Patent Application
20090173567
1. Technical Field of the Invention
This invention relates generally to loudspeaker enclosures, and more specifically to ported enclosures opposed to sealed enclosures, and yet more specifically to enclosures having triangular ducted ports which at least partially utilize existing enclosure walls to create the ducts.
2. Background Art
Throughout this disclosure, for ease of illustration, loudspeakers will be discussed as though having only a single transducer. Those skilled in the art will readily appreciate that the principles of this invention are, however, not limited to that case and that this invention may be practiced in loudspeakers having multiple transducers of the same size or type or of varying sizes or types. And, for ease of illustration, loudspeaker enclosures will be discussed as though they were in the three-dimensional shape of a rectangular prism, although those of skill in the art will readily appreciate that the invention may be practiced with other shapes of loudspeaker enclosures as well.
Loudspeaker enclosures may generally be categorized as either the sealed enclosure type, the ported type, or the bandpass type. A sealed enclosure typically has six rectangular panels coupled together to form a box enclosing a volume of air. One of the panels has a hole cut through it, into which an electromagnetic transducer (“speaker driver”) is mounted. The panels and the transducer together form a sealed enclosure, such that when the transducer's diaphragm is pulled inward by the transducer's motor, the air inside the enclosure is pressurized, and when the diaphragm is pushed outward by the motor, the air inside the enclosure is rarified. A sealed enclosure may have small, incidental air leaks, but these are undesirable and the designer and manufacturer should avoid them, because they cause noise and can somewhat alter the tuning characteristics of the enclosure.
A ported enclosure, sometimes called a vented enclosure, is constructed in that same manner, with one modification. Another hole is cut through one of the panels, typically the front panel, and a duct of a predetermined cross-sectional area and length is connected to the panel so as to extend from the hole inward into the enclosed air space. The duct alters the tuning characteristics of the enclosure in a manner determined by factors including the cross-sectional area and length of the duct, the volume of the enclosed air within the enclosure, and so forth.
One undesirable characteristic of conventional ducts is that the port hole and the transducer hole cannot occupy the same area or overlapping areas on the same panel, in other words, the front panel must be large enough to accommodate both. Both holes being circular does not lend to achieving a good packing factor. Another is that the duct and the transducer cannot occupy the same space within the enclosure. In many applications, it is desirable to make the front panel as small as possible, such that its size is limited only by the dimensions of the transducer. With a circular transducer and a square front panel, this leaves only four very small, generally triangular areas of the front panel through which a port could be cut. In many cases, these areas are simply too small for a circular duct to provide the minimum required port cross-sectional area to avoid port wind noise during high SPL operation. Some enclosures have included more than one port, but it is known that it is problematic to achieve the same results with plural ducts that can otherwise be achieved with a single duct, in part because the interior duct wall surface area to duct cross-sectional area ratio is higher with plural ducts than with a single, larger cross-sectional area duct.
In some enclosures, the desired port tuning characteristics require a duct whose length cannot fit within the internal dimensions of the enclosure. A few loudspeakers have addressed this problem by using “folded” or “bent” ducts. In some cases, the duct has been bent into an L shape. In some cases, the duct has been folded into a U shape.
And in one highly unusual loudspeaker enclosure conceived by this inventor while working at Pioneer designing a premium upgrade audio system for the Pontiac Aztec, the duct was formed as a pair of concentric tubes. In this enclosure, the smaller diameter tube was coupled to the panel hole, and the larger diameter tube was coupled to the inner surface of the opposite panel. Both ends of the smaller tube were open, but only one end of the larger tube was open—the other end of the larger tube was sealed against the inner surface of the opposite panel. The standing air column within the duct had a shape approximately like the shape of a nearly closed umbrella; from the listening space, the air column extending through the exposed port hole, down the length of the inside of the smaller duct, then folded radially outward in all directions as the far end of the smaller tube came close to but did not touch the closed end of the larger tube, then extended back in the opposite direction in the shape of an annulus or a ring, until it met the main body of the enclosed air volume within the enclosure where the larger tube ended short of the front panel.
Another issue, with both ported and sealed enclosures, is that it is generally desirable that the panels be as rigid as possible. If the panels flex during operation of the loudspeaker, they themselves act as diaphragms or radiators, reducing the quality of the sound produced by the loudspeaker. This is especially true of the panel where the transducer is mounted.
Yet another issue, with both ported and sealed enclosures, is that it is desirable to reduce or eliminate standing waves within the enclosure. Standing waves occur most readily in an enclosure in which opposing internal surfaces are parallel. Pressure waves in effect “echo” back and forth between the parallel surfaces, and cause undesirable effects on the sound produced by the diaphragm.
Still another issue with ported enclosures is the additional manufacturing cost and increased parts count caused by the duct components, which typically include one or more pipes, one or more flared ends, and one or more elbow joints.
