeners with the sound pattern, characteristic of a room with reflective, non-anechoic surfaces. Each K 240 DF is rigorously tested to assure strict adherence to the IRT standards for frequency response, channel separation and sensitivity.
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AKG'S MOST POPULAR PROFESSIONAL HEADPHONE
A classic design which has become a standard in monitoring.
The "integrated semi-open air" design incorporates a highly accurate dynamic transducer, and an acoustically tuned venting structure behind the element produces a naturally open sound quality. The circumaural (around-the-ear) pads are designed for hours of wearing comfort, while the steel-cable, self-adjusting headband construction and single-sided professional quality audio interconnect ensure extended reliability in demanding professional studio applications.