US2904123A

US2904123A - Loud-speaker enclosures

Info

Publication number: US2904123A
Application number: US612409A
Authority: US
Inventors: Nigro John
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-09-27
Filing date: 1956-09-27
Publication date: 1959-09-15
Anticipated expiration: 1976-09-15

Description

Sept. 15, 1959 .1. NIGRO LOUD-SPEAKER ENCLOSURES 2 Sheets-8119s; 1

Filed Sept. 27, 1956 [HI] I INVENTOR. dbH/v Mame Arron/Fri.

Sept. 15, 1959 J. NIGRO LOUD-SPEAKER ENCLOSURES 2 Sheets-Sheet 2 Filed Sept. 27, 1956 INVENTOR.

JoH/v MG/PO. BY WW6 01414 (7W 2' ATTORNEY-5'.

United States Patent LOUD-SPEAKER ENCLOSURES John Nigro, Florham Park, NJ. Application September 27, 1956, Serial No. 612,409 12 Claims. (Cl. 181- 31) This invention relates to sound reproducing devices and particularly to loudspeaker apparatus comprising a housing and an electrically operable loudspeaker for translating electrical signals into sound vibrations with high fidelity.

It is well known that different electrically operable loudspeakers produce audible sounds with diiferent amounts of distortion depending upon the frequency of the sounds. Thus, speakers with small diaphragms or cones translate high frequency, e.g. 5000-l5,000 c.p.s., signals with less distortion than speakers with large diaphragms whereas such speakers with large diaphragms translate low frequency, e.g. -500 c.p.s., with less distortion than such speakers with small diaphragms. Some types of speakers operate over a relatively large range of frequencies, e.g. 6012,000 c.p.s., with low distortion, but such speakers do not provide distortionless operation at the extreme ends of the audible frequency range. Accordingly, for high fidelity operation, it is customary to employ two or more speakers, separately or coaxially, connected to the electrical signal amplifier by electrical cross-over networks which separate the signals by frequency and supply them to the speaker providing substantially distortionless operation for a particular signal. For example, one speaker, having -a large diaphragm, may be operated only by signals having frequencies in the range from 30100() c.p.s. whereas the other speaker, having a smaller diaphragm may be operated only by signals having frequencies in the range from 1000-15,000

c.p.s.

Furthermore, each speaker normally is resonant at some frequencyin the. audible range so that, unlessprecautions are taken, signals at and near the resonant frequency willbe translated in incorrect volume ratio with respect to signals of other frequencies.

The translation efficiency of a speaker without a housing or battle is 10w; In addition, a housing or baflie is desirable not only to modify the operation of the speaker at its resonant frequency but also to suppress the back waves produced by the speaker and which cause distortion depending upon the mounting and location of the speaker.

When a speaker is mounted in a housing or on a bafile its ability to produce audible sounds without distortion is alfected by the area and configuration of the face of the bafile or the housing, the presence of a'chamber in the housing which resonates in the audible frequency range, the amount of movement of the, speaker diaphragm, the air pressure on opposite sides of the diaphragm, the path'length and volume from the rear'to the front of the diaphragm and other factors. For these reasons, although known types of housings and bafiles improve the performance of speakers in certain respects, they create other problems and provide distorted performance under conditions normally encountered. For example, so-called' infinite baflle systems, which as a practical matter are v finite in size, vary in response with frequency and power due to the size of the panel on "ice which the speaker is mounted and the use of a closed chamber which is resonant at certain frequencies and which provides different air pressures on the opposite sides of the speaker diaphragm when in motion and hence a symmetrical movement of the diaphragm. Other systems employing chambers, ports, etc. cause similar difficulties. Horn type enclosures are capable of distortionless radiation only over an octave dependent upon the frequency range for which they are designed, and as the power requirements increase, the frequency range for distortionless radiation becomes smaller.

