WO2008030430A2

WO2008030430A2 - End-fire sound source array

Info

Publication number: WO2008030430A2
Application number: PCT/US2007/019301
Authority: WO
Inventors: G. Douglas Meegan, Jr.; Jeffry C. Windsor
Original assignee: University of Texas System; University of Texas at Austin
Current assignee: University of Texas System; University of Texas at Austin
Priority date: 2006-09-05
Filing date: 2007-09-05
Publication date: 2008-03-13
Anticipated expiration: 2009-03-05
Also published as: WO2008030430A3

Abstract

Provided is an end-fire sound source array. The end-fire sound source array is capable of producing extremely loud sound at or near a resonant frequency in air or other gases in a very low cost, compact and efficient manner.

Description

END-FIRE SOUND SOURCE ARRAY

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority under 35 U.S. C. § 119(e) of

Provisional Patent Application No. 60/824,531, filed on September 5, 2006, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to acoustic arrays. More particularly, the present disclosure relates to an end-fire sound source array.

BACKGROUND OFTHE DISCLOSURE

[0003] The general concept of acoustic arrays has been used extensively in underwater sonar applications where a powerful and/or directional sound source is needed. However, this general concept has not heretofore been applied to generate intense sound in air or other gases for industrial processes. Instead, existing industrial acoustic transducers are based upon costly and inefficient designs. For example, air driven horns, which are often used in industrial exhaust streams, while being relatively simple to manufacture, are very inefficient in that they consume a great deal of power to provide a given acoustic energy. Other designs, such the shaker plate sound source disclosed in U.S. Patent No. 5,299,175 to Gallego-Juarez et al., are more efficient, but are very expensive to manufacture. [0004] In view of the foregoing, it would be desirable to provide a powerful acoustic source which overcomes the above-described inadequacies and shortcomings.

SUMMARY OF THE DISCLOSURE

[0005] Exemplary embodiments of the present disclosure address at least the above problems and/or disadvantages and provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an end-fire sound source array. The end-fire sound source array is capable of producing extremely loud sound at or near a resonant frequency in air or other gases at a very low cost and in an efficient manner. [0006] In accordance with other aspects of this particular exemplary embodiment, disclosed is an end-fire acoustic source array for generating and emitting acoustic waves in air or gas. The end fire acoustic source array comprises at least one substantially tubular acoustic waveguide, the at least one acoustic waveguide comprising a waveguide axis along which acoustic waves are transmitted, the at least one acoustic waveguide further comprising an opening at one end through which acoustic waves are emitted. The end fire acoustic source array further comprises a plurality of acoustic transducers positioned along and adjacent to each of the at least one acoustic waveguide, wherein each of the acoustic transducers are disposed to emit acoustic waves into the at least one acoustic waveguide through an opening in a wall of the at least one acoustic waveguide, wherein each of the openings in a wall of the at least one acoustic waveguide are substantially spaced apart one- half or an integer number of wavelengths from each other in a linear direction relative to the waveguide axis, the wavelength corresponding to a resonant frequency within the at least one acoustic waveguide.

[0007] In accordance with further aspects of this particular exemplary embodiment, the acoustic transducers comprise at least one of compression drivers, loudspeakers and piezoceramic sound sources.

[0008] In accordance with additional aspects of this particular exemplary embodiment, each of the openings in the wall of the at least one acoustic waveguide comprise a drilled and tapped hole.

[0009] In accordance with further aspects of this particular exemplary embodiment, each of the compression drivers comprise a screw-on type mount for mounting the compression drivers to respective drilled and tapped holes in the at least one acoustic waveguide.

[0010] In accordance with still further aspects of this particular exemplary embodiment, each transducer emits acoustic waves of a common frequency. Further, the common frequency may substantially be the same as the resonant frequency. [0011] In accordance with further aspects of this particular exemplary embodiment, when the openings in the wall of the acoustic waveguide are substantially spaced an integer number of wavelengths apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide substantially in phase with one another. Further, the acoustic transducers may be directly wired.

