LOUDSPEAKER SYSTEM WITH ADJUSTABLE RESPONSE

WIPO Patent Application WO/2008/025060

A method of adjusting frequency response of a loudspeaker system is disclosed. The loudspeaker system includes an enclosure, at least one electro-acoustic transducer and an acoustic filter associated with the enclosure. The method includes moving a physical structure associated with the acoustic filter and providing a corresponding compensating signal for driving the electro-acoustic transducer. The frequency response may be adjusted manually by a user or it may be adjusted automatically. The frequency response may be adjusted in response to a control signal from a player of audio content, such as a CD or DVD player or in response to intelligence that is independent from a signal driving the electro-acoustic transducer.

Velican, Zeljko (6 Sexton Court, Endeaver Hills, Victoria 3802, AU)
Huon, Graeme John (39 Monomeith Crescent, Mt. Waverley, Victoria 3149, AU)

PCT/AU2007/001215

03/06/2008

08/24/2007

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IMMERSION TECHNOLOGY PROPERTY LIMITED (30 Farringdon Street, London EC4A4HJ, GB)
Velican, Zeljko (6 Sexton Court, Endeaver Hills, Victoria 3802, AU)
Huon, Graeme John (39 Monomeith Crescent, Mt. Waverley, Victoria 3149, AU)

H04R1/28; H04R1/02

PHILLIPS ORMONDE & FITZPATRICK (Level 21 & 22, 367 Collins Street Melbourne, Victoria 3000, AU)

CLAIMS

1. A loudspeaker system including an enclosure and at least one electro acoustic transducer, said system further including an acoustic filter associated with said enclosure having an adjustable frequency response wherein said response is adjustable by moving a physical structure associated with said acoustic filter and including means for providing a corresponding compensating signal for driving said electroacoustic transducer.

2. A loudspeaker system according to claim 1 wherein said frequency response is adjustable manually by a user.

3. A loudspeaker system according to claim 1 or 2 wherein said frequency response is adjustable via remote control.

4. A loudspeaker system according to claim 1 wherein said frequency response is adjustable automatically.

5. A loudspeaker system according to claim 4 wherein said frequency response is adjustable in response to a control signal from a player of audio content.

6. A loudspeaker system according to claim 4 wherein said player includes a CD or DVD player.

7. A loudspeaker system according to claim 4 wherein said frequency response is adjustable in response to intelligence independent from a signal driving said electroacoustic transducer.

8. A loudspeaker system according to any one of the preceding claims wherein said means for providing a compensating signal includes an electrical filter.

9. A method of adjusting frequency response of a loudspeaker system including an enclosure, at least one electroacoustic transducer and an acoustic filter associated with said enclosure, said method including moving a physical structure associated with said acoustic filter and providing a corresponding compensating signal for driving said electroacoustic transducer.

10. A method according to claim 9 wherein said frequency response is adjusted manually by a user.

11. 1 1.

12. A method according to claim 9 or 10 wherein said frequency response is adjusted via remote control.

13. A method according to claim 9 wherein said frequency response is adjusted automatically.

14. A method according to claim 12 wherein said frequency response is adjusted in response to a control signal from a player of audio content.

15. A method according to claim 13 wherein said player includes a CD or DVD player.

16. A method according to claim 12 wherein said frequency response is adjusted in response to intelligence independent from a signal driving said electroacoustic transducer.

17. A method according to any one of claims 9 to 15 wherein said compensating signal is provided via an electrical filter.

18. A loudspeaker system substantially as herein described with reference to Figures 4 to 6 of the accompanying drawings.

19. A method of adjusting frequency response of a loudspeaker system substantially as herein described with reference to Figures 4 to 6 of the accompanying drawings.

LOUDSPEAKER SYSTEM WITH ADJUSTABLE RESPONSE

FIELD OF THE INVENTION

The present invention relates to a loudspeaker system and in particular relates to a loudspeaker system having an adjustable frequency response.

BACKGROUND OF THE INVENTION

With availability of increased frequency and dynamic range and improved fidelity in audio recordings there has been an increase in demand for capability in loudspeakers. Different users of a loudspeaker system may have vastly different preferences for capabilities of the system. In addition different kinds of program material may place different demands on capabilities of the system. Home theatres have recently introduced new requirements on domestic loudspeaker systems wherein the loudspeakers may be shared between home theatre use and use for enjoyment of music, requiring both high fidelity and high sound pressure capabilities.

One limitation on performance of existing loudspeakers is that in designing an associated enclosure there exists a trade-off between optimizing maximum sound level and lowest frequency for a given volume of the enclosure. If a loudspeaker system is optimised for high sound level it may not provide extended low frequency response. Conversely if the system is optimized for lower frequency capability, the sound level capability will usually be less.