In the loudspeaker apparatus of my invention, the loudspeaker is mounted in a housing comprising a pair of chambers, one of the chambers being interconnected with the other by one-way valve means which permits air to pass from said one chamber to the other and a portion of a wall of said one chamber being formed by the diaphragm or cone of the speaker, said chambers being otherwise substantially airtight. Such an arrangement provides symmetrical loading and hence, undistorted movement of the diaphragm. In addition, the valve means prevents the occurrence of undesirable resonance in the chambers.

In the preferred embodiment of the invention, the face of the wall on which the speaker is mounted is as small as possible so as to avoid the difiiculties wln'ch are encountered with bafiies of larger area. Thus, the width of the wall or panel is made substantially or approximately equal to the width of the diaphragm.

Furthermore, in order to provide the desired coupling of the speaker to the air, the speaker is arranged so as to face the corner formed by two mutually perpendicular surfaces or a flat surface adjoining a pair of surfaces perpendicular thereto and the angle of the face of the speaker wall and the location of the speaker is such that an air column of the desired figuration is provided in front of the speaker. Preferably, the two mutually perpendicular surfaces are a corner of a room, and the fiat surface is a wall of a room and the other pair of surfaces perpendicular thereto are formed by extensions on, the housing. When the speaker faces a corner of the room, improved sound dispersion is obtained.

It is one object of the invention to provide a loudspeaker housing which will provide symmetrical loading on the loudspeaker diaphragm or cone and yet will suppress back waves produced thereby.

It is a further object of the invention to provide a loudspeaker housing which has no undesirable resonant structures.

It is a further object of the invention to provide a loudspeaker housing which, when properly positioned with respect to adjacent surfaces, will provide good speaker coupling and sound dispersion.

These and other objects of the invention will be apparent from the following detailed description of the preferred embodiments of the invention, which description should be considered in connection with the accompanying drawings in which: 7

Figs. 1-3 are respectively rear elevation, vertical section and horizontal section views of the preferred embodiment of the invention;

Fig. 4 is an enlarged cross-sectional view of one form of valve means which may be employed in the various embodiments of the invention;

Fig. 5 is a horizontal sectional view of a further embodiment of the invention; and

Figs. 6 and 7 are respectively rear elevation and vertical section views of a further embodiment of the invention.

Figs. 1-3 illustrate the preferred embodiment of the invention and are respectively elevation, vertical section, and horizontal section views. The embodiment shown in these figures is particularly adapted for use in a corner of a room and provides both good sound dispersion throughout the room and good acoustical coupling. Futhermore, the housing may be simpler because it is unnecessary to provide any extensions thereon for forming an air column in front of and below the loudspeaker.

As shown in Figs. 1-3, the loudspeaker 10, which has a conical diaphragm, is maintained so that it faces into the corner formed between two mutually perpendicular surfaces 11 and 12 of the walls of the room. The fioor 13 of the room forms a further surface which is perpendicular to the surfaces 11 and 12. Of course, the surfaces 11-13 may be formed by bafiles or extensions on the housing 14, but in order to reduce the size of complexity of the housing 14, the walls and floor of the room are utilized to provide the desired operation.

The housing 14 comprises a first wall 15 having an aperture therein which is closed by the diaphragm of the speaker 10. The front surface of the Wall 15 faces into the corner formed by the surface 11 and 12, and it tilts away from the corner from the base end 16 to the upper end 17, the surface of the wall 15 intersecting the floor 13 and hence the base wall 18 at an angle preferably in the range from 7080. In the embodiment shown in Figs. 1-3, the angle is designated by the letter a and is approximately 75 By disposing the surface of the wall 15 in this manner, an air column or cavity having the desired figuration is formed in between the center 19 of the loudspeaker and the floor 13, the air column not being surrounded on all sides but being bounded by the surfaces 11 and 12, the floor 13 and the front surface of wall 15. In general, the volume of this air column should be approximately equal to twice the volume of a cone having the shape and size of the diaphragm of the speaker 10 and approximately equal to the volume of the chamber containing the diaphragm 10. Such relationship aids in providing the desired air pressure on the opposite sides of the diaphragm on the loudspeaker 10 and in providing the desired coupling of the speaker 10 to the air. The air column acts as a loading column for the speaker and the loading may be varied by adjusting the distance of the wall from the corner formed by the surfaces 11 and 12.

