Sound reinforcement enclosure employing cone loudspeaker with
United States Patent 
Andrews et al.
 Patent Number:
 Date of Patent:
Jun. 6, 1989
 SOUND REINFORCEMENT ENCLOSURE
EMPLOYING CONE LOUDSPEAKER WITH
ANNULAR CENTRAL LOADING MEMBER
AND COAXIALLY MOUNTED
 Inventors: Anthony J. Andrews, Capel; Toby C.
Hunt, Rusper; John Newsham,
London, all of England
 Assignee: Turhosound Limited, England
 Appl. No.: 929,987
 Filed: Nov. 12, 1986
 Int. Cl.4 ............................................. .. HOSK 5/00
 US. Cl. .................................. .. 181/152; 181/ 145;
181/154; 181/155;181/159; 181/187; 181/192;
 Field of Search ............. .. 181/145, 150, 154, 155,
181/156, 148, 146, 152, 153, 159, 187-192;
 References Cited
U.S. PATENT DOCUMENTS
Re. 32,183 6/1986
2,167,625 8/ 1939
Hino et a1. ................... 181/192
4,040,503 8/1977 Hino et a1. ........................ .. 181/192
Yamaha White Paper, Oct. 1981, by Gary Davis &
Assocs. Acoustical Engineering, by H. F. Olson, 1940, pp. 212-245.
Primary Examiner—Benjamin R. Fuller
Attorney, Agent, or Firm-Kenyon & Kenyon
An improved sound reinforcement enclosure is dis closed which incorporates a cone-type loudspeaker operating into a generally cylindrical channel extending from the perimeter of the cone to free air. A central member is coaxially mounted within this channel, the central member having rear surfaces substantially paral lel to the surface of the cone and external surfaces which, with the internal surfaces of the channel form an annular region, the central member also having at least one coaxial internal passage forming a concentric horn
?are. Methods of coaxially mounting a high-frequency compression driver behind the magnet assembly of the loudpseaker and of mounting a second loudspeaker internally in an enclosure are also disclosed.
12 Claims, 4 Drawing Sheets
US. Patent Jun. 6, 1989 Sheet 1 of4 4,836,327
US. Patent Jun. 6, 1989 Sheet 2 of4 4,836,327 m __ _ h
US. Patent Jun. 6, 1989 Sheet 3 of 4 4,836,327
therefore consuming considerable floor space, which
SOUND REINFORCEMENT ENCLOSURE
EMPLOYING CONE LOUDSPEAKER WITH limits the locations on a crowded stage in which the monitor will ?t; reduces the floor area available to the musician; and produces a less than desirable stage pic
This application relates to sound reinforcement equipment and, more speci?cally, to improved design ture.
Despite considerable efforts devoted to the problem, no satisfactory method of reducing the size of monitor enclosures had heretofore been developed. Loudspeak
techniques for full-range enclosures.
BACKGROUND OF THE INVENTION
Many sound reinforcement applications require the accurate reproduction of live or recorded program material that has a wide frequency range, typically
10 ers of smaller diameter have been substituted (for exam ple, two 12” diameter loudspeakers for the 15” units), but only at the cost of low frequency power-handling.
Similarly, the combination of a single 12" loudspeaker and a compression driver has been employed, but only at the cost of both power handling and low frequency
40-18,000 Hz. Yet no single transducer practical for use in the art is capable of both accurately and ef?ciently reproducing this range of frequencies at high power levels. As a result, virtually all sound reinforcement systems, divide the program material into at least two separate frequency bands and provide a separate trans ducer subsystem for each band, optimized for the repro duction of its range of frequencies, the transducers pref erably mounted in a common enclosure. response which severely limits the usefulness of such a monitor.
Existing monitor designs have other known draw backs.
It is the object of a monitor enclosure to selectively amplify those sound sources of interest to the performer at whom it is aimed. To the degree that the enclosure radiates sound or “spills” beyond this area, it has a negative impact. This monitor spill will be picked up by additional microphones, muddying both the stage sound
One such application is “stage monitoring” or “fold back”.