[0012] In accordance with additional aspects of this particular exemplary embodiment, the openings in the wall of the acoustic waveguide are substantially spaced one- half wavelength apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide with a phase that is substantially opposite to the phase emitted by any adjacent acoustic transducer. Further, the acoustic transducers may be directly wired. [0013] In accordance with still further aspects of this particular exemplary embodiment, the end fire acoustic source array is used for the acoustic agglomeration of exhaust particulates.

[0014] In accordance with further aspects of this particular exemplary embodiment, the end fire acoustic source array is used for the treatment of industrial exhaust streams. [0015] In accordance with other aspects of this particular exemplary embodiment, the end fire acoustic source array is used as a non-lethal weapon or deterrent. [0016] In accordance with still further aspects of this particular exemplary embodiment, the at least one substantially tubular acoustic waveguide is constructed from a substantially rigid material.

[0017] In accordance with additional aspects of this particular exemplary embodiment, when the end fire acoustic source array comprises a plurality of acoustic waveguides. Further, the plurality of acoustic waveguides may be formed from a single structure or individual structures that are coupled together. Still further, the openings at the ends of each of plurality of acoustic waveguides may be adjacent to one another. [0018] In accordance with aspects of another exemplary embodiment, provided is a method of generating and emitting acoustic waves in air or gas using at least one substantially tubular acoustic waveguide, the at least one acoustic waveguide comprising a waveguide axis along which acoustic waves are transmitted, the at least one acoustic waveguide further comprising an opening at one end through which acoustic waves are emitted, a plurality of acoustic transducers positioned along and adjacent to each of the at least one acoustic waveguide, wherein each of the acoustic transducers are disposed to emit acoustic waves into the at least one acoustic waveguide through an opening in a wall of the at least one acoustic waveguide. The method comprises disposing each of the openings in the wall of the at least one acoustic waveguide such that respective acoustic transducers are positioned to emit acoustic waves into the at least one acoustic waveguide at locations that are spaced apart one- half or an integer number of wavelengths from each other in a linear direction relative to the waveguide axis. The method further comprises phasing the acoustic transducers of the at least one acoustic waveguide, wherein when the openings in the wall of the acoustic waveguide are substantially spaced an integer number of wavelengths apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide substantially in phase with one another, wherein when the openings in the wall of the acoustic waveguide are substantially spaced an integer number of wavelengths apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide substantially in phase with one another, further wherein when the openings in the wall of the acoustic waveguide are substantially spaced one-half wavelength apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide with a phase that is substantially opposite to the phase emitted by any adjacent acoustic transducer. [0019] In accordance with further aspects of this particular exemplary embodiment, each transducer emits acoustic waves of a common frequency. [0020] In accordance with still further aspects of this particular exemplary embodiment, the acoustic transducers are directly wired. [0021] In accordance with additional aspects of this particular exemplary embodiment, the end fire acoustic source array comprises a plurality of acoustic waveguides. [0022] The present disclosure will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present disclosure is described below with reference to exemplary embodiments, it should be understood that the present disclosure is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein, and with respect to which the present disclosure may be of significant utility.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only.

[0024] Referring to Figure IA, there is shown an end-fire sound source array in accordance with an embodiment of the present disclosure.

[0025] Referring to Figure IB, there is shown a phasing of the acoustic transducers of the end-fire sound source array of Figure IA in accordance with an embodiment of the present disclosure.

[0026] Referring to Figure 2, there is shown a laboratory mock-up of an end-fire sound source array in accordance with an embodiment of the present disclosure. [0027] Referring to Figure 3A, there is shown another end-fire sound source array in accordance with an embodiment of the present disclosure.

[0028] Referring to Figure 3B, there is shown the alternating phasing of the acoustic transducers of the end-fire sound source array of Figure 3 A in accordance with an embodiment of the present disclosure.

[0029] Referring to Figure 4A, there is shown a side view of a multi-waveguide end- fire sound source array in accordance with an embodiment of the present disclosure. [0030] Referring to Figure 4B, there is shown a top view of the multi-waveguide end- fire sound source array of Figure 4A.