The housing 14 also comprises joining walls 2025 which with the base Wall 18 and first wall 15 form a first chamber 26 containing the diaphragm of the loudspeaker 10. As mentioned above, the volume of this chamber 26 should be approximately equal to the volume of a cone having the shape and size of the conical diaphragm of the loudspeaker 10.

The housing 14 also comprises a top wall 27 which with the first wall 15, the

side walls

20 and 24, the front wall 22 and the intermediate wall form a second chamber 28.

Walls

20, 21 and 22 form a third chamber or cavity 29 and

walls

22, 23 and 24 form a fourth chamber or cavity 30. Both of the chambers 29 and are open at their upper ends, the intermediate wall 25 being cut away for this purpose so that air may pass freely from chambers 29 and 30 into and out of the chamber 28. For this reason, the chambers 29 and may be considered as separate chambers or may be considered as forming a part of the second chamber 23.

Each of the

walls

21 and 23 has substantially one way valve means 31 thereon which permits the passage of air from the chamber 26 into the chambers 29 and 30 and hence into the chamber 28 when the air in the chamber 26 is compressed by movement of the diaphragm of loudspeaker 10 toward the wall 22. On the other hand, when the diaphragm of the speaker 10 moves toward the corner formed by the surfaces 11 and 12, the valve means closes prevent ing free movement of air from the chambers 29 and 30 into the chamber 26. However, since the valve means 31 is not completely air tight when closed, there will not be a gradual reduction of air pressure in the chamber 26 during the period of operation of the speaker 10. Instead, there will be only instantaneous or short-time variations in the air pressure in the chamber 26, the time required for pressure equalization being several times greater than the period of the lowest frequency signal to be translated by the speaker 10.

The valve means 31 is shown in greater detail in Fig. 4. Although other types of valve construction may be employed, the construction shown in Fig. 4 has been found to satisfactory results and comprises a move able closing member 32 which is hinged on the chamber wall, such as the wall 21, by means of a flexible strip 33 which may, for example, be made of leather. The strip 33 is secured to the wall 21 by means of screws or nails 34 and is secured to the member 32 by means of screws or nails 35. The member 32 strikes against a cushion strip 36 secured to the wall 21 which strip 36 may, for example, be made of felt. The member 32 may be made of wood. In one embodiment of the invention, the opening in the wall 21 is three inches square, the closing member 32 is four inches square and onehalf inch thick and the member 32, when closed, is approximately one-sixteenth inch from the wall 21.

xcept for the valve means 31 and the openings be tween the chambers 28 and 29 and the

chambers

28 and 30, all of the

chambers

26, 28, 29 and 30 are substantially air-tight. The walls of the housing 14 should be relatively rigid and may, for example, be made of heavy plywood.

If the loudspeaker 10 has the ability to provide the desired reproduction over the operating frequency range, then it is unnecessary to mount additional loudspeakers in the housing 14. However, if it is desired to employ additional speakers covering different portions of the operating frequency range, such

additional speakers

37, 38 and 39, may be mounted in obturating relationship with apertures in the first wall 15 and within the chamber 28. If a plurality of speakers are employed as shown, the speaker 10 may be employed to translate signals in the range from 30-500 c.p.s., the speaker 38 may be employed to translate signals having a frequency in the range from 500-5,000 c.p.s., and the

speakers

37 and 39 may be employed to translate signals having frequencies in the range of 5,000 to 15,000, the signals being separated and supplied to the various speakers in any conventional manner.

If it is desired to employ only two loudspeakers, the

speakers

37 and 39 and their corresponding apertures in the wall 15 may be omitted, the loudspeaker 10 being used to translate signals in the lower portion of the frequency range and the speaker 38 being used to translate signals in the upper portion of the frequency range. Also, if desired to improve the operation, the speaker 38 may be enclosed at the rear side thereof by a box 40 forming a chamber 41 at the rear of the diaphragm of the speaker 38. On the other hand, the box 40 may be omitted and satisfactory operation will still be obtained.

