Patent Publication Number: US-11393445-B2

Title: Noise management system, a window system and related methods

Description:
FIELD OF INVENTION 
     The present invention relates broadly, but not exclusively, to a noise management system for a window, to a window system, to a method of managing noise and to a method of installing a noise management system on a window. 
     BACKGROUND 
     As “unwanted” sound, noise is one of the factors determining the quality of people&#39;s life. In buildings, windows constitute the main path through which noise enters a room. Therefore, the design of windows has a significant impact on noise levels at different parts of a room or building. In addition, windows should be transparent, able to provide fresh air and enable natural ventilation into a building. When the noise level outside is high, closing the windows to reduce noise will cut off natural ventilation. Reducing noise transmission through windows while retaining natural ventilation function can contribute to achieving acoustic comfort and fresh air circulation for a room in noisy environments, such as high density urban areas with heavy traffic. 
     A double-layered window with staggered openings is one of the conventional designs to reduce noise transmission through window while retaining ventilation function. Embedding passive sound absorbing materials within a ventilation channel can lead to high frequency sound absorption. However, the passive sound absorbing technologies typically do not work effectively at low audible frequency range, which often occupies a large portion of the noise in urban environment. 
     In contrast to passive sound absorbers, active noise mitigation technologies are more effective at low frequencies. For example, a recently disclosed ventilation window structure adopts a multi-cell transparent electroactive film speaker for achieving active noise control (ANC) function. However, speakers generating the anti-phase secondary cancellation sound usually produce high frequency harmonic distortion, which is the case of the multi-cell transparent electroactive film speakers. The harmonic sound would exist as additional noise and would also disturb ANC operation, resulting in noise mitigation performance degradation. 
     A need therefore exists to provide a noise management system for a window that seeks to address at least some of the above problems. 
     SUMMARY 
     According to a first aspect, there is provided a noise management system for a window, the system comprising: an active noise control (ANC) module disposed in or adjacent a ventilation channel of the window and configured to substantially cancel low-frequency noise entering the ventilation channel; and a passive sound absorbing module disposed in or adjacent to the ventilation channel and configured to absorb both high-frequency noise entering the channel and harmonic sounds generated by the ANC module. 
     The ANC module and passive sound absorbing module in the present system can synergistically interact with each other, and the performance of ANC can be improved with the harmonic sounds from the ANC module being absorbed by the passive sound absorbing module. Advantageously, the overall noise mitigation performance with the combined ANC module and passive sound absorbing module can be superior to the sum of ANC effect and passive absorbing effect, separately. 
     The ANC module may comprise at least one multi-cell transparent electroactive film speaker comprising a plurality of electroactive cells, and each cell may be individually operable for generating a sound signal anti-phase to the low-frequency noise. 
     Each electroactive cell may comprise a transparent electroactive film, a transparent substrate, a transparent bottom electrode and a transparent top electrode. 
     The transparent electroactive film may comprise a transparent piezoelectric polymer or a transparent electroactive polymer. 
     The transparent piezoelectric polymer may comprise polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)). 
     The transparent electroactive polymer may comprise an electret or a dielectric elastomer. 
     At least one of the transparent top and bottom electrodes may comprise a coating of a transparent conductive material selected from a group consisting of indium tin oxide (ITO), carbon nano-tube, carbon nano-bud, graphene, metal nano-wires, and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). 
     The passive noise absorbing module may comprise mechano-electrical conversion elements and/or electro-thermal conversion elements. 
     The mechano-electrical conversion elements may comprise a piezoelectric polymer, a charge electret polymer, piezoelectric ceramic particles, or a combination thereof. 
     The piezoelectric polymer may comprise one selected from a group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)), polyvinylidene fluoride-co-hexafluoropropylene (P(VDF-HFP)), and the charge electret polymer may comprise one selected from a group consisting of polypropylene, polyethylene terephthalate, polytetrafluoroethylene, polyimide, polymethylmethacrylate, or ethylene vinyl acetate cyclic olefin. 
     The electro-thermal conversion elements may comprise a conductive material or a lossy material. 
     The conductive material may comprise one selected from a group consisting of carbon nanotubes (CNT), graphene, carbon black, and conductive metal particles. 
     The lossy material may comprise one selected from a group consisting of aluminum nitrate nonahydrate (Al(NO 3 ) 3 9H 2 O), aluminum chloride hexahydrate (AlCl 3 6H 2 O), tetra-n-butylammonium chloride (TBAC), and ammonium acetate (NH 4 OAc). 
     The mechano-electrical conversion elements and electro-thermal conversion elements may form a porous composite having a volume porosity of at least 85%. 
