Abstract
A sound absorbing device of the type adapted to cover the ears of a user and comprising a sound absorbing material, wherein the sound absorbing material comprises of a thixotropic material.
Claims
1. A manufacture for use in a pair of headphones, wherein the manufacture comprises a sound-absorbing device that is configured to cover an ear, wherein the sound-absorbing device comprises both a sheet and a sound-absorbing material, wherein the sheet defines a cellular scaffold that comprises cells, wherein the sound-absorbing material comprises a thixotropic material that is located in the cells of the cellular scaffold, wherein the thixotropic material exhibits a low viscosity drop in response to low intensity noise and disproportionately high viscosity decrease in response to high intensity noise, wherein the thixotropic material has an apparent viscosity that decreases in response to constant sheer stress, and wherein the apparent viscosity gradually returns to equilibrium following removal of the sheer stress.
2. The manufacture of claim 1, wherein the sound-absorbing material is enclosed within an expandable container, and wherein the expandable container expands to allow an increase in volume of the thixotropic material.
3. The manufacture of claim 1, wherein the cellular scaffold comprises a honeycomb.
4. The manufacture of claim 1, wherein the cellular scaffold comprises a polymer film having cellular compartments, and wherein the thixotropic material is located within the cellular compartments.
5. The manufacture of claim 1, wherein the cellular scaffold comprises a plurality of tubes, each of which comprises first and second ends and a thixotropic material-containing lumen extending between the ends, wherein one end of each tube is disposed within a base.
6. The manufacture of claim 1, further comprising noise protection headphone that incorporates the sheet.
7. The manufacture of claim 6, wherein the headphone comprises a resiliently deformable portion, wherein, deformation of the resiliently deformable portion applies shear to the thixotropic material.
8. The manufacture of claim 1, wherein the thixotropic material is selected from the group comprising structured liquids, suspensions, emulsions, polymer solutions, aqueous iron oxide gels, vanadium pentoxide sols, starch pastes, pectin gels, flocculated paints, clays, soil suspensions, creams, drilling muds, flour doughs, flour suspensions, fibre greases, jellies, paints, honey, carbon-black suspensions, hydrophobically modified hydroxethyl cellulose, non-associative cellulose water solutions, flocculated polymer latex suspension, rubber solutions, metal slushes, bentonite clays, modified laponites, oils, lubricants, coal suspensions, xanthan gums, organic bentonite, fumed silica, aluminum stearate, metal soap, castor oil derivatives or thixotropic epoxy resin, or combinations thereof.
9. The manufacture of claim 1, wherein the sheet is circular.
10. A method of protecting an ear from high intensity noise comprising the step of placing a sound-absorbing device of the type adapted to cover the ears of a user and comprising a sound-absorbing material contained within a container in the form of a cellular scaffold, wherein the sound-absorbing material comprises a thixotropic material that is located in the cells of the cellular scaffold over and above the ear, wherein the thixotropic material has a resting viscosity which exhibits low resistance to passage of low intensity noise, and wherein the thixotropic material decreases in viscosity in response to incident high intensity noises to thereby exhibit high resistance to the high intensity noise.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:
(2) FIG. 1 illustrates a first honeycomb layer structure for a sound absorbing device of the present invention;
(3) FIG. 2 is an exploded view of a thixotropic device of the present invention comprising a honeycomb lattice as illustrated in FIG. 1;
(4) FIG. 3 illustrates a second honeycomb layer structure for a sound absorbing device of the present invention;
(5) FIG. 4 illustrates a third honeycomb layer structure for a sound absorbing device of the present invention;
(6) FIG. 5 illustrates a cylindrical tubular structure for a sound absorbing device of the present invention;
(7) FIG. 6 illustrates a multiple interleaved cylindrical tubular structure for a sound absorbing device of the present invention;
(8) FIG. 7 illustrates (A) a side view and (B) a perspective view of a substantially U-shaped structure for a sound absorbing device of the present invention;
(9) FIG. 8 illustrates a set of headphones comprising a sound absorbing material enclosed in a container of the present invention;
