GB2283150A

GB2283150A - Loudspeaker systems

Info

Publication number: GB2283150A
Application number: GB9500068A
Authority: GB
Inventors: Peter Alexander Fryer; Steven P B Roe
Original assignee: B&W Loudspeakers Ltd
Current assignee: B&W Loudspeakers Ltd
Priority date: 1995-01-04
Filing date: 1995-01-04
Publication date: 1995-04-26
Also published as: GB9500068D0

Abstract

A loudspeaker system 1 comprises an enclosure 2 having at least one loudspeaker drive unit 3 mounted in its outer wall. At least one passive radiator diaphragm 4 is mounted in the outer wall of the enclosure and additional tuning means comprising at least one tuned port 5, or at least one further loudspeaker drive unit 302, or at least one further passive radiator diaphragm 42 is also mounted in the outer wall of the enclosure 1. The additional tuning means provides a substantially independent tuned resonance for improving the output versus frequency characteristic of the speaker system whilst retaining the advantages of the passive radiator diaphragm 4. <IMAGE>

Description

LOUDSPEAKER SYSTEMS This invention relates to loudspeaker systems.

In a loudspeaker system, the sound output depends not only on the characteristics of the loudspeaker drive unit or units but also on the characteristics of the enclosure in which the drive unit or units are mounted.

Many proposals have been made for the design of loudspeaker enclosures in attempts to enhance the sound output versus frequency characteristic of the loudspeaker system.

For example, one form of so-called bass reflex speaker system is provided with a resonant tuned port in the front wall ef the enclosure. In another form of bass reflex speaker system, it is known to use a passive radiator cone, also called a "drone cone" or ABR (auxiliary bass radiator), in place of the resonant tuned port, in which case, the free air resonance of the drone cone is made as low as possible, and the mass of the drone cone is made the same as the mass of the air in the tuned port replaced by the drone cone.

By free air resonance" is meant the resonance of the mass of the drone cone on the stiffness of its own suspension. The reason for making that resonance as low as possible is that the frequency response of a bass reflex speaker system with a drone cone exhibits a cusp or "suck-out" at the free air resonance of the drone cone and that cusp should be kept as far as possible from the useful frequencies of the system. On the other hand, a passive radiator cone does have the advantage over a tuned port that it exhibits a transmission loss to the sound present inside the enclosure and thus helps to prevent acoustic resonances present inside the enclosure from leaking to the outside. A passive radiator cone also has the potential advantage over a simple tuning port that the combination of the passive radiator cone and the air in the enclosure may be tunable to a lower frequency than is possible with a simple tuned port because the dimensions of a tuned port can become impractical at very low frequencies.

It is an object of the invention to provide a loudspeaker enclosure that enables the above-mentioned advantage of the passive radiator cone to be retained whilst allowing the above-mentioned disadvantage of it to be mitigated to a greater extent.

The present invention provides a loudspeaker system comprising: an enclosure; at least one loudspeaker drive unit mounted in the outer wall of the enclosure; at least one passive radiator diaphragm mounted in the outer wall of the enclosure; and additional tuning means comprising at least one tuned port, or at least one further loudspeaker drive unit, or at least one further passive radiator diaphragm mounted in the outer wall of the enclosure.

The invention is based on the discovery that whereas two tuned ports behave essentially like a combined single tuned port with a single resultant resonant frequency, the combination of a tuned port with a passive radiator diaphragm, or the combination of a passive radiator diaphragm and a further loudspeaker drive unit, or the combination of two passive radiator diaphragms, is able to provide, two, independently tunable, resultant resonant frequencies. Because the resultant frequencies of the passive radiator diaphragm and tuned port, or further loudspeaker drive unit and passive radiator diaphragm, or passive radiator diaphragm and further passive radiator diaphragm combination are independently tunable, greater freedom in the design of the frequency response of the loudspeaker system is possible.

