An improved loudspeaker assembly

Abstract

The loudspeaker stand 3 comprises a rigid tubular enclosure 5, and a subwoofer drive unit 10 housed within the rigid tubular enclosure. The subwoofer drive unit 10 is directed towards an end of the ri

Description

Field of the invention

[001] The invention relates to a loudspeaker assembly. In particular, the invention relates to a loudspeaker assembly comprising a subwoofer housing and a support structure for a separate host loudspeaker cabinet. More particularly, the invention relates to a bass augmentation loudspeaker assembly comprising a subwoofer housing which forms a pedestal for a separate host loudspeaker cabinet, and circuitry to connect the separate host loudspeaker cabinet and the subwoofer within the assembly. Background of the invention

[002] The purpose of a high fidelity loudspeaker system is to reproduce recorded and / or transmitted sound (such as music) as faithfully as possible. In other words, the experience of a user listening to a loudspeaker reproducing, for example, a song, should be comparable to the experience of someone listening directly to the singer.

[003] One of the most significant challenges to faithful sound reproduction, especially in domestic and similar environments where both floor space and budget are limited, is the reproduction of the lower frequency components (or "bass’ components) of the original sound.

[004] Consumer studies consistently show that a powerful and faithful bass element significantly enhances the user experience when listening to music.

[005] It is common to augment the bass reproduction capacity of speaker systems by adding separate bass speaker units (often called sub-woofers). This comes with its own technical challenges around controlling the output of each loudspeaker unit to acoustically combine so as to more faithfully reproduce the original sound at the user’s location.

[006] A new solution is needed for augmenting more precisely the bass output of an existing loudspeaker system, with lower cost and space requirements than the prior art. The present invention seeks to meet this need. Summary of the invention

[007] A first aspect of the invention provides a loudspeaker assembly comprising: a rigid tubular enclosure; a loudspeaker drive unit housed within the rigid tubular enclosure, directed towards an end of the rigid tubular enclosure, such that the outer perimeter of the drive unit is in sealing engagement with the internal surface of the rigid tubular enclosure; a cabinet support platform fixed to the distal end of the rigid tubular enclosure and perpendicular to the axis of the rigid tubular enclosure; a base structure fixed to the proximal end of the rigid tubular enclosure; a vent through which sound waves generated in use by the drive unit can exit the assembly; and an amplifier unit with a signal output connected to the loudspeaker drive unit within the tubular enclosure and with a second signal connector disposed so as to be connectable in use to a loudspeaker cabinet placed on the cabinet support platform, which provides the audio input to the electronics within this invention.

[008] Small high-quality loudspeaker systems are typically intended to be elevated in use such that their high-frequency unit is directed towards the ear of the listener. This is typically accomplished by the use of loudspeaker stands which occupy floor space. Some users augment the diminished low-frequency sonic output of such small loudspeakers with one or more separate subwoofers located in the listening room and also occupying floor space. This invention combines the convenience of a small high-quality loudspeaker with a subwoofer and provides a solution which extends the low frequency output of the system without additional floor space.

[009] Compared with previous attempts to provide stand-subwoofer solutions using passive analogue circuitry, this invention has further distinct advantages. Previous passive analogue solutions derive their audio signal for a sub-woofer drive unit from a frequency dividing network comprising heavy-duty inductors, capacitors and resistors which create an unavoidable, lossy electrical load across the host amplifier and compromise the performance of the host loudspeaker.

[010] Furthermore, the passive analogue solution is not able to optimise the relative electro-acoustic phase of the signal derived to feed the bass drive unit relative to host loudspeaker so that perfect acoustic integration of the contributions of host loudspeaker and system in the frequency region where they are both operating is not possible. [Oil] Additionally, this invention permits the user to adjust the sound volume contribution of the sub-woofer system at will and to taste, which is not possible with a passive analogue sub-woofer. Also, because the electronics of this invention include a digital signal processing unit, further optional frequency response shaping facilities can be included, for example, notch filters for counteracting room resonances typical of domestic environments.

