A PASSIVE NON-LINEAR SOUND ATTENUATING FILTER ASSEMBLY

The present invention relates to a passive non-linear sound attenuating filter assembly and in particular to a device that may be used in conjunction with acoustic devises such as earplugs, earmuffs, headphones, helmets, and microphone housings.

Background of the Invention

Due to the damage that working in noise prone environments can have on human ears, it is quite often mandatory to insist workers in these environments use some form of hearing protection. Conventional solutions to this problem largely rely on near complete attenuation of sounds entering the user's ears by means of an indiscriminately attenuating device between the sound sources and eardrum. This uniform reduction in sounds means that whilst wearing conventional hearing protection, communication and awareness of other auditory warnings is severely compromised. While improving hearing protection, conventional attenuation devices also expose the wearer to dangers around them that are exacerbated due to the reduced perception of the user.

Previous attempts at providing a passive nonlinear sound attenuation device have based their design on passing sound received via a circuitous route. Such as for example the devices described in US Patents 4441576, 4465159 and 6148821. In these devices, sound waves must pass through narrow apertures and around bends which has an effect on the types of sound waves that are ultimately allowed through the device. However, these devices have several drawbacks. Specifically, varying the rate and amount of attenuation between users or between the left and right ears (for a user with partial hearing loss) is very difficult to achieve. Also the level of intricacy of these devices can create issues with quality control problem and also provide these devices are costly to produce. Additionally, the quality of sound passed in the mid to upper volume range can be poor, i.e. considerable signal distortion can occur as the sound diffracts and echoes inside the filter or oscillates between filter elements. This frequency distortion can interfere with communicative ability.

Another drawback is that all sound levels are attenuated and in particular the low amplitude sound is significantly attenuated due to energy being absorbed or reflected by the filter. In situations where hearing quiet sounds is vital, such as in law enforcement and military situations, loosing a range of mid to low amplitude sound can be extremely disadvantageous or even life threatening. Furthermore, very low frequency, high amplitude sound created by structural collapse or large explosion may not be sufficiently limited as a large air volume may overwhelm the mechanism of these devices.

Accordingly, the present invention seeks ameliorate the shortcomings of the above described sound attenuation devices. Ih addition the present invention seeks to provide a passive non-linear sound attenuating filter assembly that is cheap to produce and which may be incorporated into a variety of acoustic devices. Furthermore, the present invention seeks to provide a passive non-linear sound attenuating filter assembly which allows low amplitude sound associated with communication to pass through the filter whilst reflecting or attenuating sound associated with high amplitude sound.

Summary of the Invention

According to one aspect the present invention provides a passive non-linear sound attenuating filter assembly including: a substantially cylindrical main body portion; a moveable diaphragm located within or at one end of the main body portion; a sound receiving cavity defined by one side of the moveable diaphragm and the substantially cylindrical main body portion; and, a sound receiving portion on the other side of the moveable diaphragm, wherein movement of the diaphragm transfers sound received on the sound receiving portion into the sound receiving cavity, the moveable diaphragm having a maximum degree of movement corresponding to a maximum sound amplitude, whereby sound received on the sound receiving surface with an amplitude less than

the maximum sound amplitude is transferred into the sound receiving cavity by the moveable diaphragm, and sound received on the sound receiving surface with an amplitude greater than the maximum sound amplitude is reflected by the moveable diaphragm.

According to one form, the diaphragm is composed of a layer of resilient material whereby movement of the diaphragm is provided by the resilience of the material. In an alternative form, the moveable diaphragm is composed of a layer of non-resilient material and wherein movement of the diaphragm is provided by a ring of resilient material integral with the main body portion and adjacent one or both sides of the moveable diaphragm.

According to another form the filter assembly further includes a tuning cap that cooperates with the cylindrical main body portion and is adjustable relative thereto, whereby the tuning cap is adapted to enclose the sound receiving portion, the tuning cap including: a substantially cylindrical cap portion with an open end where side walls of the cap portion cooperate with the side walls of the cylindrical main body portion; an end cap at the other end from the open end, the end cap including openings therethrough thereby allowing sound through the tuning cap to the sound receiving portion; and a protrusion coupled to the underside of the end cap, wherein adjustment of the tuning cap causes the protrusion to bias the moveable diaphragm thereby limiting the movement of the moveable diaphragm and increasing the rate of attenuation of the filter assembly.

According to one form the side walls of the cap portion cooperate with the side walls of the main body portion by means of a screw thread engagement.

