US3888331A

US3888331A - Power tuned wave interference silencer

Info

Publication number: US3888331A
Application number: US466526A
Authority: US
Inventors: Wei-Ming Wang
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1974-05-03
Filing date: 1974-05-03
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10
Also published as: CA1020026A

Abstract

A silencer assembly comprises a sealed housing having an inlet wave interference section and an outlet wave interference section with an open volume formed by the sealed housing therebetween. The wave interference sections are spaced within the sealed housing to produce interaction of sound wave energy for wave cancellation between each wave interference section. The first section serves as a power tuning device to reduce the overall size of the silencer having an appropriate length to produce a gas pressure pulse reflected back from the first interference section to the exhaust port of an engine for producing a negative pulse to reduce back pressure and improve exhaust port scavenging. The inlet interference section includes a set of holes therein joining one end of an outer flow path therein to the open volume with the outer path length being selected to broaded the negative pulse to achieve improved scavenging effect.

Description

United States Patent 1191 Wang 1 1 POWER TUNED WAVE INTERFERENCE SILENCER [75] Inventor: Wei-Ming Wang, Grand Blanc,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich. [22] Filed: May 3, 1974 2 1. Appl. N0.2 466,526

[52] US. Cl 181/44; 181/36 E; 181/67 [51] Int. Cl. FOln 1/00 [58] Field of Search .i 181/66, 67, 44, 46, 36 E; 60/312-316 [56] References Cited UNITED STATES PATENTS 1,612,584 12/1926 Hunter et al 181/67 2,359,365 10/1944 Katcher 181/67 2,911,055 11/1959 McDonald 181/67 3,700,069 10/1972 Rausch et a]. 181/67 X FOREIGN PATENTS OR APPLICATIONS 804,593 4/1936 France 181/67 292,323 6/1928 United Kingdom..... 677,875 6/1939 Germany 18l/67 [111 3,888,331 June 10, 1975 Primary Examiner-Richard B. Wilkinson Assistant ExaminerJohn F. Gonzales Attorney, Agent, or Firm-J. C. Evans [57] ABSTRACT A silencer assembly comprises a sealed housing having an inlet wave interference section and an outlet wave interference section with an open volume formed by the sealed housing therebetween. The wave interference sections are spaced within the sealed housing to produce interaction of sound wave energy for wave cancellation between each wave interference section. The first section serves as a power tuning device to reduce the overall size of the silencer having an appropriate length to produce a gas pressure pulse reflected back from the first interference section to the exhaust port of an engine for producing a negative pulse to reduce back pressure and improve exhaust port scavenging. The inlet interference section includes a set of holes therein joining one end of an outer flow path therein to the open volume with the outer path length being selected to broaded the negative pulse to achieve improved scavenging effect 4 Claims, 4 Drawing Figures POWER TUNED WAVE INTERFERENCE SILENCER This invention relates to engine mufflers and more particularly to engine mufflers utilizing wave interfer ence silencing techniques.

Certain vehicles are operated in a constant engine speed range, for example, snowmobiles, tractors and the like are operated in the range of 5500 to 6500 revolutions per minute. In such vehicles. it is desirable to include a silencing device that will produce good scavenging of exhaust ports in the vehicle engine within the constant operating speed range and which further, will produce attenuation of a broad range of sound frequencies in the engine exhaust. Furthermore. in such vehicles, it is desirable to maintain the silencer assembly as compact as practical while retaining the advantages of improved engine scavenging and sound attenuation.

An object of the present invention is to provide an improved silencer assembly including a sealed outer casing having wave interference sections at opposite ends thereof separated from one another by an open volume within the interior of the sealed outer casing and wherein one of the wave interference sections defines an inlet into the sealed outer casing and is tuned to produce a reflected wave pulse to the exhaust port of an engine for reducing back pressure and improving scavenging of exhaust gases from the engine and wherein both the first and second wave interference sections combine to attenuate a wide range of sound frequencies in the engine exhaust.

Still another object of the present invention is to provide an improved multiple function silencer assembly having lower cost and fewer pieces and including means for reducing back pressure at an engine exhaust port and producing less turbulent noise in the interaction regions of a pair of separated wave interference silencer sections within the assembly.

