SE538743C2

SE538743C2 - Loudspeaker enclosure with a sealed acoustic suspension chamber

Info

Publication number: SE538743C2
Application number: SE1550164A
Authority: SE
Inventors: Jaguste Rohan
Original assignee: Keyofd Ab
Priority date: 2015-02-13
Filing date: 2015-02-13
Publication date: 2016-11-08
Also published as: KR20170117478A; EP3257264B1; KR102167307B1; US20180027321A1; EP3257264A1; EP3257264A4; WO2016130077A1; CN107431853A; SE1550164A1; DK3257264T3; CN107431853B; US10362386B2; JP2018510557A

Abstract

14ABSTRACT The present invention relates to a loudspeaker enclosure housing a sealed acoustic suspensionChamber. ln the sealed acoustic suspension chamber are arranged a driver and a passiveacoustic diaphragm on opposite sides of an inner surface of the sealed acoustic suspensionchamber. The loudspeaker enclosure also houses a first band-pass chamber connected to the sealed acoustic suspension chamber by the passive acoustic diaphragm. (Figure 1 for publication)

Description

1 Loudspeaker enclosure with a sealed acoustic suspension Chamber TECHNICAL FIELD The present invention relates to a loudspeaker enclosure housing a sealed acoustic suspensionchamber. ln the sealed acoustic suspension chamber are arranged a driver and a passiveacoustic diaphragm on opposite sides of an inner surface ofthe sealed acoustic suspensionchamber, and the loudspeaker enclosure also houses a first band-pass chamber connected to the sealed acoustic suspension chamber by the passive acoustic diaphragm.

BACKGROUND ART Accurate high quality reproduction of audio signals, also referred to as high fidelityreproduction, is among others preferred in the music industry while monitoring sound duringfor instance music recording, sound mastering and audio engineering. Accurate high quality reproduction of pre-recorded audio signals is also preferred by musicians and audiophiles.

A loudspeaker is a device that converts an electrical audio signal or impulse into correspondingsound. The loudspeaker typically consists of a purpose-engineered enclosure, housing at leastone loudspeaker driver, also called transducer, and associated electronic equipment, such ascrossover circuits and amplifiers. A transducer is a device that converts an electrical signal intovariations in a physical quantity, such as sound, the conversion being the operating principle behind generally available loudspeaker systems and applications.

Loudspeaker enclosures range in design from simple, rectangular particle-board chambers tohighly sophisticated cabinets with advanced geometries. Those advanced, more complexenclosures may incorporate composite materials and state of the art components. Thegeometry ofthe enclosures, internal and external may also comprise internal sub-chambersdefined and delimited by passive acoustic radiators and/or passages there between.Expressions used for such inner or outer passages between sub-chambers are vents (ventilation passages), ports and diaphragms. 2 Conventional loudspeakers use the mentioned variety of enclosures, Chambers and sub-chambers, components and driver arrangements to reproduce sound within and beyond thecommonly accepted range of human hearing, which is between 20 Hz and 20 kHz. A full-rangedriver is a type of driver designed to reproduce most of the audible frequencies. Due tophysical and technical limitations no driver in use today can audibly reproduce all thefrequencies within this range all by itself. To overcome this limitation, it is therefore commonfor loudspeakers to utilise at least two distinct drivers. The low- and mid-range frequenciesfrom 20 Hz to up to 1500 Hz are produced using a woofer, and the high range frequencies from 1500 Hz to 20 kHz are produced using a tweeter respectively.

Despite use of a twin driver arrangement according to the above, very low frequencies areusually still attenuated well below audible levels. To counteract this, the so-called high-endloudspeakers typically reproduce sound utilising at least three drivers, using a dedicated lowfrequency woofer for reproducing the low frequencies (bass), and the mid-range driver andthe tweeter for reproducing the remaining frequencies respectively. Dedicated sub-woofers also employ this low frequency woofer to the same effect.

When more than one driver is used in a loudspeaker, a crossover circuit is required to ensurethat the multiple drivers do not reproduce the same frequencies, which could result ininterference, such as undesired coloration or cancellation ofthe sound waves beinggenerated. The crossover circuit in most cases is a combination of simple band-pass filtersconstructed using inductors, capacitors and resistors of high quality. The use of a crossovercircuit can allow for near optimal sound reproduction, but not without the overhead oflowered operating efficiency and energy loss through dissipated heat. For crossover circuits tofunction properly and not impair a near optimal reproduction of sound, they need to be madefrom high quality components. With this requirement comes the inevitable disadvantage ofadding considerable hardware costs to a sound system besides increasing complexity of the system.

