Loudspeaker housings made of Pur

Loud speaker polyurethane housings: PURistic design

Published at 09.01.2020

The new "ZERO 1" High-End active box end produced by the renowned manufacturer Avantgarde Acoustic will win you over with not just sophisticated technology but also with a housing material (still) rarely seen in the audio industry: The shapely, acoustically optimized loud speaker housings are in fact not produced in the typical manner using wood, but are rather foamed by THIEME plastic specialists using polyurethane (PUR).

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 here 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.
The creative opportunities with PUR are virtually limitless; even complex curved surfaces can be produced at minimal cost. An additional practical benefit of the PUR process is referred to as "Function Integration": Threaded inserts or other assembly parts can be integrated during the foaming process, simplifying the final assembly process.
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, a huge 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.
A job for specialists
With its selection of Thieme, Avantgarde Acoustic has consciously chosen a very experienced partner in the development of plastic housing.  Due in part to the high demands for design aesthetic and acoustics, a standard PUR process fell short.  With Thieme as the partner, the ideal PUR formula/process was determined in extensive testing.  3D design data were procedurally optimised for the PUR design at THIEME in collaboration with Tobias Adami (ADAMIDESIGN, Munich) and the product designer assigned by Avantgarde. "The PUR process enables our design ideas to be converted 1:1", states Tobias Adami, reaching a positive conclusion. "The PUR design collaboration with Thieme was very good and effective."
In order to be able to evaluate the suitability of the housing with respect to the acoustical properties, additional extensive FEM computations were made in advance. The 3D housing data developed from the theory and finalised by a Thieme design partner formed the basis for the mold construction. The first housing produced in this way was then optimized in measurement and test series for the high, middle and low sound ranges.  Once optimizes, the material characteristics were fine tuned and adjusted again. As confirmed by Holger Fromme, Managing Director of Avantgarde Acoustich, this effort paid off: "The result is a great-sounding loudspeaker with a very impressive design, sound and function."
Award-winning design
An outstanding sound however is not the only thing required by a High-End loudspeaker box like the Zero 1. The appearance also plays an important role. In terms of value, the PUR housing leaves nothing to be desired with respect to a carefully manufactured wooden box.  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 absolutely even "soft touch" surface with a leather-like feel. "The processing is excellent from all sides," concluded the Jury of the renowned IF Design Prize and awarded the "IF gold award" to the Zero 1 as an outstanding example of a modern design.