AutoSpeed - The Patent Files: Latest Speaker Designs

Hidden Ported Box

US Patent 6,076,631 was filed on June 20, 2000 by Anton Hoenninger and Karl Kuebler of DaimlerChrysler AG. The patent is for a hidden bass-reflex (ported) speaker enclosure.

Background

Bass reflex boxes require a relatively large internal volume, with sufficient space frequently unavailable in the interior of a car. In order to satisfy a desire for powerful bass for the driver and passenger, a bass reflex box located in the back of a vehicle interior requires a volume of the order of at least 15 litres. This invention is concerned with the problem of how to accommodate a bass reflex box with a relatively large volume in the interior of a car without an associated perceived reduction of interior or cargo space. In addition, a location accommodating such a box must be selected for which the sound provided for the vehicle occupants is as good as possible.

This problem is solved by locating the bass reflex box in the passenger foot area against the firewall. Bass output openings from the box lead into the interior of the vehicle from the upper area of the enclosure, which is generally not contacted by the passenger's feet.

The bass reflex box can be accommodated especially compactly when it also forms a front foot support area within the foot space of the passenger. Floor coverings - such as carpet - can cover this box, with the carpet even being integrated into the surface of the box. With clever design, an intermediate layer that absorbs impact energy can be largely eliminated from the front foot support area below the floor carpeting. The bass reflex box can also be designed as a crash element itself, so that it absorbs energy in the event of a collision.

A foot support plate (1) is mounted at a distance in front of a firewall (2). The firewall is covered with a damping layer (5) on the side facing the interior. The wedge-shaped space produced by this kind of installation between the foot support plate and the damping layer of the firewall serves as space to accommodate a bass reflex box (3). Such a box, with a volume of 10 litres for example, is designed precisely for the available installation space. The ports of the bass reflex box are in the form of two openings (4) in the carpet (6) covering the foot support. These openings are located in an area of the carpeting that projects above the foot support at the top.

By providing a bass reflex box in the front passenger foot space, an optimum sound effect can be produced within the vehicle interior with a box volume of approximately 10 litres, which otherwise could only be achieved by mounting the bass reflex box in the back of the passenger compartment with a bass reflex box volume of at least 15 litres.

With a suitably stable design, the foot support located in front of the bass reflex box described above can be eliminated. In this case, as shown here, the bass reflex box (3) itself serves as a front foot support area (7). This area can be covered as usual by floor carpeting (6). Then an impact-energy-absorbing intermediate layer can be provided between the carpet and the bass reflex box. This intermediate layer can also be integrated into the floor covering and/or into the bass reflex box. The bass reflex box can be designed with energy absorbing characteristics (8) as well to function as a crash element.

Spiral Cavity Speaker Box

US Patent 6,062,339 was filed on May 16, 2000 by Dana B Hathaway of 9 Swetts Hill, Amesbury, MA 01913. The patent is for a compact, spiral cavity loudspeaker enclosure.

Background

The current practice of installing loudspeakers into cars is to fasten the loudspeakers into holes in the interior panels of the cabin. This practice appears to make good sense because it uses the space between the interior panel and the outside panel of the car. It is however, responsible for a number of well-understood problems. The loudspeaker is exposed to the harsh environmental conditions that exist between the inside and outside panels of an automobile. Loudspeakers are routinely exposed to the water drainage from windows and door drains. As a result of this, splash shields and waterproof loudspeaker component parts are often used. The attempts to provide environmental protection of the loudspeaker mechanism are both costly and compromise the sound quality of the loudspeaker.

With the exception of costly custom-made fibreglass enclosures supplied by aftermarket installers, the loudspeakers are allowed to operate in a near free-air condition. This is a result of the very leaky air seal between the inside and outside panels in a car. Car manufacturers generally do not provide an air seal between these panels due to the requirement for water drainage openings.

