GB2291883A

GB2291883A - Resinous material and units fabricated therefrom

Info

Publication number: GB2291883A
Application number: GB9414817A
Authority: GB
Inventors: John Stride
Original assignee: PANDORA PRODUCTS Ltd
Current assignee: PANDORA PRODUCTS Ltd
Priority date: 1994-07-22
Filing date: 1994-07-22
Publication date: 1996-02-07
Anticipated expiration: 2014-07-22
Also published as: GB9414817D0; GB2291883B

Abstract

A material for use in the manufacture of an acoustic unit such as a loud speaker enclosure comprises a polyester casting resin incorporating a mineral bulking material composed of a mixture of particles, the mixture including particles lying in a range of particle sizes together with strands or crumbs of rubber or a rubber like material. The bulking material can include hollow bead components. Preferably the proportion by weight of mineral to rubber crumb lies in the range 80/20 to 90/10 and the proportion of mineral/rubber mix to resin lies in the range 80/20 to 70/30. An acoustic enclosure fabricated from the material has at least one interior volume; the thickness of the wall between the interior volume and the exterior of the enclosure being according to one version substantially uniform and in an alternative version non-uniform in a linear direction along the exterior of the enclosure.

Description

MATERIAL FOR FABRICATION AND UNITES FABRICATED THEREFROM This invention relates to material for fabrication and units fabricated therefrom.

It is particularly, though not exclusively, concerned with the use of the material in the fabrication of acoustic units such as loudspeaker enclosures.

Conventional materials used for the enclosures of current loudspeaker designs include wood or wood based materials such as block or chip board. While such materials are readily worked and machined their use does not readily result in acoustically satisfactory enclosures. Conventional loudspeaker enclosures are usually box like in form resulting in an internal shape which lead to the generation of several resonant frequencies. These require the provision of sound deadening or dampening means.

The design of a loudspeaker enclosure involves consideration of a number of factors. There is a need for the enclosure to provide for reasonable reproduction of a range of frequencies using a number of loudspeaker units. The type and number of loudspeaker units contained within an enclosure will establish the frequency range but colouration imposed by the enclosure should be kept to a minimum. In addition there are constraints arising from the size of the enclosure.

For certain applications a large enclosure is deemed desirable. Such enclosures must be sufficiently strong to provide for adequate stiffening, support for the loudspeakers and related circuitry and to provide for such porting and internal damping as is necessary.

According to a first aspect of the present invention there is provided a material for for use in the manufacture of an acoustic unit such as a loud speaker enclosure comprising a polyester casting resin incorporating a mineral bulking material composed of a mixture of particles, the mixture including particles lying in a range of particle sizes together with strands or crumbs of rubber or a rubber like material.

According to a first preferred version of the first aspect of the present invention the bulking material includes hollow bead components.

According to a second preferred version of the present invention or the first preferred version thereof wherein the proportion by weight of mineral to rubber crumb lies in the range 80/20 to 90/10 and the proportion of mineral/rubber mix to resin lies in the range 80/20 to 70/30.

According to a second aspect of the present invention therein provided an acoustic enclosure fabricated from a material according to the first aspect or any preferred version thereof having at least one interior volume; the thickness of the wall between the interior volume and the exterior of the enclosure being substantially uniform in a linear direction along the exterior of the enclosure.

According to a third aspect of the present invention there is provided an acoustic enclosure fabricated from a material according to the first aspect having at least one interior volume; the thickness of the wall between the interior volume and the exterior of the enclosure being non-uniform in a linear direction along the exterior of the enclosure.

According to a fourth aspect of the present invention there is provided an acoustic enclosure according to the second or third aspects wherein the enclosure serves to define at least two separate interior volumes adapted to have a loudspeaker located therein, each volume opening through a port in the enclosure to the exterior of the enclosure or to another interior volume.

An exemplary embodiment of the invention will now be described from two aspects, with reference to the accompanying drawings of a loudspeaker enclosure of which: Figure 1 is a front elevation: Figure 2 is a side elevation; Figure 3 is a sectional elevation on line ffl-ffl of Figure 1.

First Aspect- material A material according to the first aspect of the present invention is made up of a cast fabrication. The casting is undertaken in a mould to produce the enclosure described hereafter in connection with Figures 1 to 3. The interior of the mould is provided with a standard polyester gel coat (such as Polycor 9101). A mix is then prepared made up of a mineral bulking agent including hollow beads (such as Advanced Materials product Number FL 2/300 marketed under the trade mark 'FLOWBEAD 3000'). To this mixture there is then added a rubber crumb derived from recycled tyre material.

