GB2222745A - Suppressed air-resonance loudspeaker enclosure - Google Patents

Abstract

A loudspeaker enclosure 1 has a driver fitted into each of its two opposite ends 2 in such a manner that the two driver diaphragms effectively form the ends of the enclosure and end panels actually exist. By virtue of the resultant pipe-like enclosure shape, if the length between the driver ends is greater than the maximum diagonal dimension across the end, then the major air resonance and its harmonics are established along the axis of the enclosure which is the greatest dimension. These dimensionally defined resonances are suppressed by the two moving diaphragms which is the end planes where oscillatory nodes will be attempting to form. Radial air resonances are similarly dimensionally defined and being of much higher frequency by virtue of the lack of substantial parallel planes and the smaller dimensions, may be suppressed, together with the higher oscillation modes, by using acoustic absorption materials in the conventional manner. <IMAGE>

Description

SUPPRESSED AIR RESONANCE LOUDSPEAKER ENCLOSURE This invention relates to an audio frequency range loudspeater enclosure.

Loudspeaker enclosures are well known devices which are used to enable an electro-acoustic transducer,( the loudspeaker drive unit, hereafter referred to as withe driver" ), to reproduce audio frequency signals over a wider bandwidth than would be the case if they were not so employed.

Many kinds of enclosure have been utalised and generally they function by improving the match in acoustic impedance between the driver and the listening environment. This enables more power to be radiated, particularly at low audio freauencies, and usually there is also an increase in electrical power handling capability and a reduction in distortion.

Inclosures however are all mechanical structures and as such are subject to mechanical resonances of various kinds. A second source of resonance also occurs due to the interaction of the internal enclosure dimensions and the contained mass of air.

Most enclosures take the form of a rectangular box with the dimensions so chosen that no multiple or sub-multiple occurs between them. This reduces the amplitude of the air resonances which can occur in a two or three axes symmetry enclosure and spreads them over a wider frequency range.

Basically, three fundamental discrete resonances and their harmonics are produced and other modes are possible.

A moving driver diaphragm can suppress the air resonances which have nodes in the near vicinity or within the volume of the diaphragm and so the driver is usually positioned where it can supress as much as possible of the resonances.

This technique is only partially effective.

The invention described herein extends this principle by arranging the design of the enclosure to be such that only the one major set of resonances does occur, but that these are suppressed in a more effective manner. This is achieved by using two drivers, one at each end of the enclosure and so arranged that their diaphragms in fact form the ends of the enclosure. By this means the whole set of axial air resonances are removed since their oscillatory nodes must occur at the enclosure end walls, which are now moving diaphragms.

Mechanical resonances can be removed by using structural materials which have a high mechanical damping factor, and minor higher mode air resonances can be minimised by the use of acoustic absorbtion materials within the enclosure.

The specific embodiment of the invention which is shown in the accompanying drawing possesses the added advantage that being cylindrical, it has a high stiffness and does not suffer from flat panel resonances.

Since the troublesome air resonances are removed from the air mass within the enclosure, the contained air behaves in a more linear manner when excited by the signals being reproduced by the diaphragms. Consequently, the acoustic output is improved and the electrical impedance is better controlled with no sudden please changes. Due to the level impendance, there is a notable improvement in the interface between the loudspeaker and the power amplifier. Consistant results are now obtained between amplifiers of similar performance but different manufacture and circuit topology.

According to the present invention there is provided an enclosure for use as a loudspeaker enclosure which has a regular cross-section along the axial dimension of the enclosure with the axial dimension being greater than the major diagonal dimension of the cross-section.

The cross-section will normally take the form of an annulus, resulting in a cylindrical enclosure or it could be based on a polygon of three or more equal or unequal sides or a combination of any of these.

Whichever of these is adopted, the open ends of the enclosure so formed are both arranged to be terminated in a suitable driver diaphragm which physically forms the end walls, and so complete the loudspeaker enclosure structure, A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which Figure 1 shows a side view of a cylindrical format of the enclosure, here employed as an auxiliary bass loudspeaker.

Figure 2 shows an end view of the same enclosure which shows.

clearly how the driver forms the end of the enclosure.

Referring to the accompanying drawing, the loudspeaker enclosure comprises a cylindrical pipe 1 with a driver fitted into each open end 2 in such a manner as to totally seal them. Not shown are the protective grills for the drivers, the floor stand and any mounting bezels which may be required to mateh a particular driver chassis to the end of the pipe in the manner described.

This loudspeaker is used to augment the low frequency output of an existing pair of stereo loudspeakers in conjunction with a monophonic bass amplifier. It would normally be sited up against any convenient wall horizontally along the skirting board, for example, behind a sofa.

Claims (11)

1 A loudspeaker enclosure comprising a pair of drivers mounted into opposite ends of an enclosure such that the drivers cover most of the area of the enclosure ends and so in fact form the actual ends of the enclosure which itself has a length between the ends which is greater than the maximum dimension across the end section in which the drivers are mounted.

2 A loudspeaker enclosure as claimed in claim 1 wherein the cross-section is an annulus such that the enclosure body takes the form of a cylindrical pipe.

3 A loucspeaker enclosure as claimed in claim 1 wherein the cross-section is a regular polygon of number of sides N where N is a factorial number having values of 3,4,5,6,7,8 and so on.

4 A loudspeaker enclosure as claimed in claim 1 wherein the cros--section is an irregular polygon of number of sides Nt where N is a factorial number having values of 3,4,5,6,7,8 and so on.

5 A loudspeaker enclosure as claimed in any preceeding claim but where the cross-section tastes the form of a combination of the forms of claim 2 or claim 3 or claim 4.

6 A loudspeaker enclosure as claimed in any preceeding claim but wherein the cross-section is changed in form or dimension at some point along it's length between the ends

7 A loudspeaker enclosure as claimed in any preceeding claim wherein an acoustic filter or other acoustic device is incorporated.

8 A loudspeaker enclosure as claimed in any preceeding claim wherein one or both driver ends of the enclosure may be equipped with an acoustic diffuser to achieve radial or omni-directional radiation of the full range of audio freauencies.

9 A loudspeaker enclosure as claimed in any preceeding claim wherein the enclosure ie itself used as a component part within a larger enclosure. For example,by the use of horn-loading to increase the electro-acoustic efficiency.

10 A loudspeaker enclosure as claimed in any preceeding claim wherein the enclosure is designed to function at bass frequencies only.

11 A loudspeaker enclosure substantially as described herein which may be used horizontally, vertically or axially.