US3739096A - Loudspeaker system having a cardioid directional response pattern - Google Patents

Loudspeaker system having a cardioid directional response pattern Download PDF

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US3739096A
US3739096A US00105908A US3739096DA US3739096A US 3739096 A US3739096 A US 3739096A US 00105908 A US00105908 A US 00105908A US 3739096D A US3739096D A US 3739096DA US 3739096 A US3739096 A US 3739096A
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loudspeaker
slit
loudspeaker system
openings
equal
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W Iding
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US Philips Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
    • H04R1/345—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means for loudspeakers
    • H04R1/347—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means for loudspeakers for obtaining a phase-shift between the front and back acoustic wave

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  • ABSTRACT A loudspeaker system, preferably in the form of a straight or concavely bent column in the or each lateral wall of which at least one slit has been formed which acts only as an acoustic resistor. This ensures that the cardioid directional response pattern remains constant over a wide frequency range.
  • the directional response pattern may be influenced by varying the location and- /or the width of the or each slit.
  • This invention relates to a loudspeaker system having a cardioid directional response pattern and comprising at least one loudspeaker built in at the front face of a substantially closed enclosure, at least one of the lateral walls of which contains a slit-shaped opening the direction of length of which is substantially at right angles to the axial direction of the loudspeaker.
  • Such a loudspeaker system is described in the published German Pat. application No. 1,270,117.
  • a number of loudspeakers are arranged in the form of a column in the front wall of an enclosure.
  • the enclosure has the shape of a prism, the lateral walls being at angles of 120 to the front wall.
  • several slits have been made which, at their rear, i.e., internally of the enclosure, have been provided with rectangular tubes, the cross-sectional area of each tube corresponding to that of the associated slit.
  • This loudspeaker system has a directional response pattern the cardioid shape of which is not maintained constant as a function of the frequency owing to the tubular slits acting as acoustic masses.
  • each slit has been covered by acoustic damping material, the shortest distance of the slit from the most effectively active part of the diaphragm of the loudspeaker being about equal to the diameter of this diaphragm, while the upper limit of the frequency at which the cardioid effect still holds is about equal to the frequency associated with a wavelength equal to the circumference of the loudspeaker.
  • This provides the advantage of ensuring a cardioid directional response pattern which is maintained substantially constant over a very wide frequency range.
  • This requires the use of an acoustic resistance as a component of the acoustic elements in order to ensure that for each frequency the phase shift of the acoustic network of the enclosure is equal to the phase shift imparted to the sound by way of the outside of the system owing to the round-about path taken. The latter phase shift varies linearly with the frequency.
  • the resonant frequency of the enclosure is made to conform with that associated with a wavelength of the order of magnitude of the loudspeaker or loudspeakers used, the directional effeet of the enclosure is optimally utilized, since starting from this frequency the loudspeaker or loudspeakers ensure the directional effect for the higher frequencies.
  • An embodiment of a loudspeaker system according to the invention is characterized in that behind and parallel to each opening there has been formed a second opening of the same shape.
  • each opening may be shifted in the direction of its width, or its width may be adjustable. In all these cases the said steps influence the cardioid shape.
  • each opening may be replaced by a large number of adjoining holes.
  • Loudspeaker systems according to the invention in the shape of a column may advantageously be mounted within a pulpit.
  • the column may have a concave shape in accordance with the dimensions of the hall.
  • FIG. 4b is a sectional view of the same enclosure placed in a corner
  • FIG. 5 is a perspective view of a loudspeaker projector according to the invention.