A standard polyester casting resin (such as Neste G 103 E) is then added to the mix. The proportions of the material used depends to a substantial extent on the end product involved. However in practice it has been found that the following range of mixtures by weight are suitable: mineral 80%/rubber crumb 2070 to mineral 9070/rubber crumb 10%.

The proportion of resin then added in the range: mineral/rubber 80% - resin 20% to mineral/rubber 70% - resin 30%.

However it is stressed that the optimum proportions depends on the final product required.

Any further mechanical elements to be cast into the enclosure are located in the mould. The prepared mix with added catalyst is then deposited on the gel coat in the mould and allowed to polymerise. The contents of the mould are demoulded and post-cured for a period of up to 4 hours.

The post-cured enclosure is then trimmed, assembled and polished prior to the insertion of loud speaker units and other components.

Second aspect - fabrication The figures variously show freshly moulded enclosure 11 with two ports 12, 13 for, respectively, loudspeakers 14, 15. Enclosure 11 has an outside gel coated surface and is made up of sides 16, 17, top 18, bottom 19 and back 20 formed as an integral fabrication.

The interior of the enclosure 11 is made up of two independent plenums 21, 22 which serve to house, respectively, loudspeakers 14, 15 in relative acoustic isolation. To inhibit the formation of standing waves in the enclosure the wall thickness is varied so that the plenums 21, 22 while being each being of controlled volume are unsymmetrical in form. Thus the thickness of back 20 in the vicinity of plenum 12 in the direction of axis 23 is not uniform.

While the exemplary embodiment refers to an enclosure with non-uniform wall thickness to ameliorate. for example, the generation of specific internal resonant frequencies the material of the present invention can also be used to provide enclosures with substantially uniform wall thickness which still provide an improved acoustic performance over existing enclosures fabricated from conventional material.

In fabricating a loudspeaker enclosure from the material of the present invention it has been found that an enclosure of virtually any shape is readily fabricated and provides for a sound output with minimum colouration. The fabrication process provides all the advantages to be obtained from the use of a moulded material.

This is particularly significant in comparison with enclosures fabricated from currently used wood or wood based sheet materials.

The outer side of an enclosure according to the present invention is readily finished by veneering, spraying, gel coating or whatever.

The use of a moulding process further provides for the ready incorporation of other simple or complex shaped components and the protection of circuitry..

The use of strands or crumbs of rubber or rubber like material has been found to provide significant advantages in an acoustic context. The exemplary embodiment refers to a loudspeaker enclosure. However other applications where acoustic behaviour is significant are readily supplied such as a shelf or unit for supporting or housing acoustically sensitive components.

Claims

1 A material for use in the manufacture of an acoustic unit such as a loud speaker enclosure comprising a polyester casting resin incorporating a mineral bulking material composed of a mixture of particles, the mixture including particles lying in a range of particle sizes together with strands or crumbs of rubber or a rubber like material.

2 A material as claimed in Claim 1 wherein the bulking material includes hollow bead components.

3 A material as claimed in Claim 1 or Claim 2 wherein the proportion by weight of mineral to rubber crumb lies in the range 80/20 to 90/10 and the proportion of mineral/rubber mix to resin lies in the range 80/20 to 70/30.

4 A material for use in the manufacture of an acoustic unit as hereinbefore described with reference to the accompanying drawing.

5 An acoustic enclosure fabricated from a material according to any preceding claim having at least one interior volume; the thickness of the wall between the interior volume and the exterior of the enclosure being substantially uniform in a linear direction along the exterior of the enclosure.

6 An acoustic enclosure fabricated from a material as claimed in any of preceding claims 1 to 4 having at least one interior volume; the thickness of the wall between the interior volume and the exterior of the enclosure being non-uniform in a linear direction along the exterior of the enclosure.

7 A loud speaker enclosure comprising an acoustic enclosure according Claim

5 or Claim 6, the enclosure serving to define at least two separate interior volumes adapted to have a loudspeaker located therein, each volume opening through a port in the enclosure to the exterior of the enclosure or to another interior volume.

8 A loudspeaker enclosure as hereinbefore described with reference to the accompanying drawings.