Most of the energy of audible sounds is contained in the fundamental or low frequency waves. Accordingly, only the diaphragm of the loudspeaker which translates the lower frequency signals is required to perform relatively large excursions from a rest position and, therefore, it becomes unnecessary as a practical matter, to attempt to equalize the air pressure on opposite sides of the diaphragm of the speakers such as the speakers 3739 which translate the signals in the upper portion of the frequency range. It has been found that when provisions are made to equalize the pressure on opposite sides of the diaphragm of only the speaker which translates signals in the lower portion of the frequency range, substantially distortionless sound production is obtained over the entire audible frequency range. It is for this reason that the valve means 31 are provided only on the walls of the chamber 26.

It appears from a consideration of the operation in the apparatus shown in Figs. 1-3 that the excursions of the diaphragm of the speaker are undistorted by unequal air pressure even though the back waves are suppressed because the valve means 31 prevents the build-up of pressure at the rear of the diaphragm of the speaker 10 during rearward movement of the diaphragm, but due to the closing of the valve means 31 during the forward movement of the diaphragm, a force is applied to the diaphragm which is proportional to the force applied to the diaphragm during rearward movement thereof and caused by the resistance to displacement by the air to such rearward movement. For this reason the movement of the diaphragm of the speaker 10 is equally retarded in both directions causing symmetrical movement of such diaphragm. If the valve means 31 were omitted, rearward movement of the diaphragm of the speaker 10 would be retarded by the resistance of the air and forward movement of the diaphragm would be accelerated by expansion of the previously compressed air. The chambers 28-30 act as storage and absorbing chambers, and their combined volume preferably is at least equal to the volume of the chamber 26.

Since the excursions of the diaphragm of speakers 37--39 are relatively small, it will be apparent that they will have little effect on the operation of the speaker 10 and that they may be located in portions of the housing 14 other than those shown.

Although it will be understood that the housing 14 may have other dimensions, the dimensions of one housing which I have constructed and have found to give excellent results are as follows:

Length in inches 13 /2 29 /2 Dimensions:

The above dimensions are indicated on Figs. l-3.

If it is not possible to locate the housing of the loudspeaker apparatus adjacent a pair of mutually perpendicular surfaces, eg a corner of a. room, the embodiment shown in Fig. 5 may be employed. Fig. 5 is a horizontal section View of an embodiment which may be located adjacent a single surface 42 which may, for example, be a wall of a room. The embodiment shown in Fig. 5 is constructed in accordance with the principles described above and comprises a housing 43 containing a chamber 44 similar to the chamber 26 and a pair of

chambers

45 and 46 similar to the chambers 29 and 30. Valve means 31 are mounted on one of the walls of each of the

chambers

45 and 46 and the loudspeaker 10 is mounted in obturating relationship with an aperture 47 on a wall 48 of the housing 43. The wall 48 tilts with respect to the surface 42 in the same manner as the wall but usually the wall 48 is rectangular, as viewed from the surface 42, rather than tapered in order to obtain the desired air volume between the wall 48 and the surface 42. The housing 43 also contains a chamber (not shown) similar to the chamber 28 which communicates with the

chambers

45 and 46 and which may contain speakers 37-69.

V In order to provide the desired air column in front of the diaphragm of the speaker 10, the

side walls

49 and 50 of the housing 43 have a pair of

extensions

51 and 52 which are on opposite sides of the speaker 10 and which extend toward the surface 42. The air column is located between the surface 42, wall 48 and the

extensions

51 and 52. Within pre-determined limits, the volume of the air column may be adjusted by moving the housing 43 toward and away from the surface 42.

