360 Degree speakers

A 360 degree, in-phase audio propagation system utilizating sound propagation in conjunction with various types of active reflectors. In a first embodiment two bass speakers or woofers are mounted in an air-tight casing, the first speaker being mounted internal to the casing and facing outwardly through an aperture, the second speaker being mounted colinear with the first speaker. The casing is supported so that the first speaker is spaced from the floor facing downwardly whereby sound is reflected in a 360 degree pattern from the floor. The two speakers are driven out of phase with each other so that air within the chamber is alternately compressed and rarefied in accordance with a speaker driving signal, thereby preventing either speaker from resonating or overreacting to the driving signal. Sound from the front of the first speaker combines with and is reinforced by sound from the back of the second speaker thereby providing essentially a 360 degree propagation pattern. In one embodiment the second speaker is mounted so as to face the back side of the first speaker. In a further embodiment two dome-type speakers face each other and are spaced a predetermined distance apart. The compressed and rarefied air created by the speaker surfaces interreacts so that sound energy is propagated laterally or normally with respect to the longitudinal axes of the speakers, thereby providing a 360 degree, in-phase propagation pattern having clarity and imaging characteristics heretofore unobtainable by conventional systems. Also, there is found a greater vertical dispersion of the higher frequencies as the confronting dome surfaces of the drivers approach, or contact, one another.

FIELD OF THE INVENTION 
This invention relates to audio speaker systems and specifically to audio 
speaker systems having a 360 degree, in-phase dispersion pattern. 
BACKGROUND AND SUMMARY OF THE INVENTION 
A need for 360 degree propagation of sound energy by a sound reproduction 
system is essential if realistic reproduction of live sound propagation is 
to be effected. Virtually all live sources of music propagate sound as if 
a pebble were dropped in a three-dimensional pool. Many instruments and 
even human voices propagate with a greater intensity in the forward 
direction than in other directions. However, energy contributing to 
quality and loudness is propagated in all directions and arrives at a 
listener as reflections. The phase relationships of these direct and 
reflected sound waves allow a listener to locate a sound source respective 
its location. Many manufactures have attempted 360 degree propagation in a 
horizontal plane; the need for vertical 360 degree dispersion has not been 
demonstrated. Some have attempted 360 degree propagation by aiming a 
plurality of speakers in a plurality of directions about a circle. Some 
systems have placed all but one speaker facing backwards in order to 
reflect sound energy from a back wall, thereby attemping to achieve a 360 
degree effect. In all of these systems, sound from each source is 
initiated out-of-phase with respect to sound from the other sources due to 
the physical displacement of each speaker with respect to the other. All 
sound waves initiated by a live sound source are by definition in phase. 
It is this phase relationship that a good sound system tries to accurately 
reproduce. One way of accomplishing this is to effect 360 degree, in-phase 
propagation at a sound source, but in practice the desired high level of 
realism is not achieved. 
A speaker system of the present invention provides a 360 degree propagation 
which does achieve a high level of realism by utilizing any of various 
types of active reflectors. 
In one aspect of the invention, a first dome-type speaker having a 
longitudinal axis is positioned so that its longitudinal axis is normal to 
a surface spaced so as to provide an active reflector for sound propagated 
by the first speaker at a point touching the surface to less than two 
inches spaced therefrom. The spacing limitations respecting the active 
reflector are critical to both vertical dispersion and sound pressure 
level as well as horizontal dispersion. Within the spacing constraint of 
two inches, a dramatic increase in sound pressure level and excellent 
horizontal and vertical dispersion is observed at distances corresponding 
to one-quarter wavelength of the input sine wave, but even at touching (or 
even at a somewhat negative distance, i.e., compression) a marked 
improvement in these parameters is found compared to available speakers. 
In particular, there is found a radical increase in vertical dispersion of 
the higher frequencies (i.e., greater than 3000 Hertz) as the spacing is 
decreased to touching. 
In accordance with the principles of the invention, the reflecting surface 
could be a plane surface, a parabolic surface focused at a point within 
the prescribed distance, or a second dome-type speaker, the two speakers 
being driven in phase with each other and oriented so that their 
longitudinal axes are colinear. A speaker system as above described 
results in sound waves propagated from the first dome speaker interacting 
with sound waves coming from the second surface so as to produce a 360 
degree, in phase propagation pattern normal to the longitudinal axis of 
the first speaker. The speakers could be oriented so that their 
longitudinal axes are not colinear, thereby providing a system having 
directional propagation characteristics while still maintaining the 
advantages of in-phase propagation. 