Yet another object of the present invention is to provide a compact, power tuned wave interference silencer including an inlet wave interference section and an outlet wave interference section having a sealed open volume therebetween; the first section serving as a power tuning device of reduced dimension that will produce a reflected gas pressure pulse from the outlet end of the inlet wave interference section to the exhaust port of an engine for scavenging the exhaust port and wherein an outer flow path of predetermined length is formed between a discontinuity defined by a set of holes and the open volume to broaden the negative pulse at the engine exhaust and wherein each of the first and second wave interference sections each attenuate a separate range of sound frequencies in the engine exhaust.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the Drawings:

FIG. 1 is a longitudinal sectional view of a power tuned silencer assembly including the present inven tion;

FIG. 2 is an enlarged fragmentary sectional view taken along the line 2--2 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken along the line 3-3 of FIG. 1; and

FIG. 4 is a longitudinal sectional view of a second embodiment of the present invention.

Referring now to FIG. 1, a power tuned wave interference silencer assembly 10 is illustrated including an outer casing 12 having an inlet end closure l4 on one end thereof and an outlet end closure l6 on the opposite end thereof. The outer casing 12 includes an intermediate open volume 18 that has a first wave interference device 20 at one end thereof and a second wave interference device 22 at the opposite end thereof.

More particularly. the wave interference device 20 includes a central open ended tube 23 therein including an inlet end 24 thereof supported centrally of the end closure 14 at a tubular extension 26 thereon. The inlet end 24 is sealed with respect to the annular extension flange 26 by means of a continuously formed circumferential weld 28 between the flange 26 and the outer periphery of the inlet end 24. Inlet end 24 is connected to the exhaust pipe of an engine. The tube 23 further includes an outlet end 30 thereon located interiorly of the outer casing 12 at the open volume 18 therein.

The tube 23 has an outer diameter substantially less than the inner diameter of the outer casing 12 to form an annular outer flow path 32 therebetween. Within the outer flow path 32, a helical wave interference baffie 34 is located having an inlet end 36 thereof located immediately downstream of the conically shaped enclosure 14 and an outlet end 38 formed at the outlet end 30 of the tube 23 at the open volume 18.

The wave interference device 20 further includes a two-row set of holes 40 in the tube 23 formed immediately downstream of the tubular extension 26 to communicate the interior of the tube 23 with an annular volume 42 formed by the inner surface of the conically shaped enclosure 14 immediately upstream of the inlet end 36 of the helical baffle 34. As best shown in FIGS. 1 and 2, the set of holes 40 includes a first row of holes 44 and a second row of holes 46. The holes 44 are eight in number and each have a 0.50 inch diameter. The holes 44 are equally circumferentially spaced from one another and are axially staggered with respect to the holes 46. Likewise, the holes 46 are also eight in number; of 0.50 inch diameter; equally circumferentially spaced and alternately axially staggered with respect to the holes 44 in the first row. The total cross-sectional flow area of the set of holes 40 is approximately equal to the cross-sectional flow area of the tube 23 which in one working embodiment has a diameter of 1.875 inches. In one working embodiment, the baffle 34 has a height of 1.13 inches and a pitch of 2.29 inches and an internal diameter of 1.875 inches.

The outlet end 30 of the tube 23 and the outlet end 38 of the baffle 34 are spaced by the open volume 18 from the inlet end 48 of a second elongated tube 50 of the second wave interference section 22 and the inlet end 52 of a second helically formed wave interference baffle 54, respectively. In this embodiment of the invention, the second tube 50 is arranged coaxially of the first tube 23 and includes an outlet end 56 directed exteriorly of the outer casing 12 centrally through an annular flanged extension 58 on the conically-shaped end closure 16. The flanged extension 58 is sealed with respect to the outer surface of the outlet end 56 by means of a continuous circumferential weld 60. Likewise, the tube 50 has a diameter reduced from that of the inner diameter of the outer casing 12 to form a second helical outer flow path 62 at the opposite end of the sealed interior of the outer casing 12. The baffle 54 is located within the outer flow path 62 and is helically formed between the inlet end 52 thereof to an outlet end 64 thereof located immediately upstream of an annular chamber 66 formed by the inner surface of the conical end closure 16. The wave interference section 22 includes a set of openings 68 therein including a first row of openings 70 and a second row of openings 72 for communicating the interior of the tube 50 with the annular space 66. ln the embodiment of the invention illustrated in FIGS. 1 thru 3, there are eight holes 70 equally circumferentially spaced from one another, each of 0.44 inch diameter. Each of the holes 72 are axially staggered with respect to the holes 70, are eight in number and equally circumferentially spaced. Each of the holes 72 further have a 0.44 inch diameter. The baffle 54 has a height of 1.32 inches and an internal diameter of l .5 inches which corresponds to the outer diameter of the tube 50. The baffle 54 further includes a pitch of 1.23 inches along the length of the baffle 54. The aforesaid arrangement produces a compact silencer assembly capable of attenuating a wide range of sound frequencies in an engine exhaust.