[012] This invention lends itself to customisation according to listener height, preferences for colouring and cosmetic decoration, position of connectors and user controls, size of cabinet support platform and base plinth arrangement related to the proportions and weight of the host loudspeaker.

[013] In some embodiments the second signal connector is connectable in use to a point where the output of an amplifier of a loudspeaker cabinet placed on the cabinet support platform is connected to an input of a loudspeaker of the loudspeaker cabinet placed on the cabinet support platform. This is equivalent to the ‘high-level’ input provided commonly in sub-woofer systems. In other embodiments, the second signal connector is connectable in use to the input of an amplifier, that is, the output of a pre-amplifier, feeding a loudspeaker of a loudspeaker cabinet placed on the cabinet support platform — referred to as the ‘low-level’ input on some sub-woofer systems.

[014] In preferred embodiments, the amplifier unit comprises digital electronics.

[015] In some embodiments, the vent is in airflow communication with the loudspeaker drive unit. In some such embodiments, the drive unit is directed towards the proximal end of the rigid tubular enclosure, the distal end of the tubular enclosure is closed by the cabinet support platform, and the vent is formed through a portion of the side wall of the rigid tubular enclosure at its proximal end. Alternatively, the vent may be formed through an aperture in the base structure of the assembly, at its proximal end.

[016] Some such embodiments further comprise a baffle extending distally from the base structure, part of the distance to the loudspeaker drive unit and farther than the distal extent of the lateral vent, so as to form, in axial cross-section, a chord spanning the portion of the side wall through which the lateral vent is formed.

[017] This arrangement has been shown to achieve higher sound output and lower distortion than a simple tubular vent of similar dimensions. Alternatively, a cylindrical vent could be formed through the side wall or base of the tubular enclosure to the atmosphere via any alternative plinth arrangement.

[018] In some advantageous embodiments, the base structure is configured as a stand for the assembly, capable of supporting the assembly in an upright position on a floor surface, such that the cabinet support platform is at the top of the assembly.

[019] A second aspect of the invention provides a loudspeaker system comprising a host loudspeaker cabinet and a loudspeaker assembly according to the first aspect, wherein the host loudspeaker cabinet is placed on the cabinet support platform and connected to the second signal connector. Brief description of the drawings

[020] The invention will now be described, by way of example only, by means of a preferred embodiment and with reference to the following drawings:

[021] Figure 1 depicts a preferred embodiment of the invention in use supporting a host loudspeaker cabinet.

[022] Figure 2 depicts the preferred embodiment of the invention of Figure 1, without the host loudspeaker cabinet and in a ‘transparent’ and partly exploded view.

[023] Figure 3 depicts the interface between the tubular enclosure and the base unit of the preferred embodiment of the invention, in a partly exploded view.

[024] Figure 4 depicts a preferred embodiment of the circuitry for use with the invention. Detailed description of the drawings

[025] Throughout this specification, where use is made of relative or directional terms such as ‘upwards’, ‘downwards’, ‘front’, ‘rear’, ‘top’, ‘bottom’, they should be interpreted with reference to the imuse orientation of the system and assembly, as depicted in the Figures.

[026] Figure 1 depicts a preferred embodiment of the loudspeaker system 1 of the invention, comprising a separate host loudspeaker 2 and a loudspeaker assembly 3.

[027] The loudspeaker 2 may be any conventional loudspeaker, in some embodiments a relatively small loudspeaker cabinet, such as the Harbeth P3 or the BBC LS3 / 5a. Adaptations of this concept or design would however make it suitable for a wide range of host loudspeaker sizes. Although not shown in Figure 1, the audio input of the host loudspeaker 2 is connected to the circuitry of the loudspeaker assembly 3. This will be explained in more detail below.

[028] The loudspeaker assembly 3 comprises a cabinet support platform 4, a rigid tubular enclosure 5 and a base structure 6 which is formed of a base 7, a cover 8, and an annular side wall 9 which is formed of a grille or webbing for at least a part of its circumference. In other embodiments the base structure 6 might be formed of a casting or other device to combine parts 7, 8, 9 and also the vent 18, 19, 20 (see Figure 2).