A passive radiator diaphragm can be tuned to a frequency that is independent of that of a tuned port because the passive radiator diaphragm has its own suspension. As a result, the stiffness of the suspension of the passive radiator diaphragm appears in series with that of the air in the enclosure and the resonance frequency of the passive radiator diaphragm in combination with the air in the enclosure will be higher than that of the passive radiator diaphragm alone. The effective stiffness of the air in the enclosure is modifiable by the presence of the tuning port and so the resonant frequency of the passive radiator diaphragm can be "pulled" by means of the tuning port, particularly if the passive radiator diaphragm and the tuned port are closely coupled with one another. Nevertheless, the passive radiator diaphragm and tuned port are capable cf independent tuning which can be put to good effect in the design of a speaker system.

Preferably, the or each passive radiator diaphragm is a drone cone.

A loudspeaker system according to the invention can be made in many different forms, of which the following are examples: A plurality of loudspeaker drive units in a single box with a plurality of passive radiator diaphragms and a plurality of tuned ports.

A plurality of loudspeaker drive units in a single box with a plurality of passive radiator diaphragms and a single tuning port.

A plurality of loudspeaker drive units in a single box with a plurality of passive radiator diaphragms.

A plurality of loudspeaker drive units in a single box with a single passive radiator diaphragm with a plurality of tuned ports.

A plurality of loudspeaker drive units in a single box with a single passive radiator diaphragm with a single tuned port.

A plurality of loudspeaker drive units in a single box with a single passive radiator diaphragm and a single tuning port.

A single drive unit in a single box with a plurality of passive radiator diaphragms and a plurality of tuned ports.

A single drive unit in a single box with a plurality of passive radiator diaphragms and a single tuned port.

A single drive unit in a single box with a single passive radiator diaphragm and a plurality of tuned ports.

A single drive unit in a single box with a single passive radiator diaphragm and a single tuned port.

Although the invention may be applied to loudspeaker systems intended for the reproduction of virtually all or any part of the audio spectrum, the or each passive radiator diaphragm may, in particular, be an ABR (auxiliary bass radiator) in a system for the reproduction of bass sound.

Each sound radiating element may be tuned to a different resonant frequency.

Loudspeaker systems in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic sectional representation of a first loudspeaker system in accordance with the invention; Fig. 2 is a schematic sectional representation of a second loudspeaker system in accordance with the invention; Fig. 3 is a schematic sectional representation of a third loudspeaker system in accordance with the invention; Fig. 4 is a graph showing the log of amplitude of loudspeaker drive unit cone excursion plotted against frequency; and Fig. 5 is a graph showing the log of output pressure plotted against frequency.

Referring now to the accompanying drawings, a first loudspeaker system 1 in accordance with the invention is shown in Fig. 1 and comprises a box-like enclosure 2, a loudspeaker drive unit 3 mounted in the outer wall of the enclosure, an ABR passive radiator drone cone 4, and a tuned port 5. The enclosure 2 is a simple box (that is, it is not internally divided into two or more chambers) and its general construction is conventional. The tuned port 5 is also of conventional construction and comprises an open ended tube of suitable length and diameter.

Fig. 2 shows a second loudspeaker system 10 in accordance with the invention which comprises a box-like enclosure 20, a loudspeaker drive unit 30 mounted in the outer wall of the enclosure, and two ABR passive radiator drone cones 41 and 42. Thus, the essential difference from the system of Fig. 1 is that two ABR passive radiator drone cones are provided instead of an ABR passive radiator drone cone and a tuned port. The two ABR passive radiator drone cones 41 and 42 are tuned to different frequencies chosen so as to provide a desired sound output versus frequency characteristic for the system.

Fig. 3 shows a third loudspeaker system 100 in accordance with the invention which comprises a box-like enclosure 200, two loudspeaker drive units 301 and 302 mounted in the outer wall of the enclosure, two ABR passive radiator drone cones 401 and 402, and two tuned ports 501 and 502. By suitable tuning of the resonant frequencies of the drive units, the passive radiator drone cones and the tuned ports, a number of different resonant frequencies can be created to give a desired sound output versus frequency characteristic for the system.

Fig. 4 shows the logarithm of the amplitude of the excursion of the cone of a loudspeaker drive unit plotted against frequency when mounted in an enclosure configured in three different ways and driven with 1 watt total power. Curve A shows the results achieved when the enclosure is provided with a tuned port alone. Curve B shows the results achieved when the enclosure is provided with an ABR alone. Curve C shows the results achieved when the enclosure is provided, according to the invention, with both a tuned port and an ABR.