A typical musical performance may include as many
25 and that in the auditorium, as well as lowering the gain threshold at which feedback will occur. By increasing as ?fty separate sound sources (both acoustic and elec the distracting “noise floor” above which the adjacent tronic) onstage. While a sound reinforcement system is used to amplify and to adjust their relative levels for the audience, as many as eight essentially separate sound musician must hear, monitor spill requires a compensat ing increase in the volume of his monitor, whose own increased spill initiates further rounds of escalation. reinforcement systems are required to amplify and ad just their levels for the musicians onstage.
It is therefore a desirable object to control enclosure dispersion as a method of reducing monitor spill. The prior art use of in?nite-baffle and ported designs for the cone loudspeakers provides little control over disper instrumental pitch, timbre and tone, he must be able to hear himself. For him to maintain the correct musical relationship with the balance of the ensemble he must be sion (as well as limited ef?ciency). Further, for these reasons, and because of the lack of projection typical of such designs, and the resulting rapid decay in volume able to hear them. In popular concerts, without a moni toring system, this is frequently dif?cult or impossible. with distance, such enclosures are limited to locations
One reason is the disparity between various sources in acoustic energy; ampli?ed instruments (such as elec
40 close to the subject. Horn-loading of the loudspeakers
offers potential improvements in dispersion, ef?ciency,
tric guitars and keyboards) and even unampli?ed drums and brass will overwhelm nearby voices and acoustic and projection but would also produce an unacceptable increase in enclosure height. '
An additional drawback of prior art enclosures is the these sources about the stage, which may place a source important for a musician to hear at a considerable dis
physical separation of the low-frequency and high-fre
45 quency sources, which, given the proximity of the lis tance from him. Third, only a fraction of the available sources may be relevant to any given musician. selectively for the musician those relevant sound tener, hampers intelligibility. .
It is an object of this invention to disclose improved
design techniques for loudspeaker enclosures generally,
and for monitoring enclosures in particular, which allow the mounting of conventional components in an would otherwise render them inaudible. Monitoring is also required to overcome distracting time-delayed re?ections and reverberation from the auditorium. And,
particularly in television, ?lm, and theatrical produc
tions, it may also be necessary for the performer to
55 synchronize his actions with a prerecorded soundtrack.
There has, therefore, long been a demand for special ized sound reinforcement equipment for monitoring purposes, and particularly for suitable sound reinforce enclosure with an unprecedented reduction in both frontal area and total volume, while markedly reducing
spill, improving projection, and increasing both ef? ciency and intelligibility.
least one cone-type loudspeaker operating into a chan nel extending forwardly towards an outlet to free air. ment enclosures both of minimal size and capable of generating the required high sound pressure levels.
Monitor enclosures of this type typically employ two
15" diameter cone-type loudspeakers (such as the JBL
At least one central member is inserted within the is substantially parallel to the surface of the cone and whose sides, together-with those of the channel, pro duce an annular region having a progressively increas 2220) in an in?nite-baffle or ported arrangement for frequencies below 1200-1600Hz, in combination with a
65 horn-loaded compression driver (such as the JBL 2445] with 2385A) for frequencies above l200—l600Hz. This ing crosssectional area which couples the volume de fined by the cone with the outlet to free air.
At least one coaxial opening in the central member is produces an enclosure having a large frontal area and provided, extending from the volume de?ned by the
shape of the cone to the outlet to free air, and of pro
gressively increasing crosssection.
The resulting apparatus provides a marked improve
perimeter to a resilient “surround” 25 of rubber or simi lar material, in turn attached to a generally circular frame 26. Frame 26, which may be of stamped or cast ment in dispersion, ef?ciency and projection while re quiring an increase in enclosure depth which is only a fraction of that required by prior art methods.