The embodiment shown in Fig. 5 does not provide sound dispersion and radiation as satisfactory as the embodiment shown in Figs. l-3. In addition, because of the size of the wall 48, difficulties, similar to those described above in connection with infinite bafile systems, may be encountered. For these reasons, if it is not possible to locate the apparatus in a corner of a room, the embodiment shown in Figs. 6 and 7 is preferable to the embodiment shown in Fig. 5. The embodiment shown in Figs. 6 and 7 comprises a housing 53 containing

chambers

54, 55 and 56 as well as an additional chamber (not shown) similar and oppositely disposed with respect to the chamber 56. These chambers correspond respectively to the

chambers

26, 28, 29 and 30 shown in Figs. 'l-3. The speaker 10 is mounted on a wall 57 whose width is approximately equal to the largest diameter of the diaphragm of the speaker 10 and the diaphragm of the speaker 10 faces into the corner formed by the

surfaces

58 and 59, which may be the wall and the floor, respectively, of a room. The

speakers

37 and 38 are mounted on a wall 68 of the housing 53 and extend into the chamber 55. The chamber 56 as well as the oppositely disposed corresponding chamber (not shown) are open at their upper ends permitting free passage of air between such chambers and the chamber 55.

The housing 53 is provided with a pair of extensions 61 and 62 which separate the housing 53 from the

surfaces

58 and 59 providing air passageways or columns between the wall 63 and the surface 59, between the wall 60 and the surface 58 and between the wall 57 and the

surfaces

58 and 59. Such passageways or columns provide the desired air coupling to the speaker 10 as well as the desired sound dispersion.

While I have described the invention with reference to the preferred forms thereof, it will be understood by those skilled in the art, after understanding the invention, that modifications and changes may be made therein without departing from the spirit and scope of the invention as defined by the claims appended hereto.

What is claimed as new and what I desire to secure by Letters Patent of the United States is:

l. A loudspeaker housing having a pair of chambers therein, an exterior wall of one of said chambers having an opening therein adapted to receive and be closed by a loudspeaker diaphragm, and one-way valve means interconnecting said chambers, said valve means permitting passage of air from said one chamber into the other of said chambers and at least substantially restricting the passage of air from said other chamber into said one chamber at the frequencies of operation of said loudspeaker, and said other chamber being otherwise substantially air-tight. I

2. A loudspeaker housing having a pair of chambers therein, an exterior wall of one of said chambers having an opening therein adapted to receive and be closed by a loudspeaker diaphragm, and one-way valve means interconnecting said chambers, said valve means permitting passage of air from said one chamber into the other of said chambers and at least substantially restricting the passage of air from said other chamber into said one chamber at the frequencies of operation of said loudspeaker, and said chambers being otherwise substantially air-tight.

3. Loudspeaker apparatus comprising a housing having a pair of chambers therein, an exterior wall of one of said chambers having an opening therein, a loudspeaker mounted in and closing said opening, and one-way valve 7 means interconnecting said chambers, said valve means permitting passage of air from said one chamber into the other of said chambers and at least substantially restricting the passage of air from other chamber into said one chamber at the frequencies of operation of said loudspeaker, and said chambers being otherwise substantially air-tight.

4. Loudspeaker apparatus comprising a housing having a first air chamber therein, there being an aperture in said chamber, a loudspeaker driving unit including a diaphragm mounted in obturating relation with said aperture, one wall of said chamber having a one-way air valve therein permitting the escape of air from said chamber and at least substantially restricting the flow of air into said chamber, said chamber being otherwise substantially air-tight and said housing also comprising a second chamber in air communication with said valve for receiving air from said first chamber, said second chamber being otherwise substantially air-tight.

5. A loudspeaker housing comprising a plurality of joined walls forming a first chamber, one of said walls having an opening therein adapted to receive and be closed by a loudspeaker diaphragm and one of said walls having a valve opening therein, a one-way valve mounted in said valve opening, said valve opening outwardly of said chamber and permitting substantially free outward flow of air from said chamber and preventing free inward fiow of air into said chamber, and a further plurality of walls forming a second chamber exteriorly of said first chamber mounted to receive air from said first chamber through said valve opening, said second chamber being otherwise substantially air-tight.

