Low resonance cabinet design enhances transparency

Colouration caused by resonances in a loudspeaker cabinet, where the cabinet itself starts to radiate sound energy, can seriously degrade the sound quality by obscuring detail. Because of the very high sound level capability of the PQS-402 (118dB), we went to great pains to design a cabinet where resonances were minimized, as these would otherwise degrade the loudspeaker’s ability to resolve the fine detail that is essential in order to produce a sense of realism and hence convey the emotion that is the essence of a musical performance.

The PQS-402’s DDD drivers use very small enclosures, minimizing the area of any potential vibrating surface. Being cylindrical, they eliminate the resonances that can arise with a conventional rectangular or square section cabinet. Because they are made from aluminium, a comparatively soft metal, residual vibration of the enclosure is minimised. The DDD driver enclosure end-caps are made from non-resonant MDF and the enclosure is packed with damping material to dissipate any standing waves. The result is that the PQS-402 has the clarity that we normally associate with electrostatic loudspeakers and for the same reason: they essentially have no enclosure to colour the sound.

The bass system, which covers the range from 215Hz downwards, is divided into two independent cabinets, so the panels are smaller and therefore stiffer and more vibration-resistant than if a single large enclosure were to be used. All the cabinet vertical surfaces are non-parallel to prevent the formation of standing waves between them. Internal bracing increases rigidity to suppress resonances. Residual vibration is minimized by applying a special damping material called Hawaphon®, to the inside surface of each panel.

Hawaphon® consists of a polymer sheet containing a matrix of small cells filled with fine steel shot. It adds mass to the panels to reduce the resonant frequency and the ability of the balls in each cell to move against each other provides a very effective way of converting vibration energy into heat. Originally developed as an anti-surveillance measure for use in military and government buildings, Hawaphon® achieves broadband attenuation of structure-borne sound of more than 50dB, which is an exceptionally high figure.

To damp resonances of the air within the cabinet, the whole of the interior is lined with a 1cm thick layer of high-density felt. This is achieved by fitting pieces of felt that are precisely cut to fit each panel, rather than just inserting a roll of felt into the cabinet. This is a time consuming process, but we believe produces a superior result and is typical of the attention to detail that we lavish on all of our products.