According to another aspect of the invention, an audio speaker system 
comprises a first speaker having a forward sound propagating surface and a 
second speaker having a forward sound propagating surface, each speaker 
being oriented so that their forward surfaces face each other, and 
operating means for driving the first and second speakers simultaneously. 
The speakers are placed sufficiently close to each other so that sound 
energy propagated from one interacts with sound energy propagated from the 
other, thereby providing 360 degree, in-phase propagation. If the speakers 
are mounted so that their longitudinal axes are colinear, then the 360 
degree sound propagation will be substantially normal to the longitudinal 
axes. In a specific embodiment, two dome-type speakers, which could be 
either mid-range speakers or high frequency speakers (tweeters), are 
oriented so that the domes are facing each other, and touching or spaced 
from each other no greater than two inches in the case of the mid-range 
and one inch in the case of the tweeter. More specifically, a distance 
from touching to two inches in the general range, from a frequency of 250 
Hertz to 20,000 Hertz, whereas for speakers operating in the range of 
1000-20,000 Hertz, the distance is preferably from touching to one inch. 
The two speakers are driven in phase with each other so that sound waves 
from each act as an active reflector for sound waves of the other. The 
alternate compressing and rarefying of air contained between the two 
closely adjacent speakers provides an in-phase, 360 degree outwardly 
propagating sound wave having clarity and imaging characteristics 
heretofore unobtainable in conventional speaker systems. 
According to a further embodiment of the invention, an audio speaker 
system, which in the below-described embodiment has been found to be 
particularly useful with respect to a bass speaker system, utilizes a 
casing having a first and second aperture. A first speaker having front 
and rear sound propagating surfaces is positioned internal to the casing 
so that its front surface faces outwardly through the first aperture. It 
is mounted in sealing contact with the first aperture, its rear surface 
being in reactive contact with an air chamber partially defined by the 
casing. A second speaker also having front and rear sound propagating 
surfaces is positioned over the second aperture so that its front surface 
faces into the air chamber and is in reactive contact therewith, its rear 
surface facing outwardly from the casing. The two speakers can be mounted 
so that their longitudinal axes are colinear. The casing and the two 
speakers define a substantially air-tight chamber. The first speaker and 
second speaker are driven by the same source, each being driven 180 
degrees out-of-phase with respect to the other. The case can be spaced 
apart from a floor so that the first speaker is directed downwardly, 
thereby resulting in propagation from the rear surface of the second 
speaker having a slightly broader frequency propagation spectrum than that 
of the first speaker floor reflected spectrum due to selective higher 
frequency absorption by most floor surfaces. This reflected sound combines 
with sound propagated from the rear face of the second loud-speaker, 
thereby providing a 360 degree propagation system. The two speakers can be 
woofers, and when oriented according to the invention as above-described, 
provide 360 degree propagation of sound between 200 Hz and 600 Hz, 
frequencies below 200 Hz being generally considered non-directional. Since 
the air chamber is substantially air-tight, one can appreciate that a 180 
degree phase mismatch between the two speakers will result in air within 
the chamber being alternately compressed and rarefied, each speaker 
extending inwardly into the chamber at the same time and extending 
outwardly from the chamber at the same time. It is this constant 
compression and rarefaction that prevents resonances and speaker 
over-excursions frequently experienced by conventional speaker systems. 
The 180 degree phase mismatch also results in back emf generated by each 
speaker canceling that of the other speaker at the driving source, thereby 
eliminating undesirable reflections from entering the driving source. The 
360 degree propagation of this speaker system combined with the tendency 
of the closed air chamber to prevent unwanted speaker excursions, provides 
a realism heretofore unobtainable by conventional speaker systems. 
In a further aspect of the invention, the two woofers as previously 
described are combined in a speaker system containing two mid-range 
dome-type speakers oriented as above-described and two tweeter dome-type 
speakers also oriented as above described, so that the longitudinal axes 
of all speakers are colinear with respect to each other. This speaker 
system provides 360 degree, in-phase sound propagation having clarity and 
imaging characteristics heretofore unobtainable by conventional systems.