(10) FIG. 9 illustrates a fourth honeycomb layer structure for a sound absorbing device of the present invention;
(11) FIG. 10A-10D illustrates in more detail the substantially U-shaped structure of FIG. 7 in (A) front, (B) plan, (C) perspective and (D) side views;
(12) FIG. 11A-11D illustrates a second substantially U-shaped structure for a sound absorbing device of the present invention in (A) plan, (B) front, (C) side and (D) perspective views;
(13) FIG. 12 illustrates a third substantially U-shaped structure for a sound absorbing device of the present invention in (A) plan, (B) front, (C) side and (D) perspective views;
(14) FIG. 13 illustrates a multiple cylindrical tubular structure for a sound absorbing device of the present invention in (A) side, (B) elevation, (C) plan and (D) perspective views;
(15) FIG. 14 illustrates a second multiple cylindrical tubular structure for a sound absorbing device of the present invention (A) side, (B) elevation, (C) plan and (D) perspective views;
(16) FIG. 15 illustrates a graph of dB Change vs. Frequency (Hz) for one embodiment of the present invention as shown in FIG. 11 and the industry standard 3M® headphone;
(17) FIG. 16 illustrates a graph of dB Change vs. Frequency (Hz) for one embodiment of the present invention as shown in FIG. 3 and the industry standard 3M® headphone;
(18) FIG. 17 illustrates a graph of dB Change vs. Frequency (Hz) for one embodiment of the present invention as shown in FIG. 13 and the industry standard 3M® headphone;
(19) FIG. 18 illustrates a graph of dB Change vs. Frequency (Hz) for one embodiment of the present invention as shown in FIG. 14 and the industry standard 3M® headphone;
(20) FIG. 19 illustrates a graph of dB Change vs. Frequency (Hz) for one embodiment of the present invention as shown in FIG. 1 and the industry standard 3M® headphone;
(21) FIG. 20 is a schematic diagram of the testing environment used to determine the dB Change vs. Frequency (Hz) as shown in FIGS. 15 to 19.
DETAILED DESCRIPTION OF THE DRAWINGS
(22) The invention is based on the use of a thixotropic material as a sound absorbing medium in devices which are adapted to attach or cover a user's ear. Examples of such devices would be noise protection headphones, audio headphones, and ear plugs. The thixotropic material has a resting viscosity which decreases as sound energy is incident on the material. As the viscosity of the material decreases, the level of attenuation of the incident sound increases. Thus, when such a material is employed in noise protection headphones/earmuffs, the level of attenuation of sound will increase as the intensity of the sound increases, thereby allowing a user to hear low intensity sounds such as conversation though the headphones (when the material is at or close to a resting viscosity), while attenuating high intensity sounds.
(23) Referring now to the figures, where FIG. 1 illustrates a general embodiment of a sound absorbing device of the present invention. Specifically, FIG. 1 illustrates a perspective view of a sound absorbing device of the present invention, which in this instance is configured as a honeycomb layer and is generally referred to by reference numeral 1. The honeycomb layer 1 is arranged in a sheet 2 and is formed from polyethylene plastic foil. The sheet 2 comprises a series of rows 3 and columns 4 of a honeycomb structure or cells 5. The cells 5 are filled with a thixotropic material, in this case lubricating oil. The thixotropic material reacts in such a way as to transfer some of the entering sound energy into kinetic energy that changes the structure of the thixotropic material and lessens the amount of sound energy passing through the material. In a further embodiment, the honeycomb cells 5 are comprised of the thixotropic material. The honeycomb structure may be constructed from rigid or pliable integrity material depending on tailored use. It is seen that an expansion ability will be required in some embodiments so as pressure will not increase with phase change.
(24) In FIG. 2 there is illustrated a sound absorbing device 1 of FIG. 1 sandwiched between a series of layers of material. The sound absorbing device 1 of FIG. 2 comprises the sheet 2 of thixotropic material formed from thixotropic epoxy resin which is known to those skilled in the art in soundproofing and structural sealants for building construction sandwiched between adhesive seal layers 30,31. The outer adhesive seal layers 30,31 seal the voids of the cells 5 of the honeycomb structure. An outer layer 33 and inner layer 34 are placed on the side of the adhesive seals 30,31 facing away from the sheet 2. The combination of the sheet 2 and layers 30,31,33,34 provide a sound absorbing device 1 of the present invention.