     The passive sound absorbing module may be capable of absorbing sounds having a frequency below 1 kHz. 
     The passive sound absorbing module may comprise a sound absorbing material having a sound absorption coefficient greater than 0.5 at frequencies above 600 Hz. 
     The sound absorbing material may have a sound absorption coefficient greater than 0.8 at a frequency of approximately 1 kHz. 
     According to a second aspect, there is provided a window system comprising at least one noise management system as defined in the first aspect. 
     The ANC module of the window system may comprise a plurality of multi-cell transparent electroactive film speakers spatially disposed at different locations along the ventilation channel. 
     The window of the window system may comprise a lower part having a lower ventilation channel and an upper part having an upper ventilation channel, and an ANC module may be disposed in or adjacent each of the lower and upper ventilation channels, and a passive sound absorbing module may be disposed in or adjacent each of the lower and upper ventilation channels. 
     The noise management system may be configured to provide a noise reduction index of at least 15 dB. 
     According to a third aspect, there is provided a method of managing noise, comprising: substantially cancelling low-frequency noise entering a ventilation channel of a window using an active noise control (ANC) module disposed in or adjacent the ventilation channel; absorbing high-frequency noise entering the channel using a passive sound absorbing module disposed in or adjacent to the ventilation channel; and absorbing harmonic sounds generated by the ANC module using the passive sound absorbing module. 
     The method of managing noise may further comprise detecting the low-frequency noise using a reference microphone before substantially cancelling the low-frequency noise. 
     The ANC module may comprise at least one multi-cell transparent electroactive film speaker comprising a plurality of electroactive cells, and substantially cancelling the low-frequency noise may comprise individually operating each cell to generate a sound signal anti-phase to the low-frequency noise based on the detection. 
     The method of managing noise may further comprise detecting a remaining noise after the absorption and adjusting the ANC module based on the detected remaining noise. 
     Absorbing the harmonic sounds generated by the ANC module using the passive sound absorbing module may comprise absorbing sounds having a sound absorption coefficient greater than 0.8 at a frequency of approximately 1 kHz 
     According to a fourth aspect, there is provided a method of installing a noise management system on a window, the method comprising: disposing an active noise control (ANC) module in or adjacent a ventilation channel of the window, wherein the ANC module is configured to substantially cancel low-frequency noise entering the ventilation channel; and disposing a passive sound absorbing module in or adjacent to the ventilation channel, wherein the passive sound absorbing module is configured to absorb both high-frequency noise entering the channel and harmonic sounds generated by the ANC module. 
     The ANC module may comprise a plurality of multi-cell transparent electroactive film speakers, and disposing the ANC module may comprise spatially distributing the speakers at different locations along the ventilation channel. 
     The window may comprise a lower part having a lower ventilation channel and an upper part having an upper ventilation channel, and an ANC module may be disposed in or adjacent each of the lower and upper ventilation channels, and a passive sound absorbing module may be disposed in or adjacent each of the lower and upper ventilation channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and read in conjunction with the drawings, in which: 
         FIG. 1  is a schematic representation of a noise management window, according to an example embodiment. 
         FIG. 2 , comprising  FIGS. 2( a ) and 2( b ) , shows an exploded view of an example of a multi-cell transparent electroactive film speaker and an example of a fabricated multi-cell transparent electroactive film speaker, according to an example embodiment. 
         FIG. 3  is a chart illustrating harmonic distortion of a multi-cell transparent electroactive film speaker. 
         FIG. 4 , comprising  FIGS. 4( a ) to 4( c ) , shows an example of failure in noise mitigation in a window employing only the ANC means using a transparent electroactive film speaker. 
         FIG. 5  shows example sound pressure level (SPL) reduction of a window with three different noise mitigation designs in the ventilation channel. 
         FIG. 6 , comprising  FIGS. 6( a ) and 6( b ) , is a schematic representation of a window having ANC module comprising multiple transparent electroactive film speakers, according to another example embodiment. 
         FIG. 7  is a schematic representation of a window comprising split upper and lower parts, according to another example embodiment. 
         FIG. 8  is a schematic representation of a window comprising split upper and lower parts, and both the upper and lower parts have a ventilation channel between a plurality of front and rear sashes, according to another example embodiment. 
         FIG. 9 , comprising  FIGS. 9( a ) and 9( b ) , is a schematic representation of a window comprising a ventilation channel between a front and a rear single hung sash, an ANC module and a passive sound absorbing module in the ventilation channel, according to another example embodiment. 
         FIG. 10  is a flowchart illustrating a method of managing noise according to an example embodiment. 
