Soundproof wall

Abstract: A soundproof wall for installation along a noise source such as a road, railway, or the like, and comprising a main wall (1), a first branch wall (2) installed generally vertically on the top of the main wall (1), a second branch wall (3) extending obliquely away from the noise source, and a third branch wall (4) installed at an intermediate height of the second branch wall (3) and which extends obliquely upward toward the noise source.

Description: The present invention relates to a soundproof wall for installation along a road, railway, factory etc. to attenuate a sound or noise coming from such a noise source. Conventionally, to control an undesired sound or noise from a road, railway, factory, etc., upright or vertical soundproof walls are widely used to prevent the sound from coming directly from its source. Among various noise-control solutions, the vertical soundproof walls are relatively low in cost and effective for attenuation of sounds from various sound sources. For an improved sound attenuation, the soundproof walls should preferably be taller. However, such taller walls are correspondingly more expensive (the taller, the greater the construction costs). Also the taller walls are likely to intercept the sunlight, impair viewing and cause an oppressive sensation, poor ventilation, radio interference and turbulent flow. Further, it has been proposed to use various other types of soundproof walls such as bent-top types whose top wall portion is bent toward the sound source and curved-top types whose top wall portion is curved toward the sound source, if use of a vertical soundproof wall is not suitable for the noise problem. However, it has already been known that the latter types of soundproof walls cause the above-mentioned problems to be more serious. The recent drastic increase of traffic and higher speed of vehicles have resulted in serious environmental noise problems. Since no other effective noise control solutions have been proposed, the above-mentioned bent-top and curved-top types of soundproof walls are used in addition to the vertical soundproof walls of 5 m, 7 m and 10 m in height. The above-mentioned environmental problems remain unsolved. The conventional soundproof walls can only provide an improved sound attenuation for an increased wall height. Generally, at a remote place (about 20 meters) from a soundproof wall, the sound attenuation attainable with an increase of 1 m in height of the soundproof wall is only about 1 dB. Accordingly, soundproof walls provided on the top thereof with auxiliary walls 100 open upward as shown in Figs. 13 to 16 of the accompanying drawings have been proposed to enhance the effect of noise control without any increase of the wall height. These prior-art soundproof walls with the auxiliary walls have provided a sound attenuation improvement of several decibels (dB) in comparison with the conventional upright or vertical soundproof walls. However, this noise control is not deemed sufficient, and soundproof walls providing a further improved sound attenuation are demanded from many fields of industry. Attention is also drawn to EP-A-0695831, falling within the ambit of Article 54(3) EPC, which discloses a soundproof wall, cf. figures 9 and 20 of this document, for attenuating a sound or noise coming from a noise source, comprising: a main wall and a first branch wall installed generally vertically on the top of said main wall, cf. figure 20; a second branch wall extending obliquely away from the noise source, cf. figures 9 and 20; and a third branch wall installed at an intermediate height of said second branch wall and which extends obliquely upward toward said noise source, cf. col. 6, lines 32-35 and figure 9 of this document. The present invention aims to provide a soundproof wall capable of suppressing noise more effectively without increasing the soundproof wall height. The present invention provides a soundproof wall for installation along a road, railway, or the like, to attenuate a sound or noise coming from such a noise source, comprising: a main wall; a first branch wall installed generally vertically on the top of said main wall; a second branch wall extending obliquely away from the noise source; and a third branch wall installed at an intermediate height of said second branch wall and which extends obliquely upward toward said noise source; wherein said second branch wall has a horizontal portion connected to said main wall and/or said first branch wall. In a preferred embodiment of the invention, a sound absorbing member may be attached on at least the inner or outer side of at least one of said first, second and third branch walls. The soundproof wall according to the present invention is intended for installation along a noise source such as a road, railway, etc. It comprises a main wall, a first branch wall installed generally vertically on the top of the main wall, a second branch wall inclined away from the noise source, and a third branch wall installed at an intermediate height of the second branch wall and which extends obliquely upward toward the noise source, wherein the second branch wall has a horizontal portion connected to the main wall and/or the first branch wall. Without any increased height of the soundproof wall, the first branch wall functions to suppress mainly the sound coming directly from the noise source while the second and third branch walls effectively function to attenuate mainly the sound waves diffracted at the top of the first branch wall, thereby enhancing the effect of noise control. Also, the optional provision of a sound absorbing material on the inner or outer side of at least one of the first, second and third branch walls further improves the effect of sound attenuation. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a side elevation of a first embodiment of a soundproof wall according to the present invention: FIG. 2 shows an acoustic intensity distribution of the soundproof wall according to the first embodiment shown in FIG. 1; FIG. 3 is a side elevation of the soundproof wall according to the first embodiment shown in FIG. 1, having a sound absorbing member attached on the outer side of a first branch wall thereof, upper side of a second branch wall and both the inner and outer sides of a third branch wall; FIG. 4 is a side elevation of the soundproof wall according to the first embodiment, having a sound absorbing member attached on the inner sides of a main wall and first branch wall, respectively, facing a noise source; FIG. 5 is a side elevation of the soundproof wall according to the first embodiment, having a sound absorbing member attached on the upper side of a portion of the second branch wall as well as on the upper side of the third branch wall; FIG. 6 is a side elevation of a second embodiment of a soundproof wall of the present invention; FIG. 7 is a side elevation of a third embodiment of a soundproof wall of the present invention; FIG. 8 is a side elevation of a fourth embodiment of a soundproof wall of the present invention; FIG. 9 is a side elevation of a fifth embodiment of a soundproof wall of the present invention; FIG. 10 is a side elevation of the soundproof wall according to the first embodiment, having a sound absorbing member attached on the upper side of a portion of the second branch wall as well as on the upper side of the third branch wall, on the inner side of the main wall, and on both the inner and outer sides of the first branch wall; FIG. 11 is a side elevation of the soundproof wall according to the first embodiment, having a sound absorbing member attached on the inner side of the main wall, and on both the inner and outer sides of the first branch wall; FIG. 12 is a side elevation of a sixth embodiment of a soundproof wall of the present invention; FIG. 13 is a side elevation of a conventional soundproof wall; FIG. 14 is a side elevation of another conventional soundproof wall; FIG. 15 is a side elevation of a still another conventional soundproof wall; FIG. 16 is a side elevation of a yet another conventional soundproof wall; FIG. 17 is an explanatory drawing showing how to measure the effect of sound attenuation; and FIG. 18 shows an acoustic intensity distribution of the conventional soundproof walls in FIGS. 13 through 16. It should be noted that same or like parts are indicated with same or like references throughout the drawings. FIG. 1 is a side elevation of a soundproof wall according to a first embodiment. This soundproof wall is intended for installation along a noise source such as a railway, road, etc. As shown, the soundproof wall comprises a main wall 1 to be installed along the noise source, a first branch wall 2 installed generally vertically on the top of the main wall 1, a second branch wall 3 extending obliquely upward away from the noise source and having a horizontal portion 5 connected to the main wall 1 and first branch wall 2 and which extends horizontally away from the noise source, and a third branch wall 4 installed at an intermediate height of the inner side of the second branch wall 3 and which extends upward obliquely toward the noise source. It is assumed that the noise source exists to the right of the main wall 1 as viewed in FIG. 1, and the side of each of these walls toward the noise source will be referred to as "inner side" while the side away from the noise source will be referred to as "outer side" hereinafter. FIG. 2 shows the result of a calculation, by the boundary element method, of a flow of 250-Hz octave-band acoustic energy (acoustic intensity) travelling along the soundproof wall having the geometric structure as shown in FIG. 1. Acoustic intensity vectors are indicated with arrows. The third branch wall 4 functions to suppress the sound travelling along the second branch wall 3 located in an opposite position to the noise source. In FIG. 2 the directions of arrows are those of acoustic energy, and the longer arrows indicate larger acoustic energies. FIG. 2 shows that the sound wave from the noise source has the energy thereof drastically attenuated when travelling outwardly over the third branch wall 5. More specifically, the sound travelling along the second branch wall 3 is forced upward by the third branch wall 4, and interferes, at the top of the third branch wall 4, with the sound (direct sound wave) travelling as diffracted over the top of the first branch wall 2 toward the top of the third branch wall 4, resulting in an attenuation of the acoustic energy. As in the above, since the sound diffracted above the top of the soundproof wall is thus suppressed, considerable noise suppression can be attained in a location behind the soundproof wall as viewed from the noise source. FIG. 3 shows the soundproof wall according to the first embodiment, having a sound absorbing member 10 attached on the outer side of the first branch wall 2 thereof, upper side of the second branch wall 3, and on both the inner and outer sides of the third branch wall 4. The sound absorbing member 10 may be made of a rock wool, glass wool, ceramic, expanded concrete or the like. The sound absorbing member 10 is attached to each wall surface by bolting, pinning, striking with adhesive, enclosing with perforated plate, wire-netting or the like which is selected depending upon the material of the sound absorbing member 10. FIG. 4 shows the soundproof wall according to the first embodiment, having a sound absorbing member 10 attached on the inner sides of the main wall 1 and first branch wall 2, respectively, facing the noise source. FIG. 5 shows the soundproof wall according to the first embodiment, having a sound absorbing member 10 attached only on the upper side of a portion of the second branch wall 3, and on the upper side of the third branch wall 4. FIG. 6 shows a second embodiment of a soundproof wall according to the present invention. In this second embodiment, the soundproof wall comprises a main wall 1 to be installed