GB2428532A - An acrylic resin/mineral loudspeaker cabinet - Google Patents

Abstract

A loudspeaker cabinet has at least one curved wall and is of a solid material comprising a blend of acrylic resin and mineral. An example of a suitable mineral is Aluminium TriHydrate (ATH), a naturally occurring mineral obtainable from bauxite. A suitable resin is PolyMethyl MethAcrylate (PMMA). It is preferred that the blend is predominantly mineral, i.e. the resin content is below 50%. A commercially available material satisfying these requirements is available in the form of Corian õ , a material available from E.I. du Pont de Nemours and Co, Le Grand Saconnex, Geneva (CH). The curved wall of the cabinet is preferable a compound curve, i.e. curved in two dimensions. The resin/mineral blend of the invention is easily formed into the complex shapes called for in the design of loudspeaker cabinets. It can be thermoformed, routed, carved, sandblasted (etc) with relative ease and this enable complex shape to be formed.

Description

Loudspeakers

FIELD OF THE INVENTION

The present invention relates to loudspeakers.

BACKGROUND ART

The purpose of a loudspeaker is to convert an incoming electric signal into a corresponding audio output as accurately as possible whilst introducing as little additional audio content as possible.

The drivers are clearly an important aspect of the loudspeaker, in that it creates the pressure variations that are perceived by the human ear as an audio signal. The drivers must reproduce the audio signal as accurately as possible.

However, many other aspects of the loudspeaker are as important.

An example is the loudspeaker cabinet. In general, an aesthetically acceptable loudspeaker will include a cabinet that also contains the drivers' electronics and other supporting structure. A cabinet of some sort will also assist in hindering point reflections from those structures. However, a poorly designed cabinet will itself degrade the audio quality by providing sharp edges etc that can provide further sources of reflection. Likewise, parallel-sided cabinets offer the potential to create internal standing waves at particular frequencies. Furthermore, if the cabinet walls are insufficiently rigid then they can resonate and introduce unwanted audio output.

Thus, an ideal cabinet will have continuously curving walls with no sharp edges or parallel sides and will be of a substantial material to prevent resonance.

To date, materials such as wood have been used in high quality loudspeakers, despite the difficulty of forming this into the smoothly curved shapes required.

Examples of such loudspeakers include the KEF Reference Series and the B&W Nautilus 801.

Synthetic materials have been used in some loudspeakers, such as the B&W Nautilus, which uses a resinous material that can be set in a specific non- reflecting shape. However, the difficulty of forming synthetic materials to a rigid and accurate shape has meant that the use of such materials has been confined to very expensive loudspeakers such as the Nautilus and to lower quality loudspeakers where the synthetic material is used for its low cost despite a reduced rigidity.

SUMMARY OF THE INVENTION

The present invention therefore provides a loudspeaker cabinet having at least one curved wall and being of a solid material comprising a blend of acrylic resin and mineral.

An example of a suitable mineral is Aluminium TriHydrate (ATH), a naturally occurring mineral obtainable from bauxite. A suitable resin is PolyMethyl MethAcrylate (PMMA). It is preferred that the blend is predominantly mineral, i.e. the resin content is below 50%.

A commercially available material satisfying these requirements is available in the form of ConanTM, a material available from E.I. du Pont de Nemours & Co, Le Grand Saconnex, Geneva (CH).

The curved wall of the cabinet is preferable a compound curve, i.e. curved in two dimensions.

The resin/mineral blend of the invention is easily formed into the complex shapes called for in the design of loudspeaker cabinets. It can be thermoformed, routed, carved, sandblasted (etc) with relative ease and this enables complex shapes to be formed. This can be contrasted with wood where even simple (non-compound) curves are difficult and compound curves are essentially impossible. Meanwhile, a resin/mineral blend retains the density and rigidity that is required for the acoustic properties of the cabinet.

The present invention also relates to a loudspeaker comprising a cabinet according to any one of the preceding claims, and at least one driver unit at least partly enclosed therewithin.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; Figure 1 shows a perspective view of a loudspeaker according to the invention; and Figure 2 shows a side view of a loudspeaker according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to figures 1 and 2, a loudspeaker is shown generally as 10. This comprises a support 12 which has a generally flat under surface 14 allowing loudspeaker 10 to be placed when desired. A moulded cabinet 16 is suspended above the base 12 by way of a supporting arm 18 which extends from an upper surface of base 12 to a lower surface of the cabinet 16. The supporting arm 18 is designed so that is extends in an inclined manner so as to reduce sound reflections there from. Thus, the supporting arm 18 is connected to the base 12 at roughly the centre thereof but connects to the cabinet 16 towards the rear thereof.

