Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Mounting or support feature of housed loudspeaker
Reexamination Certificate
1999-07-07
2003-01-28
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Mounting or support feature of housed loudspeaker
C381S189000
Reexamination Certificate
active
06512834
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an acoustic protective cover for a transducer (such as a microphone, ringer or speaker) employed in an electronic device. More specifically, the present invention relates to an acoustic protective cover assembly including a microporous protective membrane that provides both low acoustic loss and the ability to withstand long-term exposure to liquid intrusion.
BACKGROUND OF THE INVENTION
Most modern electronic devices, such as radios and cellular telephones, include transducers, e.g., microphones, ringers, speakers, buzzers and the like. These electronic devices often comprise housings having small apertures or holes located over the transducers to enable the transducers to transmit or receive sound signals from within the housing. However, although this configuration protects against incidental exposure to water (e.g., a raindrop), it excessively attenuates a transducer's effectiveness and sound quality. Furthermore, it cannot resist the entry of a significant amount of water. Accordingly, acoustic protective covers have been utilized between the transducers and the housing to protect the transducers from damage due to the entry of water or other liquids.
Prior art acoustic protective covers are typically composed of a porous, fabric material constructed solely on reducing the material's resistance to air flow of which larger effective pore size resulting in thicker materials has been the means for achieving the high air flow parameters. Here, the amount of sound attenuation of the material is inversely proportional to the size of its pores, i.e., sound attenuation decreases as pore size increases. However, the size of the pores oppositely affects the water resistance of the material. Materials having extremely small or no pores are highly water resistant.
Thus, prior art acoustic protective covers have focused on having either large pores for enhanced sound transmission and quality, or extremely small pores and tighter structure for high water resistance. A focus on the former results in an acoustic protective cover that at best provides an electronic device minimal protection against exposure to water. A focus on the latter protects the electronic device from larger amounts of water, but results in poor sound quality due to high sound attenuation. Even the treatment of the porous materials for water repellency fails to permit immersion of the electronic device to significant depths because of the large pore structure.
A general description of prior art patents adhering to the above-described scientific principle follows.
U.S. Pat. No. 4,949,386, entitled “Speaker System,” teaches an environmental protective covering system, comprising in part a laminated two-layer construction defined by a polyester woven or non-woven material and a microporous polytetrafluoroethylene (“PTFE”) membrane. The hydrophobic property of the microporous PTFE membrane prevents liquid from passing through the environmental barrier system. However, although this laminated covering system may be effective in preventing liquid entry into an electronic device, the lamination causes excessive sound attenuation which is unacceptable in modern communication electronics where excellent sound quality is required. Furthermore, while it is effective at preventing instantaneous liquid entry, long-term liquid exposure is limited because of eventual breakdown of the adhesive/membrane interface.
U.S. Pat. No. 4,987,597, entitled “Apparatus For Closing Openings Of A Hearing Aid Or An Ear Adaptor For Hearing Aids,” teaches the use of a microporous PTFE membrane as a covering for an electronic transducer. The membrane restricts liquid passage through the membrane without significantly attenuating sound signals. However, the patent fails to specifically teach which material parameters of the membrane are required in order to achieve both low sound loss and long-term exposure to liquid entry, although it does generally describe the parameters in terms of porosity and air permeability.
U.S. Pat. No. 5,420,570, entitled “Manually Actuable Wrist Alarm Having A High-Intensity Sonic Alarm Signal,” teaches the use of a non-porous film as a protective layer to protect an electronic device from liquid entry. As previously discussed, although a non-porous film can provide excellent liquid entry resistance, such non-porous films suffer from relatively high sound transmission losses which excessively distort sound signals. The increase in transmission loss results from the relatively high mass associated with non-porous films.
U.S. Pat. No. 4,071,040, entitled “Water-Proof Air Pressure Equalizing Valve,” teaches the disposition of a thin microporous membrane between two sintered stainless steel disks. Although such a construction may have been effective for its intended use in rugged military-type field telephone sets, it is not desirable for use in modern communication electronic devices because the sintered metal disks are relatively thick and heavy. Furthermore, disposing a microporous membrane between two stainless steel disks physically constrains the membrane, thereby limiting its ability to vibrate, which reduces sound quality by attenuating and distorting a sound signal being transmitted.
To overcome some of the shortcomings described above with respect to the '386, '597, '570 and '040 patents, U.S. Pat. No. 5,828,012, entitled “Protective Cover Assembly Having Enhanced Acoustical Characteristics,” teaches a sound-transmissive acoustic cover assembly that has a protective membrane that is bonded to a porous support layer so that an inner unbonded region surrounded by an outer bonded region is formed. In this configuration, the membrane layer and the support layer are free to independently vibrate or move in response to acoustic energy passing therethrough, thereby minimally attenuating the acoustic energy. However, although the cover assembly reduces the acoustic attenuation, the degree of acoustic attenuation is limited because of the increase in material mass and thickness by which the acoustic energy has to pass (i.e., acoustic energy has to first pass through the membrane, and then additionally pass through the support layer).
Finally, Japanese Laid Open Patent Application No. 10-165787, entitled “Porous Polytetrafluoroethylene Film And Manufacturing Process For Same,” teaches the use of a porous PTFE film to protect an electronic device from liquid entry while maintaining sound permeability. A longitudinally-stretched PTFE membrane is coated on one or both sides with a thermoplastic resin netting that functions as both a reinforcing material and a shape stabilizing material. Using this manufacturing method, the size of the pores in the film uniformly expand to improve sound permeability by means of the thinning of the membrane without compromising the film's water resistance. Such a porous PTFE film exhibits sound attenuation of no more than 1 dB for frequencies of 300-3000 Hz (i.e., the range of frequencies known as the “telephony range”) and static water pressure resistance of 30 cm or above. However, although the PTFE film covering effects relatively low sound attenuation, overall sound transmission loss is excessive and is considered unacceptable in modern communication electronic devices. Additionally, the PTFE film lacks the ability to withstand long-term water intrusion at higher pressures.
Because the sole focus of the above-described prior art patents is on membrane porosity, the higher airflow membranes taught therein can produce low sound transmission loss but are unable to meet IP-57 level water protection as defined by the International Electrotechnical Commission (“IEC”) (1 meter water submersion for 30 minutes). The IEC is affiliated with the International Organization for Standardization (“ISO”), and publishes the IP Code, entitled “Degrees Of Protection Provided By Enclosures,” to describe a system for classifying the degrees of protection provided by enclosures for electrical equipment. One of the en
Banter Chad Anthony
Chapman Brian G.
Dabney P.
Gore Enterprise Holdings Inc.
Kuntz Curtis
Lewis White Carol A.
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