EP2187655A1

EP2187655A1 - A loudspeaker system comprising an acoustic filter

Info

Publication number: EP2187655A1
Application number: EP09175978A
Authority: EP
Inventors: Leendert De Klerk
Original assignee: Bloomline Studio BV
Current assignee: Bloomline Acoustics BV
Priority date: 2008-11-14
Filing date: 2009-11-13
Publication date: 2010-05-19

Abstract

A loudspeaker system comprising a first loudspeaker enclosure, the first loudspeaker enclosure comprises a first loudspeaker and a first bass-reflex means, the first loudspeaker is arranged for producing a sound wave comprising a high frequency part and a low frequency part, characterized in that the loudspeaker system comprises a second loudspeaker enclosure separated from the first loudspeaker enclosure by an acoustic filter, the acoustic filter is constructed for attenuating the high frequency part entering the second loudspeaker enclosure and is constructed for allowing the low frequency part to enter the second loudspeaker enclosure so as to affect a frequency response of the first bass-reflex means.

Description

FIELD OF THE INVENTION

The invention relates to a loudspeaker system comprising a first loudspeaker enclosure, the first loudspeaker enclosure comprises a first loudspeaker and a first bass-reflex means, the first loudspeaker is arranged for producing a sound wave comprising a high frequency part and a low frequency part.

BACKGROUND OF THE INVENTION

Loudspeaker systems employing the bass-reflex principle are a popular choice for loudspeaker systems with good low frequency responses yet remaining affordable compared to other solutions.

SUMMARY OF THE INVENTION

A bass-reflex means may, introduce some problems into the loudspeaker system.
If the frequency of a sound wave produced by the loudspeaker is close to a resonance frequency, also known as the tuning frequency, of the bass-reflex means, a peak of acoustic energy is stored around the resonance frequency. It is a first problem, that the decay over time of this energy causes an undesirable ringing effect at the resonance frequency.
A second problem introduced by the bass-reflex means is the leakage of specular resonances from within the enclosed air volume and of direct sound from the back of the loudspeaker through the port.
Known approaches to solving these problems include adding acoustically resistive materials to the enclosure and/or the port. Unfortunately, these also have the effect of reducing the efficiency of the bass reflex system.
Another known approach is to shape the enclosure into a tapered wave guide in order to dampen the stored energy before it can leak through either the port or the membrane of the loudspeaker. This requires a large enclosure and may introduce peaks and dips in the frequency response, especially if the port is situated at the end of the wave guide It is an object of the invention to extend the low-frequency response of a loudspeaker while reducing introduced distortions.
This and other objects are achieved by the loudspeaker system according to the invention. The loudspeaker system according to the invention comprises a second loudspeaker enclosure separated from the first loudspeaker enclosure by an acoustic filter. The acoustic filter is constructed for attenuating the high frequency part of the sound in the first loudspeaker enclosure entering the second loudspeaker enclosure and is constructed for allowing the low frequency part of the sound in the first loudspeaker enclosure to enter the second loudspeaker enclosure so as to affect a frequency response of the first bass-reflex means.
A third problem introduced by the bass-reflex means occurs if the frequency of a sound wave produced by the loudspeaker drops below the resonance frequency. When that happens, the loudspeaker becomes uncontrolled by the spring load of the air in the enclosure. This leads to excessive excursions of the loudspeaker membrane. The excursions introduce distortions and will eventually damage the loudspeaker.
Known approaches to solving the third problem include preventing the loudspeaker from playing the unwanted low frequencies by introducing an electric passive or electronic active subsonic high pass filter. This approach has the drawback that it increases the time delay of the acoustic output with decreasing frequency. Moreover a high pass filter does not diminish the ringing effects around the resonance frequency and other port related distortions.
It is a further object of the invention to reduce the excursions that occur below the resonance frequency in a loudspeaker system arranged with a bass-reflex means.
In a preferred embodiment, the second loudspeaker enclosure comprises a second loudspeaker. The second loudspeaker is arranged for producing a further sound wave derived from an audio signal supplied to the first loudspeaker in order to produce the sound wave. The further sound wave comprises a further low frequency part. The acoustic filter is arranged to propagate the further low frequency part towards the first loudspeaker for obtaining a dampening of an excursion of a moving part of the first loudspeaker.
The second loudspeaker produces further sound waves with a further low frequency part. Since the acoustic filter is arranged to propagate the further low frequency part, the further low frequency part will eventually reach the first loudspeaker. The further low frequency part will pressurize the first loudspeakers in phase with the sound wave produced by the first loudspeaker decreasing the excursion of the first loudspeaker, and thus protecting the first loudspeaker from damage.
In an embodiment, the acoustic filter comprises a division wall for separating the first enclosure from the second enclosure. In an embodiment, the division wall comprises an opening.
In an embodiment, the opening has an area which is at least twice an area of an opening of the first bass-reflex means. The opening should be large enough compared to the opening of the first bass-reflex means so that low frequencies can pass through it. The tuning frequency of the bass reflex means should be chosen on the basis of the total volume of the loudspeaker system, i.e., the volumes of the first and second enclosures.
In an embodiment, the opening has an area which is within one half and twice an area of a membrane of the first loudspeaker.
In an embodiment, the opening has an area which is substantially equal to the area of the membrane of the first loudspeaker.
Further background on bass-reflex means can be found in, e.g.,: Thiele, A. N., "Loudspeakers in Vented Boxes: Parts I and II," J. Audio Engineering Soc., Vol. 19, No. 5, May 1971, pp 382-392 (Reprinted from a 1961 publication in Proc. IRE Australia), and in Small, Richard H., "Vented-Box Loudspeaker Systems, Part I: Small- Signal Analysis", J. Audio Engineering Soc., Vol. 21, No. 5, June 1973, pp 363-444. 3.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail by way of example and with reference to the accompanying drawings, wherein:

Figure 1 is a block diagram illustrating a first embodiment of the loudspeaker system according to the invention,
Figure 2 is a block diagram illustrating a second embodiment of the loudspeaker system according to the invention,
Figure 3 is a block diagram illustrating a third embodiment of the loudspeaker system according to the invention,
Figure 3A is a block diagram illustrating a fourth embodiment of the loudspeaker system according to the invention,
Figure 4.1 is a diagram showing a 3d view of a fifth embodiment of the loudspeaker system according to the invention,
Figure 4.2 is a diagram showing an exploded 3d view of the fifth embodiment of the loudspeaker system according to the invention,
Figure 4.3 is a diagram showing a back view of the fifth embodiment of the loudspeaker system according to the invention,
Figure 4.4 is a diagram showing a bottom view of the fifth embodiment of the loudspeaker system according to the invention,
Figure 4.5 is a diagram showing a front view of the fifth embodiment of the loudspeaker system according to the invention,
Figure 4.6 is a diagram showing a left view of the fifth embodiment of the loudspeaker system according to the invention,
Figure 4.7 is a diagram showing the measures of bushes on a dampening panel in the fifth embodiment of the loudspeaker system according to the invention,
Figure 4.8 is a diagram showing a right view of the fifth embodiment of the loudspeaker system according to the invention, and
Figure 4.9 is a diagram showing a top view of the fifth embodiment of the loudspeaker system according to the invention.

Throughout the Figures, similar or corresponding features are indicated by same reference numerals.

List of Reference Numerals:

100: a loudspeaker system
110: a first loudspeaker
112: a first loudspeaker enclosure
114: a first narrow end
116: a first port
120: a second loudspeaker
122: a second loudspeaker enclosure
124: a second narrow end
126: a second port
130: a division wall
140: a valve port
200: a loudspeaker system
210: a first leg
212: a first portion
220: a second leg
222: a second portion
300: a loudspeaker system
310: a tweeter