Yet another difficulty to consider during construction and production of loudspeakers withmultiple drivers is tolerance. Precise alignment and positioning of each driver on the baffle of the loudspeaker enclosure with respect to any other drivers is crucial for accurate sound 3reproduction, as even minor deviations from the optimal alignment can lead to undesired coloration or distortion of the generated sound.

A loudspeaker enclosure can be used as a means to extend the low frequency response of thewoofer driver. For example, the enclosure can be designed to resonate at certain lowfrequencies by ventilating the volume of the air inside the enclosure via a port, thus increasingthe low frequency (bass) output from the loudspeaker. Variations of this port, which in effecthas the function of a so-called Helmholtz resonator, have been devised to optimise a widerange of woofer drivers. Such enclosures usually require a relatively large internal volumecompared with the available space for housing such a volume and the desire to keep outer dimensions of loudspeaker enclosures smallest possible.

Some loudspeakers utilise one or more passive acoustic diaphragms, which is a type of passiveacoustic radiator and which will be referred to as passive radiator henceforth, in place ofports. A passive radiator is a driver without a magnet, voice coil and terminal assembly, and ishence not physically connected or wired to the amplifier. When coupled with a suitable driver,the passive radiator vibrates in response to the changing air pressure inside the loudspeakerenclosure caused by the vibrating driver. Unlike for a port, the resonance frequency of thepassive radiator can be accurately tuned by changing its vibrating mass. Thus, tuningadjustments for a passive radiator can be accomplished more quickly than for the case of themore conventional bass reflex design, since such corrections can be as simple as a massadjustment to its diaphragm. Disadvantages are that a passive radiator must be manufacturedwith small tolerances quite like a driver. This increases production costs besides the limitations in excursion, which applies to passive acoustic diaphragms.

Several types of loudspeaker enclosure designs have been proposed for accurate reproductionof audio signals. One such design uses woofer drivers mounted inside sealed enclosures, withor without additional passive radiators. This type of enclosure provides an excellent transientresponse characteristic. Nevertheless, this design does not extend the low frequency responseof the driver below its own resonance frequency, or below the resonance frequency of thepassive radiators if any. Another design, typically created for extending the low frequency response several loudspeakers, utilises a band-pass enclosure design which is achieved by sub- 4dividing the internal volume of the enclosure into multiple sub-chambers of varying volumes.

Many high end sub-woofers on the market use the band-pass enclosure design.

An example of such a design is reflected in US 6389146, wherein a band-pass loudspeakerenclosure includes three sub-chambers, the first one being a non-Helmholtz-reflex chamber ofa sealed acoustic suspension type, and the remaining two chambers utilising two passiveacoustic radiators to achieve two Helmholtz-reflex ventilation tunings. Moreover, multiple oflow pass acoustic filters are arranged to provide an acoustic band-pass with a substantiallysecond order high pass characteristic combined with an extended, steeper, at least fourthorder slope low pass stop band characteristic. The use of multiple low pass, acoustic filtercharacteristic filters out internal resonances and minimises their acoustical output. Adisadvantage of the described loudspeaker design is that band-pass enclosures tend to have a poorer transient response as compared to that of sealed enclosures.

To achieve optimal low frequency response, band-pass enclosures require considerableinternal volume and hence have to be large in size, which means that they become heavy andbulky to handle. Furthermore, both ofthe aforementioned designs require the use of multipledrivers, a woofer, a mid-range driver and a tweeter, as well as and a crossover circuit foraccurate reproduction of audio signals. This not only increases the unit cost, but also leads tocoloration of the sound being reproduced. Furthermore, the use of multiple drivers and a crossover circuit also increases energy consumption.

The invention aims at overcoming some of the mentioned disadva ntages related to accuratesound reproduction in conventional audio systems generally and loudspeakers and their enclosures in particular.

SUMMARY OF THE INVENTION lt is therefore an object ofthe present invention to obviate or at least alleviate shortcomingsassociated with prior art technology. This object is attained at by means of a loudspeakerenclosure which houses a sealed acoustic suspension chamber, the sealed acoustic suspensionchamber comprising a driver and a passive acoustic diaphragm being arranged on opposite sides of an inner surface of the sealed acoustic suspension chamber. The loudspeaker 5enclosure also houses a first band-pass Chamber connected to the sealed acoustic suspensionchamber by the passive acoustic diaphragm, and is characterised in that the inner surface of the sealed acoustic suspension chamber is continuously curved. ln loudspeaker design art, there is an effect known as the Hoffman's Iron Law, which statesthat a loudspeaker can only possess any two of the following three characteristics: smallvolume, high sensitivity and extended low frequency response. All these three characteristicsare of course desirable, but so far due to physical and technical limitations this has not beenaccomplished. ln accordance with the present invention, all three of the aforementioneddesirable features are realised in its embodiments, thus giving the invention an advantage over most contemporary loudspeaker designs.