[0031] Referring to Figure 4C, there is shown a bottom view of the multi-waveguide end-fire sound source array of Figure 4A.

[0032] Referring to Figure 5, there is shown a graph of the pressure sensitivity measured on the end-fire sound source array laboratory mock-up of Figure 2 in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0033] Referring to Figure IA, there is shown an end-fire sound source array 10 in accordance with an embodiment of the present disclosure. Figure 2 shows a laboratory mock-up of an end-fire sound source array 10 in accordance with an embodiment of the present disclosure. The end-fire sound source array 10 is capable of producing extremely loud sound at or near a resonant frequency in air or other gases. The end-fire array provides a compact arrangement for combining numerous sound sources into a single acoustic emitter. This compact arrangement is particularly beneficial in industrial applications where space is limited and it is important to minimize the total number of distinct sound sources. In particular, the end-fire arrangement avoids the need for complicated, bulky equal-length manifolds as are conventionally used to join the output of multiple sound sources. Furthermore, the end-fire arrangement operates very efficiently at its resonance frequency. [0034] As shown in Figures IA and 2, the end-fire sound source array is illustrated with eight acoustic transducers 20a-20h that are spaced one wavelength λ apart and ported to a common air space 30 that acts in a resonant mode. While the use of eight acoustic transducers 20a-20h is preferred, any number of acoustic transducers greater than one may be implemented. Furthermore, while the use of compression drivers are preferred for acoustic transducers 20a-20h, loudspeakers, piezoceramic sound sources, or any other sound generating mechanism may be used. Moreover, while a spacing of one wavelength λ is shown between acoustic transducers 20a-20h, the spacing between acoustic transducers 20a- 2Oh may be any integer number of wavelengths.

[0035] The resonant mode produces sound more efficiently than the individual acoustic transducers would achieve if they were not combined as described above. For example, when eight compression drivers are assembled in an end- fire sound source array 10, such as shown in Figures IA and 2, the sound produced at a resonant frequency is greater than eight times louder than a single driver. For example, as shown in Figure 5, the efficiency of the eight driver end-fire sound source array 10 of Figures 1 and 2 at the resonant frequency of 2380 Hz, exceeds that of eight individual drivers.

[0036] Returning to Figures IA, a common air space 30 is located within and at least partially defined by acoustic waveguide 40. Preferably, acoustic waveguide 40 is tubular and is formed from a substantially rigid material, such as steel, aluminum or titanium. As shown in Figures IA, acoustic waveguide 40 comprises a waveguide axis X along which acoustic waves are transmitted. Acoustic waveguide 40 further comprises opening 60 through which the acoustic waves are emitted from the end-fire sound source array 10. Each of the acoustic transducers 20a-20h emits sound along axes Ya-Yh through respective openings 50a-50h in acoustic waveguide 40. While it is preferred that axes Ya-Yh be substantially perpendicular to waveguide axis X, axes Ya-Yh may intersect waveguide axis X at any angle so long as each of the axes Ya-Yh are linearly spaced an integer number (1, 2, 3, 4...) of wavelengths λ apart, relative to waveguide axis X, at their intersect point with acoustic waveguide 40. Accordingly, while it is preferred that the openings 50a-50h lie on a line that is parallel to waveguide axis X along the surface of acoustic waveguide 40, each of the openings 50a-50h may be positioned at any location around waveguide axis X so long as each of the openings 50a-50h are linearly spaced an integer number of wavelengths λ apart relative to waveguide axis X.