  • FIGS. 6a and 6b show directional response patterns.
  • FIG. 1 there is shown a pulpit which mainly comprises a desk 1 and a loudspeaker enclosure 2.
  • loudspeakers (not shown) are mounted in the shape of a column in a rear wall 3 of the enclosure.
  • slits 5 have been made in the upper face (lateral wall) of the enclosure.
  • the slits 5 have been covered by gauze 5a so that they behave as acoustic resistors.
  • buttons and switches are accommodated in a front panel 6 of the pulpit.
  • the desk part 1 is provided with a microphone 8 on a stand 7.
  • a supply voltage connection 9 is provided in a side panel.
  • the pulpit may further be mounted on removable legs 10.
  • FIG. 3 shows a modified embodiment of the pulpit of FlG.-l in which the column of loudspeakers is vertically arranged.
  • the column contains loudspeakers 13 and associated slits 12.
  • a supply voltage connection 9 is provided in a base 14.
  • FIGS. 4a and 4b show diagrammatically the manner in which a loudspeaker enclosure according to the invention may be placed.
  • the loudspeaker enclosure may contain either one loudspeaker or several loudspeakers mounted in the form of a column.
  • a loudspeaker enclosure 20 contains a loudspeaker 21 and has slits 22 and 23 formed in either lateral wall. Obviously, when the enclosure contains several loudspeakers a corresponding number of aligned slits will be provided.
  • the distance L of these slits from the most active part of the loudspeaker must be about equal to the diameter D of the loudspeaker. It is desirable for the depth H to be as small as possible.
  • the loudspeaker enclosure is placed with its rear face close to and parallel to a wall 18.
  • the slits 22 and 23 are equal in width.
  • the projector will have a directional response pattern as shown in FIG. 6a, i.e., a cardioid pattern
  • FIG. 6b shows the hyper-cardioid shape which the pattern will assume when the slits 33 are not covered.
  • a loudspeaker system having a cardioid directional response pattern comprising, at least one loudspeaker mounted at the front face of a substantially closed enclosure having lateral walls, at least one slitshaped opening located in at least one of the lateral walls, the direction of length of said opening being substantially at right angles to the direction of the axis of the loudspeaker, acoustic damping material covering each slit, each slit being located so that the shortest distance of the slit from the most effectively active part of the diaphragm of the loudspeaker is about equal to the diameter of said diaphragm, whereby the upper limit of the frequency at which the cardioid effect still holds is about equal to the frequency associated with a wavelength equal to the circumference of the loudspeaker.
  • a loudspeaker system as claimed in claim 1 characterized in that there is formed in said one lateral wall behind and parallel to each slit a second slit of equal shape.
  • each slit may be displaced in the direction of its width.
  • each slit comprises a large number of linearly disposed adjoining holes.
  • a loudspeaker system as claimed in claim 1 further comprising a plurality of other loudspeakers mounted at said front face in a line with said one loudspeaker, and a plurality of other slit-shaped openings located in said one lateral wall each with its direction of length substantially at right angles to the axial direction of its respective loudspeaker, acoustic damping material covering at least some of said other openings, and wherein the shortest distance of said other slits from the most effectively active part of the diaphragm of its respective loudspeaker is about equal to the diameter of said diaphragm.
  • a loudspeaker system as claimed in claim 6 wherein a like number of slit-shaped openings are located in a second lateral wall of the enclosure opposite said one lateral wall and in a mirror relationship to the openings in said one wall and to their respective loudspeakers, and acoustic damping material covering at least some of the openings in said second lateral wall.
  • a loudspeaker system as claimed in claim 6 wherein all of said openings are positioned with their longitudinal axes arranged in a line.
  • a loudspeaker system as claimed in claim 1 wherein said enclosure comprises a hollow cylinder with the loudspeaker mounted at one end wall and further comprising a plurality of other slit-shaped openings which, along with said one opening, are linearly aligned in a circle about the cylinder wall.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)
  • Details Of Audible-Bandwidth Transducers (AREA)