The curves show how the tuned port and the ABR can be tuned separately ta different frequencies in order to give a greater low frequency output. When the tuned port is combined with the ABR, the port "pulls" the effective resonant frequency of the ABR bouncing on the air in the enclosure but the resonant frequencies of the tuned port and the ABR nevertheless remain separate.

There is a dip in the amplitude of the drive unit excursion at both the "pulled" ABR frequency and the frequency of the tuned port providing the advantage of an extended bass response or a greater output over a range of bass frequencies. On the other hand, between the ABR free air resonance frequency and the tuned port/enclosure tuning frequency, the cone excursion is actually higher than with either the ABR on its own or the tuned port own its own. That interval of greater cone excursion can, however, be minimized by a suitable choice of the ABR mass and tuning frequency and the stiffness of the spider of the loudspeaker drive unit.

Fig. 5 shows output pressure at aa loudspeaker drive unit plotted against frequency for the same three curves A, B and C.

Although the graphs show the achievement of two separate tuning frequencies by means of the combination of a passive radiator drone cone and a tuned port, two separate tuning frequencies for the purpose of achieving a desired sound output versus frequency characteristic can also be achieved by the combination of a passive radiator drone cone with a further passive radiator drone cone or by the combination of a passive radiator drone cone with an additional loudspeaker drive unit.

Each drive unit and each passive radiator drone cone has a separate free air resonance which may be independently tuned and the speaker designer can use this plurality of separate resonances to good effect. Furthermore, other parameters of the drive units, besides their free air resonances and combined resonances with the air in the enclosure, such as the strength of their magnets may be selectively chosen to create advantageous combinations of parameters.

Although simple box enclosures have been described, it is also possible to apply the invention to systems in which an enclosure is divided internally by partitions into two or more chambers and in which one or more tuned ports and/or one or more passive radiator drone cones are provided in each partition.

It is possible to use a generally flat diaphragm in place of the cone-shaped diaphragm of the illustrated drone cones.

For the passive radiator diaphragm or cone of the loudspeaker drive unit any suitable material or material commonly-used for such a purpose can be utilized, examples being cardboard, paper, Kevlar (Registered Trade Mark), metal, woven fibre and Aerolam (a trade name for a material used in the aircraft industry and comprising a honeycomb of aluminium sandwiched between two skins of aluminium).

The enclosure can be of virtually any desired or commonly-used shape, examples being a rectangular box, a sphere and a cylinder, and the enclosure can be made by a moulding technique.

For the enclosure any suitable material or material commonly-used for such a purpose can be utilized, examples being glass fibre, a resin material, carbon fibre, plastics, wood, chipboard and Aerolam.

For the sake of completeness, it may be mentioned that a speaker system comprising a plurality of loudspeaker drive units in a single box with a plurality of tuned ports defaults, in effect, to the provision of a single tuned port, and that a speaker system comprising a plurality of speaker drive units in a single box with a single tuning port would enable some interesting experiments on tuning of the several resonances to be carried out but would be outside the scope of the present invention.

Claims

C L A I M S:

1. A loudspeaker system comprising: an enclosure; at least one loudspeaker drive unit mounted in the outer wall of the enclosure; at least one passive radiator diaphragm mounted in the outer wall of the enclosure; and additional tuning means comprising at least one tuned port, or at least one further loudspeaker drive unit, or at least one further passive radiator diaphragm mounted in the outer wall of the enclosure.

2. A system as claimed in claim 1, wherein the additional tuning means comprises at least one tuned port.

3. A system as claimed in claim 1, wherein the additional tuning means comprises at least one further loudspeaker drive unit.

4. A system as claimed in claim 1, wherein the additional tuning means comprises at least one further passive radiator diaphragm.

5. A system as claimed in any preceding claim, wherein the or each passive radiator diaphragm is a drone cone.

6. A system as claimed in any one of claims 1 to 4, wherein the system is for the reproduction of bass sound frequencies and the or each passive radiator diaphragm is an ABR (auxiliary bass radiator).

7. A system as claimed in any preceding claim, wherein the enclosure is a simple box.

8. A system as claimed in any preceding claim, wherein each sound radiating element is tuned to a different resonant frequency.