Abstract:
There is disclosed a flexible acoustic barrier for suspending from a support frame, comprising: a portion of acoustic insulation material and at least one loudspeaker configured to emit an audible sound-masking signal to mask sound from a sound source. There is also disclosed a corresponding method of mitigating noise pollution.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. §119 to GB application number 1503304.6 filed Feb. 27, 2015, which is incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a flexible acoustic barrier having a loudspeaker configured to emit an audible sound-masking signal. 
       BACKGROUND 
       [0003]    Noise pollution, such as from construction machinery, can disturb or harm those near to the source of noise. It is known to mitigate the impact of noise sources, such as construction machinery, using acoustic barriers. Acoustic barriers may be assembled around and/or above a noise source to reduce the sound level of noise for persons in the surrounding environment. 
         [0004]    Typically, the type of acoustic barrier that is provided to reduce the sound level of noise depends on the level of noise generated, and the maximum acceptable noise level for the particular environment. An acoustic barrier or acoustic barrier installation having the relevant performance characteristics is selected accordingly. The dominant performance characteristic is the level of noise reduction, and acoustic barriers of varying expense can be selected to achieve the desired performance characteristic by varying the thickness and composition of the barrier, amongst other things. 
         [0005]    However, known acoustic barriers and acoustic barrier installations are configured to reduce the impact of the absolute noise level only, and fail to mitigate the disturbing influence of the residual noise. 
         [0006]    Accordingly, it is desirable to provide an improved acoustic barrier. 
       SUMMARY 
       [0007]    According to a first aspect of the invention there is provided a flexible acoustic barrier for suspending from a support frame, comprising: a portion of acoustic insulation material; and at least one loudspeaker configured to emit an audible sound-masking signal to mask sound from a sound source. 
         [0008]    The sound source may be, for example, a construction site, transport infrastructure such as a road, equipment, people or any other source of sound. 
         [0009]    The or each loudspeaker may be integrated in the portion of acoustic insulation material. For example, the loudspeaker may be provided in a cut-out within the portion of acoustic insulation material. 
         [0010]    The acoustic barrier may further comprising an input port to receive a sound-masking signal for the at least one loudspeaker from a signal generator. The acoustic barrier may further comprise an output port for transmitting a sound-masking signal to a like acoustic barrier in a daisy-chain layout. 
         [0011]    A cable coupling the input port with the loudspeaker and/or a cable coupling the output port with the loudspeaker may extend through a portion of the acoustic barrier. For example, the cable may extend through the portion of acoustic insulation material. A portion of the cable coupling the input port with the loudspeaker and/or a cable coupling the output port with the loudspeaker may extend from a body of the acoustic barrier so that the respective part can be manipulated relative the body, for example, so as to easily connect with a corresponding port of an adjacent barrier or a signal generator. 
         [0012]    The cable may at least partly extend between the portion of acoustic insulation material and a body of the barrier to which the portion of acoustic insulation material is coupled. The portion of acoustic insulation material may be secured to the body so that the cable is securely retained between the portion of acoustic insulation material and the body. 
         [0013]    The portion of acoustic insulation material may be secured to a substrate, such as a web or mesh, and a power or signal cable for the loudspeaker may be retained between the portion of insulating material and the substrate. Accordingly, the cable may be prevented from moving relative to the portion of insulating material and may be securely retained to prevent snagging. 
         [0014]    The acoustic barrier may comprise a signal generator for generating a sound-masking signal for emission by the at least one loudspeaker. The sound-masking signal may comprise noise. The sound-masking signal may be selected from a group of noise signals consisting of: white noise, pink noise, brown noise, blue noise, violet noise and grey noise. 
         [0015]    The acoustic barrier may be configured to be folded and/or to be rolled from a deployed configuration to a compact configuration. 
         [0016]    There may be a plurality of portions of acoustic insulation material. The or each loudspeaker may be integrated in one of the portions of acoustic insulation, such as a lower portion, or different loudspeakers may be integrated in different portions of insulation material. 
         [0017]    The or each portion of acoustic insulation material may be configured to reduce the sound level of a 70 decibel sound from the sound source by at least 10 decibels. 
         [0018]    The or each portion of acoustic insulation material may have an acoustic absorption coefficient of at least 0.2, at least 0.3, at least 0.4 or at least 0.5 for frequencies in the range of 2 MHz to 10 MHz. The or each portion of acoustic insulation material may have an acoustic absorption coefficient of at least 0.1, at least 0.2 or at least 0.3 for frequencies in the range of 1 MHz to 10 MHz. The or each portion of acoustic insulation material may have an acoustic absorption coefficient of at least 0.02, 0.03, 0.04, or at least 0.05 for frequencies in the range of 0.2 MHz to 1 MHz. 
         [0019]    The or each portion of acoustic insulation material may comprise a foam material, such as polyurethane (PU) foam. The foam may be a uniform open or closed cell foam. The foam may be have a waterproof or water repellent coating, or may otherwise be treated so as to be waterproof or water repellent. The or each portion of acoustic insulation material may be at least 25 mm thick. 