(25) In FIG. 3 there is illustrated a further embodiment of the present invention where the device 1 is represented by a polymeric film having a multiplicity of honeycomb cells 5 and configured as a series of discs 10,11,12. The series of discs 10,11,12 are stacked one on top of the other with decreasing diameters to provide a conical or substantially conical shape. An outer disc 10 has a diameter larger than inner disc 11, which has a diameter larger than disc 12 when the central radius point is taken at the centre of the device 1. FIG. 4 illustrates a further embodiment of the device 1 of FIG. 3. An outer disc 20 and 21 comprise a non-thixotropic material. The honeycomb structure may be constructed from rigid or pliable integrity material depending on tailored use. It is seen that an expansion ability will be required in some embodiments so as pressure will not increase with phase change. The inner disc 22 may aid in this expansion as well as the outer circumference material 21. The outer disc 20 is rigid so as to aid manufacturing process and disposal within a housing. Between outer disc 21 and an inner disc 22 is found a collection of honeycomb cells 5. The honeycomb cells 5 are interspersed with thixotropic material-filled structures 7. In the illustrated embodiment, the honeycomb cells 5 are composed of a thixotropic material. FIG. 9 illustrates a further embodiment of the device 1 of FIG. 3. A disc 110 comprises a non-thixotropic material and having an outer rim 111. The honeycomb structure may be constructed from rigid or pliable integrity material depending on tailored use. The outer rim 111 is rigid so as to aid manufacturing process and disposal within a housing. Within the outer rim 111 is found a collection of honeycomb cells 5. The honeycomb cells 5 may be filled with thixotropic material. In the illustrated embodiment, the honeycomb cells 5 are composed of a thixotropic material.
(26) Referring to FIG. 5, these is illustrated a cellular scaffold forming part of a sound absorbing device according to an alternative embodiment of the invention. The cellular scaffold 90 comprises a cylindrical tube 91 having an exterior surface 92 and an interior surface 94 defining a lumen 96 which is filled with a thixotropic material. In use, the cylindrical tube would be arranged within the sound absorbing device (not shown) such that external sound would enter the tube at a first end 95 and travel through the tube to a second end 97. In doing so, the sound would cause some movement of the thixotropic material within the tube. The material at the walls of the tube would experience friction and be exposed to a higher shear rate than the material at the centre of the tube. Thus, the thixotropic material adjacent the walls of the tube would have greater sound absorbing capacity compared to the material at the centre of the tube.
(27) Referring to FIG. 6, these is illustrated an alternative cellular scaffold forming part of a sound absorbing device of the invention. The cellular scaffold 90 comprises a series of cylindrical tubes 91 arranged in an interleaving arrangement. In use, the cylindrical tubes would preferably be arranged within the sound absorbing device (not shown) such that external sound would enter the tube at a first end 95 and travel through the tube to a second end 97.
(28) Referring to FIG. 7 and FIGS. 10A-10D, there is illustrated a series of thixotropic material-containing cylindrical tubes 100, each tube being coiled back on itself, the series of curved tubes forming a U-shaped structure 101. Each tube has two ends which, due to the U-shape, face the same direction. In use, the U-shaped structure is disposed within a sound absorbing device such that the ends of the tube face towards incident sound, and the bend on the U-shaped structure is disposed towards the user's ear. This structure directs the incoming sound back out to the environment. As such, most of the sound energy would be directed back out to the environment even though the transmission percentage of sound in this part of the device 1 would be quite low given that the sound energy passes through thixotropic material.
(29) The housing 90 and substantially U-shaped structure 100 may be immersed in thixotropic material to further dampen and attenuate any sound not passing through the tubes.
(30) Referring to FIG. 8, there is illustrated a sound absorbing device according to the invention, in the form of a headphone set 60, and comprising a headband 61 connecting ear coverings 62,63 together. Each ear covering 62, 63 includes a thixotropic material in the form of a polymeric sheet comprising a multiplicity of cellular pockets, wherein the thixotropic material is located within the cellular pockets (not shown).
(31) When a user is listening to music on the headphones 60, thixotropic material located within the cellular pockets of the polymeric sheet within the cavities 66, 67 allows low intensity sounds like voices to be heard, while high intensity sounds like those from a pneumatic drill or jet engine reduced. As such, the user does not need to increase the volume of the music to obviate the interfering external sounds. This advantage of the sound absorbing device 1 of the invention reduces the damage done to the hearing while maintaining the enjoyment of the music being listened to.
(32) Referring to FIGS. 11A-11C and FIGS. 12A-12D, there is illustrated a further embodiment of cellular scaffold of the invention including the series of thixotropic material-containing cylindrical tubes 100 previously described with reference to FIG. 7 and FIG. 10. In the illustrated embodiments, each tube 121 is also coiled back on itself, the series of curved tubes 121 forming a substantially U-shaped structure 120. Each tube has two ends which, due to the U-shape, face the same direction. The series of substantially U-shaped structures 121 are connected to and supported by a spine 122. The spine may be flexible or rigid. The tubes 121 are connected to the spine 122 such that the tubes 121 point away from a plane X of the spine 122. As illustrated in FIG. 12A-12D, an additional series of cylindrical tubes 124 are connected to and in fluid communication with the curved tubes 121. The cylindrical tubes 124 lie perpendicular to the plane X of the spine 122. In FIGS. 13A-13D there is illustrated a further embodiment of a cellular scaffold 130 forming part of a sound absorbing device of the present invention. The cellular scaffold 130 comprises a plurality of tubes 90, as illustrated in FIG. 5, embedded in a base 131. The appearance of the scaffold 130 can be described as being like a “hedgehog”. As per FIG. 5, the plurality of tubes 90 comprises a cylindrical tube 91 having an exterior surface 92 and an interior surface 94 defining a lumen 96 which is filled with a thixotropic material. In use, the cylindrical tube would be arranged within the sound absorbing device (not shown) such that external sound would enter the tube at a first end 95 and travel through the tube to a second end embedded in the base 131. In doing so, the sound would cause some movement of the thixotropic material within the tube. The material at the walls of the tube would experience friction and be exposed to a higher shear rate than the material at the centre of the tube. Thus, the thixotropic material adjacent the walls of the tube would have greater sound absorbing capacity compared to the material at the centre of the tube. FIG. 14 illustrates a further embodiment of the cellular scaffold 130 of FIG. 13. A second end 97 of the cylindrical tube 91 is exposed by an open-ended base 132. A series of substantially U-shaped cylinders 140 are embedded in the base 131, crossing from side 133 to the opposite side 134 of the base 131. A further series of substantially U-shaped cylinders 141 are embedded in the base 131, crossing from side 135 to the opposite side 136 of the base 131, and positioned such that the cylinders 141 are lying beneath cylinders 140.
(33) Materials and Testing Method
(34) A testing environment to ascertain the sound absorbing properties of the present invention is illustrated in FIG. 20. The testing environment comprises an anechoic chamber 200 with a decibel (dB) meter 201 on one side of the chamber and a signal generator 202 on the other side of the chamber. A hearing protector 203, for example a pair of headphones, is placed in the chamber 200 between the dB meter 201 and the signal generator 202. The hearing protector 203 is constructed such that there is a join 204 running down the middle of the protector to accommodate the easy insertion and removal of a cellular scaffold 210 (with reference to any of the cellular scaffolds of the Drawings and Description) of the present invention inside the hearing protector 203. A cellular scaffold of the present invention is placed within the protector 203 between the dB meter 201 and the signal generator 202 within the chamber 200. A small speaker 205 is attached to the signal generator 202 and placed between the signal generator 202 and the cellular scaffold of the present invention. A sound sensor 206 (a Digitech QM 1592 class 2 professional sound level meter) is attached to the dB meter 201 and placed between the dB meter 201 and the cellular scaffold of the present invention.
(35) A measurement for background/ambient noise was first measured to ensure that all sound from the signal generator 202 was being received by the dB meter sound sensor 206. The control used for the experiments is the industry standard headphone ear protectors manufactured by 3M®, model type 1430C. The sound absorbing material of the control headphones were tested at frequencies indicated by the manufacturer, namely 125, 250, 500, 1000, 2000, 4000 and 8000 dB. A reading for each frequency was measured in triplicate and an average reading was calculated. The reduction in the dB level achieved by the sound absorbing material at each frequency was calculated by subtracting the measured dB level from the dB level measured when no sound absorbing material was present.
(36) Results
(37) The embodiments described in FIGS. 1, 3, 11, 13 and 14 were tested. The embodiments were assigned P1 (FIG. 11), P2 (FIG. 3), P4 (FIG. 13), P6 (FIG. 14) and P7 (FIG. 1). A summary of the results are presented below in Table 1. Overall, the embodiments of the present invention which were tested demonstrated a significant advantage in hearing protection when compared to the standard ear protection. The decibel is commonly used in acoustics to quantify sound levels relative to a 0 dB reference which has been defined as a sound pressure level of 0.0002 microbar. The reference level is set at the typical threshold of perception of an average human and there are common comparisons used to illustrate different levels of sound pressure. As with other decibel figures, normally the ratio expressed is a power ratio (rather than a pressure ratio).
(38) The human ear has a large dynamic range in audio perception. The ratio of the sound intensity that causes permanent damage during short exposure to the quietest sound that the ear can hear is greater than or equal to 1 trillion. Such large measurement ranges are conveniently expressed in logarithmic units: for example, the base-10 logarithm of one trillion (10.sup.12) is 12, which is expressed as an audio level of 120 dB.
(39) TABLE-US-00001 TABLE 1 The dB Change achieved in seven embodiments (1-7) of the present invention and the industry standard 3M ® headphone at selected frequencies (Hertz (Hz)). 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz 8000 Hz 3M 9.5 6.3 8.9 23.2 34.2 45.2 21.6 1 3.7 1.2 2.1 20.5 21.3 30 60 2 9.6 10.1 14.5 32.1 32.1 41 60 3 6.1 3.3 4.9 18.2 29.5 60 60 4 3.2 4.8 26.8 23.7 33.3 60 60 5 5.3 5.4 12.1 25.8 29 60 60 6 10.5 5.3 21.1 19.5 39.5 60 60 7 8.9 5.8 18 15.3 23.7 60 60
(40) As illustrated in FIG. 15, there was significant sound absorption rates achieved in the 4000-8000 Hz range as indicated by the superior change in decibel levels detected by the dB Meter. The cellular scaffold of the present invention excelled above 3M®'s sound absorbing material in the 8000 Hz region by 40 dB. This type of protection is highly useful in dentistry as the drills used in this profession function at that frequency level.
(41) As illustrated in FIG. 16, there was significant sound absorption rates achieved in the 125-2000 and 4000-8000 Hz range of the cellular scaffold of the present invention when compared to the 3M® standard headphone sound absorbing material. The improved hearing protection in these frequency ranges would be an advantage to those in the construction industry and in professions where people are exposed to such high frequency tones. In FIG. 17 there was significant sound absorption rates achieved in the 250-1000 and 2000-8000 Hz range of the cellular scaffold of the present invention when compared to the 3M® standard headphone sound absorbing material. The improved hearing protection in these frequency ranges would be an advantage to those exposed to such high frequency tones.
(42) In FIG. 18, it is clearly demonstrated that there was significant sound absorption rates achieved in the 250-8000 Hz range of the cellular scaffold of the present invention when compared to the 3M® standard headphone sound absorbing material. Such a significant improvement in sound absorption within this frequency range would be a distinct advantage to those working in construction surrounded by low frequency tones and those exposed to high frequency tones. FIG. 19 clearly demonstrates that there was significant sound absorption rates achieved in the 250-500 and 2000-8000 Hz range of the cellular scaffold of the present invention when compared to the 3M® standard headphone sound absorbing material.
(43) The 250-1000 Hz range is the range involved in many industrial hardware appliances and as such presents itself as a significant improvement in the area of personal protection within the construction industry. The 2000-8000 Hz range is an area of sound frequency which is related to high speed drills and electronic equipment. For example, dentists (and dental patients) are regularly at risk from high frequency drill sounds and as such, this improved protection is of significant value in this profession as a safety device. The results presented above clearly demonstrate that the sound absorbing material contained in a cellular scaffold of the present invention achieves significant improvements in sound absorption and hearing protection. Furthermore, the range of frequencies which the cellular scaffold of the present invention absorbs sound allows the user to hear conversations while dampening the harmful effects of, for example, drilling noises and the like.
(44) This technology can also be applied to other forms of hearing protection. Individual earplugs can contain an insulating core that contains a sound absorbing material comprising a thixotropic material. Anechoic chambers can be constructed from panels of insulating material that would contain an internal structure of thixotropic material.
(45) The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.
