1. Field of the Invention
The present invention relates generally to the field of audio fidelity, and more particularly to a vibration isolator such as a microphone isolation system.
2. Background of the Invention
The bandwidth capacity of telecommunications networks is expanding rapidly. This expansion has allowed commercially valuable services such as videoconferencing and voice-over-internet conferencing to become viable and be technology growth areas. These services may be enhanced with wideband telephony capabilities for enhanced audio fidelity. Of course, terminals that support these services at user locations should be designed to produce and capture wideband voice signals from users. Traditional telephony, still prominent today and spanning from approximately 200 or 300 Hertz (Hz) through approximately 3500 Hz, has existed for over a century. A contemporary wideband telephony service and terminal spans, as an example, 50-7000 Hz or 80-14 kiloHertz (kHz).
There are various drawbacks to the prior art telephony approaches. For example, when one attempts to design a terminal's speech transducers (namely, the microphone and receiver in a handset or the microphone and loudspeaker in a hands-free “speakerphone” terminal) to exhibit wideband response, many acoustical and mechanical difficulties manifest themselves.
One problem that surfaces is that the microphone is exposed to the terminal's solid borne vibrations (e.g., vibrations resulting from a table, the terminal's fan or other moving part, or the terminal's loudspeaker voice coil motion) over a much broader frequency range than otherwise experienced. This problem is particularly troublesome at lower frequencies since mass or inertia of the terminal is not very effective at attenuating such solid borne vibrations before the terminal's microphone senses the vibrations. Virtually all microphones in use today are of an electret type. In spite of the electret microphones' light diaphragms, those diaphragms will still undergo a relative motion with respect to an electret's vibrating metal outer housing, which is normally attached to the terminal in a substantially rigid manner. This relative motion causes a mechanical noise signal to be produced, thus corrupting the terminal's transmission signal.
It is noteworthy that in traditional telecommunications products, electret microphones are typically housed in a rubber “boot” assembly prior to assembly into a terminal. This type of housing is used for acoustical sealing and provides no substantial vibration isolation.
One prior art attempt at isolating vibrations is shown in J. Audio Eng're Soc., February 1971, “Microphone Accessory Shock Mount for Stand or Boom Use,” by G. W. Plice, and depicts a “new isolation mount.” The reference shows a rubber shaped structure looking like a “donut” holding a central microphone load. A continuous annular plate supports the rubber “donut.” The “donut” is curved and thus flexible in a direction normal to a bisecting horizontal plane of the load.
Referring to
In another prior art attempt, shown and described in U.S. Pat. No. 5,739,481 to Baumhauer, Jr. et al., a loudspeaker mounting arrangement uses a compliant member to support and isolate a central loudspeaker load.
Although these prior art attempts may provide some level of isolation from vibrations, the vibration isolation can be improved. Therefore, there is a need for a system and method for providing improved vibration isolation.
The present invention provides in various embodiments a microphone isolation system for isolating vibrations due to a vibratory source external to the isolator system, or one internal to the isolator system. According to one embodiment of the present invention, a vibration isolator comprises an isolation member; a support member; and two or more compliant members. The compliant members mechanically support the isolation member and isolate the isolation member from vibrations emanating from the support member. At least some of the compliant members are coupled to the isolation member, are coupled to and supported by the support member, and are continuous from the isolation member to the support member. The compliant members exhibit a relatively high and advantageous ratio of mechanical compliance in all directions in a plane of the isolation member to the compliance in a direction normal to the plane of the isolation member.
In an alternative exemplary embodiment, the vibration isolator is configured to isolate the support member from vibrations emanating from a vibrating source coupled to (e.g., supported by, etc.) the isolation member.
A further understanding of the nature and advantages of the inventions herein may be realized by reference to the remaining portions of the specification and the attached drawings.
As shown in the exemplary drawings wherein like reference numerals indicate like or corresponding elements among the figures, embodiments of a system according to the present invention will now be described in detail. The following description sets forth an example of a microphone isolation system.
Detailed descriptions of various embodiments are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, method, process, or manner.