[0037] The end of acoustic waveguide 40 that is opposite to sound opening 60 may be proximate to acoustic transducers 20a, as shown in Figure 2, or may be positioned away from acoustic transducers 20a, as shown in Figure IA. When the end of acoustic waveguide 40 that is opposite to sound opening 60 is positioned away from acoustic transducers 20a, it is preferred that the distance between acoustic transducers 20a and the end of acoustic waveguide 40 that is opposite to sound opening 60 be a multiple of one-half the wavelength. [0038] Referring to Figure IB, there is shown the phasing of the acoustic transducers of the end-fire sound source array of Figure IA in accordance with an embodiment of the present disclosure. When the acoustic transducers 20a-20h are linearly spaced one wavelength λ apart along axis X, each of the acoustic transducers 20a-20h are preferably phased substantially the same. The spacing of an integer number of wavelengths λ between identically phased acoustic transducers allows the sound input from the acoustic transducers 20a-20h into the common air space 30 to be constructively combined. If for example, the acoustic transducers 20a-20h used are compression drivers or loudspeakers, the phasing for all of the transducers are preferably the same. This may be achieved by using the same polarity for the electrical connections on each of the drivers. That is, all of the acoustic transducers 20a-20h may be connected in a similar manner (i.e., with a positive (+) driving lead connecting to a positive (+) driver terminal, and a negative (-) driving lead connecting to a negative (-) driver terminal). This phasing arrangement is simple and cost effective in that it does not require any phasing circuitry in addition to the direct wiring of the drivers. [0039] Referring to Figure 3A, there is shown another end-fire sound source array in accordance with an embodiment of the present disclosure. In the end-fire sound source array 10 of Figure 3 A, eight acoustic transducers are spaced one-half wavelength λ/2 apart in order to provide an even more compact design. In this arrangement, alternating acoustic transducers 20a-20h and respective openings 50a-50h lie in one of two lines that are parallel to waveguide axis X along the surface of acoustic waveguide 40. Herein, each of the openings 50a-50h may be positioned at any location around waveguide axis X so long as each of the openings 5Oa-50h are linearly spaced one wavelength λ/2 apart relative to axis X. In order for the sound generated from each sound source to add constructively, the phase of the acoustic transducers are alternated, as described in greater detail below. [0040] The end of acoustic waveguide 40 that is opposite to sound opening 60 may be proximate to acoustic transducers 20a, as shown in Figure 2, or may be positioned away from acoustic transducers 20a, as shown in Figure 3 A. When the end of acoustic waveguide 40 that is opposite to sound opening 60 is positioned away from acoustic transducers 20a, it is preferred that the distance between acoustic transducers 20a and the end of acoustic waveguide 40 that is opposite to sound opening 60 be a multiple of one-half or one-quarter the wavelength.

[0041] Referring to Figure 3B, there is shown the phasing of the acoustic transducers of the end-fire sound source array of Figure 3 A in accordance with an embodiment of the present disclosure. When the acoustic transducers 20a-20h are linearly spaced one-half wavelength λ/2 apart relative to axis X, each of the acoustic transducers 20a-20h are preferably arranged such that the phases of adjacent acoustic transducers 20a-20h are substantially opposite to one another. The spacing of one-half wavelength λ/2 between alternately phased acoustic transducers allows the sound input from the acoustic transducers 20a-20h into the common air space 30 to be constructively combined. If for example, the acoustic transducers 20a-20h used are compression drivers or loudspeakers, the phasing may be alternated by reversing the polarity of the electrical connections on every other driver. That is, one transducer may be connected normally and the adjacent transducer may be connected in an opposite manner (i.e., with a positive (+) driving lead connecting to a negative (-) driver terminal, and vice versa). This phasing arrangement is simple and cost effective in that it does not require any phasing circuitry in addition to the direct wiring of the drivers.

[0042] Referring to Figures 4A-4C, there is shown various views of multi-waveguide end-fire sound source array 80 in accordance with an embodiment of the present disclosure. In the multi-waveguide end-fire sound source array 80 of Figures 4A-4C, four end-fire sound source arrays, such as the end-fire sound source array discussed above with respect to Figures IA or 3 A, are used in conjunction with one another to achieve greater sound output. The use of four end-fire sound source arrays is merely exemplary as any number of end-fire sound source arrays may be used together to achieve a desired sound level. Each of the end-fire sound source arrays comprise respective waveguides 40₁-4O₄, respective sound openings 60₁- 6O₄, and respective sets of acoustic transducers 20a]-20hi, 20a₂-20h₂, 20a₃-20h₃, and 2Oa₄- 2Oh₄. Since each of the end-fire sound source arrays that make up the multi-waveguide end- fire sound source array 80 may be constructed according to the embodiments discussed above with respect to Figures IA and 3 A, a description thereof will be omitted. [0043] As illustrated in the top view of the multi-waveguide end-fire sound source array 80 in Figures 4B, the acoustic waveguides 40]-40₄ are arranged to be adjacent to one another along their entire length. However, in other embodiments, the acoustic waveguides 40₁-4O₄ may be adjacent to one another for less that their entire length. The acoustic waveguides 4Oi -4O₄ may be formed from a single body or may be constructed of separate waveguides that are coupled together.