Abstract

A loudspeaker system, preferably in the form of a straight or concavely bent column in the or each lateral wall of which at least one slit has been formed which acts only as an acoustic resistor. This ensures that the cardioid directional response pattern remains constant over a wide frequency range. The directional response pattern may be influenced by varying the location and/or the width of the or each slit.

Description

United States Patent 1 Iding LOUDSPEAKER SYSTEM HAVING A CARDIOID DIRECTIONAL RESPONSE PATTERN Inventor: Wilhelmus Hermanus lding,
Emmasingel, Eindhoven, Netherlands us. Philips Corportion, New York, NY.
Filed: Jan. 12, 1971 Appl. No.: 105,908
Assignee:
[30] Foreign Application Priority Data Jan. 31, 1970 Netherlands 7001421 US. Cl 179/1 E, 181/31 B Int. Cl. G10k 13/00 Field of Search 179/1 E; 181/31 B References Cited UNITED STATES PATENTS 2,885,024 5/1959 Jordan 181/31 B June 12, 1973 2,821,260 1/1958 Shaffer 179/1 E 3,126,450 3/1964 Neil et a1 179/1 E FOREIGN PATENTS OR APPLICATIONS 908,709 4/1946 France 181/31 B 1,154,792 4/1958 France 181/31 B 1,241,240 8/1960 France 181/31 B 1,270,117 6/1968 Germany 179]] E Primary Examine,r-Kathleen H. Claffy Assistant Examiner-Douglas W. Olms Attorney-Frank R. Trifari [57] ABSTRACT A loudspeaker system, preferably in the form of a straight or concavely bent column in the or each lateral wall of which at least one slit has been formed which acts only as an acoustic resistor. This ensures that the cardioid directional response pattern remains constant over a wide frequency range. The directional response pattern may be influenced by varying the location and- /or the width of the or each slit.
9 Claims, 8 Drawing Figures ADJUSTABLE INVEXTOR WILHELMUS H. IDING PAIENIED JUN 2191s MEIZWZ ADJUSTABLE Fig.6 a Fig.6b
INVENTOR.
WILHELMUS H IDI NG LOUDSPEAKER SYSTEM HAVING A CARDIOID DIRECTIONAL RESPONSE PATTERN This invention relates to a loudspeaker system having a cardioid directional response pattern and comprising at least one loudspeaker built in at the front face of a substantially closed enclosure, at least one of the lateral walls of which contains a slit-shaped opening the direction of length of which is substantially at right angles to the axial direction of the loudspeaker.
Such a loudspeaker system is described in the published German Pat. application No. 1,270,117. In the said system a number of loudspeakers are arranged in the form of a column in the front wall of an enclosure. The enclosure has the shape of a prism, the lateral walls being at angles of 120 to the front wall. In each of the lateral walls several slits have been made which, at their rear, i.e., internally of the enclosure, have been provided with rectangular tubes, the cross-sectional area of each tube corresponding to that of the associated slit.
This loudspeaker system has a directional response pattern the cardioid shape of which is not maintained constant as a function of the frequency owing to the tubular slits acting as acoustic masses.
The invention is characterized in that each slit has been covered by acoustic damping material, the shortest distance of the slit from the most effectively active part of the diaphragm of the loudspeaker being about equal to the diameter of this diaphragm, while the upper limit of the frequency at which the cardioid effect still holds is about equal to the frequency associated with a wavelength equal to the circumference of the loudspeaker.
This provides the advantage of ensuring a cardioid directional response pattern which is maintained substantially constant over a very wide frequency range. This requires the use of an acoustic resistance as a component of the acoustic elements in order to ensure that for each frequency the phase shift of the acoustic network of the enclosure is equal to the phase shift imparted to the sound by way of the outside of the system owing to the round-about path taken. The latter phase shift varies linearly with the frequency.
When the acoustic resistance of the slits made in the enclosure is maintained constant, the above holds true for the resonant frequency of the enclosure. If this resonant frequency is made to conform with that associated with a wavelength of the order of magnitude of the loudspeaker or loudspeakers used, the directional effeet of the enclosure is optimally utilized, since starting from this frequency the loudspeaker or loudspeakers ensure the directional effect for the higher frequencies.
An embodiment of a loudspeaker system according to the invention is characterized in that behind and parallel to each opening there has been formed a second opening of the same shape. Alternatively, each opening may be shifted in the direction of its width, or its width may be adjustable. In all these cases the said steps influence the cardioid shape.
As a further alternative, each opening may be replaced by a large number of adjoining holes.
Loudspeaker systems according to the invention in the shape of a column may advantageously be mounted within a pulpit. In this case, the column may have a concave shape in accordance with the dimensions of the hall.
Embodiments of the invention will now be described,
by way of example, with reference to the accompanyaccording to the invention, placed in front of a wall,