Thus a purchaser may be required to compromise in selecting a loudspeaker because it has to satisfy musical tastes of other listeners and to accommodate a range of different uses. The problem is worse for vehicle

manufacturers, for example, who have to guess what acoustic response the customer may want from a pre-installed loudspeaker system in a vehicle.

A variety of enclosure adjustment arrangements are known in the prior art. Firstly there are those that are largely unrelated to performance. Examples include US5, 082,084 and EP0991296, wherein a loudspeaker enclosure or set of enclosures may be reduced in volume for transport. These references have no relevance to the present invention.

Then there are directionality adjustment arrangements wherein a loudspeaker enclosure is mounted pivotally with respect to a mounting fixture. Examples include US5960095, US481 1406, US5133428, US5148490, US5319164, US6101262. These references also have no relevance to the present invention.

Somewhat related to directionality is adjustable directivity and/or combined directivity and directionality as typified by US5450495 and US5664020. In particular the prior art adjustments are made by means of reflector panels. These have no relevance to the present invention. Other adjustable prior art loudspeaker arrangements include US4164988, US4224469, US3945461 wherein adjustments are provided to permit fine- tuning. In the case of LJS4164988 the adjustment is intended to be a factory adjustment to fine-tune a tube length to free air resonance of an electroacoustic transducer. In the case of US433469 a user adjustable tuner is provided to correct air pressure for "best loading" presumably according to user judgement of what sounds best.

In the case of US3945461 a calibrated adjustment is provided for air temperature compensation. This is intended for user adjustment according to temperature and humidity conditions at the time of use. In contrast to the

present invention the intent in all three references is to permit fine tuning without a corresponding equalisation adjustment.

US6079515 (Newman) relates to a loudspeaker enclosure including slidable cylinders for varying a response beyond a fixed design with the intent of allowing a listener to achieve a desired result judged by ear. Newman has not anticipated any need for compensation or any method or mechanism for achieving compensation.

The present invention on the other hand may allow for variation in user preferences but not at the expense of loss of fidelity in high performance systems. The present invention may compensate adjustment to an enclosure structure with a corresponding correction for frequency response and relative level. No such compensation is anticipated in the prior art. The Newman reference does not relate to loudspeaker system capability. Newman provides no suggestion that his enclosure is to operate at or near its design limits or that the effects he achieves by physical adjustment could not be equally achieved by means of electrical signal processing. In contrast the present invention may provide a means for exceeding capability of a physical design by adjusting a physical structure associated with the design. The adjustment may provide a capability that may not be achieved by electrical signal processing alone.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a loudspeaker system including an enclosure and at least one electro-acoustic transducer, said system further including an acoustic filter associated with said enclosure having an adjustable frequency response wherein said response is adjustable by moving a physical structure associated with said acoustic filter

and including means for providing a corresponding compensating signal for driving said electro-acoustic transducer.

According to a further aspect of the present invention there is provided a method of adjusting frequency response of a loudspeaker system including an enclosure, at least one electro-acoustic transducer and an acoustic filter associated with said enclosure, including adjusting a physical structure associated with said acoustic filter and providing a corresponding compensating signal for driving said electro-acoustic transducer.

The present invention may increase performance capability from a loudspeaker system whereby a user may conveniently convert a loudspeaker system from one limiting case of an acoustic characteristic to another limiting case of an acoustic characteristic, without necessarily compromising performance in either case. Thus a user may be able to exceed theoretical limits of a particular enclosure design by adjusting to a different design to suit a particular application or performance. At least a part of the adjustment may include an alteration or modification to a physical structure associated with the system including the associated enclosure.

Enclosure capabilities that may be enhanced by adjustment of a physical structure include: i) extension of frequency range to a lower frequency; and ii) increased sound level capability, notwithstanding that there exists a trade-off between one and the other.

The present invention may allow an enclosure to be adjusted either manually or automatically to a chosen mode prior to use in a particular application. It may also allow the enclosure to be adjusted back and forth

between modes within an application under automatic control such as by means of a pre-recorded program or the like.

The present invention may be considered to include three separate innovations namely: i) a means for adjusting a physical structure in a loudspeaker which in turn may provide a capability that extends beyond a single design configuration; ii) a means for augmenting the adjustment function such that a single adjustment action by a user may also provide correct compensation for frequency response and/or relative level; and

(iii) a means for automatically controlling the adjustment function.

The compensation feature may make adjustment of a physical structure a viable option, while the combination of adjustment and compensation may also make automatic control a viable option. Accordingly the three innovations may be considered to interlinked parts of a single concept notwithstanding that only one or two of the three innovations may need to be present in a particular realisation of the present invention.