The continuously curved shape of the sealed acoustic suspension chamber in combinationwith a driver coupled with a passive acoustic diaphragm housed in a sealed acousticsuspension chamber has many advantages. An example is extension ofthe low frequencyresponse down to the resonance frequency of the passive acoustic diaphragm. Thecontinuously curved shape of the sealed acoustic suspension chamber also results in animproved transient response from both the driver and the passive acoustic diaphragm, whichresults in more accurate sound reproduction, i.e. enhanced quality ofthe sound generated by the loudspeaker.

The mentioned improved transient response in turn results in improved dynamic powerhandling capability, which leads to better operating efficiency without compromising the dynamics of the reproduced sound.

The driver and the passive acoustic diaphragm being arranged on opposite sides of the innersurface ofthe sealed acoustic suspension chamber allows for a more precise coupling of thepassive acoustic diaphragm with the driver in the sealed enclosure. This leads to an improved transient response of the loudspeaker enclosure. ln accordance with one embodiment ofthe present invention, the driver and the passive acoustic diaphragm are integrally formed with the sealed acoustic suspension chamber.

When the driver and the passive acoustic diaphragm are integrally arranged with each other, thus forming a tightly sealed chamber, acoustic leaks consisting of pressurised air can be 6almost entirely avoided. Air leaks are generally a substantial cause of reduced efficiency and acoustic distortion in loudspeaker enclosures. ln accordance with an alternative embodiment, the driver is a full-range driver, i.e. a driver which is able to reproduce sound over most ofthe audible spectrum.

By using one full-range driver to reproduce most ofthe frequencies within the audible rangeof 20 Hz to 20 kHz, the need for multiple drivers and a crossover circuit is eliminated, thusreducing unit costs. Very low frequencies, i.e. below 80 Hz, are audibly reproduced by usingthe aforementioned embodiment in combination with the full-range driver. Further benefitsby using a full-range driver instead of multiple drivers is that energy consumption ofthe loudspeaker is reduced and that the size of the loudspeaker enclosure can be reduced. ln one embodiment of the present invention, the surface area ofthe passive acousticdiaphragm is equal to or larger than the surface area of a corresponding diaphragm ofthe driver.

Arranging the loudspeaker enclosure so that the surface area of the passive acousticdiaphragm is at least the size of the diaphragm of the driver or large, typically two times thesize, further improves transient response and enhances operating efficiency and acousticperformance from both the driver and the passive acoustic diaphragm. The coupling ofthedriver with a suitable passive acoustic diaphragm is determined by the acoustic compliance of both the driver and the passive radiator.

Furthermore, by using a passive acoustic diaphragm with a surface area greater than that ofthe driver, it becomes physically possible to reproduce lower frequencies than otherwise. Thisimplies that the frequency response of the embodiment can be extended well below that of the smaller sized driver without the need for a larger woofer driver or large internal volume.

According to a further embodiment of the loudspeaker enclosure according to the invention, the sealed acoustic suspension chamber is substantially spherical. ln addition to the effects relating to a continuously curved suspension chamber according tothe above discussion, a substantially spherical shape ofthe suspension chamber is even morebeneficial. When the driver and the passive radiator are arranged on opposite sides of a sealed chamber that is substantially spherical, the internal diffraction of the rearward propagated 7sound waves from the driver is greatly minimised resulting in an efficient transfer of energy to the passive radiator through pistonic coupling.

Furthermore, a sphere has the smallest surface area of all surfaces that enclose a givenvolume, implying an optimal volume of air that matches the compliance ofthe driver can beenclosed in the smallest possible chamber. ln other words, the internal volume ofthe sealedacoustic suspension chamber can be minimised. Therefore, a sphere, or at least an almostspherical shape would be ideal, although other limitations in connection with the design or production of loudspeakers may in practice prevent this shape from being realised.

According to an alternative embodiment of the present invention, the loudspeaker enclosurehouses at least a second band-pass chamber, the chamber being connected to the first band- pass chamber by the passive acoustic radiator.