By mounting the high-frequency compression driver
to the rear of the loudspeaker magnet assembly such that its outlet aligns with the central opening in the construction, includes struts 27 which terminate in a circular ?ange 28 which maintains a magnet assembly
23 at a ?xed distance from the plane 45 of the front face of frame 26. Magnet assembly 23 is of circular shape, providing a cylindrical opening in which voice coil form 22 may be driven along the central axis of the latter, and by employing a horn ?are which may pass through the center of the loudspeaker voice coil form, the high frequency driver and horn may be mounted
coaxially with the loudspeaker, reducing enclosure size and improving intelligibility.
loudspeaker by suitable exitation of the coil wrapped around it.
In prior art in?nite baf?e designs, the frame 26 is bolted in a pass hole of suitable diameter, directly to the front face of the enclosure.
Both the mid-high information which radiates from the region of the loudspeaker cone immediately sur
The improved apparatus of the present invention provides an outer casing 30, cast or formed of any suit rounding the voice coil and the high frequency output of the compression driver and its associated horn couple able material, having a circular opening whose walls 32 de?ne a cylindrical channel extending forward from the to the horn ?are formed by the passage in the central member.
By mounting a second loudspeaker within the enclo perimeter of the loudspeaker cone 24 to free air. Casing
30 is attached to the enclosure by bolting ?ange 31 to bracket 9, and loudspeaker 75 is bolted to casing 30. sure centered on a common longitudinal plane with the
?rst, and by ducting its output to free air, the width of the enclosure can be halved relative to prior art enclo sures with the same components. 25
Preferably, the diameter of the opening in casing 30 gradually increases, forming a horn ?are.
Within this cylindrical channel or ?are, the improved apparatus of the present invention provides a coaxial
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general view of an enclosure employing
the improved techiques the present invention.
central member 36, which is preferably mounted by struts 39 of streamlined section, although other mount ing methods may be employed.
The exterior surface of central member 36 and the
FIG. 2 is a side elevation of the enclosure of P161
FIG. 3 is a longitudinal section through the enclosure of FIG. 1, with the various drivers removed. internal surface 32 of casing 30 form an annular region
40 of increasing crossectional area which couples the volume formed by the rear surface 35 of central mem
FIG. 4 longitudinal section of FIG.3, with a loud
_ ber 36 and loudspeaker cone 24 with free air.
It be understood in the context of US. Pat. No.
FIG. 5 is a longitudinal section of FIG.3, with the
improved of the present invention.
FIG. 6 is a longitudinal section through the improved
Re:32,l83 that the performance of the central member is a product of the change in crosssectional area produced by the combination of the member itself and the channel apparatus of invention, showing the annular central me and coaxial mounting of the high frequency driver. in which it is located, and that changes in the pro?le of either or both may be made.
FIG. 7 is a front elevation of FIG. 6.
Refer now to FIGS. 1-5, views of an enclosure adapted for monitoring purposes and employing th
The rear surface 35 of the central member 36 is gener ally parallel to that of cone 24. In the illustrated embodi
DETAILED DESCRIPTION ment, the clearance between the cone 24 and the central member 36 at the closest point 37 is approximately i", although this distance can be increased. improved techniques of the present invention. '
Like typical prior art monitor enclosures, the enclo sure of FIG.1—5 employs two 15" loudspeakers and one
Preferably, the distance between the central member
36 and cone 24 progressively increases from the smallest diameter of the former at 37 towards the perimeter of
2" compression driver. Unlike such enclosures, only the latter. one 15" driver is visible.
Referring now to FIG.3, it will be apparent that the enclosure comprises a top 2, rear 5, and bottom 6 of
appropriate material (typically Baltic birch plywood),
together with side 1 of FIG.1 (and a second side not visible in these views). Unlike typical prior art enclo
Preferably, the transition between the rear surface 35 of the central member 36 and its forwardly tapering portion 33 is located in a plane forward of the mounting plane 45 of the loudspeaker.
Preferably, the surfaces of a section 34, that section between the rear surface 35 and forwardly tapering sures, internal partitions 3, 7, and 63 of the same mate rial form plural internal compartments.
Referring to FIGS, the visible 15" loudspeaker 75 is mounted to a casing 30, which, in turn, is mechanically attached to the enclosure via brackets 9.