A loudspeaker system or enclosure according to the present invention may include controls for a user to conveniently adjust acoustic properties of the system or enclosure to suit user requirements. The acoustic properties of the system or enclosure may be changed according to known design rules.

Changes to acoustic properties may include stepped changes to physical structures including chambers or ducts forming a part of the enclosure or system such as an acoustic filter and/or other physical changes. The changes may include corresponding changes to electrical equalization of a driving signal to match the changes to physical structures. The changes may be considered

to be a form of "double switching" because in one form the enclosure may be switched (physically) from one state to another while matching equalisation may be simultaneously switched into operation to maintain a level of fidelity. More complex implementations may include a continuously variable control rather than a stepped control, automatic control and combinations thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, wherein: Fig 1 shows a vented loudspeaker system according to a prior art design including a long port tube and being equalised for a substantially flat response;

Fig 2 shows an identical vented loudspeaker system according to a prior art design including a short port tube and having the same equalisation as the loudspeaker system of Fig 1 with its level adjusted to capability of the loudspeaker system;

Fig 3 shows a comparison of frequency response for each loudspeaker system in Fig 1 and Fig 2;

Fig 4A shows a loudspeaker arrangement according to the present invention wherein the length of a port tube of a vented loudspeaker system is adjustable and wherein adjustment of port tube length is linked to a matching compensation;

Fig 4B shows a frequency response of the loudspeaker system of Fig 4A for an extended and a non-extended position of the port tube, with levels adjusted to capability of the loudspeaker system for each port tube length; Fig 4C shows one form of an equalisation (compensation) filter;

Fig 5 shows an example of a Compact Disk (CD) dynamically controlling adjustment of a loudspeaker system; and

Fig 6 shows an example of a Digital Versatile Disk (DVD) dynamically controlling adjustment of a loudspeaker system. Fig 1 shows a loudspeaker system 10 including a simple vented enclosure 1 1 , electro-acoustic transducer 12, chamber 13 and port tube 14. It exhibits good low frequency capability, but its output capability is limited. As an example transducer 12 may comprise a 300 mm electro-acoustic driver and enclosure 1 1 may measure 400 mm high x 300 mm wide x 400 mm deep internally. Port tube 14 may measure 75 mm diameter x 350 mm long.

Fig 2 shows loudspeaker system 20 including vented enclosure 21 , electro-acoustic transducer 22, chamber 23 and a shorter port tube 24 that is otherwise identical to that of Fig 1 and has the same equalisation. Loudspeaker system 20 has an improved output capability compared to loudspeaker system 10 but a reduced low frequency capability.

Fig 3 shows the accompanying frequency response graphs wherein Curve A is the frequency response for loudspeaker system 10 of Fig 1 and Curve B is the frequency response for loudspeaker system 20 of Fig 2. It can be seen that curve A extends to lower frequencies than curve B but the sound level is less. It can also be seen that the response of curve B is not flat denoting that loudspeaker system 20 may not function as a high fidelity loudspeaker. If port tube 14 of loudspeaker system 10 of Fig 1 had a means to vary its length and was contracted to the length of port tube 24 shown in Fig 2, its output capability would change but its response would not be acceptable. However if the adjustment length of port tube 24 was accompanied by a

matching compensation then the capability of loudspeaker system 10 could be changed with little or no loss of fidelity.

Fig 4a shows a loudspeaker system 40 including vented enclosure 41 , electro-acoustic transducer 42, chamber 43 and a port tube 44 that is extensible. Adjustment of length of port tube 44 is synchronised to matching compensation 45 via linked switch 46. Fig 4b shows the resulting frequency response curves for short and long adjustment positions of port tube 44 with levels adjusted to capability of loudspeaker system 40 for each respective adjustment position. In a simple form adjustment of a physical structure of a loudspeaker system may be implemented by operating a mechanical lever such that its operation may trip a limit switch to electrically provide an appropriate level of compensation. Alternatively, a switch such as an electrical switch may initiate both electrical and physical adjustments, such as by using a motor or solenoid to implement the physical adjustment. While Fig 4A shows a stepped change between two states, it is preferable to have a gradual or progressive change such as by using a potentiometer or a plurality of ganged potentiometers for adjusting electrical compensation accompanied by a sliding (trombone-like) or folding (concertina-like) adjustment of a physical structure. In an alternative form switch 46 may be operated by remote control using technology not unlike a television remote control. If loudspeaker 40 has a remote control for other functions, box adjustment with corresponding equalisation may be an added function in the remote control.