FIG. 4b is a sectional view of the same enclosure placed in a corner,
FIG. 5 is a perspective view of a loudspeaker projector according to the invention, and
FIGS. 6a and 6b show directional response patterns.
Referring now to FIG. 1, there is shown a pulpit which mainly comprises a desk 1 and a loudspeaker enclosure 2. Four loudspeakers (not shown) are mounted in the shape of a column in a rear wall 3 of the enclosure. In order to achieve a cardioid directional response pattern, slits 5 have been made in the upper face (lateral wall) of the enclosure. The slits 5 have been covered by gauze 5a so that they behave as acoustic resistors.
Various buttons and switches are accommodated in a front panel 6 of the pulpit. The desk part 1 is provided with a microphone 8 on a stand 7. A supply voltage connection 9 is provided in a side panel. The pulpit may further be mounted on removable legs 10.
FIG. 3 shows a modified embodiment of the pulpit of FlG.-l in which the column of loudspeakers is vertically arranged. The column contains loudspeakers 13 and associated slits 12. A supply voltage connection 9 is provided in a base 14.
FIGS. 4a and 4b show diagrammatically the manner in which a loudspeaker enclosure according to the invention may be placed. The loudspeaker enclosure may contain either one loudspeaker or several loudspeakers mounted in the form of a column. A loudspeaker enclosure 20 contains a loudspeaker 21 and has slits 22 and 23 formed in either lateral wall. Obviously, when the enclosure contains several loudspeakers a corresponding number of aligned slits will be provided. The distance L of these slits from the most active part of the loudspeaker must be about equal to the diameter D of the loudspeaker. It is desirable for the depth H to be as small as possible.
In the situation shown in FIG. 4a the loudspeaker enclosure is placed with its rear face close to and parallel to a wall 18. The slits 22 and 23 are equal in width.
lel rows of slits 32 and 33 of equal size have been formed around the cylindrical wall.
If the slits 33 are covered by an adjustable slide member 34, the projector will have a directional response pattern as shown in FIG. 6a, i.e., a cardioid pattern, FIG. 6b shows the hyper-cardioid shape which the pattern will assume when the slits 33 are not covered.
Obviously, these and other intermediate shapes of the directional response pattern are obtainable if the width of the slits is adjustable. This may be effected by means of simple slide mechanisms.
What is claimed is:
l. A loudspeaker system having a cardioid directional response pattern comprising, at least one loudspeaker mounted at the front face of a substantially closed enclosure having lateral walls, at least one slitshaped opening located in at least one of the lateral walls, the direction of length of said opening being substantially at right angles to the direction of the axis of the loudspeaker, acoustic damping material covering each slit, each slit being located so that the shortest distance of the slit from the most effectively active part of the diaphragm of the loudspeaker is about equal to the diameter of said diaphragm, whereby the upper limit of the frequency at which the cardioid effect still holds is about equal to the frequency associated with a wavelength equal to the circumference of the loudspeaker.
2. A loudspeaker system as claimed in claim 1, characterized in that there is formed in said one lateral wall behind and parallel to each slit a second slit of equal shape.
3. A loudspeaker system as claimed in claim 1 wherein each slit may be displaced in the direction of its width.
4. A loudspeaker system as claimed in claim 1 wherein the width of each slit is adjustable.
5. A loudspeaker system as claimed in claim 1 characterized in that each slit comprises a large number of linearly disposed adjoining holes.
6. A loudspeaker system as claimed in claim 1 further comprising a plurality of other loudspeakers mounted at said front face in a line with said one loudspeaker, and a plurality of other slit-shaped openings located in said one lateral wall each with its direction of length substantially at right angles to the axial direction of its respective loudspeaker, acoustic damping material covering at least some of said other openings, and wherein the shortest distance of said other slits from the most effectively active part of the diaphragm of its respective loudspeaker is about equal to the diameter of said diaphragm.
7. A loudspeaker system as claimed in claim 6 wherein a like number of slit-shaped openings are located in a second lateral wall of the enclosure opposite said one lateral wall and in a mirror relationship to the openings in said one wall and to their respective loudspeakers, and acoustic damping material covering at least some of the openings in said second lateral wall.
8. A loudspeaker system as claimed in claim 6 wherein all of said openings are positioned with their longitudinal axes arranged in a line.
9. A loudspeaker system as claimed in claim 1 wherein said enclosure comprises a hollow cylinder with the loudspeaker mounted at one end wall and further comprising a plurality of other slit-shaped openings which, along with said one opening, are linearly aligned in a circle about the cylinder wall.