55 section 33, all of central member 36, are substantially parallel to the adjacent surfaces 32 of casing 30, such that a plain wave tube of constant crossectional area is formed in that area.
Referring now to FIG.6, the construction of the im proved apparatus of the present invention will be de- ' scribed.
Loudspeaker 75 is a conventional 15" unit such as the
Preferably, the diameter of this passage 41 progres sively increases toward the outlet, forming a second, concentric horn ?are.
Turbosound LS-l503 or other suitable 3" voice coil
loudspeaker (although suitable loudspeakers having
other voice coil sizes may be employed) comprising a cone 24 of stiff pulp or similar material, attached at its center to a cylindrical voice coil form 22, and at its
FIG. 5 and FIG. 6 thus illustrate an annular central member 36 inserted within a generally cylindrical chan nel extending from the perimeter of a cone loudspeaker
75 to an outlet to free air, the central member having rear surfaces 35 substantially parallel to the surface of
loudspeaker cone 24; external surfaces 34 and 33 which, with the internal surfaces 32 of the channel, form an annular region 40; and internal surfaces 38 which form
mounted by means of a threaded exterior portion 12 which engages the threaded opening 11 of driver 10.
Flare 15 is also illustrated as having a ?rst portion 11 of progressively increasing crosssection, and a section a concentric horn ?are 41.
In contradistinction to classical horn-loading theory and experience which require an increase in total path length producing an unacceptable increase in enclosure size, the improved apparatus of FIG.5 and 6 produces marked improvements in ef?ciency and projection with an increase in overall path length of less than four inches, a small fraction of the requirements for a tradi tional horn ?are. Although approximately one-third the length of the apparatus disclosed in U.S. Pat. No.
Re:32,l83, the apparatus of FIG. 5 and 6 further pro portion 17 whose crosssection increases at a greater rate.
The illustrated mounting of the compression driver consumes neither additional frontal area nor does it require an increase in the depth of typical enclosures.
While classical theory teaches against abrupt changes in
cross-sectional area, the abrupt increase at the transition between horn ?are 15 and the horn ?are formed by the inner surfaces 38 of annular central member 36, which is
required to couple high-mid frequencies radiated by the
vides the same absence of undesirable coloration.
Further, the improved apparatus of the present inven inner portion 24B of cone 24, has not been found to have an unacceptable effect. In fact, the horn ?are formed by the inner surfaces 38 of annular central mem tion extends the usable frequency response of the 15" loudspeaker by exploiting a particular property of cone loudspeakers. Such loudspeakers behave as true pistons at lower frequencies, with the cone displaced linearly along the central axis of the loudspeaker, but at progres sively higher frequencies, sound radiates from progres sively smaller regions centered around the voice coil.
The concentric horn ?are 41 formed by the interior ber 36 has been found to improve not only the high-mid frequency performance of the loudspeaker but the per formance of the compression driver/horn ?are combi nation as well. method of mounting a second loudspeaker in the enclo sure. surfaces 38 of annular central member 36 efficiently
couples these high frequencies. Accordingly, the inner;
Referring to FIGA- it will be seen that internal parti tion 3 serves as a mounting surface for a second 15" diameter of the central horn ?are 41 exceeds that of the minimum diameter of the cone 24 at the voice coil form
22, such that the inner portion 24B of the cone 24 falls loudspeaker 65 (here illustrated as an Electrovoice
EVMlSB) which radiates downward through pass hole
4 into the volume 69 formed between partition 3 and within it.
The improved high frequency response of the loud speaker allows raising the crossover point between it
30 enclosure bottom 6. Port 8 provides an outlet for the acoustic output of loudspeaker 65. Partition 63 separates the compartments for loudspeaker 75 and loudspeaker
65, each of which form an acoustically closed chamber and the compression driver, allowing an increase in the
power-handling ability of the latter.
The apparatus of the present invention brings this for loading the rear of the drivers.
While a more conventional front (or rear) loading arrangement can be used to couple the acoustic output unique combination of advantages to any existing con ventional loudspeaker with a single component which is simple and inexpensive to fabricate.