6. Loudspeaker apparatus comprising a housing having a first wall having an aperture therein, a loudspeaker having a diaphragm, said diaphragm being mounted in and closing said aperture, said housing having a plurality of additional joining walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and the remainder of said additional walls forming a second chamber adjacent said first chamber, one-way valve means interposed between said first chamber and said second chamber for permitting the passage of air from said first chamber into said second chamber and at least substantially restricting the passage of air from said other chamber into said one chamber at the frequencies of operation of said loudspeaker, said first and second chambers being substantially air-tight, and a pair of substantially imperforate extensions disposed on opposite sides of said aperture and extending outwardly from said housing the space between said extensions being substantially unobstructed in at least one direction substantially parallel to said first wall.

7. Loudspeaker apparatus comprising a housing having a first wall having an aperture therein, a loudspeaker having a diaphragm, said diaphragm being mounted in and closing said aperture, said housing having a plurality of additional joining walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and the remainder of said additional walls forming a second chamber adjoining said first chamber, one-way valve means interposed between said first chamber and said second chamber for permitting the passage of air from said first chamber into said second chamber and at least substantially restricting the passage of air from said other chamber into said one chamber at the frequencies of operation of said loudspeaker, said first and second chambers being substantially air-tight, and a pair of said walls forming said first chamber with said first wall and disposed on opposite sides of said aperture having substantially imperforate portions extending outwardly from said housing and perpendicularly to the exterior surface of said first wall the space between said extended portions being substantially unobstructed in at least one direction substantially parallel to said first wall.

8. Loudspeaker apparatus adapted to be operated in a corner formed by two mutually perpendicular surfaces, said apparatus comprising a housing having a first wall adapted to face into said corner, a loudspeaker having a diaphragm, said wall having an aperture therein and said diaphragm being mounted in and closing said aperture and with the apex thereof extending inwardly of said housing, the distance between the sides of the portion of said wall having said aperture therein being approximately equal to the largest diameter of said diaphragm, said housing having a plurality of additional joining walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and the remainder of said additional walls forming a second chamber adjoining said first chamber, and one-way valve means interposed between said first chamber and said second chamber for permitting the passage of air from said first chamber into said second chamber and at least substantially restricting the passage of air from said other chamber into said one chamber at the frequencies of operation of said loudspeaker, said first and second chambers being otherwise substantially air-tight.

9. Loudspeaker apparatus adapted to be operated in a corner formed by two mutually perpendicular surfaces, said apparatus comprising a housing having a first wall adapted to face into said corner, a loudspeaker having a diaphragm, said wall having an aperture therein and said diaphragm being mounted in and closing said aperture and with the apex thereof extending inwardly of said housing, the distance between the sides of the portion of said wall having said aperture therein being approximately equal to the largest diameter of said diaphragm, said housing having a plurality of additional joining walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and the remainder of said additional walls forming second, third and fourth chambers adjoining said first chamber and with said third and fourth chambers opening into said second chamber but being otherwise substantially airtight, one-way valve means interposed in the opening between said first chamber and said third chamber and in the opening between said first chamber and said fourth chamber for permitting the passage of air from said first chamber into said third and fourth chambers, and said second chamber having an exterior wall having further aperture therein providing an opening into said second chamber but being otherwise substantially air-tight and a loudspeaker mounted in said further aperture and closing said further aperture.

10. Loudspeaker apparatus adapted to be operated in a corner formed by two mutually perpendicular surfaces, said apparatus comprising a housing having a first wall adapted to face into said corner, a low frequency loudspeaker having a conical diaphragm, said wall having an aperture therein spaced from the ends of said wall and said diaphragm being mounted in and closing said aperture and with the apex thereof extending inwardly of said housing, said aperture being spaced from said surfaces a distance which will provide an air column between said surfaces and the center of said aperture which is substantially equal in volume to twice the volume of a cone having the shape and size of said diaphragm and the distance between the sides of the portion of said wall having said aperture therein being approximately equal to the largest diameter of said diaphragm, said housing having a plurality of additional joining walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and the remainder of said additional walls forming second, third and fourth chambers adjoining said first chamber and with said third and fourth chambers opening into said second chamber, said first chamber having a volume at least equal to the volume of said air column and the combined volumes of said second, third and fourth chambers being at least equal to the volume of said first chamber, one-way valve means interposed between said first chamber and said third chamber and between said first chamber and said fourth chamber for permitting the passage of air from said first chamber into said third and fourth chambers, and said second chamber having an exterior wall having a further aperture therein providing an opening into said second chamber and a high frequency loudspeaker mounted in said further aperture and closing said further aperture.