[029] In some embodiments, the host loudspeaker 2 simply balances on the cabinet support platform 4 in use. There will be many environments, however, in which this poses a risk to the assembly 1 and to others, for example environments frequented by children or animals, who may inadvertently knock the host loudspeaker 2 from the platform 4. For this reason, it is preferable in some embodiments to provide means for reducing the risk of the host loudspeaker 2 toppling off the platform 4, for example, either a biasing or a securing means. Consequently, in some embodiments, the cabinet support platform 4 has four holes drilled through it, inset from each of its four corners in the event that the platform is square or rectangular, by means of which a user might screw or bolt the host loudspeaker cabinet 2 in place. Alternatively or additionally, larger recesses may be provided in the top of the cabinet support platform 4, inset from each corner, and corresponding feet can be secured (for example by an adhesive) to the bottom surface of the loudspeaker 2, configured to rest in the recesses in use. Alternatively or additionally, small strong magnets can be embedded into the top surface of the cabinet support platform, and corresponding magnets secured to the bottom panel of the loudspeaker enclosure 2, either internally or in an external recess, to maintain a flat bottom. It will be appreciated that some loudspeaker cabinets could be designed intentionally for use with the assembly 1, and sold with integral magnets on the underside of the cabinet. The skilled person will appreciate that there are numerous ways to reduce the risk of the host loudspeaker 2 toppling from the cabinet support platform 4, all of which fall within the scope of this invention.

[030] The material for the rigid tubular enclosure 5 should be selected to maximise practicable stiffness. As will become apparent, this enclosure 5 houses a loudspeaker drive unit for operation at bass frequencies, and it is desirable to minimise movement of the rigid tubular enclosure 5 caused by the operation of the loudspeaker drive unit, so as to reduce or substantially eliminate the distortion or “coloration’ of conventional loudspeaker enclosures.

[031] Tubular enclosure 5 is cylindrical in form, which avoids the panel resonances typically present in a cuboidal loudspeaker enclosure. Any inherently stiff and non-resonant materials are suitable for the construction of tube 5 including but not limited to wound or layered composites such as paper, carbon fibre, or Kevlar (RTM).

[032] Figure 2 depicts the same loudspeaker assembly 3 in a transparent and partly exploded view. The tubular enclosure 5 is separated into two parts: an upper part 5a and a lower part 5b. A stepped sealing ring 21 is interposed between the two parts. The central annular element of the stepped sealing ring 21 has the same outer diameter as the parts 5a 5b of the tubular enclosure 5, and is flush with them when assembled. The upper and lower annular elements of the stepped sealing ring 21 have outside diameters substantially equal to the internal diameter of the tubular enclosure 5, and fit snugly within respective parts 5a and 5b when assembled. Appropriate adhesives and / or sealants are used to secure the tubular enclosure parts 5a 5b to the stepped sealing ring 21 to ensure an air-tight seal between the three parts 5a, 5b, 21.

[033] In some embodiments, an optional third part 5c of the tubular enclosure 5 is provided, for adjusting the height of the system 1. This third part 5c is sealed at both ends, and provides no acoustic contribution to the system 1. It is fitted between the upper part 5a and the cabinet support platform 4. It 5c is fixed to the upper part 5a with appropriate sealants and adhesives or by other means so as to ensure an air-tight seal. It 5c is also fixed rigidly by appropriate means to the cabinet support platform 4, in order to ensure the structure is as rigid as possible in service to the quality of the sound produced. The dimensions of the upper 5a and lower 5b parts of the tubular enclosure 5 must be carefully selected for acoustic performance, and the outer diameter of the third part 5c should be selected to match the outer diameters of the other parts 5a, 5b, but because it provides no acoustic contribution to the system, its height can be selected according to users’ aesthetic or other preferences.

[034] The loudspeaker drive unit 10 is directed downwardly, and is m sealing engagement at its perimeter with top edge of the upper annular element of the stepped sealing ring 21, creating a sealed chamber 11 above the drive unit 10 (since the top of the rigid tubular enclosure is sealed by the cabinet support platform 4) and a vented (as will be described below) chamber 12 below the drive unit 10. This three^component mounting configuration for the drive unit 10 is advantageous because it allows a user or a maintenance professional access to the drive unit for ease of maintenance or replacement, simply by removing the upper part 5a of the tubular enclosure 5.