It will be understood that additional concentric pas sages may be formed in central member 36, for example, by the insertion of a solid'member in internal horn ?are of the second loudspeaker 65 to free air via the duct, preferably the improved technique disclosed in US.
Pat. No. Re:32,l83 is employed. The partitions 3 and 7 which form the duct are installed so as to produce the required ?rst volume 69 of progressively decreasing crosssection, a restricting throat 67, and a second vol ume 68 of progressively increasing cross-section termi within the ?rst.
Other diaphragm shapes and drivers may be em
45 nating in a port 8 to free air. In addition to the unique bene?ts in efficiency, projection, and absence of unde
A second aspect of the invention resides in an im proved method of mounting high-frequency compres sion drivers.
In prior art monitor enclosures, the compression driver and its associated horn ?are is located adjacent to the cone loudspeakers. This has the disadvantage of increasing the frontal area of the enclosure. The physi
cal separation of the drivers also hampers intelligibility.
The coaxial mounting of the compression driver for sirable coloration which attend the use of this tech nique, the resulting duct shape serves to minimize the height of the enclosure by minimizing the thickness of the duct in the same region where maximum depth is
required by the forwardly-radiating drivers.
While the duct could be placed on any side of the enclosure, its location on the bottom has the added advantage of coupling low frequencies to the floor on which the enclosure sits, producing further ef?ciency ward of cone 24 would serve to mitigate both problems, but at the cost of signi?cantly increasing total enclosure
Referring to FIG.5 it will be seen that the improved gains.
In contrast to prior art in?nite baffle and ported en closures that place dual loudspeakers in a side-by-side arrangement doubling the frontal area of the enclosure, apparatus of the present invention mounts the compres the enclosure illustrated in FIG. 1-5 locates the second sion driver 10 (here illustrated as a Beyma CPSSO) im mediately behind the magnet assembly 23, with the
‘loudspeaker internally, behind the forwardly-radiating
drivers and on a common longitudinal plane, and cou driver outlet 11 in alignment with the cylindrical open ing in magnet 23. ples the acoustic output of the former to free air by means of a duct extending parallel to one outer surface of the enclosure. The resulting enclosure presents one ing, is fabricated with an external diameter which al lows its insertion through the cylindrical volume 21 interior to voice coil form 22, such that movement of the voice coil is not impeded. Flare 15 is illustrated as
65 half the frontal area, with a minimal increase in cros ssection, as well as improving both the ef?ciency and projection of the second loudspeaker over prior art infinite baf?e designs.
The illustrated embodiment employs a passive cross over between loudspeaker 75 and compression driver
dinally extending member increasing in a direction par‘ allel to a longitudinal direction of said longitudinally
10 at or above 2400Hz and an active crossover between them and loudspeaker 65 at approximately IOO-lSOHz. extending member along the free space defined by said cone diaphragm and said rear portion of said longitudi
Other crossover points and arrangements can be em
. nally extending member.
4. The sound projection apparatus according to claim
In sum, the disclosed improved design techniques for
1, said member having a front portion, which is tapered loudspeaker enclosures generally, applied to the moni towards said acoustically open front end of said chan tor enclosure illustrated in the Figures, allow the mounting of the same drivers in an enclosure with an nel.
5. The sound projection apparatus according to claim unprecedented reduction in both frontal area and total
volume, while markedly reducing spill, improving pro jection, and increasing both ef?ciency and intelligibil
4, wherein said member tapers more abruptly towards said loudspeaker than towards said acoustically open front end of said channel. ity. These techniques allow the use of stock drivers and
6. The sound projection apparatus according to claim add little to the cost of the enclosure itself.
While one embodiment is illustrated, variations within the spirit of the invention will be apparent to
5, said front portion of said member beginning to taper toward said acoustically open front end of said channel at a point substantially forward of a forward edge of those of skill in the art, and should not be understood as said cone diaphragm. limited except by the claims.
