Loudspeaker enclosure with closeable port

Abstract

A loudspeaker device comprising a loudspeaker unit comprising a diaphragm with a first and second surface (such as the front and rear surface of the diaphragm, respectively) and an enclosure in which the loudspeaker unit is mounted such that the first surface of the diaphragm is in acoustic communication with the surroundings of the loudspeaker device. The device further comprises an internal cavity formed in the enclosure and being in acoustic communication with the surroundings of the loudspeaker device via an acoustic element. In the device, the second surface of the diaphragm is in acoustic communication with the internal cavity. The acoustic element can be varied between a state in which sound energy generated by the loudspeaker unit in the internal cavity can be emitted to the surroundings via the acoustic element and a state in which sound energy is substantially prevented from entering the surroundings via the acoustic element.

Claims

1. A loudspeaker device comprising: a loudspeaker unit comprising a diaphragm with a first and second surface and an enclosure in which the loudspeaker unit is mounted such that the first surface of the diaphragm is in acoustic communication with surroundings of the loudspeaker device; and an internal cavity formed in the enclosure and being in acoustic communication with the surroundings of the loudspeaker device via an acoustic element; wherein the second surface of the diaphragm is in acoustic communication with the internal cavity; wherein the acoustic element is configured to be changed between an open state in which the acoustic element permits sound energy generated by the loudspeaker unit in the internal cavity to be emitted to the surroundings via the acoustic element and a closed state in which the acoustic element substantially prevents sound energy from entering the surroundings via the acoustic element, wherein the acoustic element is configured to be changed between the open state and the closed state based on a threshold value of a sound pressure level that defines whether the acoustic element is to block or open acoustic communication from the internal cavity to the surroundings, wherein the threshold value is based on a diaphragm excursion limit of the loudspeaker unit such that when the sound pressure level generated by the loudspeaker device is above the threshold value, the acoustic element is configured to be in the open state to prevent non-linear distortion of an acoustic output of the loudspeaker device, and when the sound pressure level generated by the loudspeaker device is below the threshold value, the acoustic element is configured to be in the closed state.

2. A loudspeaker device according to claim 1, wherein the loudspeaker device comprises amplifier means configured to drive the loudspeaker unit and provided with a volume control by which the acoustic output of the loudspeaker device can be varied by a user, and wherein adjustment of said volume control controls the acoustic element such that the volume control controls whether the acoustic element is in the open state or the closed state.

3. A loudspeaker device according to claim 2, wherein adjustment of said volume control controls activation and de-activation of sound emission to the surroundings via said acoustic element, wherein the control of activation or de-activation takes place with hysteresis, such that when the setting of the volume control is increased to a setting S2, the acoustic element opens and when the volume control is reduced to a setting S1 below S2, the acoustic element closes.

4. A loudspeaker device according to claim 2, wherein adjustment of said volume control controls activation and de-activation of sound emission to the surroundings via said acoustic element, wherein the control of activation or de-activation takes place without hysteresis, such that when the setting of the volume control is increased above a setting S3, the acoustic element opens and when the volume control is reduced below the setting S3, the acoustic element closes.

5. A loudspeaker device according to claim 1, wherein said acoustic element is a channel provided with blocking means configured to block acoustic communication through the channel when the loudspeaker device is in the closed state in which sound energy is substantially prevented from entering the surroundings via the acoustic element.

6. A loudspeaker device according to claim 1, wherein variation of the acoustic element is controlled by a user interface.

7. A loudspeaker device according to claim 1, wherein said internal cavity and said acoustic element forms a Helmholtz resonator, whereby the loudspeaker device, in the open state of the acoustic element, functions as a bass reflex loudspeaker.

8. A loudspeaker device according to claim 1, wherein said acoustic element is a passive sound radiator.

9. A loudspeaker device according to claim 8, further comprising blocking means configured to substantially prevent the diaphragm from undergoing displacements to prevent the passive sound radiator from emitting sound energy to the surroundings.

10. A loudspeaker device according to claim 5, wherein the loudspeaker device comprises more than one channel which can be blocked individually to obtain different channel tunings, whereby it is possible to cover different frequency ranges and/or different volume ranges and thereby increasing a number of ways in which a frequency response and maximum power output can be varied.

11. A loudspeaker device according to claim 5, wherein the channel has a variable length, whereby the tuning of the channel can be steplessly changed.

12. A loudspeaker device according to claim 11, wherein the channel comprises two or more tubes provided slideably inside each other.

13. A loudspeaker device according to claim 1, wherein a state of the acoustic element is dependent on user profiles and/or music styles.

14. A loudspeaker device according to claim 1, wherein a state of the acoustic element is obtained automatically based on detection of music by a suitable digital signal processor (DSP) or in connection with a change of signal source.