Operation of the loudspeaker/woofer without acoustic loading of the rear wave radiation causes a number of problems. First, at low frequencies, only the mechanical stiffness of the suspension components controls the amount of cone motion excursions. High cone excursions can damage the loudspeaker and produce poor sound quality. Second, without containment of the loudspeaker rear wave radiation, sound pressure cancellation will occur. This has the effect of greatly reducing bass and lower midrange sound output, no matter what size loudspeaker is used.

The invention covered here is a loudspeaker assembly for controlling the rear wave radiation of a loudspeaker using an extremely compact enclosure. As part of the enclosure, a cavity, preferably a spiral cavity, is formed which produces a Helmholtz acoustic element. This element provides acoustic loading and enhances bass output to frequencies well below those achieved by conventional enclosures of the same size.

The small size and shape of the loudspeaker assembly provides easy installation in a panel location without the need for a driver mounting hole. The loudspeaker assembly eliminates the problems of conventional between-panel location. Loudspeaker rear wave radiation is totally contained by the enclosure so that sound pressure cancellation is eliminated.

Because a simple depression moulded into the interior panel can form part of the cavity enclosure, no driver mounting holes are required. Loudspeaker installation during vehicle assembly is greatly simplified. The major benefit of this invention is a loudspeaker assembly which produces a bass sound output from a loudspeaker in an enclosure so compact that it can be surface mounted on the interior panel of a passenger compartment.

Broadly, the invention comprises an inner sleeve to which a loudspeaker is secured. The inner sleeve is received within an outer sleeve, with a space left between the inner and outer sleeves. Spiral channels are formed in this space. In the preferred approach (vented or bass reflex speaker) the open rear of the inner sleeve is spaced apart from the back of the enclosure to form a vented volume. The loudspeaker driver causes the air in the channels to resonate with the volume of air contained within the open-ended inner sleeve, forming a Helmholtz element. Effectively, the enclosure that is formed has extremely long ports that are wrapped around the inner enclosure before being vented near to the front face of the speaker.

The Drawings

The design comprises a housing (12) with an outer sleeve (14), a rear wall (16) joined to the outer sleeve, and a flange (18) at the forward end of the housing. An inner sleeve (20) is concentrically aligned with the outer sleeve with a space (22) formed in between. The rear end of the inner sleeve is spaced apart from the rear wall, forming a vented volume (24).

The space between the inner and outer sleeves has placed in it an insert (such as polyurethane foam) in which two channels (28) and (30) are formed. Each channel describes a helix through a 360-degree revolution from one end of the space to the other. The channels are spaced apart in parallel relationship and offset by 180 degrees. The channels therefore describe two acoustical flow paths, each following a helical 360-degree path from one end of the gap to the other.

In a working version of the invention, the diameter of the inner sleeve was 4 inches, the gap between the inner and outer cylinders was 1 inch, and the depth of the vented volume (24) was also 1 inch. The channels were each 0.375 inches square and 18 inches in length, for a volume of 6.75 cubic inches. A 78 cubic inch internal vented volume (24) of air combines with the 13.5 cubic inches of air contained in the spiral cavities to form a Helmholtz acoustical element at 49 Hertz. Enhanced based output in a frequency range of 20 to 200Hz was realized.

Sound Bar Assembly

US Patent 5,979,590 was issued on November 9, 1999 to Robert J Telmos of Top Source Automotive, Inc. (Troy, MI) for a new roof-mounted speaker enclosure.

This invention relates to loudspeaker systems intended for use in motor vehicles and particularly to a 'sound bar assembly' that can be mounted against the roof of the vehicle. The sound bar assembly contains chambers and other structures to enhance the quality of the sound and improve the aesthetic appearance of the vehicle interior.

The sound bar assembly comprises an upper member suitable for location adjacent the inside surface of the roof of the vehicle and adjacent an edge of the roof. The upper member has a length approximately corresponding to the width of the roof. A lower member is located adjacent the upper member and has its edges in a sealed relationship with the upper member to form a chamber. The lower member has at least one opening, and a speaker assembly is mounted in the opening and is located within the chamber.