Furthermore, the tube 23 of the device has a length that is tuned to produce a reverse pressure pulse in the exhaust system of a vehicle whereby a negative pressure pulse will be produced at the exhaust port of an engine which will reduce engine back pressure and improve exhaust port scavenging. The cross-sectional flow area of the set of holes 40 and the length of the baffle 34 are selected to produce a wave interference attenuation of a first range of frequencies in the engine exhaust. The second tube and hole set 68 therein along with the baffle 54 in the outer flow path 62 will attenuate a second range of frequencies in the engine exhaust. The set of holes 40 in the tube 23 are communicated with one end of the outer path 32 which has its opposite end joined to the in-between volume 18. This produces a second reflected pulse which serves to broaden the negative pulse produced through the tuned tube 23 and reflected to the exhaust ports thereby to achieve a better scavenging effect at the exhaust ports of an engine connected to the inlet end 24 by exhaust pipe means.

The embodiment illustrated in FIGS. 1 thru 3, is designed for use with vehicle engines operated at a con' stant engine speed range, for example, snowmobiles, tractors and the like which operate in the range of 5500 to 6500 rpm. The aforedescribed arrangement gives a good scavenging of engine exhaust in this range. Furthermore, the tube 23 also serves in cooperation with the baffle 34 and discontinuities at hole set 40 to pro duce sound attenuation as well as the aforedescribed reverse negative pulse for scavenging at the engine ex haust port. These combined functions reduce the overall length of previous silencer assemblies with such combined functions. The in-between volume 18 further serves to separate the wave interference discontinuities in the first and

second sections

20, 22 to reduce noise turbulence at the discontinuities within the wave interference silencer sections of the assembly 10. The first

wave interference sections

20, 22 have a combined first and second effect to attenuate a wide range of sound frequencies. Thus. the arrangement is suitable for use in the exhaust system of internal combustion engines and is especially suited for use in exhaust systems for two-cycle internal combustion engines.

A secorn embodiment of the invention is illustrated in FIG. 4. It includes an outer casing 74 having conically formed

end closures

76, 78 at opposite ends thereof. As in the first embodiment of the invention, a first wave interference silencer 78 is located at the inlet end of the outer casing 74 closed by the closure 76. It includes an open ended tube 80 having an inlet end 82 thereof adapted to be connected to an exhaust pipe of an engine. An annular extension flange 84 on the conical enclosure 76 engages the outer periphery of the tube 80 at the inlet end 82 thereof and is sealed with respect thereto by an annular weld segment 86.

The outlet end 88 of the tube 80 is located immediately upstream of an open volume 90 in the outer casing 74 which is located upstream of the inlet end of a second wave interference assembly 92 located within the outer casing 74 upstream of the end closure 78. The wave interference assembly 92 includes an open ended tube 94 of smaller diameter than tube 80 and located coaxially thereof. It includes an inlet end 96 located in alignment with the outlet end 88 of the tube 80 and an outlet end 98 that is adapted to be connected to a tailpipe of a vehicle. The outlet end 98 is supported by an annular flanged extension 100 on the conical enclosure 78 that engages the outer surface of the outlet end 98 and is sealed with respect thereto by means of an annular weld bead 102.