         FIG. 11  is a flowchart illustrating method of installing a noise management system on a window according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be described, by way of example only, with reference to the drawings. Like reference numerals and characters in the drawings refer to like elements or equivalents. 
     Embodiments of the invention provide a window with natural ventilation and combined passive and active noise mitigation functions effective over a broad audible frequency range. The window as disclosed herein may comprise at least a ventilation channel, an ANC module in the ventilation channel to cancel low frequency noise, and a passive sound absorbing module in the ventilation channel to absorb high frequency noise. The ANC module comprises a transparent electroactive film speaker, preferably comprising a plurality of electroactive cells, to generate cancelling sound, which is a secondary sound with anti-phase to cancel the incident noise which is the primary sound. 
     A control unit, comprising a reference microphone, an analog to digital converter (ADC), a digital signal processing (DSP) unit, a digital to analog converter (DAC), a power amplifier and an error microphone, may control the transparent electroactive film speaker and its multiple cells, for achieving the ANC function. 
     The passive sound absorbing module comprises a material that absorbs sound. Preferably, the sound absorbing material has a large sound absorption coefficient, even at a low frequency below 1 kHz. To achieve such a performance, the sound absorbing material may be porous, and may comprise mechano-electrical conversion elements (such as piezoelectric polymers or polymeric electrets) and electro-thermal conversion elements (such as electrical conductive or dielectric lossy elements). The ANC module and passive sound absorbing module interact with each other and the overall noise mitigation performance with the combined active and passive module can be superior to the sum of ANC effect and passive absorbing effect separately. In addition to absorbing the high frequency primary sound, the passive sound absorbing module absorbs the high order harmonic sounds generated by the ANC module, i.e. the transparent electroactive film speaker. Such high order harmonic sounds would otherwise interfere with the control unit and may seriously reduce ANC efficiency and even cause its instability and failure. The synergistic functions of the passive sound absorbing module and ANC module employing the multi-cell transparent electroactive film speaker may result in unprecedented window design feature with superior noise mitigation performance over a broad frequency range. 
       FIG. 1  is a schematic representation of a noise management system  100  for a window, according to an example embodiment. The noise management system for a window comprises at least an active noise control (ANC) module  102  disposed in or adjacent a ventilation channel  106  of the window and configured to substantially cancel low-frequency noise entering the ventilation channel  106 . The noise management system  100  also comprises a passive sound absorbing module  104  disposed in or adjacent to the ventilation channel  106  and configured to absorb both high-frequency noise entering the channel  106  and harmonic sounds generated by the ANC module  102 . A control unit  108  is connected to the ANC module  102  to control the function of the ANC module  102 . 
     The ANC module  102  is more effective in cancelling low frequency noise (such as below 600 Hz) and the passive sound absorbing module  104  is more effective in absorbing high frequency noise (such as above 600 Hz). 
       FIG. 2 , comprising  FIGS. 2( a ) and 2( b ) , shows an exploded view of an example of a multi-cell transparent electroactive film speaker  200  and an example of a fabricated multi-cell transparent electroactive film speaker  200 , according to an example embodiment. 
     The ANC module  102  ( FIG. 1 ) may comprise at least one multi-cell transparent electroactive film speaker  200  comprising a plurality of individually operable electroactive cells  212 , wherein each cell  212  can be controlled individually for generating a cancelling sound signal anti-phase to the low-frequency noise. 
     Each electroactive cell  212  of the multi-cell transparent electroactive film speaker  200  may comprise a transparent electroactive film  208 , such as a piezoelectric film, a transparent substrate  204 , a transparent bottom electrode  206 , a transparent top electrode  210 , and a transparent grid  202 . The transparent electroactive film  208  of the multi-cell transparent electroactive film speaker  200  may be fabricated from a transparent piezoelectric polymer with sufficiently high piezoelectric strain coefficients, including but not limited to polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)). The transparent electroactive film  208  of the multi-cell transparent electroactive film speaker  200  may also be fabricated from a transparent electroactive polymer including but not limited to electrets and dielectric elastomers. The transparent top electrode  210  and bottom electrode  206  may be fabricated by coating a transparent conductive material, including but not limited to indium tin oxide (ITO), carbon nano-tube, graphene, metal nano-wires, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), on the transparent electroactive film  208 . 
     The control unit  108  ( FIG. 1 ) controlling the ANC module  102  may comprise a reference microphone, an analog to digital converter (ADC), a digital signal processing (DSP) unit, a digital to analog converter (DAC), a power amplifier, and an error microphone, in which the control system may generate single or multiple control signals for driving the multiple electroactive cells  212  of the multi-cell transparent electroactive film speaker  200  to generate the cancelling noise. 