[0044] As can be seen in Figures 4A and 4C, the multi-waveguide end-fire sound source array 80 further comprises a mounting plate 70 that is located at the end of the acoustic waveguides 40i-40₄ comprising the sound openings 60i-60₄. The mounting plate 70 is substantially perpendicular to the acoustic waveguides 40]-40₄. The mounting plate facilitates mounting of the end-fire sound source array to another structure into which the sound from sound openings 6Oi -6O₄ is emitted. In certain embodiments, the mounting plate 70 may be omitted or may take on another form to facilitate being mounted to a particular structure. Further, mounting plate 70 may be implemented in any of the embodiments described above.

[0045] Preferably, each of the sets of acoustic transducers 20aj-20hi, 20a₂-20h₂,

20a₃-20h₃, and 203₄-2Oh₄ are identically wired as disclosed above with respect to Figures IB or 3B. The use of plural end-fire sound source array to form a multi-waveguide end-fire sound source array 80 lends itself to a very compact and cost effective construction. [0046] The above-described end-fire sound source arrays or multi-waveguide end-fire sound source array may be used in industrial exhaust streams in order to produce a variety of effects including the acoustic agglomeration of exhaust particulate. In such an agglomeration application, extremely loud sound (>140 dB) near a single frequency is typically needed to produce the desired effect. The advantage of the above-described end-fire sound source array embodiments is that it produces the required high sound pressure levels (SPL) with a device that is relatively compact and inexpensive. Another example of a use for the above-described end-fire sound source array includes the use of acoustic energy for imaging purposes, such as used in the detection of buried land mines. Another possible application for the above- described end-fire sound source array includes its use as a non-lethal weapon or deterrent. Still another possible application for the above-described end-fire sound source array includes its treatment of industrial exhaust streams.

[0047] The above-described end-fire sound source array embodiments are unique in that they provide an effective, compact high-amplitude sound source that is relatively inexpensive and appropriate for use in harsh industrial environments. The design is simple and easy to manufacture. For example, the tubular waveguide or waveguides may be made from pipe or square stock. As discussed above, the use of compression drivers is preferred. Conventional compression drivers are available with screw-on type mounts. When compression drivers, with screw-on type mounts are used, the only precision machining that may be required is a line of evenly spaced drilled and tapped holes. This makes construction easy, fast, and inexpensive.

[0048] Additionally, the above-described end-fire sound source array embodiments are inherently modular. That is, the size of the above-described end-fire sound source array may be matched precisely to the amount of acoustic energy needed. Also, due to the compact nature, multiple end-fire sound source arrays may be combined to form a shorter stack with a larger opening. The flexibility of the concept makes it easy to adapt to a particular need. [0049] The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims

CLAIMS:

1. An end fire acoustic source array for generating and emitting acoustic waves in air or gas, said end fire acoustic source array comprising: at least one substantially tubular acoustic waveguide, the at least one acoustic waveguide comprising a waveguide axis along which acoustic waves are transmitted, the at least one acoustic waveguide further comprising an opening at one end through which acoustic waves are emitted; and a plurality of acoustic transducers positioned along and adjacent to each of the at least one acoustic waveguide, wherein each of the acoustic transducers are disposed to emit acoustic waves into the at least one acoustic waveguide through an opening in a wall of the at least one acoustic waveguide, wherein each of the openings in a wall of the at least one acoustic waveguide are substantially spaced apart one-half or an integer number of wavelengths from each other in a linear direction relative to the waveguide axis, the wavelength corresponding to a resonant frequency within the at least one acoustic waveguide.