DETAILED EMBODIMENTS

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more specific embodiments, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described.
Figure 1 illustrates a first embodiment of the loudspeaker system (100) according to the invention. The figure shows a cross section of the loudspeaker system.
Loudspeaker system 100 is formed as a rectangular box, but may have other shapes. For example, one or more corners may be rounded. The box is divided by a division wall 130 into a first loudspeaker enclosure 112 and a second loudspeaker enclosure 122. Division wall 130 forms first loudspeaker enclosure 112 and second loudspeaker enclosure 122 into a tapered inside shape, with a first narrow end 114 and a second narrow end 124, respectively. The tapered shape acts as a wave guide. Both enclosures also have a wide end, which is not indicated with a reference number.
The division wall 130 is here illustrated as a straight divider, such as a straight board. However, division wall 130 may also be executed in a much more intricate fashion, e.g., forming in first loudspeaker enclosure 112 and second loudspeaker enclosure 122 a more irregular wave guide. For example, the irregular wave guide may be a folded wave guide and/or a curved wave guide. A folded wave guide and/or a curved wave guide with a tapered shape also absorbs high frequency sound waves. An advantage of an embodiment wherein the wave guide is folded and/or curved is that the absorption characteristics may be further improved. Moreover, the space requirements of the loudspeaker system may be reduced.
The walls of division wall 130 and/or one or more of the inner walls of the enclosure may be dampened with a wide-frequency range sound absorption material, such as open cell foam or melamine foam, preferably of approximately 2 cm thickness. First loudspeaker enclosure 112 and/or second loudspeaker enclosure 122 may be further filled with a material that allows air flow at long wave lengths, i.e., for sound waves with low frequencies. The filling material is preferably wool, or another low density fibrous material preserving the air flow.
In both first loudspeaker enclosure 112 and second loudspeaker enclosure 122 one or more loudspeakers may be mounted near the wide end of the tapering of the enclosure. Figure 1 shows a first loudspeaker 110 in first loudspeaker enclosure 112 and a second loudspeaker 120 in second loudspeaker enclosure 122. A first port 116 may be situated, halfway the long end of first loudspeaker enclosure 112. A second port 126 may be situated halfway the long end of second loudspeaker enclosure 122. First port 116 and second port 126 are bass-reflex means.
In Figure 1 the first loudspeaker 110 and second loudspeaker 120 are arranged on opposite surfaces of the rectangular box. First port 116 is arranged on a surface adjacent to the surface on which first loudspeaker 110 is arranged; also second port 126 is arranged on a surface adjacent to the surface on which second loudspeaker 120 is arranged. Also, the surfaces on which first port 116 and second port 126 are arranged are opposite each other.
Figure 1 shows a port for the bass-reflex means but other possibilities include a hole or a radiator, also known as a passive radiator. Note that using multiple bass-reflex means may advantageously be combined with the invention. As each bass-reflex means may be tuned to a different resonance frequency, the frequency responses of the bass-reflex means can be affected by the second loudspeaker enclosure differently. This gives the advantage of even more precisely obtaining a flat frequency response for the loudspeaker system for low frequencies. A port of a bass-reflex means may be filled with absorbing material such as wool.
On division wall 130 a 'valve port' 140 is arranged. Valve port 140 is advantageously arranged around halfway division wall 130. Valve port 140 can take the shape of, e.g., one or more pipes or holes. Valve port 140 acoustically connects first loudspeaker enclosure 112's air volume directly or indirectly to second loudspeaker enclosure 122 to obtain an acoustical connection.
As noted above, valve port 140 may comprise one or multiple openings, e.g., two or even more. Having multiple openings has the advantage that the openings may be distributed better over the wave guide, in particular if the loudspeaker system is executed in a narrow and/or tapering shape.
Valve port 140 and division wall 130, together forming the previously mentioned acoustic filter, have the effect of reducing the high frequency sounds waves produced by first loudspeaker 110 from entering second loudspeaker enclosure 122 and from reflecting them back to port 116 and loudspeaker 110. High frequency sound waves traveling from the backside of first loudspeaker 110 will be absorbed in the tapered first loudspeaker enclosure 112. This prevents parasite resonances and leakage of specular resonances.
Many factors in the design of loudspeaker system 100 contribute to the reduction of the high frequency part of the sound wave produced by first loudspeaker 110 that passes through valve port 140, including: the sides of division wall 130 and first loudspeaker enclosure 112 may be arranged with a material that reduces reflections, valve port 140 may be placed relatively far from first loudspeaker 110, the size of valve port 140 may be of a comparable size to first loudspeaker 110, the shape of first loudspeaker enclosure 112 may be tapered, and high frequency sound waves propagate in a relatively linear fashion. Each of these factors reduce high frequencies passing through valve port 140 on its own, but the more so in combination. Low frequencies, however, are much less affected by these factors. There is an additional effect which makes valve port 140 more easily passable for low frequency waves. An audio wave with a wavelength comparable to the size of valve port 140, or larger, causes valve port 140 to behave as a radiation source. Thus, valve port 140 and division wall 130 together allow low frequency sound waves into second loudspeaker enclosure 122 but fewer high frequency sound waves, preferably, no high frequency sound waves.
Figure 1 thus shows two ported enclosures mutually coupled by a low frequency valve.
