Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having acoustic wave modifying structure
Reexamination Certificate
1996-03-25
2004-05-11
Barnie, Rexford (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having acoustic wave modifying structure
C381S345000, C381S348000, C381S338000
Reexamination Certificate
active
06735320
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a loudspeaker and, in particular, to a loudspeaker which is enhanced for clarity and improved response.
Loudspeakers are known in the art and examples of known loudspeakers are shown in
FIGS. 1 and 2
. Conventional loudspeakers have the problem of requiring enhancement of the clarity of the bass coming from inside the non-sealed cabinet or enclosure. As shown in
FIGS. 1 and 2
, ports are typically provided in the front or back of the enclosure, but always in a plane parallel to the plane of the speaker and/or the plane of a nearby surface, such as a wall or bookcase. This leads to added distortion.
With conventional front porting, as shown in
FIG. 2
, bass waves emanating from a front port
7
of an enclosure
5
are in negative phase with those of a bass driver
6
, causing a cancellation effect at the instant a note is played. Since there is some delay between arrival of the two waves, it actually ends up being only a delayed bass note coming from the port
7
. This provides some additional bass extension but at a loss of clarity, making the bass sound muddy.
With conventional rear porting, as shown in
FIG. 1
, a bass driver
2
faces forward and the phase is correct, but distortion problems are created by wave reentry into a rear port
3
due to reflection from the facing wall W and by standing waves formed behind the enclosure
1
. These cause peaks and dips in the bass and result in a rumbling, boomy bass.
Another disadvantage of the prior art loudspeakers is the fact that there is no ability to control the bass output, specifically to reduce unwanted sound waves from coming through the port. The bass output is controlled only on a limited basis by the length and size of the port as determined by conventional formulas.
In conventional loudspeakers, under normal tuning conditions, the placement of the port at a set distance from the driver, in combination with the volume of the port, determines the tuning characteristics. The rules are varied since cabinet or enclosure dimensions and driver characteristics are varied, but since the port is still in a parallel plane with the driver being tuned, the reflections inside the enclosure will still provide an undesirable amount of pass through of unwanted higher frequencies leading to midrange distortion.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide a more controlled approach to enhancing bass output from loudspeakers in a non-sealed enclosure.
Another object of the present invention is to enhance the clarity and improve the response in loudspeakers.
These and other objects and advantages of the present invention are achieved in accordance with the present invention by placing the port at an angle to the driver so that sound waves created by the driver can be tuned additionally by the direction of the angle which is now also a monitor of pressure level. Lower bass components contain more pressure than upper frequencies and will be allowed through the porting. However, higher and less desirable frequencies will remain in the enclosure to be continually dampened by internal insulation, of which much less is required than in conventional systems.
In accordance with the present invention, the direction of the angle of the port can be used to control the bass output. For more release of the upper notes, the port is directed at the center of the driver or speaker. For greater release of lower notes, the port is directed at the edge of the speaker cone, and for the deepest bass enhancement, the port is moved away from the cone or the steepness of the angle is increased.
Two primary enhancements result from this improvement according to the present invention. The first is the ability to fine tune bass waves created in a passive manner. The second is the reduction of standing waves on the back or rear side of the enclosure and the reduction of both phase and midrange distortion at the front of the enclosure. Both of these together create more accurate bass and improved clarity.
The angled output can be any passive device used to enhance bass, when angled in a manner which may take advantage of tuning due to the direction and angle relative to the driver being tuned.
A passive device consists of either a port or a passive radiator. A port includes an open area such as a tube which is sized in length and diameter to allow certain bass waves through. A passive radiator works in the same manner, however it uses a non-active speaker cone chosen by size and weight to select bass waves. In a particularly preferred embodiment of the present invention, ports are used for the added efficiency and for better control of frequency selection.
The angled output can be any passive device used to enhance the clarity of speakers. The port is angled in a manner which is related to the frequencies being tuned to. The angle causes the reduction of standing waves behind the enclosure and/or wave cancellation or distortion of waves caused by the port tuning in relation to sound emanating from the front of the enclosure.
The loudspeaker in accordance with the present invention comprises an enclosure including a bottom wall, a front wall extending upwardly from the bottom wall, and a rear wall extending upwardly from the bottom wall and opposite the front wall and having an angled wall portion which faces generally upwardly and rearwardly. At least one speaker is mounted on the front wall in a given plane to direct sound waves outwardly therefrom. At least one passive device is mounted on the angled wall portion to direct sound waves generally upwardly and rearwardly of the given plane.
The angled wall portion is preferably disposed at an angle of 30° to 60° with respect to the given plane and in a particularly preferred embodiment, the given plane comprises the front wall.
REFERENCES:
patent: 2801704 (1957-08-01), Martin
patent: 4146111 (1979-03-01), Mae et al.
patent: 4146744 (1979-03-01), Veranth
patent: 5173575 (1992-12-01), Furukawa
patent: 59-94992 (1984-05-01), None
patent: 5-199581 (1993-08-01), None
Adams & Wilks
Barnie Rexford
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