The provision of an optional second band-pass chamber exhibits the properties of a secondorder low-pass filter, which further extends the low frequency response of the loudspeakerenclosure ofthe present invention. The optional second band-pass chamber enables improvedlow frequency response without compromising the overall transient response of the sealed acoustic chamber embodiment. ln one embodiment of the present invention, the sealed acoustic suspension chamber is madefrom a homogenous material of high density. Conceivable materials for use are high densityfibreboard (HDF), ceramics or polymer composites, but also medium density fibreboard (I\/IDF) could be used.

When a homogenous material of high density is used to construct the loudspeaker enclosure,the resulting embodiment exhibits the characteristic of an acoustically consistent volume.Such an acoustically consistent volume allows the timbre, i.e. the character or quality of amusical sound or voice as distinct from its pitch and intensity, to remain consistent throughoutthe structure ofthe enclosure. Undesired coloration or distortion of the sound by the enclosure itself can thus be avoided.

An alternative embodiment ofthe present invention discloses an arrangement in which theloudspeaker enclosure contains foam or magnetic levitating feet in order to acoustically isolate the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS Referring now to the drawings, in which like numerals refer to like parts throughout the several views, exemplary embodiments of the present invention are described.

Figure 1 shows an overview of the loudspeaker enclosure arrangement comprising a first band-pass chamber according to a first embodiment of the present invention.

Figure 2 shows a loudspeaker enclosure comprising a second band-pass chamber in additionto the first band-pass chamber, the second band-pass chamber being connected to the first-band-pass chamber by a passive acoustic diaphragm in accordance with an alternative embodiment of the present invention.

Figures 3-5 show loudspeaker enclosure arrangements with different designs, all having a first band-pass chamber with ventilations in a variety of directions.

Figures 6-8 show loudspeaker enclosure arrangements with different designs, all having firstand second band-pass chamber in connection with each other and with ventilations of the second band-pass chamber in a variety of directions.

DETAILED DESCRIPTION The general object or idea of embodiments of the present disclosure is to address at least oneof the disadvantages with the prior art solutions described above. The various alternativeembodiments described below in connection with the figures should be primarily understoodin a logical sense and the scope of protection ofthe present invention be ascertained with reference to the appended claims.

With reference to figure 1 is disclosed a loudspeaker enclosure 10. The loudspeaker enclosurehouses a sealed acoustic suspension chamber 20, the suspension chamber comprising a driver22 and a passive acoustic diaphragm 24, which are arranged relative each other on oppositesides of an inner surface 26 of the sealed acoustic suspension chamber. The sealed acoustic suspension chamber is made from a homogenous material and/or acoustically neutral 9material of high density, such as high density fibreboard (HDF), ceramics or polymercomposites. The loudspeaker enclosure also houses a first band-pass chamber 28 connectedto the sea|ed acoustic suspension chamber by the passive acoustic diaphragm. Moreover, inaccordance with one embodiment of the present invention, the inner surface of the sea|ed acoustic suspension chamber is continuously curved.

With reference to figure 2, the loudspeaker enclosure is arranged to house at least a secondband-pass chamber 30, the second band-pass chamber being connected to the first band-pass chamber by a passive acoustic radiator 32 of the port-type with f|ared ends.

With further reference to figures 3-5, conceivable loudspeaker enclosure arrangements areshown with different designs, all having a first band-pass chamber with ventilations in avariety of directions. Both the design of the ventilation passages and the direction in which theopening is provided may differ. The design could be with either straight walls or curved walls,then with a f|ared or linear section in-between the inner and outer openings of the ventilation passage of the first band-pass chamber.

With further reference to figures 6-8, conceivable loudspeaker enclosure arrangements areshown with different designs, all having first and second band-pass chamber in connectionwith each other and with ventilations ofthe second band-pass chamber in a variety ofdirections. ln accordance with previously described figures 3-5, both the design of theventilation passages and the direction in which the opening is provided may differ. The designcould be with either straight walls or curved walls, then with a f|ared or linear section in-between the inner and outer openings of the ventilation passage of the additionally provided second ba nd-pass chamber.

From a functional perspective, conventional audio systems generally and loudspeakers andtheir enclosures in particular have long been based on more or less the same principles forconstruction. I\/|aterials used, design and production methods have slowly developed, but still,at least from the outside, not much seems to have happened. Comparing with consumerelectronics and the computer industry for example, the pace of development has been substa ntially slower for loudspea ker technology.