By placing first port 116 such that it looks into the tapered wave guide formed by division wall 130 inside the first enclosure 112, leakage of direct sound from the back of the loudspeaker will be attenuated. For example, an imaginary center line of the first port 116 may extend into the tapered wave guide.
With decreasing frequency the sound waves will more easily reach first narrow end 114 of division wall 130 but their energy will be increasingly absorbed on their way back to the loudspeaker. A part of this low frequency energy will pressurize valve port 140 before it reaches first port 116. With descending frequency the loudspeaker will be increasingly acoustically connected to second loudspeaker enclosure 122. Although the level of acoustic connection is typically a continuum, one may identify a particular frequency, such that below the particular frequency the loudspeaker will be increasingly acoustically connected to second loudspeaker enclosure 122, compared to above the particular frequency. The two wave guides formed by first portion 212 and second portion 222 cooperate in trapping low frequencies, and thereby reduce the problematic ringing effect.
At very low frequencies, below the resonance frequency, the pressure of the sound waves emitted by first loudspeaker 110 in first loudspeaker enclosure 112 will reach second loudspeaker 120 in second loudspeaker enclosure 122 "via" valve port 140. The loudspeakers now pressurize each other, which causes their excursion to be limited thus protecting the loudspeaker from damage.
A problem in bass-reflex loudspeaker system without valve port 140 and second loudspeaker enclosure 122 is overload of the amplifier due to increasing "back-EMC" with decreasing frequency. If the excursions of a loudspeaker increase, the loudspeaker will generate some electric current, because a coil is oscillating in a magnetic field, this back-EMC is routed back to the amplifier. Below the resonance frequency, with increasing excursions, the back-EMC may cause distortions to the sound and eventual damage to the amplifier. Using the loudspeaker according to the invention, the excursions below the resonance frequency are reduced and correspondingly also the back-EMC. Thus diminishing excursions of the loudspeaker also reduces distortion in the amplifier and protects the amplifier from damage.
The comments made above regarding the effect of second loudspeaker enclosure 122 on the frequency response of first loudspeaker 110 in first loudspeaker enclosure 112 also apply, vice versa, to the effect of first loudspeaker enclosure 112 on the frequency response of second loudspeaker 120 in second loudspeaker enclosure 122. Also, loudspeaker 120 has a dampening effect on loudspeaker 110.
The embodiment shown in Figure 2 is identical to the embodiment shown in Figure 1, except that second loudspeaker 120 and second port 126 have been omitted. The advantage of reduced distortions for frequencies approaching the resonance frequency also applies here. For additional flexibility of tuning the loudspeaker system second loudspeaker enclosure 122 may be provided with second port 126 (not shown in Figure 2) as in Figure 1.
The loudspeaker system 200 shown in Figure 3 , again in cross section, shows an embodiment not placed in a rectangular box. Loudspeaker system 200 has a C shape in cross section. The enclosure of loudspeaker system 200 is also divided into first loudspeaker enclosure 112 and second loudspeaker enclosure 122. First loudspeaker enclosure 112 is formed by a first leg 210 and a first portion 212. Second loudspeaker enclosure 122 is formed by a second leg 220 and a second portion 222. Second portion 222 and first portion 212 together may form a rectangular body which is divided into the two parts by division wall 130.
First portion 212 and second portion 222 typically act as a wave guide. First leg 210 and second leg 220 may act as a compression chamber for increasing the Q-factor of the loudspeaker system. The transition from one of the legs to the connected wave guide can be regarded as an impedance-jump. This impedance-jump decreases the resonance frequency of the loudspeaker system. For the resonance frequency the air-mass in first leg 210 is added to the mass of the membrane in first loudspeaker 110.
Note that first portion 212 and second portion 222 may have the same shape, and first leg 210 and second leg 220 may have the same shape. Although, first loudspeaker enclosure 112 and second loudspeaker enclosure 222 have the same volume and substantially the same acoustical properties, they do not have identical configuration, as is the case in Figure 1. Note that first loudspeaker enclosure 112 and second loudspeaker enclosure 122 need not have the same volume, their acoustical properties may be chosen such that at low frequencies both waveguides influence the dampening of the specular resonances of each one of the loudspeakers. It is an advantage to dampen with two waveguides since a better distribution of the dampening over the frequency domain can be obtained. In an embodiment, first loudspeaker enclosure 112 and second loudspeaker enclosure 122 have the same acoustical properties, e.g., the same frequency response. In this way the dampening effect at a particular low frequency is improved.
First loudspeaker 110 and second loudspeaker 120 may be placed at the end of first leg 210 and second leg 220, respectively. It is not necessary for first loudspeaker 110 and second loudspeaker 120 to be placed at the exact same place relatively to each other. First port 116 and second port 126 may be placed in the area where first leg 210 and second leg 220, respectively, connect to first portion 212 and second portion 222, respectively.
First port 116 may be placed about one third of the way from first loudspeaker 110 to valve port 140. Second port 126 may be placed about one third of the way from first loudspeaker 120 to valve port 140.
Loudspeaker system 300, shown in Figure 3A is a variant of loudspeaker system 200. The embodiment shown in loudspeaker system 300 demonstrates how the elements in loudspeaker system 200 can be alternatively configured, so as to fit the whole in a, for example, rectangular box.
