From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Detailed specification for a sound wave attenuating unit, referencing multiple figures and component designs.
| Identifier | ExFiles\Box 147\1\ scan0078 | |
| Date | 10th April 1933 guessed | |
| 6 417,935 the sound wave attenuating unit was installed therein a nodal point of the third harmonic would be located between partitions 35 and 31 and a nodal point of the fifth harmonic would be located between partition 35 and head 18 so that the resonance units 27—44—43 and 35—45—46 would communicate with the exhaust passage at a nodal point of the third harmonic and a nodal point of the fifth harmonic, respectively. In the exhaust system for which the sound wave attenuating unit illustrated in Figs. 1, 2 and 3 was designed, it was found that of the higher harmonics the intensity was so inconsiderable that it was unnecessary to reduce it, or that the frequency was so high that resonance units located at random sufficiently reduced their intensity. To attenuate the sound waves whose frequencies were higher than those of the third and fifth harmonics and yet relatively low, there were provided in addition to the resonance units 27—44—43 and 35—45—46, the resonance units 26—40, 28—41, 29—42 and 30 which were so proportioned and dimensioned that they would respond to and attenuate them. To attenuate the sound waves whose frequencies were higher than those which the resonance units mentioned in the preceding sentence were designed to attenuate, there was provided the resonance unit 36—37—38. A few general observations will do much to abbreviate the separate descriptions of the sound wave attenuating units illustrated in Figs. 4 to 7 of the drawing. These sound wave attenuating units are in general similar to that illustrated in Figs. 1, 2 and 3 of the drawing and each includes a section A (or sections A1 and A2, or A1, A2, A3, and A4) which is designed to attenuate sound waves of relatively high frequencies, and a section B (or sections B1 and B2, or B1, B2, B3, and B4) which is designed to attenuate sound waves of relatively low frequencies which travel through the sound wave passage of which the unit forms a part. Each of the sections A, A1, A2, A3, and A4 consists of a plurality of resonance units so arranged as to form a multiple-compound resonance unit and each of the sections B, B1, B2, and B3 consists of a plurality of simple and/or series-compound resonance units, of which some or all are intended to be located at nodal points of harmonics of the sound wave passage of which the unit constitutes a part. The sound wave attenuating units illustrated in Figures 4 to 7 are similar to that illustrated in Figures 1, 2 and 3 and to each other in that each includes an imperforate tubular shell 16 whose opposite ends are closed by heads 17 and 18 through which extend, respectively, openings 19 and discharge openings 21 connected by an unobstructed tubular element which constitutes a sound wave passage. In details of construction, the sound wave attenuating units illustrated in Figures 4 to 7 differ considerably from that illustrated in Figures 1, 2 and 3 and from each other, but except when the differences are important or the construction is not readily comprehensible from an examination of the drawing, these details will, for the sake of brevity, not be referred to specifically in the description of the units. In the sound wave attenuating unit illustrated in Figure 4, the tube 60 which connects the openings 19 and 21 is made of seven partly telescoped sections 61, 62, 63, 64, 65, 75 and 76, of which the sections 61, 63 and 65 are perforated similarly to the tube 52 which is shown in Figures 2 and 3 and of which the sections 62, 64, 75 and 76 are imperforate. The section A of the unit includes three resonance chambers 66, 67 and 68 which surround the section 63 of the tube 60. The section B1 includes five resonance chambers 69, 70, 71, 72 and 73 of which the chamber 69 surrounds the section 75, the chamber 70 the section 61, and the chambers 71, 72 and 73 the section 62 of the tube 60. The resonance chambers 69, 70, 71, 72 and 73 may be considered to constitute elements of a five-chamber series-compound resonance unit but are more accurately described as elements of a three-chamber unit 69—70—71 which communicates with the sound wave passage through the perforations in the section 61 and a two-chamber unit 72—73 which communicates with the sound wave passage through the chamber 70 and the annular passage 75 between section 62 of the tube 60 and the tubular element 74 which forms the inner wall of the chambers 71 and 72. The section B2 includes five resonance chambers 77, 78, 79, 80 and 81 which surround the sections 64, 65 and 76 of the tube 60 and are arranged in the same relation thereto as the chambers 69, 70, 71, 72 and 73 and 69 are arranged in relation to the sections 62, 61 and 75. In the sound wave attenuating unit illustrated in Figure 5, the tube 90 which connects the openings 19 and 21 is made of two sections 91 and 92 which abut end to end and are perforated similarly to the tubes 23 and 52, respectively, which are shown in Figures 2 and 