Why are there so many wooden speakers?

Because the surface area of a loudspeaker cabinet is many times greater than that of the drive unit diaphragms, it is all too easy for the enclosure to radiate sound at a level similar to that of the drivers, sound that is coloured by resonances within the cabinet structure. This muddies the speaker’s sound and blurs the stereo image. To prevent this, it is vital that the loudspeaker cabinet be as inert as possible. At Focal, we use MDF (medium-density fibreboard) to achieve this. It may seem a "low-tech" solution compared to some cabinet materials employed today but MDF has inherent advantages that we believe make it the optimum material from which to construct a loudspeaker.

First, it is dense enough and stiff enough – when used in a thick, heavy front baffle – to resist the magnet reaction force from the drive units. As the driver diaphragm is forced forwards by the voice coil, an equal force acts in the opposite direction on the drive unit chassis. This is one of the major inputs of vibrational energy to the cabinet and it must be resisted. This requires not just a thick baffle but also meticulously placed internal bracing. Too stiff a cabinet, though, can be as bad as one which is not stiff enough because it pushes structural resonances up in frequency to a part of the spectrum where the ear is more sensitive.

Second, MDF has something resembling a sandwich structure, in which the faces on each side of the board are denser than its core. As well as contributing to stiffness, this endows MDF with good internal damping to help suppress vibrations when they occur. Sopra and Utopia front baffles use MDF plates thick laminated to multiply the sandwich effect (69mm thick for Sopra). Third, MDF can easily formed into curved cabinet forms. These are good both acoustically, because they allow the radiated sound to diffract smoothly around the cabinet without secondary radiation from sharp cabinet edges, and structurally because curved panels are stiffer than conventional flat ones. This combination of a thick front baffle, extensive internal bracing and curved panel forms (all constructed using MDF) we call Focal’s Gamma Structure. It is as important to the sound of our top loudspeakers as the drive units themselves.