However, during the last years, the field has evolved by the introduction of new materials foruse when producing enclosures for loudspeakers and previously unknown methods ofmanufacturing have been proposed. The present invention proposes materials to be used forthe loudspeaker enclosure having acoustically isolating properties. ln addition to that,automated manufacturing methods are proposed employing CNC-milling of a high density,homogeneous and acoustically neutral material so as to obtain more accurate reproduction ofsound, high performance and consistent quality, while keeping production costs, required size and complexity to a minimum.

When a driver is mounted on a sealed acoustic suspension chamber, the embodiment exhibitsthe characteristic of a critically damped system. This implies that when audio power throughan audio signal is supplied to the driver, its diaphragm will vibrate to match the amplitude ofthe audio signal with high accuracy. The volume of air trapped inside the sealed acousticsuspension chamber critically damps the driver. This corresponds to a precise transient(impulse) response characteristic. Such an arrangement requires a marginal increase in the supplied audio power to counter internal air pressure.

When a passive radiator, or passive acoustic diaphragm, is mounted on the opposite side ofthe driver within the mentioned hermetically sealed chamber, the resulting arrangementexhibits characteristics similar to that of pneumatic piston wherein the rearward facingpassive radiator vibrates near instantaneously in response to the vibrating forward facingdriver, albeit 180° out of phase from driver. Thus, the precise transient response characteristic is preserved.

Furthermore, the acoustic compliance of a system according to the present invention isincreased, which drives the passive radiator without the need for an increase in the audiopower supplied to the driver. When the driver and the passive radiator are arranged onopposite sides of a sealed chamber that is continuously curved or even substantially sphericalor spherical, the internal diffraction of the rearward propagated sound waves from the driver is greatly minimised resulting in an efficient transfer of energy to the passive radiator.

As previously mentioned, a continuously curved, or to be more precise, a spherical inner surface of the sealed acoustic suspension chamber exhibits the smallest surface area of all 11surfaces that enclose a given volume. This enables an optimal volume of air to be used that matches the compliance of the driver that can be enclosed in the smallest possible chamber.

Claims

CLA|l\/IS

1. A loudspeaker enclosure (10) housing a sealed acoustic suspension Chamber (20), thesuspension chamber comprising a driver (22) and a passive acoustic diaphragm (24)being arranged on opposite sides of an inner surface (26) of the sealed acousticsuspension chamber, wherein the loudspeaker enclosure also houses a first band-passchamber (28) connected to the sealed acoustic suspension chamber by the passiveacoustic diaphragm, characterised in that inner surface of the sealed acoustic suspension chamber is the The loudspeaker enclosure according to claim 1, wherein the driver and the passive acoustic diaphragm are integrally formed with the sealed acoustic suspension chamber. The loudspeaker enclosure according to anyone of claims 1-2, wherein the driver is a full-range driver. The loudspeaker enclosure according to anyone of claims 1-3, wherein the surface area(24') ofthe passive acoustic diaphragm is equal to or larger than the surface area (22') of a corresponding acoustic diaphragm ofthe driver. __., q .\;..\.._\.. ~: ,. 7,41. mv., M. . ,..., :. “- . ..,.1,..._\;..i .s *_ 1, \..-_c.=\..-i. el. . t» sewe. t M .\\.\N.\..\. _-. l . . l ..~ _1 tv. ~,. i_.~..i.\. .\..f.\.. .v ..~,. _...,.. .t,....\...... .w N. .v ..d. s =..t.\-c._.\cf“.- c.- cu .ß ...a 4.1. .i ock., Jing, t . fwwc-i. . Wen. . . ,-\;L\,,\»:~,\.. q-:a _c. chwoc Usch _ c ___The loudspeaker enclosure according to anyone claims 1-{§¿'§š¿, wherein the loudspeaker enclosure houses at least a second band-pass chamber (30), the chamber being connected to the first ba nd-pass chamber by a passive acoustic radiator (32). The loudspeaker enclosure according to anyone of claims 1-' wherein the sealed MJ acoustic suspension chamber is made from a homogenous material of high density, such 1 2 as high density fibreboard (HDF), ceramics or polymer composites. ~fl~*.______The loudspeaker enclosure according to anyone of claims wherein the sealed acoustic suspension chamber is made from an acoustically neutral material, such as high density fibreboard (HDF), ceramics or polymer composites. li ~ï' _____The loudspeaker enclosure according to anyone of claims wherein the enclosure is acoustically iso|ated using foam or magnetic levitating feet, or a combination thereof.