Patent Publication Number: US-6334506-B1

Title: Muffler arrangements and methods

Description:
TECHNICAL FIELD 
     This disclosure relates to silencers, such as mufflers. In particular, this disclosure relates to methods and arrangements for mufflers, which, in addition to normal attenuation duties, are particularly useful for silencing the types of noise associated in the cab environment of a truck, especially a heavy duty truck. 
     BACKGROUND 
     In the trucking industry, there is greater attention being paid to the comfort of the driver. The trucking industry typically uses heavy duty engines, on the order of a horsepower of 300-600 HP. These engines are typically noisy, emitting sound pressure levels on the order of 89-104 dB(A) at full throttle. 
     Because of the noise produced by these engines, there have been muffler arrangements of various types developed to reduce this noise. There are regulations to require noise abatement produced by heavy duty engines. By-and-large, the focus of these regulations has been directed to “drive-by” conditions. That is, the noise is measured from a position that is a set distance away from and external to the truck. 
     The cabs in trucks have been changing over the years to accommodate sleeping quarters. In some instances, the trucks are driven by a team, such that while one person is driving, the other person is resting or sleeping in the sleeping quarter of the cab. Thus, the noise level in the cab needs to be low enough to permit comfort for both the driver and for the team member who is resting. 
     SUMMARY 
     Silencers or muffler arrangements are described that, in certain preferred situations, are particularly useful for attenuating low frequency noise associated with the internal volume of cabs or sleepers in heavy duty trucks. In general, muffler arrangements described herein have an outer wall defining an internal volume; an inlet tube oriented at least partially within the internal volume; an outlet tube construction oriented at least partially within the internal volume and including a diverging section and a choke extension; and a first baffle structure securing the outlet tube construction within the internal volume. Muffler arrangements constructed according to principles described herein will have “extended chokes.” In other words, in preferred constructions, a ratio of the diverging section axial length to the choke extension axial length is preferably less than 3:1. In many preferred embodiments, the first baffle structure defines an aperture arrangement therein to permit gas flow communication therethrough. 
     Methods of muffling heavy duty trucks and of installing mufflers will preferably utilize mufflers constructed according to principles described herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic, perspective view of one embodiment of a truck, depicting its exhaust system; 
     FIG. 2 is a schematic, fractional, top plan view of a cab of the truck with a sleeper cab and an exhaust system; 
     FIG. 3 is a schematic, cross-sectional view of a first embodiment of a muffler arrangement, constructed according to principles of this disclosure; 
     FIG. 4 is a schematic, cross-sectional view of a second embodiment of a muffler arrangement, constructed according to principles of this disclosure; 
     FIG. 5 is a schematic, cross-sectional view of a third embodiment of a muffler arrangement, constructed according to principles of this disclosure; 
     FIG. 6 is a schematic, cross-sectional view of a fourth embodiment of a muffler arrangement, constructed according to principles of this disclosure; 
     FIG. 7 is a schematic, cross-sectional view of a fifth embodiment of a muffler arrangement, constructed according to principles of this disclosure; and 
     FIG. 8 is a schematic, cross-sectional view of a sixth embodiment of a muffler arrangement, constructed according to principles of this disclosure. 
    
    
     DETAILED DESCRIPTION 
     I. Truck Exhaust Noise 
     In connection with the following discussions of preferred muffler designs, it should be understood that preferred mufflers designs need to achieve several principal objectives: 
     1. Satisfactory muffling of ordinary engine exhaust noise that includes both exhaust gas and muffler shell noise (referred to as positive power operation); 
     2. Offer no greater than acceptable levels of back pressure to the system, typically 40 inches of water (about 76 mm of mercury) maximum; 
     3. Satisfactory muffling of engine exhaust noise during both positive power and intermittent use of an engine compression brake, as assessed from within the cab of the truck; and 
     4. Meet size, weight, and shape criteria. 
     As used herein, the term “engine compression brake”, and variants thereof, is used to refer to a type of diesel engine retarder that is used to slow down vehicles, such as trucks, by use of a device in the engine valve train that opens the exhaust valve a slight amount at the end of the usual compression stoke. As a result, the engine is turned into an inefficient pump. The energy input to this pump, i.e., to the engine, comes from the inertia of the moving truck through the power train. This pumping process significantly slows down the moving truck. When used, compression brakes can introduce a great deal of noise, both in exterior conditions and to the interior of the cab. More details about engine compression brakes, noise characteristics, and certain muffler systems used to address engine compression brake noise is described in U.S. Pat. No. 6,082,487, issued on Jul. 4, 2000, and application Ser. No. 09/571,342 filed May 16, 2000, which documents are incorporated herein by reference. 
     Regulations are in place with the intention of managing the issue of exhaust noise. In general, these regulations are intended to address the “total noise” heard by those outside of a truck. This is referred to as “drive-by” conditions. The testing procedures for compliance with the regulations mandate measurement of the noise from some certain distance away from the engine, and outside of the cab. 
     In the past, many muffler arrangements have been built and designed with the objective of complying with the government regulations. Many of these types of muffler arrangements have been focused on the drive-by noise level. It has been found, however, that muffler designs that address drive-by noise conditions may not necessarily address the noise problems inside of the cab of the truck. 
     With certain engines, the cab can be turned into a “drum”, depending upon the geometry of the cab and the particular engine. Some cabs may resonate at the natural frequency that may be driven by the engine fundamental, creating permanent, standing waves in the interior volume of the cab. This aggravates noise conditions within the cab. 
     With drivers acting in teams (one driving while the other person rests), it becomes even more important to manage the noise level inside of the cab. In driving teams, the person not driving needs the cab to be quiet enough to permit rest, so that this person is well rested when taking over driving duties. Even without team driving approaches, it is desirable to improve the overall comfort of the driver. Driver comfort can lead to a less stressed and safe driver. In addition, any long term negative effects on the hearing ability of the driver are reduced with reduced in-cab noise. 
     II. In-Cab Noise Problems 
     Applicants have learned that exhaust noise, when measured in the interior of a truck&#39;s cab, is greatest for the low frequency octave bands, typically at or below 350 Hz. It is believed that low frequency octave bands are more of a problem than high frequency octave bands in the interior of cabs for a variety of reasons. For example, high frequency octave bands are often absorbed and muffled by the upholstery in the cab interior. Low frequency octave bands have longer wavelengths, which tend to resonate in the cab interior. 
     Historically, the focus of noise abatement for exhaust systems has been on total noise. Noise abatement, in general, has not been focused on attenuation of particular octave bands. By designing mufflers focused on low frequency attenuation, and with appropriate levels of attenuation on broad bands common to heavy duty engines, there can be compliance with the government noise abatement regulations for heavy duty trucks as well as reduced in-cab noise for the comfort of the occupants of the cab. 
     III. Techniques in Low Frequency Octave Band Attenuation 
     It has been found by applicants that certain techniques, when designed as part of overall muffler arrangements, will attenuate low frequency octave bands and address the problem of in-cab noise. In general, these techniques can be characterized as mufflers having outlet tubes with extended chokes. By “choke”, “choke extension” or variations thereof it is meant the region of the muffler, typically a tube, that has the smallest cross-sectional area in which gas flow must pass through. A “choke extension” will have a length with an internal dimension, analogous to a diameter, that varies by no more than about 5% along its length. While typically cylindrical, a choke extension may vary somewhat from a true cylinder shape to accommodate dimples, beads, or a small amount of tapering. By “extended choke”, it is meant a choke that has a length, when compared to certain other portions of the muffler, that is longer than many typical prior and conventional muffler arrangements. Typically, “extended chokes” will have a length that, when compared to the length of the diverging section, will have a preferred ratio (i.e., diverging section length to extended choke length ratio of under 3:1; many times, under 2:1; and in some cases, under 1:1.) 
     Further, it has been found that utilizing air flow passages, between a volume referred to as an “inlet chamber” and a volume referred to as an “outlet chamber,” is also helpful (in connection with extended chokes) in low frequency attenuation by reducing back pressure and stabilizing overall temperature. 
     IV. Low Frequency Attenuation Techniques As Applied to Muffler Constructions 
     As mentioned above, the preferred muffler designs need to meet size, weight, shape criteria. In general, for typical heavy-duty trucks, the total vertical distance available for the positioning of the muffler is limited. Standard muffler shapes are cylindrical or oval. For cylindrically-shaped mufflers, the outer dimension will be a diameter. In preferred arrangements, the diameter should be typically no greater than 12 inches. Typical, conventional sizes for cylindrical mufflers for trucks, for example, for heavy duty trucks, have a nominal diameter of 11 inches or a nominal diameter of 10 inches. By “nominal diameter of 11 inches”, it is meant an actual, measured diameter of 10.5 inch to just under 11.5 inch. By “nominal diameter of 10 inches”, it is meant an actual, measured diameter of 9.5 inch to just under 10.5 inch. The inlet and outlet tubes typically are of a standard dimension, such that they can fit with other conventional, standardized tubing in an exhaust system. Typically, this diameter of the inlet and outlet tubes is about 5 inches. For typical heavy-duty trucks, the total vertical distance available for positioning the muffler is limited. The standard muffler lengths for a 10-inch diameter muffler is about 45 inches. With certain heavy-duty trucks, there is a vertical space of up to about 55 or 60 inches available. Many of these 55-inch mufflers will also have outer shell diameters of 11 inches. 
     To address the noise caused by heavy-duty engines experienced internally within the cab of the truck, certain preferred techniques to attenuate low frequency should be applied to the internal design of the muffler. In particular, it has been found that the choke should be made to be longer than conventional designs, on the order of at least 8 inches. For mufflers having an overall length of 55 inches and a diameter of 11 inches, the choke length should be on the order of at least 15 inches, and typically 17-25 inches. Mufflers having an overall length of 45 inches and a diameter of 10 inches should typically be designed with choke lengths at least 6 inches, and typically on the order of 8-15 inches. It is believed that mufflers, when designed with unusually long chokes such as those described herein, are better attenuated then previously existing mufflers to muffle low frequency octave bands that are often the source of noise inside of the cab of trucks. 
     Further, the choke should be designed to have a diameter that is no greater than 4 inches, and usually 3.5 inches or less. 
     Adjacent to the choke extension and leading to the outlet tube of the muffler, there should be included a tubular portion with a diverging or sloping sidewall. As used herein, this section will be referred to as a “diverging section.” The length of the diverging section should usually be less than that of the length of the choke. For mufflers having a diameter of 11 inches, the length of the diverging section should usually be less than ⅔ of the length of the choke. In many instances, it is preferred to have the diverging section less than ⅗ of the length of the choke. For mufflers having a diameter of 10 inches, the length of the diverging section will usually be less than the length of the choke. In many instances, the diverging section is less than 90 percent of the length of the choke. Again, it has been found that when constructed according to these principles, there is a greater attenuation of low frequency octave bands than in previously existing mufflers. 
     The diverging section will typically have a greatest cross-sectional diameter of at least 4 inches, and often about 5 inches. The greatest cross-sectional diameter will be the widest cross-sectional portion of the diverging section. In these instances, the ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be at least 2:1, and often at least 2.5:1. 
     In general, the choke should be a solid section, without perforations. The diverging section should usually have at least some perforations, and in some instances, be perforated for its entire length. In some instances, it has been found that the use of absorbent packing material may be used to attenuate certain octave bands, usually high frequency octave bands. It has been found that usually a full choke is preferred on the inlet tube, either through a star crimp or through a uncrimped, plugged end. By “star crimp”, it is meant that the tube has a cross-sectional at its end region that is substantially different from the cross-section of the tube, sometimes resembling a star type of shape. 
     V. Example Mufflers 
     A. Mufflers Having a Shell Diameter of 11 Inches 
     Attention is first directed to FIG.  3 . In FIG. 3, a first improved muffler design constructed according to principles of this disclosure is generally presented. The specific muffler design of FIG. 3 has an overall outer diameter of about 11 inches. By “outer diameter”, it is meant the largest dimension of a cross-section taken substantially perpendicular to a line from the inlet to the outlet. For typical mufflers, the outer shell is a cylindrical body, and the outer diameter is the diameter of this cylindrical body. 
     The overall length of the outer shell for the embodiment of FIG. 3 is about 55 inches. Herein, the term “length” refers to the length of the outer shell or the outer diameter body, i.e., to the longitudinal length of the wide part of the shell. That is, the length of tubes at the inlet and outlet are generally disregarded when this reference is made. 
     1. The Embodiment of FIG.  3   
     The arrangement of FIG. 3 is well adapted for use with heavy-duty trucks. The arrangement of FIG. 3 is particularly suitable for use with a dual exhaust system (DVV). 
     Referring still to FIG. 3, the improved muffler is generally indicated at reference number  10 . The muffler  10  includes an outer casing, shell, or body  12  with an outer wall  13  having first and second opposite ends  14  and  15 . The longitudinal distance between ends  14  and  15  preferably is about 55 inches. 
     The muffler  10  includes an inlet tube  16 , projecting from end  14 , and an outlet tube  17 , projecting from end  15 . In operation, engine noise and exhaust are directed into the muffler  10  through inlet tube  16 , with the exhaust eventually passing outwardly through outlet tube  17 . In general, in operation, muffler  10  will be positioned vertically, with inlet tube  16  toward the bottom. The preferred muffler  10  depicted has an “in-line” design. That is, a centerline  16   a  of the inlet tube  16  is substantially co-linear with a centerline  16   b  of the outlet tube  17 . This avoidance of a substantially tortuous exhaust flow path inhibits flow loss (back pressure build up) during operation. 
     Inlet tube  16  is secured within end  14  by baffles  19  and  20 . Baffle  19  is an end baffle enclosing end  14 , and has a central aperture  23  through which inlet tubes  16  extends. Baffle  19  can be a standard baffle for an 11-inch diameter muffler. 
     As indicated previously, inlet tube  16  is also secured in position by extending through baffle  20 . Baffle  20  is positioned secured against the outer shell  13  and spaced inwardly from the baffle  19  a distance of about 3-4 inches. Baffle  20  preferably is a solid, unperforated baffle. The baffle  20  includes a central aperture  24  through which inlet tube  16  extends, and by which inlet tube  16  is secured in position, for example through a weld. Note that the inlet tube  16  preferably includes a series of open grooves or slots  32 . These slots  32  can be for aiding connection and clamping to other tubes in the exhaust assembly. Slots  32  are generally of a type described in U.S. Pat. No. 4,113,289, which patent is incorporated by reference herein. 
     Attention is now directed to region  27  of inlet tube  16 . Region  27  preferably comprises a perforated section  28  of inlet tube  16  positioned between baffles  19  and  20 . As a result of perforated section  28 , exhaust gasses and exhaust sound entering muffler  10 , through inlet tube  16 , can expand into volume  30  between baffles  19  and  20 . Volume  30  acts as an expansion-can resonator. 
     Continuing inwardly and away from end  14 , the inlet tube  16  has a solid, unperforated region  33 . Moving further inwardly from solid region  33 , perforated region  36  is encountered. Perforated region  36  allows exhaust gasses and sound within inlet tube  16  to expand into volume  38  referred to herein as “inlet chamber.” 
     Beyond perforated region  36 , inwardly is positioned unperforated end section  40 . Preferably, end section  40  is a non-crimped construction but can be crimped, in other embodiments. By “non-crimped”, it is meant that the inlet tube has a cross-section at its end region that is not substantially different from the cross-section of the inlet tube. If circular, the inlet tube has a diameter at its end region that is not more or less than about 10 percent from the diameter of the rest of the inlet tube. 
     Inlet tube  16  is designed to function as a full choke. By “full choke”, it is meant that the airflow through the inlet tube  16  must flow through a perforated region in the inlet tube, and if there is any opening axially in the inlet tube, the open area is smaller than one perforation. The full choke of the inlet tube  16  disrupts the airflow by, in this instance, plug  41  and forcing the air to flow through the perforated region  36 . 
     Attention is now directed to the outlet tube construction. Outlet tube construction  50 , in the embodiment illustrated, has four main regions: a choke extension  52 ; a diverging section  54 ; a bell mouth inlet  62 ; and an outlet section  56 . The outlet tube construction  50  is secured within the shell  12  by baffle  51 , baffle  68 , and baffle  70 . The outlet tube construction  50  has a total length, from end  58  to the portion  60  that ends at the end  15  of at least 30 in., typically 40-45 in. At the end  58  is a bell  62 . The bell  62  helps to direct gas flow inwardly through the outlet tube construction  50 . Adjacent to the bell  62  is the choke extension  52 . The choke extension  52  is preferably cylindrical in shape, with a diameter of at least 2 inches, no greater than 4 inches, and typically 3-3.5 inches. The choke extension  52  will have a length at least 14 inches, no greater than 30 inches, and typically 18-25 inches. Among other things, the choke extension  52  functions to attenuate low frequency octave bands, on the order of 350 Hz and below. 
     Adjacent to the choke extension  52  and moving in a direction toward end  15 , there is the diverging section  54 . The diverging section  54  has a tapered or angled sidewall  64  that angles in a direction radially outwardly, extending from the choke  52  toward the outlet section  56 . In particular, the sidewall  64  extends at an angle relative to the longitudinal axis  16   b  of at least 5°, no greater than about 13°, and typically about 8°. Preferably, the wall  64  has a circular cross-section, such that the diverging region  54  forms a frusto-conical section. A portion  65  of the diverging region  54  is perforated, to permit gas flow to travel from the outlet tube construction  50  into the volume  66 . Volume  66 , between baffle  51  and baffle  68  is referred to herein as “outlet chamber.” The projected length of the diverging section  54  is at least 5 inches, no greater than 15 inches, and typically 8-12 inches. It can be seen that the preferred ratio of the length of the diverging section  54  to the length of the choke  52  is less than 1:1, typically less than 0.9:1 and in this case, about 0.7:1-0.8:1. 
     Adjacent to the diverging section  54  is the outlet tube section  56 . This is defined as the section between the end  15  of the muffler  10  and the point at which the diverging wall  64  stops diverging and is shaped in a straight, cylindrical section. Note that baffles  68 ,  70  hold the outlet tube  50  in place relative to the outer shell  12  adjacent to the end  15 . There is a volume  72  defined between baffle  68  and baffle  70 . The extension  74  of outlet tube section  56  that extends between baffle  68  and baffle  70  is perforated, to allow exhaust gas to flow into the volume  72 . 
     The outlet tube section  56  further continues from extension  74  to end  15 . Beyond end  15 , there is a portion  76  with a plurality of slots  78 , which allows fastening and connection to other exhaust flow tubes. 
     The diverging section  54  will have a greatest area of diameter at the point in which it terminates, and where the outlet section  56  begins. The diameter of the diverging section  54  at this point will be greater than the diameter of the choke  52 . In this case, the diameter of the diverging section  54  will be at least 4 inches, and typically about 5 inches. A ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be greater than 2.0:1, typically greater than 2.5:1, and in this case, about 2.6-3.0:1. 
     Still in reference to FIG. 3, attention is directed to the baffle  51 . The baffle  51  has an aperture  53  for accommodating the outlet tube construction  50 . In referred embodiments, the aperture  53  is centered in the baffle  51 . The baffle  51  also includes an aperture arrangement  55  to pennit gas flow between the inlet chamber  38  and the outlet chamber  66 . The aperture arrangement  55  includes at least one, no more than ten, and in some cases four apertures extending completely through the baffle  51 . In the particular embodiment illustrated in FIG. 3, there is a single aperture  57 , sometimes referred to as a “bleed through aperture.” Preferably, the aperture arrangement  55  will have a total open area, as compared to the total perimeter cross-sectional area of the baffle  51 , that is sufficient to relieve the back pressure through the choke  52 . Further, with the use of aperture arrangement  55 , the outlet chamber  66  maintains a temperature close to the temperature of the inlet chamber  38 . In addition, the aperture arrangement  55  helps to allow for an outlet tube construction  50  that is “anti-whistle bead free.” In other words, the outlet tube construction  50  generally has a straight wall and is absent any indents or projections that are sometimes put in outlet tubes to prevent whistling. Anti-whistle beads are described in U.S. Pat. No. 4,023,645, incorporated by reference herein. Usable ratios of the total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle  51  are as follows: at least 1:77, no greater than 1:484, and preferably 1:200-1:400. By the term “total cross-sectional, perimeter area of the baffle  51 ,” it is meant the total area within the perimeter of the baffle  51 , including the area occupied by the aperture arrangement and the area occupied by the aperture  53  (i.e., the “foot print” of the baffle  51 ″). In this instance, because the cross-sectional area of the baffle  51  is generally circular, the total cross sectional perimeter area of the baffle  51  is approximately πr 2 . 
     2. The Embodiment of FIG.  4   
     Attention is directed now to FIG.  4 . In FIG. 4, another improved muffler design constructed according to principles of this disclosure is generally presented. The specific muffler design of FIG. 4, as with FIG. 3, has an overall outer diameter of about 11 inches and an overall length of the outer shell of about 55 inches. The muffler of FIG. 4 is particularly suited for use with a single vertical exhaust system (SVV). 
     Referring still to FIG. 4, the improved muffler is generally indicated at reference  100 . The muffler  100  includes an outer casing, shell, or body  102  with an outer wall  103  having first and second opposite ends  104  and  105 . The longitudinal distance between ends  104  and  105  preferably is about 55 inches. 
     The muffler  100  includes an inlet tube  106 , projecting from end  104 , and an outlet tube  107 , projecting from end  105 . In operation, engine noise and exhaust are directed into the muffler  100  through inlet tube  106 , with the exhaust eventually passing outwardly through outlet tube  107 . 
     Inlet tube  106  is secured within end  104  by baffles  109  and  120 . Baffle  109  is an end baffle enclosing end  104 , and has a central aperture  123  through which inlet tubes  106  extends. Baffle  109  can be a standard baffle for an 11-inch diameter muffler. 
     As indicated previously, inlet tube  106  is also secured in position by extending through baffle  120 . Baffle  120  preferably is a solid, unperforated baffle. The baffle  20  includes a central aperture  124  through which inlet tube  106  extends, and by which inlet tube  106  is secured in position, for example through a weld. Note that the inlet tube  106  preferably includes open grooves or slots  132 . These slots  132  can be for aiding connection and clamping to other tubes in the exhaust assembly. 
     Attention is now directed to region  127  of inlet tube  106 . Region  127  preferably comprises a perforated section  128  of inlet tube  106  positioned between baffles  109  and  120 . As a result of perforated section  128 , exhaust gasses and exhaust sound entering muffler  100 , through inlet tube  106 , can expand into volume  130  between baffles  109  and  120 . Volume  130  acts as an expansion-can resonator. 
     Continuing inwardly and away from end  104 , the inlet tube  106  has a solid, unperforated region  133 . Moving further inwardly from solid region  133 , perforated region  136  is encountered. Perforated region  136  allows exhaust gasses and sound within inlet tube  106  to expand into volume  138 . 
     Beyond perforated region  136 , inwardly is positioned crimped section  140 . The crimped section  140  is preferably perforated, and bent as described in U.S. Pat. No. 4,580,657, incorporated herein by reference. By “crimped”, it is meant that the inlet tube has a cross-section at its end region that is substantially different from the cross-section of the inlet tube. For example, the outer periphery of the inlet tube at the end region may be bent inwardly toward the center of the tube, to a point where it either nearly touches or touches another portion of the periphery. As used in the construction herein, inlet tube  106  operates as a full choke. 
     Attention is now directed to the outlet tube construction. Outlet tube construction  150 , in the embodiment illustrated, has four main regions: a choke extension  152 ; a diverging section  154 ; a bell  162 ; and an outlet section  156 . The outlet tube construction  150  has a total length, from end  158  to the portion  160  that ends at the end  105  of at least 32 in., typically 40-48 in. At the end  158  is bell  162 . The bell  162  helps to direct gas flow inwardly through the outlet tube construction  150 . Adjacent to the bell  162  is the choke extension  152 . The choke extension  152  is preferably cylindrical in shape, with a diameter of at least 2 inches, no greater than 4 inches, and typically 3.25-3.75 inches. The choke extension  152  will have a length at least 14 inches, no greater than 30 inches, and typically 18-25 inches. Among other things, the choke  152  functions to attenuate low frequency octave bands, on the order of 350 Hz and below. 
     Adjacent to the choke extension  152  and moving in a direction toward end  105 , there is the diverging section  154 . The diverging section  154  has a tapered or angled sidewall  164  that angles in a direction radially outwardly, extending from the choke  152  toward the outlet section  156 . In particular, the sidewall  164  extends at an angle relative to the longitudinal axis  106   b  of at least 5°, no greater than about 13°, and typically about 8°. Preferably, the wall  164  has a circular cross-section, such that the diverging region  154  forms a frusto-conical section. The entire portion of the diverging region  154  is perforated, to permit gas flow to travel from the outlet tube construction  150  into the volume  166 . The projected length of the diverging section  154  is at least 5 inches, no greater than 15 inches, and typically 8-12 inches. It can be seen that the preferred ratio of the length of the diverging section  154  to the length of the choke  152  is less than 1:1, typically less than 0.7:1 and in this case, about 0.5:1-0.6:1. 
     Adjacent to the diverging section  154  is the outlet tube section  156 . This is defined as the section between the end  105  of the muffler  100  and the point at which the diverging wall  164  stops diverging and is shaped in a straight, cylindrical section. Note that there are pair of baffles  168 ,  170  that hold the outlet tube  150  in place relative to the outer shell  102  adjacent to the end  105 . There is a volume  172  defined between baffle  168  and baffle  170 . The extension  174  of outlet tube section  156  that extends between baffle  168  and baffle  170  is perforated, to allow exhaust gas to communicate with the volume  172 . 
     The outlet tube section  156  further continues from extension  174  to end  105 . Beyond end  105 , there is a portion  176  with a plurality of slots  178 , which allow fastening and connection to other exhaust flow tubes. 
     The diverging section  154  will have a greatest area of diameter at the point in which it terminates, and where the outlet section  156  begins. The diameter of the diverging section  154  at this point will be greater than the diameter of the choke  152 . In this case, the diameter of the diverging section  154  will be at least 4 inches, and typically about 5 inches. A ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be greater than 1.5:1, typically greater than 1.75:1, and in this case, about 2.0:1. 
     The baffle  151  has an aperture  153  for accommodating the outlet tube construction  150 . In preferred embodiments, the aperture  153  is centered in the baffle  151 . The baffle  151  also includes a bleed hole or an aperture arrangement  155  to permit gas flow between the inlet chamber  138  and the outlet chamber  166 . The aperture arrangement  155  includes at least one, no more than ten, and in some cases four apertures extending completely through the baffle  151 . As with the FIG. 3 embodiment, aperture arrangement  155  will have a total open area, as compared to the total perimeter cross-sectional area of the baffle  151 , that is helpful in: relieving the back pressure through the choke  152 ; maintaining temperature of the outlet chamber  166  close to the temperature of the inlet chamber  138 ; and allowing for an anti-whistle bead free outlet tube construction  150 . Usable ratios of the total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle  151  are as follows: at least 1:77, no greater than 1:484, and preferably 1:250-1:350. 
     3. Common Properties of 11 Inch Mufflers. 
     In general, many preferred mufflers having shell diameters of 11 inches will have a choke length that is greater than the length of the diverging section. Typically, for example, the length of the diverging section will be less than ¾ and often less than ⅔ of the length of the choke (i.e., a ratio of diverging section length to choke length of less than 0.75:1, and often less than 0.67:1). The length of the choke will usually be at least 15 inches, and typically greater than 17 inches, with the length of the diverging section no greater than 22 inches, and usually at least 7 inches. 
     Many typical mufflers having shell diameters of 11 inches will also have an aperture arrangement or bleed hole through the baffle that separates the inlet chamber from the outlet chamber. The total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle will generally, for example, be at least 1:50, no greater than 1:500, and typically 1:200-1:400. As explained above, the aperture arrangement helps to reduce back pressure through the choke, as compared to arrangements that would not have a bleed through aperture arrangement. Also, the aperture arrangement helps to maintain a uniform temperature throughout the interior volume of the muffler. Further, the aperture arrangement in the baffle allows for an anti-whistle bead free outlet tube construction. 
     For many mufflers, they will be constructed of metal, usually steel. Many parts are constructed of 14-20 gauge steel. 
     B. Mufflers Having a Shell Diameter of 10 Inches 
     1. The Embodiment of FIG.  5   
     Attention is directed now to FIG.  5 . In FIG. 5, another improved muffler design constructed according to principles of this disclosure is generally presented. The specific muffler design of FIG. 5 has an overall outer diameter of about 10 inches and an overall length of the outer shell of about 45 inches. The muffler of FIG. 5 is particularly suited for use with a dual vertical exhaust system (DVV). 
     Referring still to FIG. 5, the improved muffler is generally indicated at reference  200 . The muffler  200  includes an outer casing, shell, or body  202  with an outer wall  203  having first and second opposite ends  204  and  205 . The longitudinal distance between ends  204  and  205  preferably is about 45 inches. 
     The muffler  200  includes an inlet tube  206 , projecting from end  204 , and an outlet tube  207 , projecting from end  205 . In operation, engine noise and exhaust are directed into the muffler  200  through inlet tube  206 , with the exhaust eventually passing outwardly through outlet tube  207 . 
     Inlet tube  206  is secured within end  204  by baffles  209  and  220 . Baffle  209  is an end baffle enclosing end  204 , and has a central aperture  223  through which inlet tubes  206  extends. Baffle  209  can be a standard baffle for a 10-inch diameter muffler. 
     As indicated previously, inlet tube  206  is also secured in position by extending through baffle  220 . Baffle  220  preferably is a solid, unperforated baffle. The baffle  220  includes a central aperture  224  through which inlet tube  206  extends, and by which inlet tube  206  is secured in position, for example through a weld. Note that the inlet tube  206  preferably includes open grooves or slots  232 . These slots  232  can be for aiding connection and clamping to other tubes in the exhaust assembly. 
     Attention is now directed to region  227  of inlet tube  206 . Region  227  preferably comprises a perforated section  228  of inlet tube  206  positioned between baffles  209  and  220 . As a result of perforated section  228 , exhaust gasses and exhaust sound entering muffler  200 , through inlet tube  206 , can expand into volume  230  between baffles  209  and  220 . Volume  230  acts as an expansion-can resonator. 
     Continuing inwardly and away from end  204 , the inlet tube  206  has a solid, unperforated region  233 . Moving further inwardly from solid region  233 , perforated region  236  is encountered. Perforated region  236  allows exhaust gasses and sound within inlet tube  206  to expand into volume  238 . 
     Beyond perforated region  236 , inwardly is positioned unperforated end section  240 . Preferably end section  240  is a non-crimped construction. Inlet tube  206  is designed to function as a full choke. 
     Attention is now directed to the outlet tube construction  250 . Outlet tube construction  250 , in the embodiment illustrated, has four main regions: a choke extension  252 ; a diverging section  254 ; bell  262 ; and an outlet section  256 . The outlet tube construction  250  has a total length, from end  258  to the portion  260  that ends at the end  205  of at least 25 in., typically 30-35 in. At the end  258  is bell  262 . The bell  262  helps to direct gas flow inwardly through the outlet tube construction  250 . Adjacent to the bell  262  is the choke extension  252 . The choke extension  252  is preferably cylindrical in shape, with a diameter of at least 2 inches, no greater than 4 inches, and typically 3.0 inches. The choke extension  252  will have a length at least 5 inches, no greater than 30 inches, and typically 7-15 inches. Among other things, the choke extension  252  functions to attenuate low frequency octave bands, on the order of 350 Hz and below. 
     Adjacent to the choke extension  252  and moving in a direction toward end  205 , there is the diverging section  254 . The diverging section  254  has a tapered or angled sidewall  264  that angles in a direction radially outwardly, extending from the choke extension  252  toward the outlet section  256 . In particular, the sidewall  264  extends at an angle relative to the longitudinal axis  206   b  of at least 5°, no greater than about 13°, and typically about 8°. Preferably, the wall  264  has a circular cross-section, such that the diverging region  254  forms a frusto-conical section. A portion  257  of the diverging region  254  is perforated, to permit gas flow to travel from the outlet tube construction  250  into the volume  266 . The projected length of the diverging section  254  is at least 8 inches, no greater than 22 inches, and typically 14-17 inches. It can be seen that the preferred ratio of the length of the diverging section  254  to the length of the choke extension  252  is greater than 1.0:1, typically less than 3.0:1 and in this case, about 2:1. 
     Adjacent to the diverging section  254  is the outlet tube section  256 . This is defined as the section between the end  205  of the muffler  200  and the point at which the diverging wall  264  stops diverging and is shaped in a straight, cylindrical section. Note that there are pair of baffles  268 ,  270  that hold the outlet tube  250  in place relative to the outer shell  202  adjacent to the end  205 . There is a volume  272  defined between baffle  268  and baffle  270 . The extension  274  of outlet tube section  256  that extends between baffle  268  and baffle  270  is perforated, to allow exhaust gas to flow into the volume  272 . 
     The outlet tube section  256  further continues from extension  274  to end  205 . Beyond end  205 , there is a portion  276  with a plurality of slots  278 , which allow fastening and connection to other exhaust flow tubes. 
     The diverging section  254  will have a greatest area of diameter at the point in which it terminates, and where the outlet section  256  begins. The diameter of the diverging section  254  at this point will be greater than the diameter of the choke extension  252 . In this case, the diameter of the diverging section  254  will be at least 4 inches, and typically about 5 inches. A ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be greater than 1.5:1, typically greater than 2.0:1, and in this case, about 2.8:1. 
     The baffle  251  has an aperture  253  for accommodating the outlet tube construction  250 . As with the previously described embodiments, the baffle  251  also includes a bleed hole or an aperture arrangement  255  to permit gas flow between the inlet chamber  238  and the outlet chamber  266  and to achieve the advantages also described above. The aperture arrangement  255  includes at least one, no more than eight, and in some cases four apertures extending completely through the baffle  251 . Usable ratios of the total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle  251  are as follows: at least 1:77, no greater than 1:484, and preferably 1:275-1:325. 
     2. The Embodiment of FIG.  6   
     Attention is directed now to FIG.  6 . In FIG. 6, another improved muffler design constructed according to principles of this disclosure is generally presented. As with the embodiment of FIG. 5, the specific muffler design of FIG. 6 has an overall outer diameter of about 10 inches and an overall length of the outer shell of about 45 inches. The muffler of FIG. 6 is particularly suited for use with a single vertical exhaust system (SVV). 
     Referring still to FIG. 6, the improved muffler is generally indicated at reference  300 . The muffler  300  includes an outer casing, shell, or body  302  with an outer wall  303  having first and second opposite ends  304  and  305 . The longitudinal distance between ends  304  and  305  preferably is about 45 inches. 
     The muffler  300  includes an inlet tube  306 , projecting from end  304 , and an outlet tube  307 , projecting from end  305 . In operation, engine noise and exhaust are directed into the muffler  300  through inlet tube  306 , with the exhaust eventually passing outwardly through outlet tube  307 . 
     Inlet tube  306  is secured within end  304  by baffles  309  and  320 . Baffle  309  is an end baffle enclosing end  304 , and has a central aperture  323  through which inlet tubes  306  extends. Baffle  309  can be a standard baffle for an 10-inch diameter muffler. 
     As indicated previously, inlet tube  306  is also secured in position by extending through baffle  320 . Baffle  320  preferably is a solid, unperforated baffle. The baffle  320  includes a central aperture  324  through which inlet tube  306  extends, and by which inlet tube  306  is secured in position, for example through a weld. Note that the inlet tube  306  preferably includes open grooves or slots  332 . These slots  332  can be for aiding connection and clamping to other tubes in the exhaust assembly. 
     Attention is now directed to region  327  of inlet tube  306 . Region  327  preferably comprises a perforated section  328  of inlet tube  306  positioned between baffles  309  and  320 . As a result of perforated section  328 , exhaust gasses and exhaust sound entering muffler  300 , through inlet tube  306 , can expand into volume  330  between baffles  309  and  320 . Volume  330  acts as an expansion-can resonator. 
     Continuing inwardly and away from end  304 , the inlet tube  306  has a solid, unperforated region  333 . Moving further inwardly from solid region  333 , perforated region  336  is encountered. Perforated region  336  allows exhaust gasses and sound within inlet tube  306  to expand into volume  338 . 
     Beyond perforated region  336 , inwardly is positioned crimped end section  340 . Preferably, crimped end section  340  is a “star crimp” construction. Inlet tube  306  is designed to function as a full choke. 
     Attention is now directed to the outlet tube construction  350 . Outlet tube construction  350 , in the embodiment illustrated, has four main regions: a choke extension  352 ; a diverging section  354 ; a bell  362 ; and an outlet section  356 . The outlet tube construction  350  has a total length, from end  358  to the portion  360  that ends at the end  305  of at least 20 in., typically 30-35 in. At the end  358  is bell  362 . The bell  362  helps to direct gas flow inwardly trough the outlet tube construction  350 . Adjacent to the bell  362  is the choke extension  352 . The choke extension  352  is preferably cylindrical in shape, with a diameter of at least 2 inches, no greater than 4 inches, and typically 3.0 inches. The choke extension  352  will have a length at least 5 inches, no greater than 30 inches, and typically 7-15 inches. Among other tings, the choke extension  352  functions to attenuate low frequency octave bands, on the order of 350 Hz and below. 
     Adjacent to the choke extension  352  and moving in a direction toward end  305 , there is the diverging section  354 . The diverging section  354  has a tapered or angled sidewall  364  that angles in a direction radially outwardly, extending from the choke extension  352  toward the outlet section  356 . In particular, the sidewall  364  extends at an angle relative to the longitudinal axis  350   b  of at least 5°, no greater than about 13°, and typically about 8°. Preferably, the wall  364  has a circular cross-section, such that the diverging region  354  forms a frusto-conical section. A portion  357  of the diverging region  354  is perforated, to permit gas flow to travel from the outlet tube construction  350  into the volume  366 . The projected length of the diverging section  354  is at least 5 inches, no greater than 30 inches, and typically 6-15 inches. It can be seen that the preferred ratio of the length of the diverging section  354  to the length of the choke extension  352  is less than 2.0:1, typically less than 1.5:1 and in this case, about 0.9:1-1.2:1. 
     Adjacent to the diverging section  354  is the outlet tube section  356 . This is defined as the section between the end  305  of the muffler  300  and the point at which the diverging wall  364  stops diverging and is shaped in a straight, cylindrical section. Note that there are pair of baffles  368 ,  370  that hold the outlet tube  350  in place relative to the outer shell  302  adjacent to the end  305 . There is a volume  372  defined between baffle  368  and baffle  370 . The extension  374  of outlet tube section  356  that extends between baffle  368  and baffle  370  is perforated, to allow exhaust gas to flow into the volume  372 . 
     The outlet tube section  356  further continues from extension  374  to end  305 . Beyond end  305 , there is a portion  376  with a plurality of slots  378 , which allow fastening and connection to other exhaust flow tubes. 
     The diverging section  354  will have a greatest area of diameter at the point in which it terminates, and where the outlet section  356  begins. The diameter of the diverging section  354  at this point will be greater than the diameter of the choke extension  352 . In this case, the diameter of the diverging section  354  will be at least 4 inches, and typically about 5 inches. A ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be greater than 1.5:1, typically greater than 2.0:1, and in this case, about 2.8:1. 
     The baffle  351  has an aperture  353  for accommodating the outlet tube construction  350 . As with the previously described embodiments, the baffle  351  also includes a bleed hole or an aperture arrangement  355  to permit gas flow between the inlet chamber  338  and the outlet chamber  366  and to achieve the advantages also described above. The aperture arrangement  355  includes at least one, no more than ten, and in some cases four apertures extending completely through the baffle  351 . Usable ratios of the total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle  351  are as follows: at least 1:77, no greater than 1:484, and preferably 1:250-1:350. 
     3. The Embodiment of FIG.  7   
     Attention is directed now to FIG.  7 . In FIG. 7, another improved muffler design constructed according to principles of this disclosure is generally presented. As with the embodiment of FIG. 5, the specific muffler design of FIG. 7 has an overall outer diameter of about 10 inches and an overall length of the outer shell of about 45 inches. The muffler of FIG. 7 is particularly suited for use with a single vertical exhaust system (SVV). As described below, it is also well suited for use with engines equipped with engine compression brakes. 
     Referring still to FIG. 7, the improved muffler is generally indicated at reference  400 . The muffler  400  includes an outer casing, shell, or body  402  with an outer wall  403  having first and second opposite ends  404  and  405 . The longitudinal distance between ends  404  and  405  preferably is about 45 inches. 
     The muffler  400  includes an inlet tube  406 , projecting from end  404 , and an outlet tube  407 , projecting from end  405 . In operation, engine noise and exhaust are directed into the muffler  400  through inlet tube  406 , with the exhaust eventually passing outwardly through outlet tube  407 . 
     Inlet tube  406  is secured within end  404  by baffles  409  and  420 . Baffle  409  is an end baffle enclosing end  404 , and has a central aperture  423  through which inlet tubes  406  extends. Baffle  409  can be a standard baffle for an 10-inch diameter muffler. 
     As indicated previously, inlet tube  406  is also secured in position by extending through baffle  420 . Baffle  420  preferably is a solid, unperforated baffle. The baffle  420  includes a central aperture  424  through which inlet tube  406  extends, and by which inlet tube  406  is secured in position, for example through a weld. Note that the inlet tube  406  preferably includes open grooves or slots  432 . These slots  432  can be for aiding connection and clamping to other tubes in the exhaust assembly. 
     Attention is now directed to region  427  of inlet tube  406 . Region  427  preferably comprises a perforated section  428  of inlet tube  406  positioned between baffles  409  and  420 . As a result of perforated section  428 , exhaust gasses and exhaust sound entering muffler  400 , through inlet tube  406 , can expand into volume  430  between baffles  409  and  420 . Volume  430  acts as an expansion-can resonator. 
     Continuing inwardly and away from end  404 , the inlet tube  406  has a solid, unperforated region  433 . Moving further inwardly from solid region  433 , perforated region  436  is encountered. Perforated region  436  allows exhaust gasses and sound within inlet tube  406  to expand into volume  438 . 
     Beyond perforated region  436 , inwardly is positioned crimped end section  440 . Preferably, crimped end section  440  is a “star crimp” construction. Inlet tube  406  is designed to function as a full choke. 
     Spaced from the outer wall  402  is an inner wall  411 . The inner wall  411  extends between baffle  420  and  451 . Preferably, the inner wall  411  is spaced about ⅛-¾ inches, typically about ⅜ inches from the outer wall  402  to define an annular volume  412  therebetween. The volume  412  is filled with packing material  413 , typically fiberglass packing. This helps to attenuate noise, on the order of greater than 500 Hz. High frequency noise is often problematic when utilizing engine compression brakes. More details regarding the use of packing materials in mufflers and the noise problems associated with engine compression brakes are discussed in U.S. Pat. No. 6,082,487, and application Ser. No. 09/571,342 filed May 16, 2000 which is incorporated herein by reference. Packing material, such as fiberglass packing, can be used in an analogous manner in other embodiments, such as the embodiments depicted in FIGS. 3-6, in order to achieve certain results, such as high frequency noise attenuation. 
     Attention is now directed to the outlet tube construction  450 . Outlet tube construction  450 , in the embodiment illustrated, has four main regions: a choke extension  452 ; a diverging section  454 ; a bell  462 ; and an outlet section  456 . The outlet tube construction  450  has a total length, from end  458  to the portion  460  that ends at the end  405  of at least 20 in., typically 25-35 in. At the end  458  is bell  462 . The bell  462  helps to direct gas flow inwardly through the outlet tube construction  450 . Adjacent to the bell  462  is the choke extension  452 . The choke extension  452  is preferably cylindrical in shape, with a diameter of at least 2 inches, no greater than 4 inches, and typically 3.0 inches. The choke extension  452  will have a length at least 5 inches, no greater than 30 inches, and typically 7-15 inches. Among other things, the choke extension  452  functions to attenuate low frequency octave bands, on the order of 350 Hz and below. 
     The choke extension  452  is preferably perforated and circumscribed by a wall  453 . The wall  453  is spaced at least about 0.1 inch, and no greater than about 1 inch from the choke extension  452 . Between the wall  453  and the choke extension  452 , the volume  451  is filled with a packing material  463 , preferably, fiberglass packing. The packing material  463  helps to attenuate high frequencies associated with engine compression braking. 
     Adjacent to the choke extension  452  and moving in a direction toward end  405 , there is the diverging section  454 . The diverging section  454  has a tapered or angled sidewall  464  that angles in a direction radially outwardly, extending from the choke extension  452  toward the outlet section  456 . In particular, the sidewall  464  extends at an angle relative to the longitudinal axis  450   b  of at least 5°, no greater than about 13°, and typically about 8°. Preferably, the wall  464  has a circular cross-section, such that the diverging region  454  forms a frusto-conical section. A portion  453  of the diverging region  454  is perforated, to permit gas flow to travel from the outlet tube construction  450  into the volume  466 . The projected length of the diverging section  454  is at least 5 inches, no greater than 30 inches, and typically 6-15 inches. It can be seen that the preferred ratio of the length of the diverging section  454  to the length of the choke extension  452  is less than 1.5:1, typically less than 1.0:1 and in this case, about 0.7:1-0.9:1. 
     Adjacent to the diverging section  454  is the outlet tube section  456 . This is defined as the section between the end  405  of the muffler  400  and the point at which the diverging wall  464  stops diverging and is shaped in a straight, cylindrical section. Note that there are pair of baffles  468 ,  470  that hold the outlet tube  450  in place relative to the outer shell  402  adjacent to the end  405 . There is a volume  472  defined between baffle  468  and baffle  470 . The extension  474  of outlet tube section  456  that extends between baffle  468  and baffle  470  is perforated, to allow exhaust gas to flow into the volume  472 . 
     The outlet tube section  456  further continues from extension  474  to end  405 . Beyond end  405 , there is a portion  476  with a plurality of slots  478 , which allow fastening and connection to other exhaust flow tubes. 
     The diverging section  454  will have a greatest area of diameter at the point in which it terminates, and where the outlet section  456  begins. The diameter of the diverging section  454  at this point will be greater than the diameter of the choke extension  452 . In this case, the diameter of the diverging section  454  will be at least 3 inches, and typically about 5 inches. A ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be greater than 1.5:1, typically greater than 1.75:1, and in this case, about 2.0:1. 
     The baffle  451  has an aperture  453  for accommodating the outlet tube construction  450 . As with the previously described embodiments, the baffle  451  also includes a bleed hole or an aperture arrangement  455  to permit gas flow between the inlet chamber  438  and the outlet chamber  466  and to achieve the advantages also described above. The aperture arrangement  455  includes at least one, no more than ten, and in some cases four apertures extending completely through the baffle  451 . Usable ratios of the total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle  451  are as follows: at least 1:77, no greater than 1:484, and preferably 1:200-1:400. 
     4. The Embodiment of FIG.  8   
     In FIG. 8, another improved muffler design constructed according to principles of this disclosure is generally presented. The specific muffler design of FIG. 8 has an overall outer diameter of about 10 inches and an overall length of the outer shell of about 45 inches. The muffler of FIG. 8 is particularly suited for use with a dual vertical exhaust system (DVV). As described below, it is also well suited for use with engines equipped with engine compression brakes. 
     Referring still to FIG. 8, the improved muffler is generally indicated at reference  500 . The muffler  500  includes an outer casing, shell, or body  502  with an outer wall  503  having first and second opposite ends  504  and  505 . The longitudinal distance between ends  504  and  505  preferably is about 45 inches. 
     The muffler  500  includes an inlet tube  506 , projecting from end  504 , and an outlet tube  507 , projecting from end  505 . In operation, engine noise and exhaust are directed into the muffler  500  through inlet tube  506 , with the exhaust eventually passing outwardly through outlet tube  507 . 
     Inlet tube  506  is secured within end  504  by baffles  509  and  520 . Baffle  509  is an end baffle enclosing end  504 , and has a central aperture  523  through which inlet tubes  506  extends. Baffle  509  can be a standard baffle for an 10-inch diameter muffler. 
     As indicated previously, inlet tube  506  is also secured in position by extending through baffle  520 . Baffle  520  preferably is a solid, unperforated baffle. The baffle  520  includes a central aperture  524  through which inlet tube  506  extends, and by which inlet tube  506  is secured in position, for example through a weld. Note that the inlet tube  506  preferably includes open grooves or slots  532 . These slots  532  can be for aiding connection and clamping to other tubes in the exhaust assembly. 
     Attention is now directed to region  527  of inlet tube  506 . Region  527  preferably comprises a perforated section  528  of inlet tube  506  positioned between baffles  509  and  520 . As a result of perforated section  528 , exhaust gasses and exhaust sound entering muffler  500 , through inlet tube  506 , can expand into volume  530  between baffles  509  and  520 . Volume  530  acts as an expansion-can resonator. 
     Continuing inwardly and away from end  504 , the inlet tube  506  has a solid, unperforated region  533 . Moving further inwardly from solid region  533 , perforated region  536  is encountered. Perforated region  536  allows exhaust gasses and sound within inlet tube  506  to expand into volume  538 . 
     Beyond perforated region  536 , inwardly is positioned unperforated end section  540 . Preferably, end section  540  is a non-crimped construction. Inlet tube  506  is designed to function as a full choke. 
     Spaced from the outer wall  502  is an inner wall  511 . The inner wall  511  extends between baffle  520  and  551 . Preferably, the inner wall  511  is spaced about ⅛-¾ inch, typically, about ⅜ in., from the outer wall  502  to define an annular volume  512  therebetween. The volume  512  is filled with packing material  513 , typically fiberglass packing. This helps to attenuate noise, on the order of greater than 500 Hz. High frequency noise is often problematic when utilizing engine compression brakes. More details regarding the use of packing materials in mufflers and the noise problems associated with engine compression brakes are discussed in U.S. Pat. No. 6,082,487, which is incorporated herein by reference. 
     Attention is now directed to the outlet tube construction  550 . Outlet tube construction  550 , in the embodiment illustrated, has four main regions: a choke extension  552 ; a diverging section  554 ; a bell  562 ; and an outlet section  556 . The outlet tube construction  550  has a total length, from end  558  to the portion  560  that ends at the end  505  of at least 20 in., typically 30-35 in. At the end  558  is bell  562 . The bell  562  helps to direct gas flow inwardly through the outlet tube construction  550 . Adjacent to the bell  562  is the choke extension  552 . Among other things, the choke extension  552  is preferably cylindrical in shape, with a diameter of at least 2 inches, no greater than 4 inches, and typically 3.0 inches. The choke extension  552  will have a length at least 5 inches, no greater than 30 inches, and typically 7-15 inches. The choke extension  552  functions to attenuate low frequency octave bands, on the order of 350 Hz and below. 
     The choke extension  552  is preferably perforated and circumscribed by a wall  553 . The wall  553  is spaced at least about 0.1 inches, no greater than about 1 inch and typically about 0.4-0.6 in. from the choke extension  552 . Between the wall  553  and the choke extension  552 , the volume  551  is filled with a packing material  563 , preferably, fiberglass packing. The packing material  562  helps to attenuate high frequencies associated with engine compression braking. 
     Adjacent to the choke extension  552  and moving in a direction toward end  505 , there is the diverging section  554 . The diverging section  554  has a tapered or angled sidewall  564  that angles in a direction radially outwardly, extending from the choke extension  552  toward the outlet section  556 . In particular, the sidewall  564  extends at an angle relative to the longitudinal axis  550   b  of at least 5°, no greater than about 13°, and typically about 8°. Preferably, the wall  564  has a circular cross-section, such that the diverging region  554  forms a frusto-conical section. The entire portion of the diverging region  554  is perforated, to permit gas flow to travel from the outlet tube construction  550  into the volume  566 . The projected length of the diverging section  554  is at least 5 inches, no greater than 30 inches, and typically 10-25 inches. It can be seen that the preferred ratio of the length of the diverging section  554  to the length of the choke extension  552  is less than 3.0:1, typically less than 2.5:1 and in this case, 1.6:1-2:1. 
     Adjacent to the diverging section  554  is the outlet tube section  556 . This is defined as the section between the end  505  of the muffler  500  and the point at which the diverging wall  564  stops diverging and is shaped in a straight, cylindrical section. Note that there are pair of baffles  568 ,  570  that hold the outlet tube  550  in place relative to the outer shell  502  adjacent to the end  505 . There is a volume  572  defined between baffle  568  and baffle  570 . The extension  574  of outlet tube section  556  that extends between baffle  568  and baffle  570  is perforated, to allow exhaust gas to flow into the volume  572 . 
     The outlet tube section  556  further continues from extension  574  to end  505 . Beyond end  505 , there is a portion  576  with a plurality of slots  578 , which allow fastening and connection to other exhaust flow tubes. 
     The diverging section  554  will have a greatest area of diameter at the point in which it terminates, and where the outlet section  556  begins. The diameter of the diverging section  554  at this point will be greater than the diameter of the choke extension  552 . In this case, the diameter of the diverging section  554  will be at least 3 inches, and typically about 5 inches. A ratio of the cross-sectional area of the diverging section as compared to the cross-sectional area of the choke will be greater than 1.5:1, typically greater than 1.75:1, and in this case, about 2.75:1. 
     The baffle  551  has an aperture  553  for accommodating the outlet tube construction  550 . As with the previously described embodiments, the baffle  551  also includes a bleed hole or an aperture arrangement  555  to permit gas flow between the inlet chamber  538  and the outlet chamber  566  and to achieve the advantages also described above. The aperture arrangement  555  includes at least one, no more than ten, and in some cases four apertures extending completely through the baffle  551 . Usable ratios of the total open area of the aperture arrangement as compared to the total, cross-sectional, perimeter area of the baffle  551  are as follows: at least 1:77, no greater than 1:484, and preferably 1:250-1:350. 
     5. Common Properties of 10 Inch Mufflers 
     In general, many preferred mufflers having shell diameters of 10 inches will have a choke length that is at least 7 inches, no greater than 30 inches, and typically about 8-15 inches. Typically, the length of the diverging section will at least 5 inches, no greater than 30 inches, and typically about 8-25 inches. 
     For 10-inch mufflers, the ratio of the diverging section to the choke in many arrangements will be less than 3.0:1, typically less than 2.5:1. In many instances, the ratio of the length of the diverging section to the length of the choke will be less than 1.0:1. 
     Further, for many arrangements, 10-inch mufflers will also have the aperture arrangement or a bleed hole in the baffle that separates the inlet chamber from the outlet chamber. As described above, this aperture arrangement helps to reduce back pressure through the choke, provide uniform temperature throughout the interior of the muffler, and result in an outlet tube construction with straight walls that is anti-whistle bead free. 
     For many mufflers, they will be constructed of metal, usually steel. Many parts are constructed of 14-20 gauge steel. 
     C. Installation 
     The muffler arrangements of FIGS. 3-8 can be mounted in a variety of locations on a truck, relative to the driver&#39;s position. Where and how the muffler is installed can affect the amount and the sound quality of in-cab noise. 
     Attention is directed to FIGS. 1 and 2. FIG. 1 shows a schematic view of a typical heavy duty truck  600  having an exhaust system  602  and a cab  603 . A muffler is shown (under a heat shield  605 ) at  604  mounted on the truck frame  606 , and in gas flow communication with the exhaust system  602 . 
     In FIG. 1, the muffler  604  is shown secured to the truck fame  606  through a mounting arrangement  608 . In some instances, mufflers are secured directly to a sidewall of the cab. This can exasperate in-cab noise problems. 
     FIG. 2 shows a schematic, fractional, top plan view of a truck  700 . This view illustrates some of the common places a muffler will be mounted, relative to the position of the driver. In FIG. 2, the truck  700  has a cab  702  and a sleeper  704 . The cargo area of the truck is shown at  706 , with a portion of the length broken away. In the cab  702 , the windshield  708  is schematically depicted as a broken line. A driver seat  710  is illustrated schematically in the cab  702  to generally indicate the position of the driver. Inside of the sleeper  704 , there may typically be a bed, cot, or other sleeping arrangements. 
     Typical places that mufflers are often mounted are illustrated in FIG.  2 . For example, one typical place mufflers are mounted is adjacent to the cab  702  and in front of the sleeper  704 . The muffler can be on the driver&#39;s side, such as position  720 , or on the passenger side, such as position  722 . Another typical place that mufflers are often mounted is behind the sleeper  704 . Again, this can be on the driver&#39;s side such as  730 , or on the passenger side, such as position  732 . Depending on where the muffler is mounted, there will be different sound properties and noise levels conveyed to the person in the driver&#39;s seat  710  and the person resting in the sleeper  704 . 
     The above specification, examples and data provide a complete description of the manufacture and use of the invention. Many embodiments of the invention can be made.