along a noise source, a first vertical branch wall 2 installed generally vertically on the top of the main wall 1, a second vertical branch wall 2' having a horizontal portion 5' connected to the main wall 1 and first vertical branch wall 2 and which extends out horizontally away from the noise source, a second branch wall 3 extending obliquely upward away from the noise source and having another horizontal portion 5 extending out contiguously from the horizontal portion 5' in the direction horizontally away from the noise source, and a third branch wall 4 installed at an intermediate height of the second branch wall 3 and extending obliquely toward the noise source. As seen, the second vertical branch wall 2' is connected to the main wall 1 and first vertical branch wall 2 by means of the first horizontal portion 5' extending out horizontally away from the noise source. The second branch wall 3 is connected to the second vertical branch wall 2' by means of the second horizontal portion 5 and extends out obliquely from the second horizontal portion 5. Also, a sound absorbing member 10 is attached on the outer side of the first vertical branch wall 2 and inner side of the second vertical branch wall 2'. The sound absorbing member 10 may also be attached on the inner side of the first vertical branch wall 2 and outer side of the second vertical branch wall 2' or on the inner or outer side of the third branch wall 4. Further, the sound absorbing member 10 may be attached on the inner or outer side of the second branch wall 3. Thus, the location of the sound absorbing member 10 may be freely selected. It is assumed the noise source exists to the left of the main wall 1 as viewed in FIG. 6. In the following description of the third through fifth embodiments of the present invention illustrated in FIGS. 7 through 9, it is assumed that the noise source exists to the right of the main wall 1 as viewed in these Figures. In the third embodiment shown in FIG. 7, the horizontal portion 5 has installed at an intermediate portion thereof a fourth branch wall 2A extending vertically upward in parallel with the first branch wall 2. In the fourth embodiment shown in FIG. 8 the second branch wall 2 has installed on the top thereof a fourth branch wall 2B of which the cross-section has a "V" shape. In the aforementioned third and fourth embodiments, the main wall 1 of the soundproof wall is an upright one. However, the main wall 1 may be of a bent-top type or curved-top type which have previously been described. According to the fifth embodiment shown in FIG. 9, the first branch wall 2 has installed on the top thereof a mount 2C which supports the assembly of the first branch wall 2, second branch wall 3 with the vertical portion 5, and the third branch wall 4. FIGS. 10 and 11 show examples of attached sound absorbing members 10. FIG. 12 shows the sixth embodiment of a soundproof wall according to the present invention, in which the top end of the second branch wall 3 is designed to be higher than the top end of the second branch wall 2 to enhance the effect of noise control of the soundproof wall. FIGS. 13 to 16 show constructions of conventional soundproof walls, and FIG. 17 shows the method of measuring the effect of sound attenuation of the conventional soundproof walls. As a sound source, a speaker was placed at a distance of 4 meters from the soundproof wall. To measure the noise attenuation by the soundproof wall, a microphone was placed behind the soundproof wall as viewed from the noise source and in a position 10 meters from the soundproof wall. Noise measurement was done with a sound generated at each of 250 Hz-, 500 Hz- and 1 kHz-octave bands. FIG. 18 shows the acoustic intensity distribution of the conventional soundproof wall shown in FIG. 14. As shown, the sound diffracted at the end of the auxiliary wall 100 facing the noise source travels along the oblique auxiliary wall 100. As apparent from comparison with the acoustic intensity distribution shown in FIG. 2 the conventional soundproof wall has no means of suppressing the sound travelling along the oblique auxiliary wall 100, while the soundproof wall according to the present invention is provided with the third branch wall 4 which further enhances the sound attenuation by the soundproof wall. Sound measurement similar to that shown in FIG. 17 was done with the embodiments shown in FIGS. 1,3 and 5, respectively. The results obtained are shown in Table 1. Sound attenuation by soundproof walls (in dB) Soundproof Wall 250HZ 500Hz 1Khz No. 1 embodiment (FIG. 1) 8 9 12 No. 1 embodiment with sound absorbing member (FIG. 3) 10 12 15 No. 2 embodiment (FIG. 5) 10 11 14 Conventional one (FIG. 13) 5 6 8 Conventional one (FIG. 14) 7 7 9 Conventional one (FIG. 15) 5 6 8 Conventional one (FIG. 16) 4 6 8 Table 1 shows the measured values of sound attenuation in comparison with those attained only by a conventional upright soundproof wall of 3 meters in height.

Claims: A soundproof wall for installation along a road, railway, or the like, to attenuate a sound or noise coming from such a noise source, comprising: a main wall (1); a first branch wall (2) installed generally vertically on the top of said main wall (1); a second branch wall (3) extending obliquely away from the noise source; and a third branch wall (4) installed at an intermediate height of said second branch wall (3) and which extends obliquely upward toward said noise source; wherein said second branch wall (3) has a horizontal portion (5) connected to said main wall (1) and/or said first branch wall (2). A soundproof wall as claimed in claim 1, characterized by further comprising a sound absorbing member (10) attached on at least the inner or outer side of at least one of said first, second and third branch walls (2,3,4).

Inventors: SHIMA HIROSHI, WATANABE TOSHIYUKI, SHIMA, HIROSHI, WATANABE, TOSHIYUKI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1996
Main classification: E01F8
IPC codes: G10K11, E04B1, E01F8