7. The sound projection apparatus according to claim
These techniques may be applied individually or in
5 or 6, a section of said annular region de?ned between combination. While their advantages are described in said exterior sides of said member and said acoustically the context of monitor enclosures it will be apparent closed sides of said housing de?ning said channel being that they may be applied to sound reinforcement enclo of substantially ‘constant cross-sectional area immedi sures more generally to decrease the frontal area and volume of an enclosure while improving ef?ciency,
25 ately forward of a point where said rear portion of said projection, and intelligibility. One application is enclo sures for permanent installations in existing ornamental member becomes more abruptly tapered toward said
interiors, and another temporary installations for con
8. The sound projection apparatus according to claim
1, 2, 4 or 5, said loudspeaker having a magnet assembly certs, stage plays, and television performances; both of including a coaxial central opening, said sound, projec which place a premium on minimizing the frontal area of the enclosures. tion apparatus further including a high frequency com
What is claimed is: pression driver having an outlet, said driver located coaxially and behind said magnet assembly, such that de?ning a longitudinally extending channel enclosing a free space, said channel having an acoustically open
35 front end and an acoustically closed rear end and acous said outlet and said central opening are aligned.
9. The sound projection apparatus according to claim
8, and further including a horn ?are coaxially mounted within said central opening of said magnet assembly and tically closed sides; a loudspeaker having a centerdriven cone diaphragm, said cone diaphragm de?ning a sub stantially frustoconical shape thereby de?ning a sub stantially frustoconical volume and operating into the channel at the rear end of said channel; and a coaxial longitudinally extending member within the channel directly in front of the loudspeaker to restrict the free space within the channel, said member having a longitu» dinal axis and further having exterior sides, said exterior
45 sides and said acoustically closed sides of said housing de?ning an annular region extending from said volume to said acoustically open front end, said channel increas ing in cross-sectional area toward said open front end, said member having a rear portion, which is tapered towards said loudspeaker and projects into said volume, said member further including at least one coaxial longi extending from said outlet to said volume de?ned by said center-driven cone diaphragm.
10. The sound projection apparatus according to claim 1 or 2, said loudspeaker having a voice coil form disposed centrally in said loudspeaker and said cone diaphragm having a minimum diameter at said voice coil form, said coaxial longitudinally extending passage way having a diameter at said rear portion of said mem ber substantially greater than the minimum diameter of said cone diaphragm at said voice coil form.
11. The sound projection apparatus according to claim 5, said loudspeaker having a voice coil form dis posed centrally in said loudspeaker and said cone dia phragm having a minimum diameter at said voice coil form, said coaxial longitudinally extending passageway tudinally extending passageway, said passageway in creasing in cross-sectional area toward said open front end and extending between said volume and said acous having a diameter at said rear portion of said member substantially greater than the minimum diameter of said cone diaphragm at said voice coil form. tically open front end, said passageway opening rear
wardly centrally into said volume along the longitudi
nal axis of said member.
2. The sound projection apparatus according to claim
1, wherein said rear portion is of part frustoconical
3. The sound projection apparatus according to claim
12. The sound projection apparatus according to claim 9, said loudspeaker having a voice coil from dis posed centrally in said loudspeaker and said cone dia phragm having a minimum diameter at said voice coil
form, said coaxial longitudinally extending passageway
having a diameter at said rear portion of said member substantially greater than the minimum diameter of said
1 or 2, a distance between said loudspeaker cone dia= phragm and a surface of the rear portion of said longitu cone diaphragm at said voice coil form.
* * * * *
UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION
PATENT NO. 2
June 6, 1989
ANDREWS, et a1
It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:
Col. 3, line 33, after "FIG. 4", insert ——is the——.
Col. 3, line 34, after "speaker" insert —-installed——.
Col. 3, line 35, change "a" to ——the——.
Col. 3, line 36, after "improved" insert ——apparatus——.
Col. 3, line 38, after "of" insert ——the present——.
Col. 3, line 38, change me" to —-member——.
Signed and Sealed this
Seventh Day Of August, 1990
HARRY F. MANBECKv JR.
Commissioner of Patents and Trademarks
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