     An incident noise as the primary sound entering the ventilation channel  106  can be sensed by the reference microphone. The ANC control unit  108  may convert the input analog primary noise signal to digital format data which is processed by the DSP, based on a digital signal processor or field programmable gate array (FPGA), based on Filter-X Least Mean Square (FXLMS) adaptive algorithm, to generate a suitable digital output signal to be fed to the DAC to produce an analog signal to control the multi-cell transparent electroactive film speaker  200  for generating the secondary sound as the cancelling noise of anti-phase with the incident noise. The destructive interaction of the primary sound and the secondary sound within the ventilation channel  106  may result in reduced noise transmitted through the window at a low frequency range. The residual noise measured by the error microphone can be used as the active feedback for adjusting the phase as well as sound pressure level of the cancelling noise for optimizing the ANC effect. 
     Compared to the conventional electromagnetic speakers, multi-cell transparent electroactive film speakers  200  may have higher harmonic distortion. When the multi-cell transparent electroactive film speaker  200  is driven at a certain frequency, it may generate harmonic sounds at higher frequencies. The present inventors have noted that the excessive harmonic sound generated due to the harmonic distortion of the multi-cell transparent electroactive film speaker  200  may be picked up by the reference and error microphones which may cause interference or error to the control unit  108  of the ANC module  102 , hence the ANC module  102  may fail in effectively cancelling the noise or may experience instability and failure. 
       FIG. 3  is a graph  300  illustrating harmonic distortion of a typical multi-cell transparent electroactive film speaker. 
       FIG. 4 , comprising  FIGS. 4( a ) to 4( c ) , shows an example of failure in noise mitigation in a window  400  employing only the ANC means using a transparent electroactive film speaker.  FIG. 4( a )  shows harmonic sounds generated by a typical multi-cell transparent electroactive film speaker when driven at 500 Hz.  FIG. 4( b )  shows the measured noise when ANC is OFF (i.e. only primary sound) and  FIG. 4( c )  shows the measured noise when ANC is ON. The typical multi-cell transparent electroactive film speaker may generate significant second and third harmonic components when it is driven at 500 Hz as shown in  FIG. 4( a ) . When ANC is OFF, the primary sound has a pure 500 Hz component as shown in  FIG. 4( b ) . By turning ON the ANC, although the 500 Hz noise is reduced by about 6 dB, excessive higher frequency components are generated by the multi-cell transparent electroactive film speaker, the overall noise increases and the ANC fails completely as shown in  FIG. 4( c ) . 
     According to the example embodiment, the passive sound absorbing module  104  is disposed in the ventilation channel  106 . The passive sound absorbing module  104  can perform two functions: absorb the high frequency primary sound travelling in the ventilation channel  106  of the window, and substantially absorb the harmonic sounds generated by the multi-cell transparent electroactive film speaker  200 , thereby reducing the error introduced to the ANC control unit  108 , avoiding its instability and failure, and increasing its noise reduction efficiency. 
     The passive sound absorbing module  104  of the example embodiment preferably exhibits a large sound absorption coefficient even at low frequency below 1 kHz. To achieve such a performance at frequency below 1 kHz, the sound absorbing module  104  can be porous and comprise mechano-electrical conversion elements and/or electro-thermal conversion elements. 
     The mechano-electrical conversion elements may be selected from any piezoelectric and charge electret polymer including but not limited to polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)), polyvinylidene fluoride-co-hexafluoropropylene (P(VDF-HFP)), polypropylene, polyethylene terephthalate, polytetrafluoroethylene, polyimide, polymethylmethacrylate, or ethylene vinyl acetate cyclic olefin or any other hybrid and blend of these polymers with other polymers, or piezoelectric ceramic particles. The electro-thermal conversion elements may be selected from any conductive material including but not limited to carbon nanotubes (CNT), graphene, carbon black, and conductive metal particle, or lossy material including but not limited to hydrated or hygroscopic materials such as aluminum nitrate nonahydrate (Al(NO 3 ) 3 9H 2 O), aluminum chloride hexahydrate (AlCl 3 6H 2 O), tetra-n-butylammonium chloride (TBAC), and ammonium acetate (NH 4 OAc). The porosity of the passive sound absorbing module is in range of 50% to 95%, preferably larger than 85%, and the pore size is preferably in the range of 50 μm to 600 μm. For example, the mechano-electrical conversion elements and electro-thermal conversion elements may form a porous composite having a volume porosity of at least 85%. 
     More preferably, the passive sound absorbing module  104  is porous and comprises a composite of PVDF and 5 wt % CNT. Table 1 shows sound absorption coefficients of a passive sound absorbing module comprising a porous composite of polyvinylidene fluoride (PVDF) and 5 wt % carbon nanotubes (CNT), in comparison with several commonly used sound absorbing materials. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Frequency 
                 Sound Absorption Coefficient 
               