By way of example, loudspeaker system 300 is formed as a rectangular box. On a first side of the box a first loudspeaker 110 and second loudspeaker 120 is placed. Opposite the first side of the box, is a second side. A first end of a division wall 130 with a valve port 140 is connected to the second side, away from a middle of the second side, at an angle, and running into a region which extends lengthwise into the box. The other end of division wall 130 reaches about halfway into the box, across from the second side to the first side. Connected to the other end of division wall 130 a further division wall is placed at an angle. The division wall 130, the second wall and the further division wall form two tapered wave guides which are placed against each other in a Z shaped formation. A connecting wall connects the further division wall with the first side of the box, see connecting wall 130a in Figure 3A. As is shown in Figure 3A, connecting wall 130a also partitions the box into two separate loudspeaker enclosures. Division wall 130, further division wall end the connecting wall together partition the box into two separate loudspeaker enclosures. The two loudspeaker enclosures are connected via the valve port 140. The loudspeakers 110 and 120 are arranged such that each loudspeaker enclosure encloses one of the loudspeakers. The further division wall, the connecting wall and the first side forms two legs: leg 210 and leg 220. The legs act as compression chambers, as explained above. First leg 210 and second leg 220 are placed such that they meet at the connecting wall.
In an embodiment, at the place where the connecting wall meets the first wall, a tweeter 310 is placed. A tweeter does not typically suffer from under dampening at low frequencies; it is therefore an advantage to place the tweeter at this point. At the place where the connecting wall meets the first wall, a high frequency driver may be placed, such as tweeter 310 or a mid-toner. As is known in the art a high frequency driver, such as tweeter 310 or a mid-toner, may have its own air volume, not connected to a main air volume of the loudspeaker system, i.e., not connected to enclosures 210 and 220.
Figures 4.1 to 4.9 show a fifth embodiment of the invention, similar to the embodiment shown in Figure 3. The figures show sizes, taken in millimeters. Experiments have shown that this configuration is of particular advantage. Nevertheless, this and the other embodiments are shown only to illustrate, rather than to limit the invention. In particular, the invention may also be applied with different sizes; for example, the invention may be applied in a desktop model, for use with a desktop computer.
The current invention, in one of the embodiments using two loudspeakers, in particular the embodiments described in figures 3, 3a or 4.1 to 4.9 are well suited to be combined with the loudspeaker arrangement described in the international patent application "A Transducer Arrangement Improving Naturalness of Sounds", with publication number WO/2006/100250 , which is incorporated by reference. For example, the current invention may well be combined with the configuration shown in Figure 1 and described in the corresponding description, of that patent application.
Figure 4 . 1 is a diagram showing a 3d view of the fifth embodiment. Visible is the first leg 210 connected to the top of a rectangular body and the second leg 220 connected at the bottom of the body. The body extends in a lengthwise direction. The fifth embodiment uses two loudspeakers, L1 and L2, each having a convex cone that extends outside the loudspeaker enclosure. The cone is used as a membrane. Also visible in figure 4.1 are two back-wave-dampers, BWD1 and BWD2, suppressing the back-wave of the loudspeakers. The back-wave dampers are optional, and are attached to the side of the leg, opposite the place, where the loudspeaker is attached. The back-wave dampers are shown as black half-spheres. Back-wave-dampers, BWD1 and BWD2 may be filled with absorption material, such as wool.
First leg 210 is arranged with a first loudspeaker, which is arranged to radiate in a direction parallel with the lengthwise direction. Second leg 220 is arranged with a second loudspeaker, which is arranged to radiate in a direction perpendicular to the lengthwise direction.
Just visible at the top of Figure 4.1 behind the back-wave-damper is the opening of a port, which serves as a bass-reflex means. Also visible in Figure 4.1, is an absorption panel which is placed on the front outside of the loudspeaker system, between the upper and lower loudspeaker. The absorption panel is placed to reduce reflection of the upper loudspeaker on the outside of the loudspeaker system. The upper loudspeaker is placed facing a different direction than the lower loudspeaker. In figure 4.1, the upper loudspeaker faces in a downward direction, and the lower loudspeaker faces in a sideways direction, perpendicular to the downward direction. The placing of the lower loudspeaker is such that sound waves produced by it are not likely to reflect of the front of the loudspeaker system. Since the absorption panel reduces the reflections of the upper loudspeaker, the reflection patterns of both loudspeakers become more alike.
The first and second loudspeakers both may comprise a concentrically arranged low/mid speaker and/or a tweeter. Both the low/mid speaker and the tweeter may have a convex cone.
Figure 4 . 2 shows an exploded 3d view of the fifth embodiment. Inside the loudspeaker system divisional wall 130 is visible. Divisional wall 130 extends diagonally from one side of the rectangular body to an opposite side of the rectangular body. Two tapered wave guides are formed by the divisional wall. Valve port 140 is not visible in this figure.
Suitable materials for the design shown in Figure 4.2 include plastics and metals, in particular aluminum. The design may be obtained by molding or casting. Good results were obtained using a milling cutter. Note that, after design of Figure 4.2 has been realized various parts may be added. For example, the valve port 140 and/or ports 116 and 126 are not shown in the figure.
Figure 4.4 shows the circle-shaped end of a bass-reflex port 126, and the relative positioning thereof.
Figure 4.9 shows the circle-shaped end of a bass-reflex port 116, and the relative positioning thereof.