         [0020]    The acoustic barrier may further comprise a body for mounting to a support frame, and the or each portion of acoustic insulation material may be mounted to or retained by the body. 
         [0021]    The body may be flexible. The body may be a sheet, such as a substrate or backing, to which the or each portion of acoustic insulation material is mounted. The body may comprise front and/or back covers for the or each portion of acoustic insulation material. The body may comprise one or more pockets for receiving the or each portion of insulation material. The body may be composed of plastics material, such as polyvinylchloride (PVC). The body may be waterproof. 
         [0022]    According to a second aspect of the invention there is provided an acoustic barrier installation comprising: at least one acoustic barrier in accordance with the first embodiment of the invention; and a support frame from which the or each acoustic barrier is suspended. 
         [0023]    The acoustic barrier installation may further comprise a signal generator for generating the sound-masking signal for the or each loudspeaker of the or each acoustic barrier. The signal generator may be integrated into one of the acoustic barriers, or it may be structurally separate from the or each acoustic barriers and coupled to at least one acoustic barrier to provide the sound-masking signal to the or each acoustic barrier. 
         [0024]    The acoustic barrier installation may further comprise a microphone for monitoring the sound environment of the acoustic barrier installation, and the signal generator or a controller for the signal generator may be configured so that the sound-masking signal for the or each loudspeaker is dependent on at least one characteristic of the sound environment based on an output signal from the microphone. 
         [0025]    The signal generator or a controller for the signal generator may be configured so that the sound-masking signal for the or each loudspeaker is dependent on the power spectrum distribution (power spectral density) or the power intensity of the sound environment monitored by the microphone. 
         [0026]    There may be at least two acoustic barriers and at least one of the acoustic barriers may comprise an output port for transmitting a sound-masking signal to a like acoustic barrier in a daisy-chain layout. 
         [0027]    According to a third aspect of the invention there is also provided a kit of parts for an acoustic barrier installation in accordance with the second aspect of the invention, the kit of parts comprising at least one acoustic barrier in accordance with the first aspect of the invention and a signal generator. 
         [0028]    According to a fourth aspect of the invention there is provided a method of mitigating noise pollution from a noise source, the method comprising: installing an acoustic barrier installation in accordance with the second aspect of the invention; generating a sound-masking signal for the or each loudspeaker of the installation; and audibly emitting the sound-masking signal using the or each loudspeaker to mask noise from the noise source. 
         [0029]    The method may further comprise monitoring the sound environment using a microphone of the acoustic barrier installation and generating a sound-masking signal for the or each loudspeaker which is dependent on at least one characteristic of the sound environment, based on an output signal of the microphone. The sound-masking signal for the or each loudspeaker may be dependent on the power spectrum distribution or the power intensity of the sound environment monitored by the microphone. 
         [0030]    According to a fifth aspect of the invention there is provided an acoustic barrier installation comprising: at least one acoustic barrier comprising a portion of acoustic insulation material; a support frame for the or each acoustic barrier; and at least one loudspeaker disposed above and spaced apart from the or each portion of acoustic insulation material. 
         [0031]    The or each loudspeaker may be supported so that it is spaced apart from the or each portion of acoustic insulation material by at least 0.5 m, at least 0.75 m, at least 1 m, or at least 2 m. The or each loudspeaker may be supported on a speaker support, such as a post. The speaker support may be integrated with the support structure for the or each acoustic barrier. Alternatively, the speaker support may be integrated in the or each acoustic barrier, such as in the body of the acoustic barrier. The acoustic barrier may be flexible and may have any of the features described above. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0032]    The invention will now be described, by way of example, with reference to the following drawings, in which: 
           [0033]      FIG. 1  schematically shows a front view of an acoustic barrier according to an embodiment of the invention; 
           [0034]      FIG. 2  schematically shows a side view of the acoustic barrier of  FIG. 1 ; 
           [0035]      FIG. 3  schematically shows a perspective view of the acoustic barrier of  FIG. 1 , including a detail view of the pocket; 
           [0036]      FIG. 4  schematically shows a cross-sectional view of a portion of a cabling arrangement between a portion of acoustic insulation material and a substrate; and 
           [0037]      FIG. 5  shows a further embodiment of an acoustic barrier. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]      FIGS. 1 and 2  show an acoustic barrier  10  in the form of a flexible acoustic curtain for suspending from a frame, such as a temporary scaffold. 
         [0039]    The flexible acoustic curtain comprises a body  12  having a rectangular flexible polyvinylchloride (PVC) sheet and upper and lower pockets  14 ,  16  for retaining upper and lower portions  18 ,  20  of acoustic insulation material respectively. In this embodiment the pockets  14 ,  16  are also composed of flexible PVC material and can be stitched, welded, or otherwise fastened to the flexible PVC sheet of the body  12  to form part of the body  12 . 