According to a preferred form the protrusion is composed of a resilient material that deforms when biasing the moveable diaphragm thereby decreasing the void volume between the end cap and the thereby creating an impendence for sound received through

the openings in the end cap. According to a further preferred form the protrusion is composed of a material with a high porosity to increase the level of sound impendence.

According to another aspect the present invention further provides an acoustic device which includes the filter assembly as described above. In a preferred form, the acoustic device is a sound protection device.

Brief Description of the Figures

The present invention will become better understood from the following detailed description of preferred but non-limiting embodiments thereof, described in connection with the accompanying figures, wherein:

Figure 1 is a cross sectional view of one embodiment of the present invention; Figure 2 is an exploded view of the same embodiment as depicted in Figure 11 without the tuning cap;

Figure 3 is an exploded view of a further embodiment of the present invention without the tuning cap;

Figure 4 is an exploded view of the tuning cap in accordance with another embodiment of the present invention; Figure 5 is a cross sectional view of a further embodiment of the present invention without the tuning cap;

Figure 6 is a cut away cross section depicting another embodiment of the present invention in the form of a single use ear plug;

Figure 7 is a cut away cross section depicting another embodiment of the present invention together with the tuning cap in the form of a single use ear plug; and,

Figure 8 is a cut away cross section depicting another embodiment of the present invention in the form of an ear muff.

Detailed description of the invention and preferred embodiments

The present invention provides a cost effective passive tunable nonlinear sound attenuation

filter that may be incorporated into existing sound protection and ear wear to prevent hearing damage, or as a protective filter to prevent overload of electronic sound devices such as for example microphones. The present invention may be incorporated into acoustic devices such as earplugs, earmuffs, headphones, helmets, and microphone housings to allow the transmission of low amplitude sounds while limiting the maximum amplitude of sound passed.

The present invention will now be further described in connection with various embodiments. The first embodiment is an example of a low cost disposable filter for use in single use devices such as for example earplugs. A further embodiment is also described for a more durable arrangement for use in earmuffs, headphones and other reusable acoustic devices. Both of these embodiments are capable of accommodating a tuning cap into the assembly to progressively add attenuation to customize the attenuation to a specific user's requirements

Referring now to figures 1 and 2 there is shown an embodiment of the present invention consisting of a passive non-linear sound attenuating filter assembly including a substantially cylindrical main body portion 1 and a moveable diaphragm 2. Li this embodiment the moveable diaphragm is composed of a flexible or resilient material which is able to receive sound on the sound receiving portion 13 and transfer this into the sound receiving cavity 12. The resilience of the diaphragm 2 provides that a maximum sound amplitude is able to be transferred via the diaphragm 2 into the sound receiving cavity 12. Once this maximum sound amplitude is exceeded, the sound can no longer be transferred via the moveable diaphragm 2 and it is instead reflected away from the device.

The cylindrical main body portion 1 is acoustically sealed and the sound receiving cavity would be located adjacent the ear canal such that sound is only received via the sound receiving portion 13 and then transferred through the assembly, whereby sound with an amplitude greater than the maximum is reflected.

The assembly further includes an optional tuning cap 15 which includes a substantially

cylindrical cap portion 3 that cooperates with the cylindrical main body portion 1 via screw thread engagement 20. When in place the tuning cap 15 covers the sound receiving portion 13 with only openings 5 provided in an end cap portion 6 which permit sound waves to travel through into the filter assembly 10.

In addition, a protrusion 4 in the form of a truncated double cone is attached to the underside of the end cap portion 6 such that when the tuning cap 15 is gradually screwed in engagement with the main body portion 1, the protrusion 4 is pushed harder into the moveable diaphragm 2. This effectively causes the tension in the moveable diaphragm in increase which thereby decreases the maximum amplitude of sound wave that will be transferred into the sound receiving cavity 12. This provides that the more the tuning cap 15 is screwed into engagement with the main body portion 2, the more the protrusion 4 acts on the moveable diaphragm 2 and restricts its movement thereby increasing the sound attenuation of the filter assembly 10

In the present embodiment the shape of the protrusion 4 is such that when being forced against the moveable diaphragm 2, the protrusion expands into the cavity between the moveable diaphragm and the end cap portion thereby inhibiting sound waves that pass into the filter assembly via openings 5 and further increasing the impendence of the filter assembly 10. In addition, the protrusion may be chosen of a material such as foam which has a high porosity also increasing the impedance of the filter assembly 10.

Sound is transmitted into the sound receiving portion 12 solely by the movement of this moveable diaphragm 2. The moveable diaphragm 2 is constructed so that a small amount of free movement away from the neutral position is permitted. This small range of movement allows the transmission of low amplitude sound into the sound receiving cavity 12. Further movement of the diaphragm 2 is restricted by the elasticity and/or the tension of the diaphragm 2.