Claims

A loudspeaker system comprising a first loudspeaker enclosure,
the first loudspeaker enclosure comprises a first loudspeaker and a first bass-reflex means, the first loudspeaker is arranged for producing a sound wave comprising a high frequency part and a low frequency part,
characterized in that

the loudspeaker system comprises a second loudspeaker enclosure separated from the first loudspeaker enclosure by an acoustic filter,

the acoustic filter is constructed for attenuating the high frequency part entering the second loudspeaker enclosure and is constructed for allowing the low frequency part to enter the second loudspeaker enclosure so as to affect a frequency response of the first bass-reflex means.
A loudspeaker system as in Claim 1 wherein the acoustic filter comprises a division wall for separating the first enclosure from the second enclosure.
A loudspeaker system as in Claim 2 wherein the division wall is arranged and shaped to obtain a tapered shape of both the first enclosure and the second enclosure.
A loudspeaker system as in any one of Claims 2 and 3 wherein the first enclosure forms a wave guide and/or a transmission line.
A loudspeaker system as in any one of Claims 2 to 4, wherein the division wall comprises an opening.
A loudspeaker system as in Claim 5 wherein the opening has an area which is at least twice an area of an opening of the first bass-reflex means.
A loudspeaker system as in Claim 5 wherein the opening has an area which is within one half and twice an area of a membrane of the first loudspeaker.
A loudspeaker system as in Claim 5 wherein the opening has an area which is substantially equal to the area of the membrane of the first loudspeaker.
A loudspeaker system as in any one of the preceding claims wherein the first bass-reflex means is at least one of a port or a radiator.
A loudspeaker system as in any one of the preceding claims comprising a third loudspeaker enclosure separated from the first loudspeaker enclosure by a further acoustic filter.
A loudspeaker system as in any one of the preceding claims, wherein the second loudspeaker enclosure comprises a second loudspeaker, being arranged for producing a further sound wave derived from an audio signal supplied to the first loudspeaker in order to produce the sound wave, the further sound wave comprising a further low frequency part, the acoustic filter is arranged to propagate the further low frequency part towards the first loudspeaker for obtaining a dampening of an excursion of a moving part of the first loudspeaker.
A loudspeaker system as in any one of the preceding claims, wherein the second loudspeaker enclosure is arranged with a second bass-reflex means, the first bass-reflex means and the second bass-reflex means being tuned to substantially the same frequency.
A loudspeaker system as in any one of the preceding claims, wherein the second loudspeaker enclosure has a volume substantially equal to a volume of the first loudspeaker enclosure.
A loudspeaker system as in Claim 13, wherein the second loudspeaker enclosure has a configuration substantially equal to a configuration of the first loudspeaker enclosure.
A loudspeaker system as in any one of Claim 11 to 14, wherein the further sound wave is substantially equal to the first signal.
A loudspeaker system as in any one of Claim 11 to 15, wherein the second loudspeaker is substantially equal to the first loudspeaker.