15. A loudspeaker device according to claim 1, wherein the loudspeaker device is provided with digital signal processing (DSP) filter means that interacts with a state of the acoustic element, whereby different filter adjustments can be applied to a input signal to the loudspeaker device dependent on the state of the acoustic element.

16. A method for improving sound quality especially at low frequencies of a loudspeaker device, which method comprises: providing a loudspeaker device comprising a loudspeaker unit having a diaphragm with a first surface and a second surface, wherein the loudspeaker unit is mounted in an enclosure having an internal cavity such that the first surface of the diaphragm radiates sound energy into surroundings of the enclosure and the second surface of the diaphragm radiates sound energy into the internal cavity of the enclosure, and wherein the internal cavity is acoustically connected to an opening in the enclosure such that sound energy can enter the surroundings of the enclosure through the opening, wherein the acoustic connection takes place through an acoustic element in which the acoustic element is configured such that the acoustic element can block or open the acoustic connection from the internal cavity to the surroundings; providing activating means configured to block or open said acoustic connection from the internal cavity to the surroundings; setting a threshold value based on a diaphragm excursion limit of the loudspeaker unit that defines whether the activating means shall block or open the acoustic connection from the internal cavity to the surroundings; providing means for determining if said threshold value is exceeded; if the threshold value is not exceeded, placing the acoustic connection in a blocked state; and if the threshold value is exceeded, placing the acoustic connection in an open state to prevent non-linear distortion of an acoustic output of the loudspeaker device.

17. A method according to claim 16, wherein said threshold value is related to the setting of a volume control that controls a sound volume determined by a sound pressure level (SPL) produced by the loudspeaker device or a loudness produced by the loudspeaker device such that the enclosure acts as a closed box at a low SPL or a low loudness and such that the enclosure acts as an open box at a high SPL or a high loudness of the sound produced in the surroundings of the enclosure by the loudspeaker device.

18. A method according to claim 17, wherein adjustment of said volume control controls activation and de-activation of sound emission to the surroundings via said acoustic element, wherein the control of activation or de-activation takes place with hysteresis, such that when the setting of the volume control is increased to a setting S2, the acoustic element opens and when the volume control is reduced to a setting S1 below S2, the acoustic element closes.

19. A method according to claim 17, wherein adjustment of said volume control controls activation and de-activation of sound emission to the surroundings via said acoustic element, wherein the control of activation or de-activation takes place without hysteresis, such that when the setting of the volume control is increased above a setting S3, the acoustic element opens and when the volume control is reduced below the setting S3, the acoustic element closes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further benefits and advantages of the present invention will become apparent after reading the detailed description of non-limiting exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein

(2) FIG. 1 shows a plot of loudspeaker driver diaphragm excursion as a function of frequency for a loudspeaker driver mounted in a closed box and a ported box, respectively, necessary for the given loudspeaker to generate a sound pressure level of 88 dB SPL at a distance of 1 metre from the loudspeaker box;

(3) FIG. 2 shows a plot of obtainable frequency responses at a sound pressure level of 94 dB SPL for a loudspeaker driver mounted in a closed box and a ported box, respectively;

(4) FIG. 3 shows a plot of obtainable frequency responses at a sound pressure level of 104 dB SPL for a loudspeaker driver mounted in a closed box and a ported box, respectively;

(5) FIG. 4 shows a plot of an obtainable frequency responses at a sound pressure level of 114 dB SPL for a loudspeaker driver mounted in a closed box and a ported box, respectively;

(6) FIG. 5 shows acoustic the response of the loudspeaker driver mounted in the closed box with and without equalization and the corresponding equalizer frequency response;

(7) FIG. 6 shows the acoustic response of the loudspeaker driver mounted in the ported box with and without equalization and the corresponding equalizer frequency response;

(8) FIG. 7 shows a schematic block diagram illustrating signal processing required in order to take account of the state of the box, i.e. whether it is closed or ported;

(9) FIGS. 8(a) and (b) show a schematic representation of an embodiment of an opening/closing mechanism for application in an embodiment of the present invention;

(10) FIG. 9 shows a schematic representation of a first implementation of the opening/closing mechanism shown in FIGS. 8(a) and (b);

(11) FIG. 10 shows a schematic representation of a dual channel embodiment of the invention comprising two separate channel portions that are both in acoustic communication with a common port region, wherein the opening/closing mechanism illustrated in FIGS. 8(a), 8(b) and 9 are used.

(12) FIGS. 11(a) and (b) show schematic representations of the first implementation of the opening/closing mechanism mounted in a loudspeaker enclosure; and

(13) FIG. 12(a) through (e) show schematic representations of different implementations of opening/closing mechanisms for application in embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(14) In the following a detailed description of an example embodiment of the invention is given. It is, however understood that the principles of the invention could be embodied in other ways.