            
           
           
               
               
               
               
               
            
               
                 (Hz) 
                 PVDF/5 wt % CNT 
                 Cotton Fiber 
                 Polyurethane 
                 Rockwool 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 200 
                 0.08 
                 0.06 
                 0.06 
                 0.06 
               
               
                 400 
                 0.30 
                 0.12 
                 0.12 
                 0.10 
               
               
                 600 
                 0.54 
                 0.20 
                 0.22 
                 0.18 
               
               
                 800 
                 0.74 
                 0.29 
                 0.33 
                 0.32 
               
               
                 1000 
                 0.87 
                 0.39 
                 0.46 
                 0.41 
               
               
                 1200 
                 0.94 
                 0.48 
                 0.58 
                 0.61 
               
               
                 1400 
                 0.98 
                 0.58 
                 0.69 
                 0.92 
               
               
                 1600 
                 0.99 
                 0.67 
                 0.79 
                 0.95 
               
               
                   
               
            
           
         
       
     
     Compared to the commercially available sound absorbing materials, the passive sound absorbing module  104  comprising a composite of PVDF and 5 wt % CNT exhibits much larger sound absorption coefficient in a wide frequency range, even up to relatively lower frequencies (below 1 kHz). For example, the sound absorbing material forming the passive sound absorbing module  104  may have a sound absorption coefficient greater than 0.5 at frequencies above 600 Hz, preferably a sound absorption coefficient greater than 0.8 at a frequency of approximately 1 kHz. The higher sound absorption coefficient of the passive sound absorbing module  104  over a broad frequency range with the low frequency end extended below 1 kHz is critical to absorbing the harmonic sounds of the multi-cell transparent electroactive film speaker  200  during ANC operation. 
     When the incident noise enters the ventilation channel  106  of the window, high frequency noise may be absorbed by the passive sound absorbing module  104  and low frequency noise is cancelled by the ANC module  102 . Furthermore, the passive sound absorbing module  104  may absorb the harmonic sounds generated by the multi-cell transparent electroactive film speaker  200 , and may substantially reduce the error introduced to the ANC control unit  108 . Consequently ANC can become more effective. The synergistic interaction of the ANC module  102  and the passive sound absorbing module  104  can result in a significantly improved overall noise mitigation performance of the window in a broad audible frequency range.  FIG. 5  shows plots illustrating example sound pressure level (SPL) reduction of a window with three different noise mitigation designs in the ventilation channel  106 . The three different noise mitigation designs are ANC module  102  only, passive sound absorbing module  104  only, and both ANC module  102  and passive sound absorbing module  104  according to the example embodiment. 
     The window with the synergistic interaction from both the ANC module  102  and the passive sound absorbing module  104  can have a significantly improved noise mitigation performance in a wider frequency range compared to the windows with only one of them. The passive sound absorbing module  104  not only can absorb some of the noise but can also improve the performance of the ANC module  102  by absorbing the harmonic sounds generated by the ANC module  102 . The SPL reduction of the window with the combined two modules according to the present embodiments is even much larger than the sum of SPL reduction of the window only with the ANC module  102  and with the passive sound absorbing module  104 , separately. The window with the noise management system as described can have a noise reduction index of at least 15 dB. 
     Noise reduction index (NRI) is defined in Equation 1 below: 
                   NRI   =         Δ   ⁢   S   ⁢   P   ⁢     L     2   ⁢   5   ⁢   0         +     Δ   ⁢   S   ⁢   P   ⁢     L     5   ⁢   0   ⁢   0         +     Δ   ⁢   S   ⁢   P   ⁢     L     1   ⁢   0   ⁢   0   ⁢   0         +     Δ   ⁢   S   ⁢   P   ⁢     L     2   ⁢   0   ⁢   0   ⁢   0           4             (   1   )               
where ΔSPL is the sound pressure level reduction. The window according to an embodiment has a significantly larger NRI of 15.9 dB compared to 3.4 dB of the window only with ANC module  102  and 10.3 dB of the window only with passive sound absorbing module  104 , noting that the unit is on logarithmic scale.
 