11. Loudspeaker apparatus adapted to be operated in a corner formed by three mutually perpendicular surfaces, said apparatus comprising a housing having a base adapted to rest on one of said surfaces and a first Wall adapted to face into the corner formed by the other two of said surfaces and the outer surface of which slopes away from said last-mentioned corner from the base end thereof to the top end thereof at an angle in the range from 70 to 80 with respect to said base, a loudspeaker having a conical diaphragm, said wall having an aperture therein spaced from said ends and said diaphragm being mounted in and closing said aperture and with the apex thereof extending inwardly of said housing, said aperture being spaced from said base end a distance which will provide an air column between said surfaces and below substantially the center of said aperture which is substantially equal in volume to twice the volume of a cone having the shape and size of said diaphragm and the distance between the sides of the portion of said wall having said aperture therein being approximately equal to the largest diameter of said diaphragm, said housing having a plurality of additional joining walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and forming a second chamber with said first wall, said first chamber having a volume substantially equal to the volume of said air column and the volume of said second chamber being at least equal to the volume of said first chamber, and oneway valve means interposed between said first chamber and said second chamber for permitting the passage of air from said first chamber into said second chamber.

12. Loudspeaker apparatus adapted to be operated in a corner formed by three mutually perpendicular surfaces, said apparatus comprising a housing having a base adapted to rest on one of said surfaces and a first wall adapted to face into the corner formed by the other two of said surfaces and the outer surface of which slopes away from said last-mentioned corner from the base end thereof to the top end thereof at an angle in the range from 70 to 80 with respect to said base, a low frequency loudspeaker having a conical diaphragm, said wall having an aperture therein spaced from said ends and said diaphragm being mounted in and closing said aperture and with the apex thereof extending inwardly of said housing, said aperture being spaced from said base end a distance which will provide an air column between said surfaces and below substantially the center of said aperture which is substantially equal in volume to twice the volume of a cone having the shape and size of said diaphragm and the distance between the sides of the portion of said wall having said aperture therein being approximately equal to the largest diameter of said diaphragm, said housing having a plurality of additional joining Walls, a plurality of said additional walls forming a first chamber with said first wall which contains said diaphragm and forming a second chamber with said first wall and the remainder of said additional walls forming third and fourth chambers adjoining said first chamber and opening into said second chamber, said first chamber having a volume substantially equal to the volume of said air column and the combined volumes of said second, third and fourth chambers being at least equal to the volume of said first chamber, one-Way valve means interposed between said first chamber and said third chamber and between said first chamber and said fourth chamber for permitting the passage of air from said first chamber into said third and fourth chambers, said first wall having a plurality of further apertures therein providing openings into said second chamber and plurality of high frequency loudspeakers mounted one in each of said further apertures and closing said further apertures.

References Cited in the file of this patent UNITED STATES PATENTS 1,891,968 Bidwell et a1 Dec. 27, 1932 2,337,213 Topping Dec. 21, 1943 2,491,982 Kincart Dec. 20, 1949 2,704,185 Travares Mar. 15, 1955 2,710,662 Camras June 14, 1955 2,757,751 Tavares Aug. 7, 1956 2,801,704 Martin Aug. 6, 1957 2,834,423 Bradford May 13, 1958 FOREIGN PATENTS 506,042 Great Britain May 19, 1939 OTHER REFERENCES Exponential Bafiles for Custom Installations, by George Augspurger, Audio Engineering, vol. 35-Issue, pages 24- 27, 67, published Nov. 1, 1951.