PURistic design – loudspeaker housings made of polyurethane

  • PUR replaces wood in high-grade loudspeakers
  • Lower number of components, higher level of automation
  • Properties similar to those of wood

The new “ZERO 1” High-End active loudspeaker produced by the renowned manufacturer Avantgarde Acoustic does not only feature sophisticated technology but also a housing material rarely seen in the audio industry: The acoustically optimized loud speaker housings are not produced in the typical manner using wood, but are foamed by using polyurethane (PUR).

Cost-effective alternative to wood

Housings for high-grade loudspeakers are generally hand produced using various woods and wooden composites. Manual production with numerous work steps has its price, with design options being restricted at the same time. A material like PUR, which can be shaped in almost any way possible, offers an interesting alternative in terms of both design freedom and production costs. This is because in contrast to the wood design, the lower number of individual components and the higher level of automation used in this production process enables not just considerable cost savings, but also time-related benefits: “The complete development time of a series production moulding including prototype production take just six to ten months”, explains Hartmut Bührer, Sales Manager of Thieme‘s Plastics business unit. Another advantage of the PUR process is the function integration”: threaded inserts or other assembly parts can be integrated during the foaming process, simplifying the final assembly process.

drawing of the loud speaker

Properties similar to those of wood

An essential requirement for the replacement of wood was the favourable material properties of the polyurethane composites which resemble those of wood in many aspects. PUR exhibits an adjustable density ranging from 0.4 kg/dm³ to 1.15 kg/dm³ which lies in the range of typical soft and hard woods. Even the surface does not have a plastic feel, but rather feels warm and natural. A benefit with respect to wood components is that PUR absorbs almost no water at all. Swelling in moist environments can therefore be ruled out, an advantage over wood.

The high acoustical quality of the housing material was also essential for the loud speaker application. The selected PUR, integral hard foam constructed in sandwich form with an average wall thickness of 10 to 16 mm, exhibits nearly constant mechanical damping over the entire sound frequency range. This means that the one-piece PUR housing has even better acoustic properties than a wooden housing made from various multiplex and wood components.

Paint lends the boxes an even soft touch surface

An outstanding sound, however, is not the only thing required by a High-End loudspeaker box. The appearance also plays an important role. The Avantgarde loudspeaker was equipped with a very attractive, minimalist front design with free-form surfaces. Since the front and all four sides form a single molded part, the surface is fully homogeneous without protruding edges or joints. The rear side with functional fins on the inside (also made from PUR) and the cover over the electronics (manufactured by the injection molding process) are installed separately. A special, resistant PUR structural paint lends the boxes an even soft touch surface.

The Zero-1 loud-speaker housing will be exhibited at the #Fakuma 2014 at the Thieme Stand.

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