[035] Although the loudspeaker drive unit 10 is directed downwardly in the depicted embodiment, it may be pointed upwardly in other embodiments, in which case the sealed chamber 11 would be below the drive unit 10 and the vented chamber 12 would be above it.

[036] It is important that drive unit 10 is properly and permanently sealed to the interior of tubular enclosure 5 via the stepped mounting ring 21 to avoid air leaks which degrade the performance of assembly 3. Similarly, the passages for signal cables throughout assembly 3 are carefully sealed with appropriate materials to negate air leaks which would spoil the performance of the system.

[037] An annular hollow is formed around the base end of the rigid tubular enclosure 5, between the base 7 and cover 8, although the annular hollow may be, as noted above, replaced by an alternative plinth arrangement. An amplifier unit 13 is housed within this space. The internal workings of the amplifier unit 13 will be discussed in more detail below, but externally it comprises a power input connection 14, and a signal connector 15, for receiving audio signals from host loudspeaker 2. The amplifier unit 13 also has an output connection 16 to the drive unit 10.

[038] As shown in Figure 3, it is preferable for the tubular enclosure 5 to be covered by an aesthetically pleasing fabric cover 22, anchored by a seam at the interface between the tubular enclosure 5 and the cover 8 of the base structure 6. In order to hide the seam from view, an annular cover 23 can be placed over it, in a specially formed recess formed at the inner edge of the cover 8. This allows access for maintenance without compromising the aesthetic appeal of the device.

[039] It will be appreciated by the skilled reader that some conventional loudspeakers are passive, receiving a high-level audio signal from an amplifier unit, while others are powered or ‘active’, receiving a separate electrical power input. The amplifier unit 13 and its input connection 16 can be configured for use with either an active or a passive host loudspeaker 2, or can be configured to be operable with both.

[040] A vent 18 is formed in the vented chamber 12 by a baffle 19 extending from the base 7 into the vented chamber 12. The baffle 19 extends laterally from a first vertical line on the internal surface of the rigid tubular enclosure 5 to a second vertical line on the internal surface of the rigid tubular enclosure 5. This divides the lower part of the vented chamber 12 into two regions, with the vent 18 typically being the smaller region. The vent 18 is in air flow communication, via a lateral vent 20 formed through the surface of the rigid tubular enclosure 5 with the grille or webbing portion of the lateral wall 9.

[041] In an alternative arrangement, components 6, 7, 8, 9, 18, 19, 20 might be combined in a cast, or otherwise formed, plinth.

[042] Figure 4 depicts an exemplary circuit for use in the amplifier unit 13 of the invention. Although in the preferred embodiment the amplifier unit 13 is shown contained in a single housing, this is not essential. The circuitry of the assembly 3, as well as the cables and input / output connections, may be distributed throughout the assembly 3 in any suitable way.

[043] The exemplary amplifier 13 takes a parallel ‘listen’ feed from the host loudspeaker 2 driven from its host amplifier via a balanced attenuator, series 5 resistors and an audio transformer. This provides galvanic isolation of amplifier 13 from the host amplifier and host loudspeaker, isolating the signal and ground paths from the host equipment, and facilitating connection to single-ended balanced and bridged analogue and digital host amplifier outputs without affecting the host loudspeaker or its amplifier. The attenuator precedes the audio transformer to 10 prevent saturation of the transformer core with low frequency energy when the host loudspeaker is played at a high level.

[044] The balanced attenuator is adjustable by the user, and has a centre detent ‘click-stop’ position at which the acoustic contributions of the host loudspeaker and sub-woofer’s sound output are well-matched under laboratory conditions. 15 However, the user can change the level of the sub-woofer acoustic contribution using the attenuator control to suit the wide range of domestic acoustic environments, host loudspeakers, programme material and user tastes.

[045] Low- and high-pass filters set overall limits of the drive unit 10 acoustic response. The low-pass filter is preferably set to approximate the turnover 20 frequency of the host loudspeaker.