Small amplitude sound waves are freely transmitted through the filter assembly 10. In the elastic range moderately high amplitude sound is attenuated as a function of the amplitude

of said sound. Movement beyond a small range is prevented due to the diaphragm's 2 attachment to the cylindrical main body portion 1. The maximum deflection of the diaphragm 2 corresponds to the maximum amplitude of sound passed. Sound exceeding this maximum limit is reflected producing an upper limit for passed amplitudes.

Another embodiment of the present invention that provides a more durable filter assembly is depicted in Figures 3, 4 and 5. Here a cylindrical main body portion 30 includes a moveable diaphragm 25 which in this embodiment is composed of a rigid material. What makes it moveable in two rings of resilient material 9 which sandwich the moveable diaphragm 25 within the cylindrical main body portion 30. When sound is received in the sound receiving portion 35, the moveable diaphragm transfers the sound into the sound receiving portion by the diaphragm compressing itself against the flexible rings 9. Once a maximum amplitude is reached again the sound is not transferred into the sound receiving cavity 38 but is instead reflected.

As described above in connection with the previous embodiment, a tuning cap 40 depicted in figure 4 may be screwed onto the filter assembly and engaged with the cylindrical main body portion 30 such that the protrusion 42 acts on the moveable diaphragm 25 and biases the diaphragm against the resilient rings 9 and thereby progressively attenuating mid-range sound as a function of amplitude.

Further embodiments are shown in figures 6, 7 and 8 wherein the embodiment of the present invention depicted in figures 1 and 2 is shown incorporated into an earplug, that may be disposable, figures 6 and 7. And in Figure 8, the embodiment depicted in figures 3, 4 and 5 is incorporated in a more permanent and durable ear protection device in the form of an ear muff.

The present invention does not use a circuitous route to attenuate sound. Sound in the low to mid volume range is passed with little to no frequency distortion. The tuning cap, by compressing an elastomeric protrusion onto the moveable diaphragm, is able to progressively vary the amount and rate of attenuation. This allows variation between users

or between the left and right ears of users with partial hearing loss. The simple shape lends itself to ease of construction. This significantly reduces the cost of manufacture.

The range of diaphragm movement close to its neutral position is free; this allows very low amplitude sound to pass with null or negligible attenuation. This gives superior performance at low sound levels. Further deflection needed to translate higher amplitude sound operates as elastic movement which provides progressive attenuation in the mid to high amplitude ranges without significant distortion or echo. Once the limit of elastic movement is reached the diaphragm stops, preventing the transmission of damaging amplitudes at all frequencies.

Various applications include military, security and law enforcement, forestry and industrial manufacturing environments. In any situation where communication is important and the likelihood of damaging levels of sound is great.

The present invention is intended to be used as a filter bypassing sound attenuation material in conventional sound protection devices. While allowing low amplitude sound to pass freely this filter also limits the maximum amplitude passed. Bypassing sound attenuation material allows the filter to translate quiet sounds into the ear or microphone.

The present invention adds functionality to sound attenuation devices by allowing non damaging sound levels through while maintaining protection from damaging levels of sound, hi a military or law enforcement setting protecting the ear from dangerous sudden noise such as gunfire or explosion is extremely important, however maintaining communicative ability is also extremely important. With the present invention both are possible simultaneously. Similar situations exist in forestry and construction settings, whereby the likelihood of sudden damaging sound is great and the need for auditory awareness is also of high importance.

The method by which the present invention achieves selective attenuation is as follows; sound reaches the diaphragm in the central cavity as a pressure wave. Said wave applies

force to the diaphragm in direction parallel with the central sound receiving cavity. Said force being proportional to both the cross-sectional area of the diaphragm, and the driving force of the sound. In order to propagate the sound into the central sound receiving cavity the diaphragm must deflect. The amplitude of the sound propagated into the central cavity and hence through the filter is proportional to the cross-sectional area of the diaphragm and the distance of deflection from its neutral position. Therefore controlling the distance the diaphragm travels from a neutral position controls the amplitude of the sound passed and hence limiting this distance enacts an absolute amplitude limit. By allowing a small range of free movement without hindrance the filter passes very low amplitude sound with no or negligible attenuation. By elastically suppressing movement outside of a small range mid to high amplitude sound is attenuated as a function of its amplitude. So the full action of the present invention is to limit the upper amplitude of sound passed, allow low level sound to pass unimpeded and attenuate mid to high amplitude sound as a function of said sound.

Although several embodiments have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein by one ordinarily skilled in the art without departing from the spirit or scope of the present invention.