As in the first embodiment, the length of the tube 80 is selected to produce a reflected negative pulse back to the inlet manifold of the engine for scavenging exhaust flow therefrom. Furthermore, it supports a helical baffle 104 on the outer surface thereof which has an inner edge 106 in engagement with the outer surface of the tube 80 and an outer edge 108 thereon in engagement with the inner surface of the outer casing 74. The baffle 104 includes an inlet end 110 in communication with an annular cavity 112 formed by the closure 76 and an outlet end 114 at the in between volume 90. The helical baffle 104 forms an elongated flow path 116 which winds around the outer circumference of the tube 80 to have a length greater than the length of the tube between the inlet end 110 and the outlet end 114 of the baffle 104. The wave interference section 78 includes a set of openings 118 in the tube 80 at the location of the cavity 112. These holes have a crosssectional flow area approximately equal to the cross sectional flow area of the tube and serve as the entrance to the elongated path 116 formed by the helical baffle 104. In accordance withknown wave interference theory, the length of the path 116 is selected to produce an attenuation of a first frequency of sound in the engine exhaust as the exhaust passes through the wave interference section 78. This silencing action is in addition to the function of the tuned tube 80 to produce a negative scavenging pulse at the exhaust port of the engine.

In this embodiment of the invention, the second wave interference silencer section 92 is modified as compared to the wave interference silencer section 54 in the first embodiment. lt includes a second tube 120 located radially outwardly of and in spaced relationship to the tube 94. Tube 120 is open ended and extends from the upstream end 96 of the tube 94 to a point immediately upstream of an annular cavity 122 formed by the end closure 78. The annular cavity 122 is communicated through a set of holes 124 corresponding to the set of holes in the wave interference section 22 in the embodiment of FIGS. 1-3. The section 92 includes a first helical baffle 126 extending about the outer sur face of the tube 94 between the inlet end 96 thereof and the cavity 122. it includes an inner edge 128 thereon in engagement with the outer surface of the tube 94 between the aforesaid mentioned points and an outer edge 130 that is in engagement with the inner surface of the tube 120 thereby to define an elongated helical groove or flow path 132 from the inlet end 96 of the tube 94 to the cavity 122. Further, the assembly 92 includes an outer baffle 133 formed as a helix and wound around the outer surface of the tube 120 between the inlet end 134 thereof and the outlet end 136 thereof to the cavity 122. The vane includes an inner edge 138 thereon in engagement with the outer surface of the support tube 120 and an outer edge 140 in engagement with the inner surface of the outer casing 92 to define an elongated helical flow path 142 from the open volume 90 to the cavity 122. In this embodiment, the

elongated paths

142, 132 within the wave interference silencer section 92 serve to attenuate three distinct ranges of sound frequencies in addition to the at tenuation effect produced by the elongated flow path 116 in the wave interference silencer section 78.

In this embodiment of the invention, the openings 118 serve to bridge the open volume 90 to spread the negative pulse produced by the power tuned tube 80 to improve scavenging effect and to produce less turbulence noise at the interacting areas defined by the

openings

118, 124.

While the embodiments of the present invention, as herein disclosed constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is:

l. A silencer assembly for muffling noise and scavenging exhaust from an exhaust port of an engine comprising: an outer casing having an inlet end and an outlet end; a first open ended tube having one end located outside said casing and the other end thereof interiorly of said outer casing at the inlet end thereof to define a first outer flow path between said outer casing and said first tube, a second open ended tube having one end lo' cated outside said casing and the other end thereof directed interiorly of said outer casing at the outlet end thereof to define a second outer flow path between said outer casing and said second tube, said first and second tubes being located coaxially of one another and having open ends thereon located opposite one another in spaced relationship with respect to one another, said outer casing defining an open volume between said oppositely located open ends of said first and second tubes, a first wave interference helical baffle vane located within said first outer flow path having an inlet end and an outlet end in communication with said open volume, a second wave interference helical baffle vane located within said second outer fiow path having an inlet end in communication with said open volume and an outlet end, means forming openings in said first tube communicating the interior of said tube with said first outer flow path at the inlet end of the first turn of said first helical baffle vane for producing a reflected wave from the open volume to the exhaust port of the engine, said first tube having a tuned length for producing a negative pressure at the exhaust port to reduce back pressure and to improve volumetric efficiency of the engine, said first interference helical baffle vane and said openings further serving to produce an interference wave for attenuating a first range of sound waves in said engine exhaust, said second tube having openings therein within said outer case in communication with the second outer flow path at the outlet end of said helical baffie vane to produce an interference wave to attenuate a second range of sound frequencies within said exhaust.

2. A silencer assembly comprising: an outer casing defining an interior volume, first wave interference means for directing exhaust into the interior volume of said outer casing, second wave interference means for directing exhaust from said interior volume of said outer casing, said first wave interference means including a first open ended inner tube with one end of said tube outside said casing and the other open end inside said casing and having a length to reflect an exhaust gas pressure pulse from the other open end of the first inner tube within the interior volume of the outer casing to the exhaust port of an engine to produce a negative pulse at the engine exhaust port for producing a scavenging effect, said second wave interference means including an open ended inner tube located coaxially of said first tube in spaced relationship therewith and defining an exhaust path from said outer casing, said first and second wave interference means each including a helical baffle defining a flow path located radially outwardly of each of said first and second tubes, said tubes and said outer flow paths being spaced apart from one another by an open volume within said interior volume of said outer casing, and holes within said first tube communicating with the inlet end of the outer path of said first wave interference silencer means to join with the open volume thereby to broaden the negative pulse at the exhaust port of an engine.

3. A power tuned silencer assembly comprising: an outer tubular casing having end closures to define a sealed interior volume, first wave interference means within one end of said volume including a first open ended tube with an inlet exterior of said casing and an outlet end located adjacent the midpoint of the interior volume of said outer casing, second wave interference means within said sealed volume including a second open ended tube located coaxially of said first tube and including an inlet end thereof located coaxially of the outlet end of said first tube in spaced relationship therewith within said outer casing and an outlet end ex terior of said outer casing, said first tube having a length to produce a reflected wave from the interior volume to an engine exhaust port for producing a negative pulse at the engine exhaust port for scavenging an engine cylinder, said first wave interference means including means for attenuating a first range of sound frequencies in an engine exhaust, said second wave interference means including means for attenuating a second range of sound frequencies in the engine exhaust, said first interference means including a helical baffle on the exterior of said first tube to define an outer acoustical path open to said interior volume, said first tube having a plurality of openings at the inlet end thereof to intercommunicate said outer acoustical path and said sealed interior volume of said outer casing to broaden the negative pulse at the engine exhaust to improve scavenging of exhaust flow therefrom.

4. A power tuned silencer assembly comprising: an outer casing having closures on opposite ends thereof, a first open ended tube supported on one end of said outer casing centrally thereof, said first tube including an inlet end exterior of said casing adapted to be connected to the exhaust pipe of an engine and an outlet end located within the interior of said outer casing, a second tube supported on the opposite end of said outer casing including an inlet end located in spaced relationship to the outlet end of said first tube and including an outlet end adapted to be connected to a tailpipe, said outlet end of said first tube and the inlet end of said second tube having an open space volume therebetween within said outer casing, means forming a plurality of openings in said first tube immediately downstream of said inlet end thereof at a point within said outer casing, said openings having a cross-sectional flow area approximately equal to the cross-sectional flow area of said first tube, means defining a second plurality of openings in said second tube adjacent the opposite end wall of said outer casing having a cross sectional flow area approximately equal to the crosssectional flow area of said second tube, a first helical baffle connected between the outer surface of said first tube and the inner surface of said outer casing including an inlet end in communication with said first plurality of openings and an outlet end in communication with said open space volume, a second helical baffle wound on the outer surface of said second tube and connected between said second tube and the inner surface of said outer casing including an inlet end in communication with said open space volume and an outlet end in communication with said second plurality of openings said first tube having a length tuned to produce a reflected wave with a negative pulse at the exhaust port of an engine connected to the inlet end of said first tube for scavenging exhaust gases therefrom. said first plurality of holes communicating said outer path defined by said first baffle to join the in-between open space volume with said first tube interior at said openings to broaden the negative pulse of the reflected wave, said first tube and said first helical baffle in communication with said first plurality of openings further serving to attenuate a first range of sound frequencies in the engine exhaust. said second tube and said second wave interference baffle and said second plurality of openings serving to attenuate a second range of sound frequencies in the exhaust from the engine.

Claims

1. A silencer assembly for muffling noise and scavenging exhaust from an exhaust port of an engine comprising: an outer casing having an inlet end and an outlet end; a first open ended tube having one end located outside said casing and the other end thereof interiorly of said outer casing at the inlet end thereof to define a first outer flow path between said outer casing and said first tube, a second open ended tube having one end located outside said casing and the other end thereof directed interiorly of said outer casing at the outlet end thereof to define a second outer flow path between said outer casing and said second tube, said first and second tubes being located coaxially of one another and having open ends thereon located opposite one another in spaced relationship with respect to one another, said outer casing defining an open volume between said oppositely located open ends of said first and second tubes, a first wave interference helical baffle vane located within said first outer flow path having an inlet end and an outlet end in communication with said open volume, a second wave interference helical baffle vane located within said second outer flow path having an inlet end in communication with said open volume and an outlet end, means forming openings in said first tube communicating the interior of said tube with said first outer flow path at the inlet end of the first turn of said first helical baffle vane for producing a reflected wave from the open volume to the exhaust port of the engine, said first tube having a tuned length for producing a negative pressure at the exhaust port to reduce back pressure and to improve volumetric efficiency of the engine, said first interference helical baffle vane and said openings further serving to produce an interference wave for attenuating a first range of sound waves in said engine exhaust, said second tube having openings therein within said outer case in communication with the second outer flow path at the outlet end of said helical baffle vane to produce an interference wave to attenuate a second range of sound frequencies within said exhaust.

3. A power tuned silencer assembly comprising: an outer tubular casing having end closures to define a sealed interior volume, first wave interference means within one end of said volume including a first open ended tube with an inlet exterior of said casing and an outlet end located adjacent the midpoint of the interior volume of said outer casing, second wave interference means within said sealed volume including a second open ended tube located coaxially of said first tube and including an inlet end thereof located coaxially of the outlet end of said first tube in spaced relationship therewith within said outer casing and an outlet end exterior of said outer casing, said first tube having a length to produce a reflected wave from the interior volume to an engine exhaust port for producing a negative pulse at the engine exhaust port for scavenging an engine cylinder, said first wave interference means including means for attenuating a first range of sound frequencies in an engine exhaust, said second wave interference means including means for attenuating a second range of sound frequencies in the engine exhaust, said first interference means including a helical baffle on the exterior of said first tube to define an outer acoustical path open to said interior volume, said first tube having a plurality of openings at the inlet end thereof to intercommunicate said outer acoustical path and said sealed interior volume of said outer casing to broaden the negative pulse at the engine exhaust to improve scavenging of exhaust flow therefrom.

4. A power tuned silencer assembly comprising: an outer casing having closures on opposite ends thereof, a first open ended tube supported on one end of said outer casing centrally thereof, said first tube including an inlet end exterior of said casing adapted to be connected to the exhaust pipe of an engine and an outlet end located within the interior of said outer casing, a second tube supported on the opposite end of said outer casing including an inlet end located in spaced relationship to the outlet end of said first tube and including an outlet end adapted to be connected to a tailpipe, said outlet end of said first tube and the inlet end of said second tube having an open space volume therebetween within said outer casing, means forming a plurality of openings in said first tube immediately downstream of said inlet end thereof at a point within said outer casing, said openings having a cross-sectional flow area approximately equal to the cross-sectional flow area of said first tube, means defining a second plurality of openings in said second tube adjacent the opposite end wall of said outer casing having a cross-sectional flow area approximately equal to the cross-sectional flow area of said second tube, a first helical baffle connected between the outer surface of said first tube and the inner surface of said outer casing including an inlet end in communication with said first plurality of openings and an outlet end in communication with said open space volume, a second helical baffle wound on the outer surface of said second tube and connected between said second tube and the inner surface of said outer casing includiNg an inlet end in communication with said open space volume and an outlet end in communication with said second plurality of openings, said first tube having a length tuned to produce a reflected wave with a negative pulse at the exhaust port of an engine connected to the inlet end of said first tube for scavenging exhaust gases therefrom, said first plurality of holes communicating said outer path defined by said first baffle to join the in-between open space volume with said first tube interior at said openings to broaden the negative pulse of the reflected wave, said first tube and said first helical baffle in communication with said first plurality of openings further serving to attenuate a first range of sound frequencies in the engine exhaust, said second tube and said second wave interference baffle and said second plurality of openings serving to attenuate a second range of sound frequencies in the exhaust from the engine.