DETAILED DESCRIPTION 
As required, detailed illustrative embodiments of the invention are 
disclosed herein. These embodiments exemplify the invention and are 
currently considered to be the best embodiments for such purposes. 
However, it is to be recognized that other speaker configurations and 
phase relationships could be utilized in conjunction with the principle of 
achieving 360 degree, in-phase propagation by active reflectors. 
Accordingly, the specific embodiments disclosed are representative in 
providing a basis for the claims which define the scope of the present 
invention. 
As previously explained, the invention discloses various speaker systems in 
which an active reflective means is utilized to propagate sound energy 
outwardly. In a first embodiment of the invention two bass speakers are 
utilized and mounted in a case so that their longitudinal or 
symmetry-defining axes are colinear, the case and speakers defining a 
substantially air-tight chamber. The speakers are positioned so that one 
faces outwardly from the case and one faces inwardly into the case, each 
speaker being in reactive contact with air within the chamber. The 
speakers are operated 180 degrees out of phase with each other so that air 
within the chamber is alternately compressed and rarefied. This alternate 
compression and rearefaction prevents the speakers from resonating or 
overreacting to input signals, thereby more accurately reproducing 
relatively low frequency input signals. 
Referring to FIG. 1, a case in the form of a cube 20 is provided, the cube 
20 having an aperture formed in an upper face 22 and a lower face 24. An 
upper speaker 26 is mounted in sealing contact with the upper aperture and 
a lower speaker 28 is sealing contact with the lower aperture. Legs 30 are 
provided to raise the lower speaker 28 from a floor, thereby allowing 
sound propagated from the speaker 28 to be reflected downwardly to and 
upwardly from the floor. It is felt that this particular mounting 
arrangement is especially useful when the upper and lower speakers 26 and 
28 are bass speakers or woofers. In a first embodiment the speakers are 
mounted as shown in FIG. 2 whereby the front surface 32 of the upper 
speaker diaphragm 34 faces into an air chamber 36 partially formed by the 
cube 20, and the front surface 38 of the lower speaker diaphragm 40 faces 
outwardly from the air chamber 36. The cube 20, upper speaker 26 and lower 
speaker 28 are constructed and mounted so that the air chamber 36 is 
substantially air-tight. The upper and lower speakers 26 and 28 are 
oriented so that their longitudinal axes are substantially colinear as 
shown at 42, although angled longitudinal axes could be utilized to 
achieve special effects. As one can appreciate by referring to the two 
speakers 26 and 28 shown in FIG. 2, if their respective diaphragms 34 and 
40 move at the same frequency but in a 180 degree out-of-phase 
relationship with respect to each other, then the upper diaphragm 34 will 
be at its furthest excursion point into the chamber 36 at the same time 
that the lower diaphragm 40 is at its furthest excursion into the air 
chamber 36. At this point the air contained within the chamber 36 will be 
compressed slightly with respect to an ambient pressure. Likewise, when 
the speaker 26 is driven so that the upper speaker diaphragm 34 is at its 
furthest excursion outwardly from the air chamber 36, and the lower 
speaker diaphragm 40 is also at its furthest excursion outwardly from the 
air chamber 36, then the air within the chamber 36 will be rarefied with 
respect to the ambient pressure. Therefore as the two speakers 26 and 28 
are driven in a 180 degree phase relationship to each other, air contained 
within the air chamber 36 will be alternately compressed and rarefied in 
accordance with movement of the speaker diaphragms 34 and 40. It is this 
alternate compression and rarefaction that causes the speakers 26 and 28 
to perform in an optimum manner by preventing the diaphragms from either 
resonating or over-responding to driving signals, the compressed air 
acting as a reactive barrier to inward excursions and the rarefied air 
acting as a reactive barrier to outward excursions. Conventional speakers, 
on the other hand, tend to be noisy and sometimes have a "booming" 
characteristic due to over-excursion of the diaphragm because of 
resonances, etc. Thus the enclosed air within the chamber 36 acts as a 
damper at both excursion extremes of the speaker diaphragms 34 and 40, the 
rarefied air tending to draw the diaphragms 34 and 40 back into the 
chamber 36, and the compressed air tending to push the diaphragms 34 and 
40 outwardly from the chamber 36. Listener directed sound waves produced 
by this system propagate from the front surface 38 of the lower speaker 
diaphragm 40 and the rear surface 44 of the upper speaker diaphragm 34. 