The sound bar assembly preferably has a wedge-shaped cross-section with a narrow front portion and a wide rear portion. This enables mounting the speaker assemblies at a forward angle so that they project sound more directly into the passenger compartment.

The lower member preferably has a speaker assembly near each end to provide sound generation at the sides of the vehicle and resulting sound separation. Speaker assemblies capable of bass and mid-range sounds are mounted in the lower member so that each speaker assembly is located within its own chamber. Sound from these bass and mid-range speakers reach the ears of the vehicle occupants in relatively undistorted form.

Additional openings can be formed in the lower or upper member for speaker assemblies capable of generating high range sounds (tweeters). Best sound quality is obtained by locating these tweeter assemblies so they project sounds directly at the passengers. The openings for the tweeter assemblies are preferably located in forward-facing surfaces of either the lower or upper members. For enhanced space utilization, these tweeter openings are outboard of the bass and mid-range speaker assemblies.

Each speaker assembly capable of generating bass and midrange sounds is located within its own separate chamber. Moulding divider walls in one or both of the lower and upper members forms these chambers. A separate chamber for each speaker assembly enables improved sound quality.

Each chamber is designed so its shape and its size enhance the sound capabilities of its particular speaker assembly and the particular vehicle environment. Each vehicle environment, and each vehicle design, form a unique combination in which enhancement or suppression of certain sound frequencies is desired. In practice, the process of developing a sound bar assembly consists of mapping the vehicle to determine the frequency modes that need enhancement or suppression, selecting a speaker with desirable size and sound characteristics, and designing the size and shape of the chambers to take advantage of or correct targeted frequency modes.

The lower member and the upper member of the sound bar assembly are preferably made of polycarbonate, ABS, or S-RIM materials. These materials can be moulded and formed to the tolerances necessary for proper sealing and air containment without the need for additional gasketing materials. The lower and upper members also can be fabricated from sheet metal if desired.

The Drawings

Referring to the drawing, a sport utility vehicle has a sound bar assembly (12) mounted against the inside surface of the vehicle roof. The sound bar assembly is located at the rear edge of the roof and extends laterally across the entire width of the rear edge of the vehicle roof.

As shown here, the sound bar assembly consists of a lower member (20) and an upper member (22). The lower member has enlarged and widened end portions (24) and (26), and the end portions contain downwardly and forward-facing openings (28) and (30) that accept bass/midrange speakers. Openings (28) and (30) are angled forward so the speakers project sounds both downward and forward into the passenger compartment of the vehicle. Smaller openings (36) and (38) are formed in the lower member outboard of the other openings. These smaller openings face more forward than downward, and tweeters are mounted in them.

As shown more clearly here, the edges of the lower and upper member fit together in a sealed relationship and define an internal chamber (44). The upper member is shaped to conform essentially to the rearward portion of vehicle roof and to the structural members (46) that form the rear edge of the vehicle roof. The lower member has a bass/midrange speaker (32) mounted in its opening so that the speaker is located in the chamber and is sealed to the lower member. The lower member has a moulding portion (48) that projects beyond the junction of the lower and upper members. This covers the lower portions of structural members from view when the sound bar assembly is in place in the vehicle.

This diagram also illustrates the wedge shape of the preferred sound bar assembly. This shape is achieved by having a generally narrow forward dimension and a generally wider rearward dimension for the sound bar assembly. The resulting sound bar assembly maximizes usage of the space at the rear surface of the roof of a vehicle and enables mounting the speakers at a forward angle so they direct sound into the passenger compartment.

A sport utility vehicle is selected for the detailed description, as it is a popular application of sound bar assemblies of the type of this invention. The sound bar assembly also can be applied to passenger cars and the cabs of light, medium, and heavy trucks. Each application requires tuning of the chambers to the desired size and shape to enhance the quality of the sound produced by the sound bar assembly.

Noise Absorbing Cover

On December 7, 1999, United States Patent 5,996,727 was issued to Henry Francis Blind, David Alan Dage and Alan Scott Phillips, all of Ford Global Technologies, Inc. The patent was for a noise absorbing cover designed to stop road noise passing into the cabin through the speakers, while at the same time not degrading speaker performance.