What is desirable, then, is an improvement in ported loudspeaker enclosures, which makes better use of front panel surface area than a circular duct can, and which provides the length advantage of a folded duct in a limited dimension enclosure, and which optionally also improves enclosure rigidity and helps reduce standing waves, and potentially lowers cost.
The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments described, but are for explanation and understanding only.
The enclosure includes one or more folded triangular ducted ports, each of which extends through one of the panels. In the embodiment shown, there are two ports 16 and 18, and they both extend through the front panel. The generally triangular shape of the ports enables them to make excellent use of the generally triangular shape of the portions of the front panel in the corners of the front panel beyond the perimeter of the generally circular transducer.
The standing air column in the folded port 16 includes three general portions. From the external listening space, it extends through the generally triangular hole in the front panel, then along a first primary portion 16a having a generally triangular cross-sectional shape bounded by the inner surface of the left panel, the inner surface of the bottom panel, and a first surface of the first internal duct panel 20. The first internal duct panel is coupled to the left panel, bottom panel, and front panel, but ends short of the back panel. An intermediate portion 16b of the standing air column turns around the rear end of the first internal duct panel. And a second primary portion 16c of the standing air column extends forward to the near end of the second internal duct panel 22. This second portion of the standing air column has a generally trapezoidal cross-sectional shape bounded by a second surface of the first internal duct panel, a first surface of the second internal duct panel, the inner surface of the left panel, and the inner surface of the bottom panel. The intermediate portion joins the first and second primary portions.
Similarly, the standing air column in the folded port 18 includes three portions 18a, 18b, and 18c, formed by the top panel, right panel, back panel, and third and fourth internal duct panels 24, 26.
In another such embodiment, the front and/or back panels may be formed separately from a central monolithic piece that includes the four side panels and the four internal duct panels; in such an embodiment, the central component can be cut from e.g. a metal extrusion and then machined to achieve the appropriate duct wall lengths for the first and third, and second and fourth internal duct panels.
A transducer 14 is coupled at a hole through an internal panel 50 of the enclosure such that a first surface (not visible) of its diaphragm is in the first chamber, and a second surface 52 of its diaphragm is in the second chamber. In the embodiment shown, the motor 54 of the transducer is disposed within the first chamber; in another embodiment the transducer could be reversed such that its motor is disposed within the second chamber. Having the motor in the first chamber may provide some small amount of cooling of the motor by air flow through the ducted port.
Optionally, the loudspeaker may further include an amplifier 56 and a torroidal transformer 58 coupled to drive the transducer. In the embodiment shown, these may be disposed within the second chamber of the enclosure. It may be advantageous to not have the transducer motor and the amplifier in the same chamber, especially the sealed second chamber, to avoid overheating.
A transducer 14 is coupled at a hole through an internal panel 70 of the enclosure such that a first surface (not visible) of its diaphragm is in the second chamber, and a second surface 72 of its diaphragm is in the first chamber.
A passive radiator 74 is coupled at a hole through an exterior panel of the enclosure so as to have its back surface in the second chamber. Thus, sound pressure produced by the first (in this case front) surface of the transducer's diaphragm is coupled to the listening environment by the passive radiator, and sound pressure produced by the second (in this case rear) surface of the transducer's diaphragm is coupled to the listening environment by the folded triangular ducted port. The use of at least one passive radiator in a bandpass enclosure is particularly advantageous because it can serve a second purpose as an access panel to the internal active driver, by simply using a passive radiator that is sufficiently larger than the active driver.
In the embodiment shown, the ducted port is folded once (into a U shape), with the result that the sound from the ducted port and the sound from the passive radiator are produced from opposite sides of the loudspeaker. In another embodiment, the ducted port could be folded twice (into a Z shape), and the sound from both the ducted port and the passive radiator would be produced from the same side of the loudspeaker. In still other embodiments, the passive radiator could be mounted to a wall that is perpendicular to the port opening wall, such that the passive radiator or the port is side firing.
The optional second folded triangular ducted port 18 has portions 18a and 18c similarly shaped in the embodiment shown.
An optional third inner duct panel 106 is mounted as shown, and forms a third portion 108c of a Z-shaped duct as described above. Alternatively, the third inner duct panel could be slid downward to mate with the second inner duct panel at the left corner, just as the first and second inner duct panels mate, which could also allow more clearance for a woofer above.
A second inner duct panel 132 is coupled to the left panel and the bottom panel, and may advantageously be slid down the left panel until it meets the first inner duct panel as shown, to form a second triangular portion 130b of the folded duct. In the case of a U-shaped folded duct, the second inner duct panel would end short of the front panel (not shown). In the case of a Z-shaped double-folded duct as shown, the second inner duct panel extends to the front panel except for a portion 134 which ends short of the front panel. In this case, a third inner duct panel 136 is coupled to the second inner duct panel and to another panel—in the instance illustrated, the right panel 138—to form a third portion 130c of the folded duct and does not extend all the way to the back panel.