Soundwaves propagated in the chamber 36 as a result of movement of the 
diaphragms 34 and 40 tend to cancel each other and generally are not 
perceptable to a listener. Although a cube 20 has been shown for the 
chamber 36 enclosure, other shapes could be utilized such as a rectangular 
case, cylindrical case, octagonal case, etc. In addition, the case could 
be adapted to support a plurality of additional speakers, each being 
either in phase or 180 degrees out of phase with one of the first pair of 
speakers 26 and 28. 
In order for the speaker system to perform as above described, it is 
necessary that the two speakers 26 and 28 be wired so that their 
diaphragms move 180 degrees out-of-phase with each other, that is, as the 
lower speaker diaphragm 40 is moving away from its driver 46 the upper 
speaker diaphragm 34 is moving towards its driver 48. There are two ways 
in which the speakers can be wired with respect to a driving source 50 in 
order to achieve this 180 degree phase relationship. Referring to FIG. 3A, 
if the upper speaker driver 48 is wired in series with the lower speaker 
driver 46 so that the positive terminals of each drive 46 and 48 are 
connected across the output terminals of the driving source 50, then the 
two speakers 26 and 28 will operate 180 degrees out-of-phase with each 
other and in accordance with the desired method of operation above 
described. As can be seen, each speaker 26 and 28 has a positive input 
terminal as indicated at 51 by a cross and a negative input terminal as 
indicated at 52 by a minus. A positive signal across the plus and minus 
terminals will always cause the drivers 46 and 48 to deflect their 
respective diaphragms in the same direction. Therefore, a positive voltage 
applied to the positive terminal 51 of the upper speaker 26 and a positive 
voltage applied to the negative terminal 52 of the lower speaker 28 will 
cause the diaphragms 34 and 40 of the two speakers to move oppositely with 
respect to each other. 
The two speakers 26 and 28 can also be interconnected in a parallel 
configuration as shown in FIG. 3B. A first output line 53 of the driving 
source 50 is connected to the positive terminal 51 of the upper speaker 26 
and the negative terminal 52 of the lower speaker 28, the negative 
terminal 52 of the upper speaker 26 and positive terminal 51 of the lower 
speaker 28 being connected to each other and a return line 54 to the 
driving source 50. Both the serial and parallel wiring configurations 
shown in FIGS. 3A and 3B provide a means for the speakers to be operated 
simultaneously while being driven 180 degrees out-of-phase with respect to 
each other. The 180 phase mismatch is required so that a back emf 
generated by one speaker is also 180 degrees out-of-phase with a back emf 
generated by the other speaker, the back emf's canceling each other at the 
terminals of the driving source 50. This cancelation eliminates a feedback 
into the driving source 50 frequently experienced in conventional audio 
systems, and contributes to the quality of sound reproduction obtained by 
the speakers 26 and 28. Thus, one can appreciate that while undesired back 
emf signals are canceling each other, a backward movement of the rear 
surface 44 of the upper speaker diaphragm 34 which occurs during the 
forward movement of the front surface 38 of the lower speaker diaphragm 40 
propagates a sound wave which combines and reinforces the sound wave 
propagated by the lower speaker 28, thereby resulting in an additive sound 
level with respect to a listener. 
Dome-type speakers capable of operation at mid-range and higher frequencies 
have recently become commercially available, these type of speakers being 
especially adaptable for practicing the principles of the subject 
invention in which active reflectors are utilized to obtain 360 degree, 
in-phase sound propagation. Referring to FIG. 4, an upper dome-type 
speaker 80 and a lower dome-type speaker 82 are mounted so that their 
respective domes 84 and 86 are adjacent to each other. Each dome is 
positioned so that its longitudinal axis is colinear with that of the 
other dome as represented at 88, although the axes could be angled with 
respect to each other to achieve special effects. The domes 84 and 86 are 
touching or are spaced apart less than two inches in the case of the 
mid-range speakers or less than one inch in the case of tweeters. It has 
been found that excellent results are obtained if the domes just touch 
each other at their maximum excursions during propagation of their highest 
frequency. 
