Audio loudspeaker enclosure

An audio loudspeaker enclosure is presented. The enclosure has surfaces which resonate across a broad band of low frequencies produced by the loudspeaker, thus enhancing the quality of low frequency sound reproduction.

BACKGROUND 
1. Field of the Invention 
The present invention relates to an enclosure for audio loudspeakers, and 
more particularly, to an improved enclosure which resonates across a low 
frequency band to enhance low frequency sound reproduction. 
2. Discussion of the Prior Art 
Loudspeaker enclosures are generally well known. Typically, various 
loudspeaker and enclosure combinations are used to reproduce music as part 
of a home or commercial audio entertainment system. At low frequencies, 
i.e., less than 250 Hz, it is known that direct radiating loudspeakers 
tend to be omnidirectional, producing soundwaves from the front and back 
of the loudspeaker which are of equal intensity, but opposite phase. The 
forward and backward traveling soundwaves thus interfere destructively, 
reducing effective power output and reducing the volume of sound produced 
at those frequencies. 
This problem can be solved through the use of a baffle, and an enclosure 
for the loudspeaker acts as a baffle. The backward traveling soundwaves 
are bounced off the back surface of the enclosure to interfere 
constructively, rather than destructively, with the forward traveling 
soundwaves. Thus, increased power and efficiency result from a well 
designed baffle. However, since wavelength is inversely proportional to 
frequency, a relatively large volume enclosure is required at low 
frequencies. 
The use of baffles introduces another problem. The resulting enclosure is 
subject to developing resonance at one or more frequencies. This resonance 
increases power output at the resonating frequencies and results in a 
"boominess" that dominates, or at least interferes with faithful sound 
reproduction across the broad range of frequencies in the source program. 
Since this resonance occurs only at particular frequencies, the prior art 
enclosure designs have sought to eliminate the resonance completely, and 
rely solely on the source program and amplifying and equalization 
equipment to obtain an improved sound reproduction at low frequencies. See 
U.S. Pat. No. RE 31,483 (Hruby). It would be desirable to take advantage 
of the tendency to develop low frequency resonance to reinforce and 
enhance the reproduction of low frequency source material. 
SUMMARY OF THE INVENTION 
An enclosure for an audio loudspeaker is presented. First and second 
flexible, symmetrical panels are positioned in correspondence with each 
other. Means are provided to couple the first and second panels together 
in such a way that the panels are free to resonate. Means are provided to 
support the loudspeaker between the panels. 
In the preferred embodiment, the first and second panels are equilateral 
right triangles. The first and second panels are coupled together along 
their equilateral sides by third and fourth panels. The third and fourth 
panels are each preferably three-sided, with two long sides converging at 
one end and extending in a convex manner symmetrically about a central 
axis to the other end, where they meet the third side which is 
perpendicular to the central axis. A fifth panel having an opening for 
mounting a loudspeaker therein is mounted between the respective 
hypotenuses of the first and second panels. 
A better understanding of the features and advantages of the present 
invention will be obtained by reference to the following detailed 
description of the invention and accompanying drawings which set forth an 
illustrative embodiment in which the principles of the invention are 
utilized.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is an audio loudspeaker enclosure having surfaces 
which resonate across a band of low frequencies produced by the 
loudspeaker, thus enhancing the quality of low frequency sound 
reproduction. Referring to FIG.. 1, the basic components of the enclosure 
10 are top panel 12, bottom panel 14, front panel 16, left panel 18, and 
right panel 18'. 
The left panel 18 is made of rigid material such as 3/4" fir stock. Panel 
18 has three edges 22, 24, and 26. Edges 22 and 24 converge at one end of 
the panel and extend as convex curves in symmetry about the central 
longitudinal axis of the panel. The third edge 26 is perpendicular to the 
central axis and has a notch 28 for coupling with the front panel 16. A 
sound port 30 may also be provided in left panel 18. The right panel 18' 
is identical to left panel 18, having edges 22', 24', 26'. 
The front panel 16 is also made of a rigid material, and has elliptical 
openings 32 for the mounting of loudspeakers. The front panel 16 has two 
short sides 34, 36 each having a tab 38, 40, respectively, to couple with 
the corresponding notches 28, 28' in panels 18, 18'. The front panel 16 
also has two long sides 42, 44. The purpose of the front panel is 
primarily as a loudspeaker mounting member, although some structural 
support is gained by attaching the top panel 12 and bottom panel 14 to the 
front panel 16. 
The top panel 12 and bottom panel 14 are preferably identical and opposing 
equilateral right triangles. The front panel 16 is mounted between the 
hypotenuse of top panel 12 and the hypoteneuse of bottom panel 14. The top 
panel 12 and the bottom panel 14 are coupled together along left panel 18 
and right panel 18'. Thus, the top panel 12 and bottom panel 14 must be 
flexible enough to conform to the convex edges of the left panel 18 and 
right panel 18', and the top and bottom panels are flexed outwardly, as 
shown in FIG. 2, as a result of the coupling. This creates a pair of sound 
ports 54, 56 between the front panel 16, and top panel 12 and bottom panel 
14, respectively. 
Ideally, the hypotenuse of top panel 12 and bottom panel 14 should be as 
long as possible to allow the surface of each panel to develop resonance 
at the lowest possible frequencies. The lengths required to resonate 
particular frequencies can be determined from the well-known wave 
relationship .nu.=f.lambda., where .nu.=wave velocity, f =wave frequency, 
and .lambda.=wavelength. For example, given that the speed of sound in air 
at 70.degree. F. and 1 atmosphere .nu.=1130 feet/second, then panel 
resonance at 20 Hz (lowest audible frequency to the human hear) is 
developed across a length of 56.5 feet (1130 feet/second .div.20 
cycles/second). Obviously, such a large structure would prove impractical 
for most applications. In practice, the use of quarter wave resonance will 
permit reasonable sizing of the enclosure and still obtain effective 
resonance quality. A preferred construction takes into account 
commercially available materials, such as 4'.times.8' sheets of plywood 
stock. A 1/4" thick, 4'.times.8' sheet of marine grade Douglas Fir plywood 
yields good results. From such stock, three panels may be cut, two of 
which have a hypotenuse of 68". At this length, quarter wave resonance can 
be developed at 49.9 Hz. Additionally, a panel with an 8' hypotenuse and 
identical 5'8" sides may be cut from the sheet, and an 8' hypotenuse 
develops quarter wave resonance for 35.3 Hz. It should be noted that the 
calculated frequencies are for peak resonance only. In practice, resonance 
is heard at frequencies well below the peak value. Advantageously, the 
enclosure is positioned in a standard room relative to the corner of the 
room such that the right angle corners of top panel 12 and bottom panel 14 
correspond to the right angle corner of a room (not pictured), such that 
the effective enclosure size is increased by making use of the walls to 
reflect rearward travelling sound waves and gain the benefit of 
reverberation to enhance the sound quality. 
It should be understood that the invention is not intended to be limited by 
the specifics of the above-described embodiment, but rather defined by the 
accompanying claims.