         [0040]    The periphery of the body  12  is provided with eyelets  13  for securing the acoustic barrier to a support frame, for example, by a chord or security straps. In other embodiments, at least the lateral borders of the body  12  may be provided with hook and loop fasteners, or other fasteners, for quickly connecting adjacent acoustic barriers together. 
         [0041]    Each pocket  14 ,  16  is provided with a flap  40  for opening and closing the pocket, as shown in  FIG. 3 . In this embodiment, the flaps  40 ,  42  can be secured in a closed position using corresponding hook and loop fasteners provided on at least the upper flap  42  and the front portion  44  of each pocket  14 ,  16 . 
         [0042]    Referring again to  FIG. 1 , the portions of acoustic insulation material  18 ,  20  are received in the pockets  14 ,  16 . In this embodiment, the portions of acoustic insulation material are composed of an open cell foam, for example a polyurethane foam having a density between 75 and 95 kg/m 3 . In other embodiments, the foam may have a closed cell structure. 
         [0043]    In this embodiment, the portions of acoustic insulation material  18 ,  20  are approximately 50 mm thick. The upper portion  18  has a width of approximately 1100 mm and a height of approximately 500 mm. The lower portion  20  has a width of approximately 1100 mm and a height of approximately 1200 mm. 
         [0044]    The curtain can be folded, for example, at the gap between the two pockets  14 ,  16 , so as to occupy less space. This can be useful for shipping or storing the product. Alternatively, the curtain can be rolled, as the portions of acoustic insulation material  18 ,  20  are flexible. 
         [0045]    A sound-masking system is integrated with the curtain, and includes two loudspeakers  22 , input and output ports  24 ,  26  provided with corresponding input and output cables  28 ,  30 , and a connecting cable  32  extending between the two loudspeakers. 
         [0046]    In this embodiment, each one of the loudspeakers  22  is integrated within the lower portion of acoustic insulation material  20 . In particular, the lower portion  20  is provided with corresponding cutouts in which the loudspeakers  22  are received. 
         [0047]    The input and output cables  28 ,  30 , and the connecting cable  32  extend laterally from the loudspeakers  22  along the rear face of the lower portion of acoustic insulation material  20 , sandwiched between the lower portion  20  and a backing mesh  34 , as shown in  FIG. 4 . In this example, the backing mesh is a flexible PVC mesh (or web) adhered to the lower portion of acoustic insulation material  20 , so as to retain the cables  28 ,  30 ,  32  therebetween. In other embodiments, the backing mesh  34  may be replaced with an alternative layer, such as a layer of fabric, a layer of sheet PVC, or a second layer of acoustic insulation material. 
         [0048]    In use, a plurality of acoustic barriers  10  are suspended from a support frame using the eyelets  13 , such as a scaffold around a construction site, to reduce the sound level of noise from a noise source. The plurality of acoustic barriers  10  may be coupled together using the eyelets  13 , or with hook and loop fasteners as described above. 
         [0049]    A signal generator (not shown) is coupled to a first one of the acoustic barriers to provide a sound-masking signal for emission from the loudspeakers  22 . The output port  26  of the first acoustic barrier  10  is coupled to the input port  24  of a like adjacent second acoustic barrier  10  in a daisy-chain layout so that the sound-masking signal is carried to each of the acoustic barriers  10  for emission by the respective loudspeakers  22 . 
         [0050]    The signal generator is configured to generate a sound-masking signal which has the effect of masking noise generated by a noise source (or other sounds which may not be considered to be noise) for those operating in the environment, by providing a background noise level. In this example embodiment, the signal generator is configured to generate a white noise sound-masking signal, which is a random signal characterised by having a constant power spectral density (i.e. the sound level is constant at all frequencies of the signal). White noise is considered to be particularly effective in masking noise generated by a noise source. In other example embodiments, the signal generator may be configured to generate other standard noise signals, such as pink noise and brown noise, in which the power spectral density is defined by standard specific rules (for example, for pink noise, the power spectral density is inversely proportional to frequency). In yet further embodiments, the signal generator may be configured to generate a customised sound-masking signal having a pre-determined power spectral density (or power distribution). 
         [0051]    In yet further alternative embodiments, the signal generator may be configured to generate sound-masking signal dependent on the sound environment, for example, based on a signal from a microphone coupled to the signal generator. The sound-masking signal may be responsive to the sound environment, so as to mask the effect of particular noises from the sound environment that are detected by the microphone. For example the signal generate may generate a noise signal having a frequency range including the frequency of a noise within the sound environment, such as a particular piece of construction machinery. 
         [0052]      FIG. 5  shows a second embodiment of an acoustic barrier  10 ′ which differs from the first embodiment described above only in that a signal generator  50  for the sound-masking signal is integrated in the acoustic barrier  10 ′, in particular, within the lower portion of acoustic insulation material  20 . The input cable extends directly between the signal generator  50  and the first of the two loudspeakers  22 .