In the case of the Z-shaped duct, coupling the third inner duct panel to the right panel provides some stiffening of the right panel.
A second portion of the folded duct is formed by the first internal duct panel, the bottom panel, a second internal duct panel 144, and a third internal duct panel 146. The second internal duct panel is coupled to the first and third internal duct panels and to the front and back panels.
A third portion of the folded duct is formed by the third internal port panel, the bottom panel, and the right panel. The third internal port panel mates with the front panel except at a cutout 148, and with the back panel except at a cutout 152.
The cutout 150 connects the triangular first portion of the folded duct to the trapezoidal second portion of the duct. The cutout 148 couples the trapezoidal second portion of the duct to the triangular third portion of the duct. The cutout 152 couples the triangular third portion of the duct to the enclosed air volume within the loudspeaker enclosure. The port hole through the front panel vents the triangular first portion of the folded duct to the listening environment.
The first and second internal duct panels are rigidly coupled to the left and bottom panels, and the third and fourth internal duct panels are rigidly coupled to the right and top panels, which may provide significant gusset type bracing which stiffens the side panels, reducing their tendency to vibrate and distort the sound produced by the loudspeaker.
The angles of the second (upper) surface of the first internal duct panel and of the second (upper) surface of the second internal duct panel are not parallel to the inner surface of the right panel nor to the inner surface of the top panel, which they generally face. This will help reduce standing waves between the left and right panels, and between the top and bottom panels.
For convenience, the first and second internal duct panels are shown as being substantially parallel, but this is not a necessary limitation of all embodiments of the invention. In other words, the third portion of the standing air column does not necessarily have a normal trapezoidal cross-sectional shape. In some embodiments, the internal duct panels are formed of flat panel material, but other shapes may be used in other embodiments. And for convenience, the internal duct panels are shown as extending generally parallel to the line formed by the intersection of the left and bottom panels, but in other embodiments they could be coupled at other angles within the enclosure in order to achieve gradually changing cross-sectional area. And for convenience, the first and second internal duct panels are shown as being coupled to the enclosure at approximately a 45° angle, so as to give the outside port hole a substantially isosceles triangle shape, but in other embodiments, they could be coupled at other angles.
In the embodiment shown, a second such duct is formed in the opposite corner of the enclosure. In other embodiments, a second duct could instead be formed in an adjacent corner such as the lower right corner. This may provide even greater reduction of standing waves, as it will tend to not only reduce the amount of the right panel's surface area that is exposed to the parallel left panel, but also to avoid standing waves between the respective ducts' internal duct panels themselves.
And in the embodiment shown, the ports all extend through either the front panel or the rear panel. In other embodiments they could extend through other panels such as side panels.
The left, right, top, and bottom panels of the enclosure may collectively be termed “side panels”. The side panels, front panel, and back panel may collectively be termed “exterior panels”. If the enclosure has four side panels, it will have a generally rectangular shape; if it has three side panels, it will have a generally triangular shape; and so forth. In some embodiments such as certain pyramid or wedge shaped enclosures, the rear panel may be omitted, or, more accurately, its function may be performed by one or more of the other panels having a suitable shape or angle. The panels may be distinct components glued etc. together, or two or more of them may be formed as a monolithic whole—in the extreme, the entire enclosure may be formed e.g. as a monolithic cast body.
The first and second internal duct panels need not necessarily be coupled to the same side panels, especially in the unusual case of e.g. an octagonal enclosure. And in the unusual cases of a circular enclosure or a spherical enclosure, the respective arc segments of the exterior panel(s) may be considered as though they were individual side panels, for purposes of understanding this invention.
In the embodiment shown, the folded duct includes only a single fold. That is, it forms a generally U shape. In other embodiments having one or more additional internal duct panels (in the same folded duct structure), a greater number of folds can be achieved, enabling the use of a duct length greater than twice the internal dimension of the enclosure. For example, if three internal duct panels are used, the folded duct has a generally Z shape, with three substantially parallel air column portions extending in alternating directions. However, it should be noted that with a front port opening, all of the “odd numbered” internal duct panels are coupled to the front panel, which limits the placement of the transducer if it is coupled to the front panel. The Z etc. embodiments may find best advantage with a port opening which is not on the same panel as the transducer, or when the depth of the enclosure is a key limiting factor.
When one component is said to be “adjacent” another component, it should not be interpreted to mean that there is absolutely nothing between the two components, only that they are in the order indicated.
The various features illustrated in the figures may be combined in many ways, and should not be interpreted as though limited to the specific embodiments in which they were explained and shown.
Those skilled in the art, having the benefit of this disclosure, will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present invention. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define the scope of the invention.