     In one implementation, the transparent top electrode  210  of the transparent electroactive film speaker  200  can be patterned in the shape of flowers to improve aesthetics. 
     Embodiments of the invention also provide a window system comprising at least one noise management system as described above. 
       FIG. 6 , comprising  FIGS. 6( a ) and 6( b ) , is a schematic representation  600  of a window having ANC module  602  comprising multiple transparent electroactive film speakers, according to an example embodiment.  FIG. 6( a )  depicts a top view and  FIG. 6( b )  depicts a perspective view of the window. Such window may be capable of achieving larger SPL reductions and more uniform noise mitigation performance. 
       FIG. 7  is a schematic representation of a window  700  comprising split upper and lower parts  704 ,  708 , according to another example embodiment. The lower part  708  can be a conventional window without ventilation channel. The upper part  704  can have a ventilation channel  706  with an ANC module  702  and a passive sound absorbing module  710 . 
       FIG. 8  is a schematic representation of a window  800  comprising split upper and lower parts  808 ,  812 , and the upper and lower parts  808 ,  812  have respective ventilation channels  810   a ,  810   b  between a plurality of front sashes  806   a ,  806   b  and rear sashes  802   a ,  802   b , according to another example embodiment. In one implementation, the window  800  can have an ANC module  804  comprising four multi-cell transparent electroactive films speakers  814 , three in the ventilation channel  810   a  of the upper part  808  and one in the ventilation channel  810   b  of the lower part  812 . Top, bottom and side walls of ventilation channel  810   a ,  810   b  of both the upper and lower parts  808 ,  812  are covered with the passive sound absorbing modules  816 . Compared to the other embodiments, the window  800  allows more ventilation as well as effective noise mitigation performance. 
       FIG. 9 , comprising  FIGS. 9( a ) and 9( b ) , is a schematic representation of a window  900  comprising a ventilation channel  904  between a front and a rear single hung sash  906 ,  908 , an ANC module  902  and a passive sound absorbing module  910  in the ventilation channel  904 , according to another example embodiment.  FIG. 9( a )  shows a perspective view and  FIG. 9( b )  shows a cross section view. The front and rear single hung sashes  906 ,  908  of the window  900  may be configured to move upward and downward. 
       FIG. 10  is a flowchart  1000  illustrating a method of managing noise according to an example embodiment. At step  1002 , low-frequency noise entering a ventilation channel of a window is substantially cancelled using an active noise control (ANC) module disposed in or adjacent the ventilation channel. At step  1004 , high-frequency noise entering the channel is absorbed using a passive sound absorbing module disposed in or adjacent to the ventilation channel. At step  1006 , harmonic sounds generated by the ANC is absorbed using the passive sound absorbing module. Step  1006  may comprise absorbing sounds having a frequency below 1 kHz. 
       FIG. 11  is a flowchart  1100  illustrating a method of installing a noise management system on a window according to an example embodiment. At step  1102 , an active noise control (ANC) module is disposed in or adjacent a ventilation channel of the window. The ANC module is configured to substantially cancel low-frequency noise entering the ventilation channel. At step  1104 , a passive sound absorbing module is disposed in or adjacent to the ventilation channel. The passive sound absorbing module is configured to absorb both high-frequency noise entering the channel and harmonic sounds generated by the ANC module. 
     It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.