The dome speakers 80 and 82 are operatively coupled to a driving means so 
that they operate in phase with each other, that is as the upper dome 84 
is in a maximally extended condition the lower dome 86 is also in a 
maximally extended condition. As the speakers are driven in the 
above-described configuration and in phase with each other, sound wave 
propagation from each dome interacts with sound wave propagation from the 
other dome thereby producing sound waves propagating outwardly in a 
direction normal to the longitudinal axes of the domes as represented at 
90, these waves being propagated in-phase and in a 360 degree pattern. 
These 360 degree, in-phase propagations provide sound having clarity and 
imaging characteristics heretofore unobtainable by conventional speaker 
systems. In-phase operation of the two dome speakers 80 and 82 can be 
achieved by wiring the speakers in parallel with a driving source 92. 
Referring to FIG. 5, the driving source 92 is connected so that a first 
output line 94 is connected to the positive terminals of each of the 
speakers 80 and 82, the negative terminals being interconnected via a 
return line 96. It has also been found that sound propagated from a single 
dome-type speaker 98, as shown in FIG. 6, will actively react with 
reflected sound from a plane reflecting surface 100 previously propagated 
by the dome-type speaker 98, the speaker being located at the 
above-prescribed distance. A speaker 98 and reflecting surface 100 as 
above-described provides a 360 degree, in-phase propagation pattern 
similar to that provided by the two dome configuration previously 
explained. In addition a parabolic reflecting surface, if focused within 
the prescribed distance as above described, will also provide an active 
reflector as required to practice the teachings of the invention. 
Utilizing the two-speaker configuration shown in FIG. 4, frequency 
dependent intensity lobes have been measured as shown in FIG. 7. The 
patterns of FIG. 7 are diagramatic only and are not representative of 
actual measurements taken either with respect to relative amplitudes or 
the number of lobes shown. However, it has been determined that the 
intensity of propagated sound energy at a predetermined distance from the 
sound source varies as a function of an azimuthal angle. For a 
predetermined propagation frequency .lambda..sub.1, at a constant distance 
from the speakers 80, the intensity might vary as shown at 110. However, 
as the frequency changes to a second predetermined frequency 
.lambda..sub.2,.vertline..lambda..sub.1 -.lambda..sub.2 .vertline. being 
relatively small, the side lobe orientation might change markedly as shown 
in phantom at 112. It is theorized that one contributor to the remarkable 
clarity and imaging apparent to a listener from speakers configured 
according to the present invention in this rapid change in frequency 
dependent intensity lobes as the frequency of the propagated sound waves 
varies. For example, as the frequency increases the frequency dependent 
lobes tend to rotate rapidly in a horizontal plane, this rapid rotation 
perhaps contributing to a realistic effect. 
A speaker system 120 containing woofers, mid-range speakers and tweeters 
configured according to the present invention is shown in FIG. 8. This 
speaker system 120 comprises a rectangularly shaped holding lattice 121 
having a cube 122 mounted in its bottom. The cube 122 supports two woofers 
123 and 124 in accordance with the FIG. 1 and FIG. 2 embodiment, the cube 
122 bottom being spaced apart from the floor by four legs 128. Both 
speakers are wired to operate 180 degrees out-of-phase with respect to 
each other as previously explained. The speakers are mounted to the cube 
122 so that their longitudinal axes are substantially vertical and 
colinear. The mid-range speaker system consists of two dome-type speakers 
comprising an upper speaker 130 and a lower speaker 132, both of which 
have their longitudinal axes colinear with those of the woofers 123 and 
124. These speakers are attached to the holding lattice 121 by horizontal 
supporting arms 133. Likewise, a tweeter system consisting of two tweeter 
dome-type speakers 136 and 138 is also connected to the holding lattice 
121 by horizontal supporting arms 140, the longitudinal axis of each 
dome-type speaker also being colinear respect to with the longitudinal 
axis of the speaker system 120 are represented at 134. Although separate 
dome-type speakers are shown for the tweeter speakers 136 and 138, and 
separate dome-type speakers are shown for the mid-range speakers 130 and 
132, a single dome-type speaker pair mounted in accordance with the 
teachings of the invention could also be utilized. In operation, and as 
above discussed, the two woofers are driven out-of-phase with respect to 
each other whereas each dome-type speaker pair is driven in phase with 
each other. Two of the speaker systems 120 above described could be spaced 
apart for stereo operation, the combination of the two speaker systems 
providing sound reproduction having a realism heretofore unobtainable with 
conventional systems.