Headphones

Designing a closed-back headphone is much more complex than taking an open-back design and slapping a capsule closure on it. Whereas in the case of an open-back headphone the rear of the driver diaphragm radiates into a large volume of air, allowing the rear radiation to be ignored, in a closed-back headphone the rear radiation is contained and, as a result, is subject to resonances and reflections. The situation is analogous to that with loudspeaker enclosures except that the reflections have much shorter delays and the enclosed air resonances occur at higher frequencies. The capsule of a closed-back headphone acts as a simple pressure chamber up to around 1kHz, at which point the wavelength of sound in air – 17cm at 2kHz – begins to become comparable to the internal dimensions of the enclosure and resonances become possible. To suppress these in the Elegia and Stellia, Focal's designers have incorporated a mix of diffusion and absorption of the rear radiation within the capsule space. KH