(15) With reference to FIG. 1 there is shown a plot of loudspeaker driver diaphragm excursion as a function of frequency for a loudspeaker driver mounted in a closed box 2 and a ported box 1, respectively, necessary for the given loudspeaker to generate a sound pressure level of 88 dB SPL at a distance of 1 metre from the loudspeaker box.

(16) With reference to FIG. 2 there is shown a plot of obtainable frequency response at a sound pressure level of 94 dB SPL for a loudspeaker driver mounted in a closed box 5 and a ported box 4, respectively. and with a driver diaphragm excursion limit of 6 mm.

(17) With reference to FIG. 3 there is shown a plot of obtainable frequency response at a sound pressure level of 104 dB SPL for a loudspeaker driver mounted in a closed box 9 and a ported box 10, respectively and with a driver diaphragm excursion limit of 6 mm.

(18) With reference to FIG. 4 there is shown a plot of an obtainable frequency response at a sound pressure level of 114 dB SPL for a loudspeaker driver mounted in a closed box 13 and a ported box 14, respectively. And with a driver diaphragm excursion limit of 6 mm.

(19) With reference to FIG. 5 there is shown acoustic response of the loudspeaker driver mounted in the closed box with 16 and without 15 equalization and the corresponding equalizer frequency response 17.

(20) With reference to FIG. 6 there is shown acoustic response of the loudspeaker driver mounted in the ported box with 18 and without 19 equalization and the corresponding equalizer frequency response 20.

(21) With reference to FIG. 7 there is shown a schematic block diagram illustrating signal processing required in order to take account of the state of the enclosure 28, i.e. whether the port 30, 34 is closed or open as schematically illustrated by the closing means 32. In order to accommodate the acoustic system, the acoustic change of the system should be accompanied by a change in the signal processing feeding the amplifier of the driver. The signal processing change will be comprised by different equalizations and protection limiter settings.

(22) The signal processing comprises first and second equalizers 22, 26 that receive an input signal 21 and which are configured to provide low frequency equalization. These equalizers 22 and 26 are linear filters which equalize the low frequency response to obtain the desired low frequency roll off. The desired low frequency roll-off is different depending on whether the enclosure is closed or ported. If the port is open (a ported enclosure), the switch 25 is in position P as shown in FIG. 7, whereas if the port is closed (a closed enclosure), the switch 25 is in position C. The port velocity limiter 23 is only present in the signal processing path in the case where the enclosure is ported and limits the air velocity in the port in order to keep port noise at a minimum. The displacement limiters 24, 27 limit the excursion of the loudspeaker diaphragm 29 to avoid damage to the diaphragm, its suspension and the loudspeaker driver and jarring sounds from the loudspeaker.

(23) In an embodiment, the limiters 23, 24, 27 are implemented by level adjustments, which are controlled by the input level at 21. Thereby the limiters 23, 24, 27 are designed such that the level of the signal provided to the loudspeaker driver will be proportional to the level of the input signal at 21 until a threshold value is reached. Above this threshold value the level of the signal provided to the loudspeaker driver is maintained substantially constant even if the level of the input signal increases, for instance by the provision of suitable AGC or compressor means.

(24) The following figures show various embodiments of the channel entity, i.e. the sound channel leading from the interior space of the loudspeaker enclosure via the port opening to the surroundings and the opening/closing mechanism provided in the channel. Throughout, sound entrance from the interior space of the enclosure to the channel entity is indicated by an arrow designated In and sound exit from the port opening is indicated by an arrow designated Out.

(25) With reference to FIGS. 8(a) and (b) there is shown a schematic representation of an embodiment of an opening/closing mechanism 35 for application in an embodiment of the present invention. The port region of the channel leading from the interior of the enclosure to the surroundings is designated by 36 and the entrance to the channel from the interior of the enclosure is designated by 39. In the channel 37 there is provided an opening/closing mechanism formed as a cylindrical body 40 mounted for rotation about the longitudinal axis C of the cylindrical body 40. Through the cylindrical body 40 there extends a channel portion 45 bounded by wall portions 43 and 44 that in the shown embodiment provides a continuation of the interior wall portions 37 and 37, respectively of the channel 36. The curvatures of the interior surface of the body portion 41 and the interior surface of body portion 42, respectively correspond to the outer circumferential surface of the cylindrical body 40, whereby the cylindrical body 40 can rotate (as indicated by arrow R) within these body portions of the channel 37.

(26) When the cylindrical body 40 is rotated as indicated by arrow R, it is brought to the state shown in FIG. 8(b) in which it tightly closes the channel 37.

(27) With reference to FIG. 9 there is shown a schematic representation of a practical implementation of a port channel unit comprising the opening/closing mechanism illustrated in FIGS. 8(a) and (b). FIG. 9 shows the port region 36 of the channel and the entrance region 39 connecting the channel with the interior space of the enclosure. The cylindrical body 40 is rotated by means of an actuator or motor 46 via a transmission 47.