3. The section A of the unit includes ten resonance chambers 93, 94, 95, 96, 97, 98, 99, 100, 101 and 102 which surround the section 417,935 7 a portion of the section 92 of the tube 90. By reason of the fact that the wall of the chambers 93, 94, 95, 96, 97, 98, 99, 100, 101 and 102 is made of conical shape and the annular walls 104 which separate the several chambers are spaced apart the same distance axially, the chambers 93, 94, 95, 96, 97, 98, 99, 100, 101 and 102 successively decrease in size and have different response characteristics. The inner edges of the annular walls 104 are connected to the sections 91 and 92 through tubular portions 105 which surround the sections and close some of the perforations therein and, consequently, reduce the acoustical conductivity of the passages between the several chambers and the sound wave passage. The section B of the unit includes seven resonance chambers 106, 107, 108, 109, 110, 111 and 112 of which the chambers 106 and 107 surround the section A of the unit, the chambers 108 and 109, the chambers 110, 111 and 112, a portion of the section 92 of the tube 90 which is surrounded by the section A and the chambers 108 and 109, the chambers 110, 111 and 112 and the portion of the section between the section A and the head 18. The chambers 106, 107 and 111 constitute elements of a three-chamber series-compound resonance unit which communicates with the sound wave passage through perforations in the section 92 of the tube 90. The chambers 108, 109 and 112 constitute elements of a three-chamber series-compound resonance unit which communicates with the sound wave passage through perforations in the section 92 of the tube 90. The chamber 110 constitutes a simple resonance unit which communicates with the sound wave passage through perforations in the section 92 of the tube 90. In the sound wave attenuating unit which is shown in Figure 6 the tube 120 which connects the openings 19 and 21 is made in two sections 121 and 122 which abut end to end and are perforated similarly to the tube 52 which is shown in Figures 2 and 3. The sections 121 and 122 differ materially only in that the section 121 is of larger diameter than the section 122. The section A1 of the unit includes three resonance chambers 123, 124 and 125 which surround the section 121 of the tube 120. The section A2 of the tube 120 is surrounded by five resonance chambers 126, 127, 128, 129, 130, 131, 132, 133 and 134 of which the chambers 126 and 127 constitute the section A2 of the unit and the chambers 128, 129, 130, 131, 132 and 133 the section A3 of the unit. The outer wall of the chambers 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133 and 134 is formed by three coextensive telescopically related tubular members 135, 136 and 137 which are, respectively, a tube of sheet metal 135 which is imperforate except for the openings which extend therethrough and connect the chambers 128 and 139 and the chambers 134 and 137 to connect the chambers 128 and 139 and the chambers 134 and 141, a tube of asbestos or other suitable sound absorbing material 136, and a tube of sheet metal 137 perforated similarly to the tube 52 shown in Figures 2 and 3 which keeps the tube 136 which constitutes a sound absorbing lining for the chambers 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133 and 134 in place against the inner wall of the tube 135. The section B of the unit includes six resonance chambers 138, 139, 140, 141 and 134 of which the chambers 128, 139, 140 and 141 surround the sections A1, A2, and A3 and the chambers 128 and 134 of the section B which are located, respectively, between the sections A2 and A3, and between the section A3 and the head 18. The chambers 138, 139 and 128 constitute elements of a three-chamber series compound resonance unit which communicates with the sound wave passage through the perforations in the portion of the section 122 of the tube 120 which is surrounded by the chamber 128. The chambers 140, 141 and 134 constitute elements of a three-chamber series-compound resonance unit which communicates with the sound wave passage through the perforations in the portion of the section 122 of the tube 120 which is surrounded by the chamber 134. It will be noted that the passages which connect the chambers 128 and 139 and the chambers 134 and 141 pass through the layer of sound absorbing material 136 which reduces their acoustical conductivity. In the sound wave attenuating unit which is illustrated in Figure 7, the passage 140 which connects the openings 19 and 21 includes six tubular sections 141, 142, 143, 144, 145 and 146 which are perforated similarly to the tube 52 which is shown in Figures 2 and 3, and an imperforate tubular section 147. The sections 141, 143, and 145 are of considerably larger diameter than the sections 142, 144, 146 and 147 and, in effect, constitute expansion chambers. Each of the sections A1, A2, and A3 of the unit, which surround, respectively, the sections 141, 143 and 145 of the passage 140, consists of two resonance chambers 148 and 149. Each of the sections B1 and B2 of the unit, which surround, respectively, the sections 142 and 144 of | ||