Claims (9)

1. A loudspeaker system having a cardioid directional response pattern comprising, at least one loudspeaker mounted at the front face of a substantially closed enclosure having lateral walls, at least one slit-shaped opening located in at least one of the lateral walls, the direction of length of said opening being substantially at right angles to the direction of the axis of the loudspeaker, acoustic damping material covering each slit, each slit being located so that the shortest distance of the slit from the most effectively active part of the diaphragm of the loudspeaker is about equal to the diameter of said diaphragm, whereby the upper limit of the frequency at which the cardioid effect still holds is about equal to the frequency associated with a wavelength equal to the circumference of the loudspeaker.
2. A loudspeaker system as claimed in claim 1, characterized in that there is formed in said one lateral wall behind and parallel to each slit a second slit of equal shape.
3. A loudspeaker system as claimed in claim 1 wherein each slit may be displaced in the direction of its width.
4. A loudspeaker system as claimed in claim 1 wherein the width of each slit is adjustable.
5. A loudspeaker system as claimed in claim 1 characterized in that each slit comprises a large number of linearly disposed adjoining holes.
6. A loudspeaker system as claimed in claim 1 further comprising a plurality of other loudspeakers mounted at said front face in a line with said one loudspeaker, and a plurality of other slit-shaped openings located in said one lateral wall each with its direction of length substantially at right angles to the axial direction of its respective loudspeaker, acoustic damping material covering at least some of said other openings, and wherein the shortest distance of said other slits from the most effectively active part of the diaphragm of its respective loudspeaker is about equal to the diameter of said diaphragm.
7. A loudspeaker system as claimed in claim 6 wherein a like number of slit-shaped openings are located in a second lateral wall of the enclosure opposite said one lateral wall and in a mirror relationship to the openings in said one wall and to their respective loudspeakers, and acoustic damping material covering at least some of the openings in said second lateral wall.
8. A loudspeaker system as claimed in claim 6 wherein all of said openings are positioned with their longitudinal axes arranged in a line.
9. A loudspeaker system as claimed in claim 1 wherein said enclosure comprises a hollow cylinder with the loudspeaker mounted at one end wall and further comprising a plurality of other slit-shaped openings which, along with said one opening, are linearly aligned in a circle about the cylinder wall.
US00105908A 1970-01-31 1971-01-12 Loudspeaker system having a cardioid directional response pattern Expired - Lifetime US3739096A (en)

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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3921016A (en) * 1973-12-12 1975-11-18 Proctor & Assoc Co Sonic signal generator and housing
US4054748A (en) * 1975-10-22 1977-10-18 Elektroakusztikai Gyar Cardioid electro-acoustic radiator
US4421957A (en) * 1981-06-15 1983-12-20 Bell Telephone Laboratories, Incorporated End-fire microphone and loudspeaker structures
FR2668015A1 (en) * 1990-10-16 1992-04-17 Piccfaluga Pierre METHOD FOR IMPROVING THE QUALITY OF THE RESTORATION OF A SOUND ATMOSPHERE, AND IMPLEMENTATION APPARATUS COMPRISING AT LEAST ONE SPEAKER EMITTING IN THREE DIRECTIONS.
US5552569A (en) * 1995-03-08 1996-09-03 Sapkowski; Mechislao Exponential multi-ported acoustic enclosure
US5588063A (en) * 1992-10-30 1996-12-24 International Business Machines Corporation Personal multimedia speaker system
US5809150A (en) * 1995-06-28 1998-09-15 Eberbach; Steven J. Surround sound loudspeaker system
US5956411A (en) * 1994-05-18 1999-09-21 International Business Machines Corporation Personal multimedia speaker system
US20100254558A1 (en) * 2009-03-20 2010-10-07 Meyer John D Loudspeaker with passive low frequency directional control
US20130272562A1 (en) * 2012-04-11 2013-10-17 Guan-Hua Tzeng Loudspeaker
US9568179B2 (en) * 2014-01-13 2017-02-14 Rockwell Automation Technologies, Inc. Modular stack light with central connectors
US10123111B2 (en) 2016-06-03 2018-11-06 Fulcrum Acoustic, LLC Passive cardioid speaker
US10422821B2 (en) 2017-04-17 2019-09-24 Rockwell Automation Technologies, Inc. System and method of identifying a module in a stack light
US11102570B2 (en) 2019-06-11 2021-08-24 Bose Corporation Auto-configurable bass loudspeaker
US11153680B2 (en) 2020-02-13 2021-10-19 Bose Corporation Stackable loudspeakers