(28) With reference to FIG. 10 there is shown a schematic representation of a dual channel embodiment of the invention comprising two separate channel portions 49, 50 with sound inlets 51 and 52, respectively configured to be in acoustic communication with the interior space of the loudspeaker enclosure. The two channel portions 49, 50 coincide to the port tuning and are both in acoustic communication with a common port region 48 (alternatively designated by reference numeral 36 in FIG. 9), wherein the opening/closing mechanism illustrated in FIGS. 8(a), 8(b) and 9 is inserted between the channels 49, 50 and the common port region 48 (36).

(29) With reference to FIGS. 11(a) and (b) there are shown images of the port channel entity shown in FIG. 9 comprising the sound inlet portion 39, the port region 55 (alternatively designated by reference numerals 36 and 48 in FIGS. 8 and 9, respectively), and the cylindrical body 40 of the opening/closing mechanism illustrated in FIGS. 8(a) and 8(b) mounted in a loudspeaker enclosure 53 with an internal space with which the sound inlet portion 39 is in acoustic communication. The opening of the port region 55 (36, 48) is provided in an extension 54 to the loudspeaker enclosure 53 in which the opening 56 for the loudspeaker driver is provided.

(30) With reference to FIG. 12(a) through (e) there are shown schematic representations of alternative implementations of opening/closing mechanisms for application in embodiments of the present invention.

(31) FIG. 12(a) illustrates a first alternative opening/closing mechanism provided in a sound channel with a sound inlet 39 and a sound outlet (port region) 36. The opening/closing mechanism comprises a rotatable plate member 57, the length of which is chosen such that it blocks sound passage through the channel in the closed state as indicated by reference numeral 58 and opens the sound channel in the open state as indicated by 58. The rotatable plate member 57 is coupled to a controllable actuator (not shown in the figure).

(32) FIG. 12(b) illustrates a second alternative opening/closing mechanism comprising a plate member 59 connected to a wall portion of the channel by a hinge member 61 such that the plate member can rotate about the hinge member 61 between an open state indicated by 60 and a closed state indicated by 60.

(33) FIGS. 12(c1 and c2) illustrates two different configurations of a third alternative opening/closing mechanism designed to be provided in a dual channel embodiment of the invention.

(34) With reference to FIG. 12(c1) there is shown a schematic representation of the channel and port seen from above (as opposed to the embodiments shown in FIGS. 12(a) and 12(b) in which the channel and port are seen from the side). The port region (corresponding to 36 in FIG. 12(a)) is designated by 64 and two branches 62, 63 of the channel are leading from the enclosure to the port 64 via the opening/closing mechanism 65, 66, 67, 68.

(35) Two blocking members 65 and 66, respectively are mounted for rotation about an axle, such that they can be brought from the closed position (65, 66) to the open position as indicated by 68 and 67, respectively, in which position the two members 65 and 66 extend in opposite directions as shown in the figure.

(36) With reference to FIG. 12(c2) there is shown a schematic representation of the channel and port seen from above (as opposed to the embodiments shown in FIGS. 12(a) and 12(b) in which the channel and port are seen from the side). The port region (corresponding to 36 in FIG. 12(a)) is designated by 64 and two branches 62, 63 of the channel are leading from the enclosure to the port 64 via the opening/closing mechanism 65, 66, 67, 68.

(37) Two blocking members 65 and 66, respectively are mounted for rotation about an axle, such that they can be brought from the closed position (65, 66) to the open position as indicated by 67 and 68, respectively, in which position the two members 65 and 66 extend parallel to each other as shown in the figure.

(38) FIG. 12(d) illustrates a fourth alternative opening/closing mechanism in which a plate member 69 is mounted for introduction into the channel portion in a direction substantially perpendicular to the sound channel. The plate member 69 is operated by a controllable activator 70.

(39) FIG. 12(e) illustrates a fifth alternative opening/closing mechanism inserted as an integral part of the sound channel 71 between the sound inlet 73 and the sound outlet (port region) 72. The opening/closing member comprises a flexible tubular member 74 forming a tight seal with the respective channel portions and being dimensioned such that a closing mechanism 75 can bring the flexible tubular member from a state in which its diameter is substantially equal to the diameter of the sound channel at the portion hereof, in which the flexible tubular member 74 is provided to a state in which the flexible tubular member closes the passage through the channel as indicated by 74 in the figure.

(40) In all of the described embodiments of opening/closing mechanismsas well as in any other opening/closing mechanisms that should be used in the present invention, it is important that a tight blockage of the sound channel is provided in the closed state and the respective opening/closing mechanisms may therefore be provided with suitable means, such as this rubber strips, to ensure that a sufficiently tight seal is indeed achieved in the closed state.

(41) Although the invention has been explained in relation to the embodiments described above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention.