US2056608A

US2056608A - Silencer

Info

Publication number: US2056608A
Application number: US703548A
Authority: US
Inventors: William A Jack
Original assignee: C F BURGES LAB Inc
Current assignee: C F BURGES LAB Inc; C F BURGES LABORATORIES Inc
Priority date: 1933-12-22
Filing date: 1933-12-22
Publication date: 1936-10-06
Anticipated expiration: 1953-10-06

Description

Oct. 6,"19364 W A ACK 3D.' 2,056,608

SILENCER Filed Deo. 22, 1933 FiF-7- 2-1 3 Sheets-Sheet l ATTORNEYS ct. 6, 1936. w, A, JACK, 3D' 2,056,608

SILENCER Filed DeC. 22, 1935 I6 F1 5r Z /6 3 Sheets-Sheet 2 OOO OOO OOO OOO 000 OOO ODO OOo OOO OOO OOO OOO ATTORNEYS Oct, 6, 1936. W. A JACK, 3D 2,056,608

SILENCER Filed Dec. 2 2, 1933 3 Sheets-Sheet 3 fm, JY/m ww zo,

ATTO R N EYS Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE `SILENCER Application December 22, 1933, Serial No. 703,548

` 1s claims. (ci. 181-48) This invention relates to improvements in silencers and particularly those used to silence the intakes and exhausts of internal combustion engines, compressors, pumps and the like. In particular, it relates to an improvement in the type of silencer disclosed and claimed in my copending application Serial No. 545,776, filed June 20, 1931 which includes means for attenuating sounds composed of both high and loW frequencies.

In an exhaust system, gas pulses at high pressure and sounds are both present. Since sound is an alteration in pressure, or a super-position of a number of pressure alterations, propagated in an elastic medium, a sound propagated in gas or air may be called a gaseous pressure wave. It is an object of this invention to provide an improved silencer which attenuates gaseous pressure Waves comprising both sounds and gas pulses of a wide range of frequencies. If the gas pulses are not attenuated or altered in form within the silencer, upon their emergence therefrom they expand into the atmosphere and create sounds. When the attenuation of sound is spoken of herein, it is meant to include the attenuation of gaseous pressure waves which would otherwise result in objectionable sounds being heard.

It is an object of this invention to provide an improvement in the construction of the low frequency attenuating means of such a silencer whereby the effectiveness thereof is increased.

It is a further object of this invention to combine and arrange the high frequency attenuating means with the low frequency attenuating means in such a. manner that greatest possible effects are obtained from both for the size and/or quantity of attenuating means used.

It is a further object of the invention to provide an improved low frequency attenuating construction which may be used by itself, and which is particularly effective for exhausts, where gas pulses are involved.

By way of a brief statement of the principle of the present invention, in the silencers con.- templated herein, the high frequency attenuating means usually comprises a wall of gaseouspressure wave absorbing material along at least a portion of the passage through which the sounds travel through the silencer and the low frequency attenuating means comprises one or more space-volumes connected in side-branch relation to said passage. In such relation the space-volumes and their connection to the passage are called resonators and the space-volumes are called resonance chambers.

I have found that, if the communication between the passage and the space volumes, which may be called the entrance to the resonance chambers, or the neck of the resonators, is constructed in the form of an elongated slot opening extending longitudinally of the passage, low frequency attenuation is highly effective and that the effectiveness is most pronounced when gas pulses are present with the sounds to be silenced. If the entrance to the resonance chambers is of appreciable length, as by incorporating spaced lips or flanges along the longitudinal edges of the slot, the effectiveness of attenuation is further improved. The frequency' for which the low frequency attenuating means is most effective can also be conveniently regulated in this manner. With an entrance of given dimensions, in order to attenuate sounds of predetermined frequency, a resonance chamber of a particular volume must be used. It has been found that if the resonance chamber is subdivided into a number of smaller chambers the attenuating effect is further improved. The present invention comprises the incorporation of these discoveries into a silencer to provide highly desirable improvements in attenuating characteristics.

In the drawings:

Fig. 1 is a longitudinal, sectional view of one form of the silencer of my invention along line l-l of Fig. 2;

Fig. 2 is a transverse, sectional view of the same structure along line 2-2 of- Fig. 1;

Fig. 3 is a longitudinal, detail View of a portion of the conduit of the silencer of Figs. 1 l

and 2;

Fig. 4 is a transverse, sectional view along line 4 4 of Fig. 3;

Figs. 5, 6, and 7 are longitudinal, sectional views of modifications of the silencer of my invention;

Fig. 8 is a transverse, sectional view of the silencer shown in Fig. '7;

Fig. 9 is a longitudinal, sectional View of another form of the invention;

Fig. 10 is a transverse, sectional view of the silencer shown in Fig. 9;

Fig. 11 is a, longitudinal, sectional view of another form of the invention;

Fig. 12 is a transverse, sectional view of a further modication;

Fig. 13 is a longitudinal, sectional View of another form of the invention;

Fig. 14 is a transverse, sectional view thereof; and.

Figs. 15 through 22 are transverse views of conduits for my improved silencer showing modifications of the means for providing communication between the conduit and the spacevolumes or chambers.

The silencer shown in Figs.. 1 to 4 consists of an imperforate outer shell or casing I. The casing is provided with end walls 2 and 3 havingl alined

eccentric openings

4 and 5 respectively. A conduit 6 is disposed longitudinally within casing I and extends between

openings

4 and 5. Its inlet end 4' and its outlet end 5' extend beyond

openings

4 and 5 respectively. Conduit 6 is provided with av longitudinal slot 'I which extends substantially the length of the conduit. In the use of the silencer, the direction of gas ow is substantially parallel to slot 'I. Flanges or lips 8 and 9 extend outwardly from the conduit along the longitudinal edges of slot 'I and are in spaced substantially parallel relation, be'ing spaced apart by suitable means such as indents I (see Fig. 4), and held in such spaced relation by suitable means such as spot welding at said indents.

In order to show the relative proportion of the slot dimensions'to the rest of the silencer, the dimensions of a successfully operating silencer will be given. In a silencer in which the casing I has an inside diameter of 5 inches andthe conduit 6 an inside diameter of 1% inches, lips 8 and 9 extend l inch laterally outward from the periphery of the conduit and are spaced` g1g inch apart. These dimensions may vary with silencers which are designed for different engines, but the space between lips 8 and 9 ordinarily should not be more than 1A, inch and usually ranges from 1A; to gli inch. The lips may bey of any suitable length but should not approach the interior walls of the shell I so closely as to restrict the free movement of sound and gas out of and into the conduit. The end portions of conduit 6 are foraminous as shown at II and I2. The wall of that part of said conduit may be .of screen, but it is preferred to make it of metal perforated with a large number of small holes. Lips 8 and 9 are preferably omitted at foraminous portions II and I2 y of conduit 6, and slot I may also beIo'mitted at these portions.

A plurality of lateral partitions I3' are arranged in longitudinally spaced relation along conduit 6 and extend between conduit 6 and casing I and are preferably welded in place. Partitions I3 divide the space between the casing and the conduit into a plurality of closed chambers I5.v The partitions adjacent the end walls are preferably located at the boundary of the perforated portions of the conduit. The end chambers thus formed surrounding perforated portions II and I2 of conduit 6 are lled with gaseous-pressure wave absorbing material I4, of the character described in the Schnell United States Patent No. 1,811,762. The remaining chambers I5 are allowed to remain empty of such material.

For engine and compressor intakes, flammable absorbing materials such as cotton, wool, hairfelt, wood ber and the like may be used whereas for gas engine exhausts and other hot gases, non-flammable absorbers should be used, such as steel wool andother metallic wool, exfoliated vermiculite, asbestos fibers, rock wool, pumice, Haydite and other loose ceramic aggregates.

The aggregates may be bonded together in a manner so as to leave intercommunicating absorbing channels, as disclosed in Jack United States Patent No. 1,921,468.

In the acoustic action of the system, the lipped slot or slots constitute the entrances or necks'of the resonators. The neck of the resonator contributes acoustic inductance to the system and the volume contributes acoustic capacity. Regulation of these two factors determines the frequency for which the system is most effective. Increasing the acoustic inductance, or`the acoustic capacity, or both inductance and capacity lowers this frequency and decreasing these factors raises it. The acoustic inductance of the resonator may be increased by reducing the transverse dimensions of the pasasge (preferably by narrowing the slot), or by increasing its length. The acoustic capacity may be increased by increasing the volume of the chamber.

The chambers I5 surrounding conduit 6 act as expansion chambers or surge chambers for attenuating the gaspulses. The great length of slot 'I along the path of gas ow and the concavity of the interior of conduit 6 allow a more ready flow of gas pulses from conduit 6 into the spaces surrounding it, than do the types of openings used heretofore. After the gas has expanded, the extreme thinness ofpassage 'I and the convexity of the exterior of conduit 6 cause it to filter back into conduit 6 relatively gradually. In this manner the wide, slit-like passage acts as a trap`which permits the ready flow of gas out of the conduit but prevents its rapid return. Means will be described hereinafter for making this entrapping action more e'ective.

In silencers for both exhausts and intakes the ow of gases or air through the silencer may create a high frequency, whistling. sound. The section of gaseous-pressure wave absorbing material adjacent the outlet end of the silencer attenuates any Such sound which may be created.

All the chambers shown in Fig. 1 are of the same dimensions, but this is not essential and it may be found that a series of chambers each having a different length or volume is more effective for the particular engine with which the silencer is to be used. As explained heretofore, the dimensions of the slot and the lips along its edges and the volume of the chambers are factors which determine the frequency at which the low frequency attenuating section has its greatest eiect, and they may be so proportioned as to attenuate sounds of any predetermined, objectionable bands of frequencies.

One method for broadening the frequency range of attenuation is to vary the length of the lips continuously from one end of the sec.

tion to the other. For example, the length of the lips at the inlet end may be 11A inches and the length at the outlet end may be 3A inch. Such an arrangement is shown in Fig. 5 which illustrates a modification of the silencer shown in Fig. 1. An imperforate casing or shell 3| is provided with

end walls

32 and 33 having alined

eccentric openings

34 and 35 respectively. A conduit l38 is disposed between

openings

34 and 35. Its inlet and outlet ends 36 and 3l, respectively, project beyond the corresponding ends of casing 3|. The outlet end portion of conduit 38 is foraminous as shown at 39, and the remaining portion of conduit 38 has a longitudinal slot 40 therein. Lips 4I extend outwardly along the edges of slot 49. Lips 4I are held in spaced relation and vary in length continuously, as shown, from one end of slot 40 to the other. The variation may be in stepped increments instead of continuous. A plurality of partitions 42 are mounted in longitudinally spaced relation between conduit 38 and casing 3I to form a plurality of chambers 43. The partition adjacent the outlet end of the silencer is mounted on conduit 38 at the,boundary of the foraminous portion 39 thereof. The chamber surrounding foraminous portion 39 of conduit 38 is iilled with gaseous-pressure wave absorbing material 44. The size and number of empty chambers and the size of the chamber filled with absorbing material may be varied to meet conditions encountered in various engines. The gas flow through the silencer may be reversed so that opening 35 serves as the inlet opening and 34 serves as the outlet opening. Two or more of the chambers 43 may be connected as by means of connecting tube 63 or by openings in partitions 42.

Fig. 6 illustrates a further modification of the silencer shown in Fig. 1. In this modification a conduit 18 is located concentrically within a casing 19 and the chambers surrounding conduit 18 are substantially annular. The chamber of gaseous-pressure wave absorbing material 45 is located between two low frequency

sound attenuating sections

46 and 41 in place of being located at one or both ends of the silencer as shown in Fig. l5 and Fig. 1 respectively. Lips 98 and 99 form passages from' the slots in conduit,

18 to the low

frequency attenuating sections

46 and 41. The portions of lips 98 within one of the chambers of section 46 are omitted, said chamber being connected to the conduit by the slot only. The omission' of said portions of lips 98 results in a change in the frequency range for which section 46 is effective.

In addition to its acoustic effect, the silencer exerts an effect upon the action of the gases passing therethrough. When the device is used as an exhaust silencer pulses of exhaust gas of relatively great force emerge from the* engine and enter the inlet opening of the silencer. The force of these pulses is reduced appreciably by the section of absorbing material adjacent the inlet end of the silencer in Figs. 1 to 4. In some situations, the device of Fig. l has Aadvantages over those lof Figs. 5 and 6. In the latter constructions, the gas pulses, immediately upon entering the muffler, expand into the unoccupied spaces of, the first chambers. With pulses of sufllcient magnitude it has been found that the gas expands into an unoccupied space with such force as to result in mechanical impact upon the casing, which creates a clinking vsound of high frequency which is audible from the exterior. With the device of Fig. l the force of the entering gas pulses is reduced sufficiently by the time they reach the following unoccupied chambers to prevent such action.

Figs. 7 and 8 illustrate a further modification of the silencer of niy invention. An imperforate casing or shell I6 is provided with endwalls I1 and I8 having openings I9 and 20, respectively. Conduit 23 is arranged longitudinally within casing I6 and connects openings I9 and 20. inlet and outlet ends 2| and 22 extend beyond the ends of casing I6. Conduit 23 is foraminous, preferably throughout its length, and has a longitudinal slot 24 therein which also extends substantially the length thereof. Lips 25 extend Its the high frequency' attenuating outwardly along the edges of slot 24 and are in spaced substantially parallel relation. An intermediate shell 26 is arranged in exterior spaced relation to conduit 23 and has a longitudinal slot 21 therein extending substantially the length of shell 26. Slot 21 is alined with slot 24 and the outer edges of lips 25 may be fastened along the edges of slot 21, as by spot welding. Lips 25 may extend beyond intermediate shell 26. The space between conduit 23 and intermediate shell 26 is lled with gaseous-pressure wave absorbing material 28. When a molded gaseouspressure Wave absorbing material is used, it is possible to omit conduit 23 or intermediate shell 26 or both. A plurality of partitions 29 are arranged in longitudinally spaced relation between intermediate shell 26 and casing I6, forming a plurality of closed chambers 30. All of the chambers are shown in Fig. '1 to be of the same size, but the size and number of chambers may be varied to suit conditions. This arrangement results in a very effective silencer since substantially the entire surface of conduit I6 is lined with absorbing material and a large volume is still available for low frequency attenuation.

A further arrangement is illustrated in Figs. 9 and 10. An imperforate casing or shell 48 is provided with

end walls

49 and 58 having alined openings 5I and 52 respectively. Foraminous Y conduit 55 is disposed within casing 48 and connects openings 5I and 52. Its inlet and outlet ends 53 and 54 extend beyond the ends of casing 48. Conduit 55 is provided with a longitudinal slot 56 extending substantially the length of said conduit. Lips 51 extend outwardly along the edges of slot 56 and are in spaced substantially parallel relation. A longitudinal partition 58 divides the cylindrical space within the casing 48 into two volumes. Fig. l0 shows these volu ines to be substantially equal, but they may be of different sizes as well. Partition 58 is provided with a longitudinal slot through which lips 51 may pass. The partition may be fastened to both casing 48 and lips 51 by suitable means such as spot welding. Conduit 55 is enclosed in one of the volumes. 'Ihe volume containing conduit 55 is filled with gaseous-pressure wave absorbing material 59. The remaining volume is divided into a plurality of closed chambers 60 by means of spaced lateral partitions 6I.

Fig. 11 illustrates a construction in which the high frequency silencing means comprises a plurality of resonance chambers. The resonance chambers and the openings connecting them to the silencer conduit are so proportioned and arranged that they give satisfactory performance in attenuating the objectionable high frequency sounds. Casing 64 has

end walls

65 and 66. A conduit 61 extends longitudinally through the casing. At the inlet and outlet ends of conduit 61 are arranged resonance chambers 68, connected to conduit 61 by relatively large openings 69. Resonance chambers 1D are arranged adjacent chamber 68 and connected to conduit 61 by openings 1I.

Chambers

68 and 10 and openings 69 and 1I are so proportioned and arranged that they attenuate the high frequency sounds in conduit 61. Between the high frequency attenuating sections formed by

chambers

68 and 10, there are arranged a plurality of chambers 12. These latter chambers are usually larger than chambers. Chambers 12 are connected to conduit 61 by a slot opening 1,3 which may be provided with lips (not shown) extending into chambers 12.

Chambers 12 and slot 13 are so proportioned and arranged as to attenuate low frequency sounds in conduit 61. Two or more of the chambers 12 may be connected as by means of connecting tube 14 or by openings in partition 15 to provide series connected chambers.

A further modication of the silencer is illustrated in Fig. 12. An imperforate casing is provided with end walls (not shown).l AThis casing is shown oval or elliptical in transverse section, but it may be rectangular or other shape if desired. The interior of the casing is divided by longitudinal partitions |0| and |02, as shown. The partitions may be rigidly fastened to casing |00 by suitable means, such as spot welding. Longitudinal partitions |0| and |02 divide vthe casing into a number of volumes. The volumes between partition |0| and casing |00 and between partition |02 and casing |00 are filled with gaseous-pressure wave absorbing material |04. The remaining volumes are allowed to remain empty of such material. Volumes |05 may be divided into a plurality of smaller volumes by means of lateral partitions (not shown), asv

Figs. 13 and 14 illustrate a further modification of the silencer in which the positions of the gas passage and the space volumes are reversed. An imperforate casing |01 is provided with end walls |08 and |09 having openings ||0 and respectively. Openings |0 and are adapted to receive inlet du'ct |0' and outlet duct respectively. An inner shell ||2 is arranged longitudinally within casing |01 and is held in spaced relation thereto by means of spacing members ||3. Shell ||2 is provided with end walls-H4 and ||5. The gases pass through the annular duct formed between the casing and the shell. The ends of shell ||2 may be conical,

. if desired, to minimize resistance to the flow of gas through the silencer. The end walls ||4 and ||5 and the end portions of the side walls of shell ||2 are perforated, the remaining portion of the shell having a longitudinal slot ||9 therein. Lips |20 extend inwardly along the edges of slot ||9 and are maintained in spaced relation. A plurality of partitions ||6 are arranged in longitudinally spaced relation within shell ||2 to form a plurality of closed chambers ||1. The partitions adjacent the end walls ||4 and ||5 are preferably located at the boundary of the perforated portions of the shell. The volumes thus formed adjacent the end walls are filled with gaseous-pressure wave absorbing material ||8. The remaining chambers are allowed to remain empty of such material. The perforated portions of shell 2 thus contain the gaseous-pressure wave absorbing material and lipped slot ||9 provides entrance to unoccupied chambers ||1.

Figs. 15, 16. and 17 illustrate modications of the form of the passage between the conduit and the space-volumes. As shown in Fig. 15, a conduit 80 is provided with two oppositely disposed longitudinal 4slots 8| having spaced outwardly extending lips 82 along the edges of the slots. The lips at one side of conduit 80 project radially while those at the other side project at an angle.

In Figs. 1 to 14, inclusive; the lips along the edges of the slots have been shown as being in substantially parallel spaced'relation. The lips may also diverge slightly as they proceed outwardly from the conduit, as shown at 83, in Fig. 16. This arrangement has the advantage of promoting the ease of passage of the gas pulses into the space volume surrounding the conduit.

The lips may also converge, as shown at 84 in Fig. 17. This arrangement increases the effectiveness of the entrapping action exerted by the lips upon the gases and increases the resistance to the return of the pulsations of gas to the conduit while it still does not prevent its return ow in the form of a more or less steady stream.

The divergence and convergence of

lips

83 and 84 of Figs. 16 and 17, respectively, are not so abrupt as to change the character of the passage formed between them from a passage having length to a mere orice. The dilerence between the small transverse dimensions at the inlet and outlet ends of the passage should vbe not more than about 1A; inch and preferably is about 51E to inch.

The length of the passage may be increased by arranging baies 81 adjacent and extericrly of lips 86 as shown in Fig. 18. A single passage is formed between lips 86 and a double passage is formed from the ends of lips 86 to the volume within casing 80.

The acoustical characteristics may be further varied by providing a double passage as shown in Fig. 19. In this case baiile 89 is arranged between lips 90. Such a passage tends to increase the width of the band of frequencies attenuated.

A double passage may be provided by means of the arrangement shown in Fig. 20. In this form lips are not provided in attached relation to the longitudinal edges of slot 9|. A mere slot opening is provided. An arcuate bafile 92 is arranged in substantially parallel spaced exterior relation to conduit 93 and extends longitudinally thereof with its mid portion opposite the slot opening 9|. Baiile 92 may be supported by the ends of casing 94 or at intervals along the length of conduit 93.

The entrance to the space volumes may also be provided by forming the conduit with its portions 95 adjacent the longitudinal edges (which normally form the seams) arranged in spaced overlapping relation as shown in Fig. 21. The length of overlap may be varied as desired. Spacing members or indents, similar to indents I0 (see Figs. 3 and 4) may be employed to properly space the overlapped portions 95. Overlapping portions 95 may be considered to be the lips upon the. edges of the slot opening, or the exterior portion 95 may be'considered to be a baille similar to balle 92 of Fig. 20.

Fig. 22 illustrates a further modification which provides length for the passage into the space volume without necessitating excessive radial projection of the lips from the conduit.

Lips

96 and 91 are spaced from each other in the ordinary manner, but lip 96 is considerably longer than lip 91 and turns backward beyond the end engine.

of lip 91 to provide successive lengths of the passage on opposite sides of lip 91.

' Other changes in design may be made. The size and number of closed chambers may be varied to meet the requirements of a particular The partitions within the casing need not be perpendicular to the conduit and casing, but may be placed at an angle other than 90. They slot opening may vary in width at points along its length. The slot opening may be made discontinuous. Each chamber may be provided with an individual slot opening in the conduit. The slot opening may be of a length less than that of the chamber.

I claim:

l. A silencer for attenuating sounds composed of both high and low frequencies comprising a substantially imperforate casing having openings in the ends thereof, a conduit for the sound to be silenced within said casing extending between said openings, and spaced partitions between said casing and said conduit. dividing said casing longitudinally into a plurality of closed chambers, the chambers adjacent the ends of said casing being filled with gaseous-pressure wave absorbing material, the portions of said conduit surrounded by said absorbing material being perforated, the portions of said conduit surrounded by said unoccupied chambers having a longitudinal slot therein, spaced substantially parallel lips upon the longitudinal edges of said slot projecting exteriorly of said conduit, the total length of slot opening connecting said conduit with said unoccupied chambers being not more than twice the total longitudinal length of said unoccupied chambers.

2. Apparatus for silencing sounds comprising in combination, a conduit for the sound to be silenced, a series of closed chambers disposed longitudinally of and surrounding said conduit, the end chambers of said series being lled with gaseous-pressure wave absorbing material, the portions of said conduit surrounded by said absorbing material being foraminous, the intermediate chambers of said series being unoccupied and defining closed space-volumes, the portion of said conduit surrounded by said intermediate chambers having a longitudinal slot therein, and substantially parallel lips upon the longitudinal edges of said slot and projecting into said intermediate chambers, the total length of slot opening connecting said conduit with said unoccupied chambers being not more than twice the total longitudinal length of said-unoccupied chambers.

3. A silencer for attenuating sounds composed of both high and low frequencies, comprising a conduit for the sounds to be silenced, a series of closed chambers disposed longitudinally of and surrounding said conduit, said conduit having a longitudinal slot therein communicating with the interior of said chambers, spaced lips upon the edges of said slot and projecting into said chambers, the total length of slot opening concasing and said conduit dividing said casing longitudinally into a plurality of closed chambers, and gaseous-pressure wave absorbing material arranged in some of said chambers, the portions of said conduit surrounded by said absorbing material being perforated and a longitudinal slot in said conduit connecting said conduit with said unoccupied chambers, the total longitudinal length of said slot opening connecting said conduit with said unoccupied chambers being not more than twice the total longitudinal length of said unoccupied chambers.

5. A silencer for attenuating sounds composed of both high and low frequencies comprising a conduit for the sound to be silenced, a series of closed chambers disposed longitudinally of and surrounding said conduit, gaseous-pressure wave yabsorbing material arranged in some of said chambers, the portions of said conduit surrounded by said absorbing material being foraminous, others of said chambers comprising closed space-volumes, the portions of said conduit surrounded by said space-volumes having longitudinal slots therein connecting said chambers with said portions of said conduit, and substantially parallel lips upon the longitudinal edges of said slots and extending exteriorly of said conduit the total longitudinal length of the slot opening connecting said conduit with said unoccupied chambers being not more than twice the total longitudinal length of said unoccupied chambers.

6. A silencer for attenuating sounds composed of both high and low frequencies comprising a conduit for the sounds to be silenced, high frequency attenuating means surrounding a portion of said conduit, a series of closed chambers disposed longitudinally of and surrounding a further portion of said conduit, said portion of said conduit surrounded by said closed chambers having a longitudinal slot therein, and spaced lips along the longitudinal edges of said slot and projecting exteriorly of said conduit the longitudinal length of the slot opening connecting said closed chambers to said conduit being substantially equal to the total length of said closed chambers.

7. A silencer for attenuating sounds composed of both high and low frequencies comprising a substantially imperforate casing havingl openings therein, a conduit for the sound to be silenced within said casing and connecting said openings, a layerY of gaseous-pressure wave absorbing material exposed in the walls of said conduit, said conduit having a longitudinal slot therein, and spaced partitions within said casing, dividing at least a portion of said casing into a plurality of space-volumes, said space-volumes being connected in side-branch relation to said conduit by means of said slot, the total longitudinal length of slot opening connecting said spacevolumes to said conduit being not more than twice the total longitudinal length of said spacevolumes. A

necting said conduit with said unoccupied chamw 8. A silencer for attenuating sounds composed bers being not more than twice the total longitudinal length of said chambers, andhigh fre- ,quency attenuating means surrounding said conduit at the ends of said series of chambers.

4. A silencer for attenuating sounds composed of both high and low frequencies comprising a substantially imperforate casing having openings in the ends thereof, a conduit for the sound to` be silenced within said casing extending between said openings, spaced partitions between said of both high and low frequencies comprising a conduit for the sounds to be silenced, a gaseouspressure wave absorbing wall for at least a portion of said conduit, said conduit having an elongated opening extending longitudinally thereof, spaced, outwardly extending lipsalong the longitudinal edges of said opening, and at least one closed chamber in communication with said conduit by means of said opening, the total longitudinal length of slot opening connecting said closed chamber to said conduit being not more than twice the total longitudinal length of said closed chamber.

9. A silencer for attenuating sounds composed of both high and low frequencies comprising a conduit for the sounds to be silenced having high frequency attenuating means associated with at least a portion of the wall of said condui-t, and a closed chamber disposed longitudinally of and adjacent to said conduit, said conduit having an elongated slot extending longitudinally thereof, said slot providing communication between said conduit and said closed chamber, the total longitudinal length of slot opening connecting said closed chamber to said conduit being not more than twice the total lon-` gitudinal length of said closed chamber.

10. A silencer comprising a substantially imperforate casing, a conduit for the sound to be silenced extending through said casing, gaseouspressure wave absorbing material substantially surrounding said conduit and exposed in the walls thereof, said absorbing material partially lling said casing, said conduit and absorbing material having coinciding slots therein extending longitudinally thereof, said slot providing communication from said conduit to the space in said casing.

11. A silencer comprising a substantially imperforate casing, a partition extending longitudinally of said casing dividing said casing into two chambers, a I'llling of gaseous-pressure wave absorbing material in one of said chambers, the other chamber constituting a space volume, a conduit for the sounds to be silenced passing through said lled chamber, said absorbing material being exposed in the walls of said conduit, said conduit having an elongated slot therein extending longitudinally thereof, and spaced lipsl along the longitudinal edges of said slot, said partition and said absorbing material having openings therein coinciding with said slots, said lips extending through said openings and pro-\ viding communication between said conduit and said spacevolume.

12. A silencer comprising a substantially imperforate casing having openings in the ends thereof, a partition extending longitudinally of said casing dividing said casing into two chambers, a filling of gaseous-pressure wave absorbing material in one of said chambers, the other chamber constituting a space volume, a conduit for the sounds to be silenced passing through said filled chamber, said absorbing material being exposed in the walls of said conduit, said conduit having an elongated slot therein extending longitudinally thereof, spaced lips along the longitudinal edges of said slot, said partition and said absorbing material having openings coinciding with said slots, said lips extending through said openings and providing communication between said conduit and said space volume, and lateral partitions spaced longitudinally within said space volume, subdividing said space volume into a phirality of smaller space volumes.

13. In a silencer comprising a conduit providing a, through passage for the sounds to be silenced, a closed chamber disposed adjacent said passage, said conduit having an elongated slot opening therein extending longitudinally thereof and connecting said closed chamber in side branch relation to said conduit and at least one plate disposed adjacent said slot and exteriorly of said conduit and extending longitudinally of said conduit, said plate forming a passage of slit-like lateral dimensions between said slot opening and said closed chamber, the total longitudinal length of slot opening connecting said closed chamber to said conduit being not more than twice the total longitudinal length of said closed chamber.

14. A silencer comprising a conduit providing a through passage for the sounds to be silenced and the gases passing therethrough, aA closed chamber disposed adjacent said conduit, said conduit having an elongated slot opening therein extending in the direction of gas ow, and spaced lips along the edges of said slot and forming a passage of slit-like lateral dimensions connecting said conduit with said closed chamber in side-branch relation to said conduit, the total longitudinal` length of slot opening connecting said closed chamber to said conduit being not more than twice the total longitudinal length of said closed chamber.

15. In a silencer comprising a through type passage for the sounds to be silenced, a conduit comprising said passage, a, plurality of closed chambers disposed longitudinally along and surrounding said conduit, said conduit having an elongated slot therein extending longitudinally thereof, and spaced lips upon the 1ongitudinal edges of said slot, said slot and lips forming a passage of slit-like lateral dimensions connecting said conduit and said chambers in side branch relation, the total longitudinal length of slot opening connecting said closed chambers .to said conduit being not more than twice the total longitudinal length of said closed chambers.

16. In a device of the class described, a conduit comprising a through passage, a closed chamber adjacent said passage, said conduit having an elongated slot therein extending longitudinally thereof and connecting said closed chamber in side branch relation to said conduit, and spaced lips upon the longitudinal edges of said slot and projecting exteriorly of said conduit, said lips converging gradually as they proceed away from said conduit.

17. In a silencer comprising a conduit providing a through passage for the sounds to be silenced and thegases passing therethrough, and' a closed chamber disposed adjacent said conduit, said conduit having an elongated slot opening therein extending in the direction of gas flow, said slot opening connecting said closed chamber in side-branch' relation to said conduit, the total length of slot opening being not more than twice the total length of said closed chamber.

18. In a silencer comprising a conduit providing a through passa'ge for the sounds to be silenced and the gases passing therethrough, .and a closed chamber disposed adjacent said conduit, said conduit having an elongated slot opening therein extending in the direction of gas ow, said slot opening connecting said closed charnber in side-branch relation and having a length substantially equal to the length of said closed chamber.

WILLIAM A. JACK, 3RD.