2. An end fire acoustic source array according to claim 1, wherein the acoustic transducers comprise at least one of compression drivers, loudspeakers, and piezoceramic sound sources.

3. An end fire acoustic source array according to claim 2, wherein each of the openings in the wall of the at least one acoustic waveguide comprise a drilled and tapped hole.

4. An end fire acoustic source array according to claim 3, wherein each of the compression drivers comprise a screw-on type mount for mounting the compression drivers to respective drilled and tapped holes in the at least one acoustic waveguide.

5. An end fire acoustic source array according to claim 1, wherein each transducer emits acoustic waves of a common frequency.

6. An end fire acoustic source array according to claim 5, wherein the common frequency is substantially the same as the resonant frequency.

7. An end fire acoustic source array according to claim 1, wherein when the openings in the wall of the acoustic waveguide are substantially spaced an integer number of wavelengths apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide substantially in phase with one another.

8. An end fire acoustic source array according to claim 7, wherein the acoustic transducers are directly wired.

9. An end fire acoustic source array according to claim 1, wherein when the openings in the wall of the acoustic waveguide are substantially spaced one-half wavelength apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide with a phase that is substantially opposite to the phase emitted by any adjacent acoustic transducer.

10. An end fire acoustic source array according to claim 9, wherein the acoustic transducers are directly wired.

11. An end fire acoustic source array according to claim 1, wherein the end fire acoustic source array is used for the acoustic agglomeration of exhaust particulates.

12. An end fire acoustic source array according to claim 1, wherein the end fire acoustic source array is used for the treatment of industrial exhaust streams.

13. An end fire acoustic source array according to claim 1, wherein the end fire acoustic source array is used as a non-lethal weapon or deterrent.

14. An end fire acoustic source array according to claim 1, wherein the at least one substantially tubular acoustic waveguide is constructed from a substantially rigid material.

15. An end fire acoustic source array according to claim 1, wherein when the end fire acoustic source array comprises a plurality of acoustic waveguides.

16. An end fire acoustic source array according to claim 15, wherein the plurality of acoustic waveguides are formed from a single structure or are individual structures that are coupled together.

17. An end fire acoustic source array according to claim 15, wherein the openings at the ends of each of plurality of acoustic waveguides are adjacent to one another.

18. An method of generating and emitting acoustic waves in air or gas using at least one substantially tubular acoustic waveguide, the at least one acoustic waveguide comprising a waveguide axis along which acoustic waves are transmitted, the at least one acoustic waveguide further comprising an opening at one end through which acoustic waves are emitted, a plurality of acoustic transducers positioned along and adjacent to each of the at least one acoustic waveguide, wherein each of the acoustic transducers are disposed to emit acoustic waves into the at least one acoustic waveguide through an opening in a wall of the at least one acoustic waveguide, the method comprising: disposing each of the openings in the wall of the at least one acoustic waveguide such that respective acoustic transducers are positioned to emit acoustic waves into the at least one acoustic waveguide at locations that are spaced apart one-half or an or an integer number of wavelengths from each other in a linear direction relative to the waveguide axis; and phasing the acoustic transducers of the at least one acoustic waveguide, wherein when the openings in the wall of the acoustic waveguide are substantially spaced an integer number of wavelengths apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide substantially in phase with one another, further wherein when the openings in the wall of the acoustic waveguide are substantially spaced one-half wavelength apart, each of the acoustic transducers are arranged to emit acoustic waves into the acoustic waveguide with a phase that is substantially opposite to the phase emitted by any adjacent acoustic transducer.

19. The method according to claim 18, wherein each transducer emits acoustic waves of a common frequency.

20. The method according to claim 18, wherein the acoustic transducers are directly wired.

21. The method according to claim 18, wherein when the end fire acoustic source array comprises a plurality of acoustic waveguides.