As noted above loudspeaker system 10 in Fig. 1 will yield a frequency response corresponding to curve A of Fig 3. If port 14 is shortened the output capability of loudspeaker system 10 will increase but its frequency response will

become distorted as shown by curve B of Fig 3. Accordingly an equalisation adjustment is typically required to restore a flat frequency response. It is possible to make this adjustment electrically. For example if port 14 is shortened to 35 mm the equalisation required may be provided by a two pole low pass filter as shown in Fig 4c. With this equalisation the frequency response may be restored to a substantially flat response. Output capability of the loudspeaker system may be increased 1 OdB and cut off frequency may be increased from 20Hz to 60 Hz. Accordingly the present invention may allow a user to trade off low cut off frequency for higher output or vice versa by synchronous switching of box configuration and electrical equalisation.

Fig 5 shows in schematic form how program material recorded on an audio compact disk (CD) may dynamically control adjustment of loudspeaker system 50. The diagram represents a CD carrier 51 that includes program instructions reflecting a producer's desired dynamic adjustments for loudspeaker system 50. A CD player 52 includes a CD reader 53 and decoders including control decoder 54 and audio stream decoder 55. When CD reading begins but before an audio stream commences, the control instructions may be decoded and actuator 56 associated with loudspeaker system 50 may adjust an associated physical structure and corresponding compensation. Fig 6 shows in schematic form how program material recorded on a digital versatile disk (DVD) may dynamically control adjustment of loudspeaker system 60. The diagram represents a DVD carrier 61 that includes program instructions reflecting a producer's desired dynamic adjustments for loudspeaker system 60. A DVD player 62 includes a DVD reader 63 and decoders including control decoder 64, audio stream decoder 65 and video stream decoder 66 that feeds a video signal to video monitor 67. During a

video session, control instructions may be decoded and actuators 68, 69 including proportional actuators associated with loudspeaker system 60 may be activated to reflect the producer's intentions. The actuators 68, 69 may include low frequency extension or higher output capability. Program control source may include CD, DVD, MP3 stream, video tape, audio tape, DAT tape, broadcast, internet and the like.

A further option (not illustrated) may be to provide sufficient intelligence to an automatic control mechanism such that it may decide independently from the nature of the program material (ie. the signal driving the electro-acoustic transducer) what an ideal loudspeaker configuration should be in the circumstances and if automatic control is selected by a user the automatic control mechanism may adjust the loudspeakers accordingly.

At a user interface level the adjusting control may include a mechanical lever or the like or an electrical button or electrical dial or the like. Remote control may be actuated manually and achieved by means of a hand held remote control unit or automatically via program source equipment. In the case of a remote control unit there may be included multiple channels to control a number of functions on one or more loudspeaker enclosures. The user interface may include a switch for switching from manual to program or automatic control.

Compensation in relation to the present invention may include equalisation of frequency response and equalisation of sound levels relative to other loudspeakers in the listening environment. Compensation may be coupled to an adjusting control function by mechanical, electrical, infrared or radio frequency means.

In a multi-band loudspeaker system, adjustments in accordance with the present invention may be applied to one or more frequency bands.

The nature of structural adjustments and adjustment mechanisms will now be described. In most cases an adjustment mechanism according to the present invention may include a reliable seal or seals to prevent gas flow through closed joints. Reliable seals may be achieved for example by the use of O rings on lubricated surfaces or the like.

According to known design rules it is possible to alter acoustic capabilities of a loudspeaker enclosure by changing volumes of chambers forming part of Helmholtz resonators; changing port tube length or port tube diameter of Helmholtz resonators; changing length of resonant tubes; changing from vented to sealed enclosures or vice versa; changing discontinuities in a waveguide and the like. The present invention regards all such methods legitimate means for adjusting a loudspeaker enclosure under user or program control to adjust its capabilities to suit desired requirements of a listening session.

Numerous mechanisms may be used to achieve such adjustment. However for the purpose of the present invention the following generic examples are given: A. To change length of a duct or port tube, the tube may be made extensible by incorporating a telescopic element.

B. To change from a sealed to a vented enclosure a valve may be incorporated in a duct or port tube at an inner end.

C. To change diameter of a port tube valves may be incorporated in multiple tubes and unwanted valves may be switched off.

D. Where adjustments are made by means of mechanical controls it is preferable that an adjustment control positively engages a setting or state at a desired position. This may be achieved for example by friction or any other suitable means. The locking mechanism preferably should be immune to vibrations of the associated enclosure.

The present invention may provide a loudspeaker system with a capacity for both extended low frequency response and high sound level without appreciably varying enclosure size, shape or cost. A loudspeaker system according to the present invention may maintain fidelity of performance including flat frequency response over a band of operation. A loudspeaker system according to the present invention may provide an acoustic result that matches the intent of the producer of the program material being used.

The present invention may permit a smaller enclosure to achieve a level of performance in varied circumstances that could only be achieved by a larger enclosure according to a prior art design, or by two prior art enclosures.

Finally it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.