[046] The EQ block preferentially implemented by Digital Signal Processing contains response-shaping filters and allows for the implementation of room boundary compensation and other frequency response shaping options.

[047] The phase shift network helps to integrate the drive unit 10 with the host 25 loudspeaker 2 in the frequency region where both host loudspeaker 2 and subwoofer assembly 5 are together radiating sound.

[048] The dynamics processing provides drive unit protection and optionally compensates for reduced sensitivity of the human ear to low frequencies as loudness diminishes. As is well established the sensitivity of the human ear to low frequency sound is affected by the absolute level of that sound. As a consequence, bass notes appear to sound quieter than the centre of the audible spectrum when a system is played as diminished loudness. This invention may optionally contain a code module within the Digital Sound Processing arrangement to compensate for this effect by raising the level of lower frequency energy produced by the subwoofer system as the absolute level of the audio input decreases, and doing so in proportion with standard hearing sensitivity curves (e.g. in IEC263), commonly known as the Fletcher-Munson curves. The DSP system may do this by continuous monitoring of the input audio signal at the host loudspeaker’s input. The consequence of this is that bass notes do not appear to become quieter as the overall volume decreases.

[049] The standard DSP code containing all the above facilities and modules is considered universally applicable to domestic hifi music installations, but the apparatus includes a programming port, not normally accessible to the user, and alternative, improved, enhanced or application-specific software features could be implemented at a later date.

[050] Although the invention has been described above with reference to a specific embodiment, the embodiment is not limiting. The scope of the invention is limited only by the claims.

Claims

1. A loudspeaker assembly comprising: a rigid tubular enclosure; a loudspeaker drive unit housed within the rigid tubular enclosure, directed towards an end of the rigid tubular enclosure, such that the outer perimeter of the drive unit is in sealing engagement with the internal surface of the rigid tubular enclosure; a cabinet support platform fixed to the distal end of the rigid tubular enclosure and perpendicular to the axis of the rigid tubular enclosure; a base structure fixed to the proximal end of the rigid tubular enclosure; a vent through which sound waves generated in use by the drive unit can exit the assembly; and an amplifier unit with a signal output connected to the loudspeaker drive unit and with a second signal connector disposed so as to be connectable in use to a loudspeaker cabinet placed on the cabinet support platform.

2. A loudspeaker assembly according to claim 1 wherein the second signal connector is connectable in use to a point where the output of an amplifier of a loudspeaker cabinet placed on the cabinet support platform is connected to an input of a loudspeaker of the loudspeaker cabinet placed on the cabinet support platform.

3. A loudspeaker assembly according to claim 1 wherein the second signal connector is connectable in use to a point between an output of a pre-amplifier amplifier unit and an input of an amplifier of a loudspeaker cabinet placed on the cabinet support platform.

4. A loudspeaker assembly according to any one of claims 1 to 3 wherein the amplifier unit comprises digital electronics.

5. A loudspeaker assembly according to any preceding claim wherein the vent is in airflow communication with the loudspeaker drive unit.

6. A loudspeaker assembly according to claim 5 wherein: the drive unit is directed towards the proximal end of the rigid tubular enclosure; the distal end of13the tubular enclosure is closed by the base structure; and the vent is formed through a portion of the side wall of the rigid tubular enclosure at its proximal end.

7. A loudspeaker assembly according to claim 6 further comprising a baffle extending distally from the base structure, part of the distance to the loudspeaker5 drive unit and farther than the distal extent of the lateral vent, so as to form, in axial cross-section, a chord spanning the portion of the side wall through which the vent is formed.

8. A loudspeaker assembly according to any preceding claim wherein the base structure is configured as a stand for the assembly, capable of supporting the10 assembly in an upright position on a floor surface, such that the cabinet support platform is at the top of the assembly.

9. A loudspeaker system comprising a loudspeaker cabinet and a loudspeaker assembly according to any preceding claim, wherein the host loudspeaker cabinet is•J V—} J JL JLplaced on the cabinet support platform and connected to the second signal15 connector.

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