The cabinet 16 contains three drivers, a woofer, mid range and tweeter each set in their own pod. Thus, three pods are provided, a lowermost and largest pod 20 for the woofer, a intermediate sized pod 22 located above the lower pod 20 and containing the mid range speaker, and a smaller upper pod 24 at the upper extremity of the cabinet 16 for the tweeter. Each pod is formed in a generally faired-in shape, essentially efliptical in section with a forward, narrower, end truncated to receive the driver. Thus, the woofer 26 is visible in the front of the lower pod 20, the mid range driver 28 is visible in the front of the intermediate pod 22, and the tweeter 30 is visible in the front of the upper pod 24. Present trends in speaker design are for the drivers to be visible in this way, although aesthetic considerations may call for them to be provided with a

suitable mesh cover.

The individual pods are joined and/or supported by a lower web 32 which extends from the lower pod 20 to the intermediate pod 22, and an upper web 34 extending from the intermediate pod 22 to the upper pod 24.

As can be seen in figures 1 and 2, the design incorporating the series of truncated elliptical pods, each joined via a web and each varying in size to accommodate the appropriate driver and in longitude naught position to provide time alignment between the drivers leads to a highly complex external shape.

Each pod has a compound curvature, elliptical in the longitudinal (horizontal) dimension and circular in the vertical dimension. Forming such shapes out of the wood that is traditional in loudspeaker cabinet manufacture is essentially impossible.

However, the particular shape disclosed is desirable both on aesthetic grounds and in terms of the sound quality that such a cabinet is capable of achieving. Thus, in order to prepare a cabinet in a shape such as this, manufacturers have resorted to resinous compounds or other formable polymeric compositions.

Table 1

Material Typical Specific Static Bending Gravity Modulus of Elasticity (MPa) Oak 0.61 11 Conan 1.78 10000 ABS plastics 1.03 40-60 Table 1 above gives typical densities and bending moduli for available materials. It would immediately be seen that the bending modulus for wood is considerably less than that of synthetic materials and thus it is usual to use relatively thick sections of wood in the construction of loudspeaker cabinets.

This imposes further difficulties in the forming of such materials into complex shapes.

The ABS plastics that are commonly used for manufacture of a wide variety of items offer a significantly higher bending modulus and specific gravity.

Thus, they are at first sight a desirable material for such applications. However, it will be noted that Conan1M, an example of material falling within the definition set out herein, offers a bending modulus elasticity that is dramatically greater than plastics due its nature as a composite of a ceramic material in a resinous matrix. This very high bending modulus of elasticity allows rigid structures to be produced that are resistant to harmonic vibration and thus relatively light weight even given the greatest specific gravity of Conan1M as compared to ABS plastics.

Meanwhile the very high formability of Conan1M through established procedures such as thermoforming and machining allows intricate shapes such as that shown in figures 1 and 2 to be produced without difficulty.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.

Claims (11)

1. A cabinet for a loudspeaker, having at least one curved wall and being of a solid material comprising a blend of acrylic resin and mineral.

2. A cabinet according to claim 1 in which the mineral is Aluminium TriHydrate.

3. A cabinet according to claim 1 or claim 2 in which the resin is PolyMethyl MethAcrylate.

4. A cabinet according to any one of the preceding claims in which the blend is predominantly mineral.

5. A cabinet according to any one of claims 1 to 3 in which the resin content of the blend is below 50%.

6. A cabinet according to any one of the preceding claims in which the solid material is ConanTM.

7. A cabinet according to any one of the preceding claims in which the curved wall is a compound curve.

8. A cabinet according to any one of the preceding claims in which the curved wall is formed by at Jeast one of thermoforming, routing, carving and sandblasting.

9. A loudspeaker comprising a cabinet according to any one of the preceding claims, and at least one driver unit at least partly enclosed therewithin.

10. A cabinet for a loudspeaker substantially as described herein with reference to and/or as illustrated in the accompanying figures.

11. A loudspeaker substantially as described herein with reference to and/or as illustrated in the accompanying figures.