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB388348A (en) * 1932-10-26 1933-02-23 Gen Electric Co Ltd Improvements in loudspeakers
DE968490C (en) * 1949-06-05 1958-02-27 Siemens Ag Loudspeaker group arrangement consisting of several loudspeakers built in a row in a common slat-like baffle

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3921016A (en) * 1973-12-12 1975-11-18 Proctor & Assoc Co Sonic signal generator and housing
US4054748A (en) * 1975-10-22 1977-10-18 Elektroakusztikai Gyar Cardioid electro-acoustic radiator
US4421957A (en) * 1981-06-15 1983-12-20 Bell Telephone Laboratories, Incorporated End-fire microphone and loudspeaker structures
FR2668015A1 (en) * 1990-10-16 1992-04-17 Piccfaluga Pierre METHOD FOR IMPROVING THE QUALITY OF THE RESTORATION OF A SOUND ATMOSPHERE, AND IMPLEMENTATION APPARATUS COMPRISING AT LEAST ONE SPEAKER EMITTING IN THREE DIRECTIONS.
WO1992007448A1 (en) * 1990-10-16 1992-04-30 Pierre Piccaluga Method of improving the quality of sound reproduction and apparatus for carrying out said process comprising at least one loudspeaker emitting in three directions
US5446793A (en) * 1990-10-16 1995-08-29 Piccaluga; Pierre Method of improving the quality of sound reproduction and apparatus for carrying at least one loudspeaker emitting in three directions
US5588063A (en) * 1992-10-30 1996-12-24 International Business Machines Corporation Personal multimedia speaker system
US5956411A (en) * 1994-05-18 1999-09-21 International Business Machines Corporation Personal multimedia speaker system
US5552569A (en) * 1995-03-08 1996-09-03 Sapkowski; Mechislao Exponential multi-ported acoustic enclosure
US5809150A (en) * 1995-06-28 1998-09-15 Eberbach; Steven J. Surround sound loudspeaker system
US20100254558A1 (en) * 2009-03-20 2010-10-07 Meyer John D Loudspeaker with passive low frequency directional control
US8428284B2 (en) 2009-03-20 2013-04-23 Meyer Sound Laboratories, Incorporated Loudspeaker with passive low frequency directional control
US20130272562A1 (en) * 2012-04-11 2013-10-17 Guan-Hua Tzeng Loudspeaker
US8666107B2 (en) * 2012-04-11 2014-03-04 Cheng Uei Precision Industry Co., Ltd. Loudspeaker
US9568179B2 (en) * 2014-01-13 2017-02-14 Rockwell Automation Technologies, Inc. Modular stack light with central connectors
US9845949B2 (en) 2014-01-13 2017-12-19 Rockwell Automation Technologies, Inc. Modular stack light with central connectors
US10123111B2 (en) 2016-06-03 2018-11-06 Fulcrum Acoustic, LLC Passive cardioid speaker
US10422821B2 (en) 2017-04-17 2019-09-24 Rockwell Automation Technologies, Inc. System and method of identifying a module in a stack light
US11102570B2 (en) 2019-06-11 2021-08-24 Bose Corporation Auto-configurable bass loudspeaker
US11153680B2 (en) 2020-02-13 2021-10-19 Bose Corporation Stackable loudspeakers

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FR2077430A1 (en) 1971-10-22
DE2100884A1 (en) 1971-08-12
AT308863B (en) 1973-07-25
NL7001421A (en) 1971-08-03
DE2100884B2 (en) 1976-07-22
FR2077430B1 (en) 1974-04-26

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