Background

Noise, vibration, and harshness (NVH) performance is a critical concern in the design of passenger cars and trucks. The primary sources of objectionable noise during driving conditions are road and wind noise originating outside of the vehicle passenger compartment. Various structures and materials have been employed to block sound energy from entering the passenger compartment, such as noise-absorbing sheets installed inside vehicle doors and other body panels. Moulded cotton or synthetic fibre sheets are often used for their light weight and high coefficient of sound absorption.

Speakers are typically mounted in the interior sides of vehicle doors and body panels (eg rear quarter-panels) that contain noise-absorbing sheets. Since the speaker freely transmits sound through its mounting hole, the importance of the noise-absorbing sheet at that location is even greater. Thus, previous noise-absorbing sheets have included an integral chamber to house the rear portion of the speaker. During operation of the speaker, however, the chamber becomes pressurized because the noise-absorbing sheet also blocks the flow of air produced by the vibrating cone of the speaker. The pressurized chamber reduces the sound production of the speaker at low frequencies, thereby creating a reduction in bass output.

The Drawings

Referring to the diagram, a previous design noise-absorbing sheet (10) is shown in relation to a vehicle door (11). The sound-absorbing sheet includes an indentation (12) for receiving the rear structure of a loudspeaker. The door typically includes a structural panel on its interior side composed of sheet metal. Sheet 10 is typically included in a composite trim panel placed on the interior side of the door structural panel.

As shown in cross section here, the door structural panel (13) includes an opening (14) for receiving a speaker (15). Sheet 10 lines the interior side of panel 13. An indentation (12) creates a space (15) for receiving the speaker. Panel 13 could alternatively be a rear parcel tray or a rear quarter panel of a vehicle, or any other vehicle surface for supporting a loudspeaker. In each case, exterior noises from outside panel 13 would be transmitted through the speaker cone of speaker to the interior passenger compartment, if not for the indentation of the sound-absorbing barrier (10). However, since the speaker is entirely enclosed at the back, there is a loss in low frequency output due to the small trapped-air cavity in space 15. Loss of speaker output occurs between about 25 and 1000Hz; a maximum loss has been measured of up to 5 dB at frequencies of about 50 to 100Hz.

The present invention is shown in cross section here. Speaker 16 is again mounted to panel 13. A sound absorbing cover (25) has a 'salad bowl' shape for substantially enclosing the rear of the speaker. An air gap (27) is provided at the outside edge of the cover for venting the space behind the speaker. A noise-absorbing sheet (26) is provided on panel 13.

Cover 25 and sheet 26 are preferably composed of a moulded, needled reclaimed fibre padding of uniform construction. A homogenous mixture of synthetic and/or natural fibres is needled in a random orientation. The material is treated with a thermal setting resin and then compressed and moulded to shape in a heated die set.

The inventers have employed a cover comprising resonated cotton and synthetic fibres providing sound absorption characteristics of 4% at 250Hz, 12% at 500Hz, 30% at 1000Hz, and 63% at 2000Hz. Thus, noise blocking is achieved primarily for middle and high frequency noises from about 200 Hz to about 20 kHz, which are the most objectionable to the vehicle occupants.

The air gap is oriented such that although airflow through the air gap is permitted to avoid pressurizing the space behind the speaker, noise blocking is maintained by avoiding direct line-of-sight paths between the exterior noise sources and the cone of speaker. This property of the air gap is insured since the footprint of the cover projects onto panel to fully block the hole for the speaker. Since higher frequency noises (eg greater than about 200Hz) require direct transmission paths, noise at such frequencies are not transmitted through the air gap.

The air gap has a total cross-sectional area sufficient to allow unimpaired low frequency output from the speaker but small enough to maintain the directional noise reductions characteristics required. For good low frequency speaker response, the area of air gap need be no larger than the total area of the speaker cone.

The cover is attached to the speaker by glue or by a screw as shown here.

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