As mentioned herein, various drawbacks to the prior art telephony approaches exist. For example, when one attempts to design a terminal's speech transducers to exhibit wideband response, there are numerous acoustical and mechanical difficulties that arise. One problem that arises is that the microphone is exposed to the terminal's solid borne vibrations (e.g., vibrations resulting from a table, the terminal's fan or other moving part, or the terminal's loudspeaker voice coil motion) over a much broader frequency range than otherwise. This problem is particularly troublesome at lower frequencies since the mass or inertia of the terminal is not very effective at attenuating such solid borne vibrations before the microphone senses the vibrations. It is especially helpful to be able to adequately attenuate vibrations in planes substantially orthogonal to the direction of gravity. The prior art does not accomplish this kind of attenuation satisfactorily.
Referring to
Referring now to
The compliant members 304 mechanically support the isolation member 300 and separate the isolation member 300 from vibrations emanating from the support member 302. Further, the support member 302 is isolated from vibrations emanating from a vibrating source (e.g., the electret microphone 202 (
The isolation member 300 is configured to support the electret microphone 202 (not shown). A clamping arrangement 306 secures the electret microphone 202 to the isolation member 300. A wedge 308 facilitates securing of the isolation member 300 to the weight 208 (
Additionally, an extended area 310 juts out slightly from a sidewall 312 of the top unit 206. The extended area 310 facilitates securing of the isolation member 300 to the base unit 210 (
One or more of the compliant members 304 of the top unit 206 are curved in shape, in one embodiment. In the present embodiment, all of the compliant members 304 are curved. The curvature exists in a plane parallel to the isolation member 300. As mentioned herein, prior art devices existed where curvature existed in a direction normal to a bisecting horizontal place of a microphone, as opposed to parallel. Moreover, the compliant members 304 are orthogonally symmetric (i.e., have a pattern that repeats itself every 90 degrees) in a plane parallel to the isolation member 300, and are radially oriented and emanate from the support member 302. This configuration ensures that external vibratory excitation in any direction in the plane of the isolation member 300 sees the same isolating mechanical compliance.
It is noteworthy that the shapes of the compliant members 304 substantially resemble arcs of circles in one embodiment. That is, the compliant members 304 have constant radii of curvature. In one embodiment, the curvature of the compliant members 304 spans an included angle of greater than 30 degrees. In another embodiment, the curvature of the compliant members 304 spans an included angle of greater than 90 degrees. However, it is envisioned that the curvatures can span any suitable number of degrees.
Further to the embodiment shown in
In further embodiments of the present invention, the support member 302 is circular in shape, having an inner diameter and an outer diameter. Preferably, the inner diameter is less than 30 millimeters (mm). However, it is contemplated that the inner diameter can be greater than or equal to 30 mm.
In prior art devices such as those of
Moreover, high normal compliance can result in large initial (elastic) deflections under gravity and large viscoelastic “creep” deflections over time and temperature in service. The microphone isolation system 200 (
For example, suppose one desires to isolate a microphone from all frequencies above f Hz by at least D dB. In one embodiment, referring to
In one embodiment, the compliant members 304 are molded integral with the isolation member 300 and support member 302 from rubber to obtain high compliance as well as to reduce assembly costs and assembly issues such as mechanical buzz and rattle, etc. One type of rubber that can be used is Santoprene Rubber, namely, Santoprene 211-45. Santoprene 211-45 is a thermoplastic vulcanizates (TPV) rubber that can be injection molded. This material is characterized by a Young's (Tensile) Modulus, E, of about 2.5 MPa (per Am. Soc for Testing and Materials (ASTM) D 797.89) at 23° C., and damping “tan(delta)” of 0.07 at 23° C.
At 100 Hz, near the lower end of the transmission band where means to isolate vibration is most difficult, and a terminal operating temperature of 40° C., the viscoelastic and dynamical nature of the Santoprene Rubber yields an effective stiffness modulus of 5.9 MPa (at room temperature it would be even stiffer at 7.1 MPa for reference). In one exemplary embodiment, design optimization of the microphone isolation system 200 uses the full dynamical viscoelastic properties of the material (see ASTM D 5992.96), namely, a 23° C. master curve of the stiffness modulus E(t*) and the compliance modulus D(t*) both over, say, 500 years of time-temperature accelerated time, t*, and an Arhennius plot determining the relation between t* and real time. Note that measured master curves of the moduli E(t*) and D(t*) are inversely related but generally not reciprocal. For further insight, one may consult the paper “Taking the Mystery out of Creep,” Plastics Design Forum, January/February 1982, for a review of viscoelastic creep, time-temperature superposition and modulus master curves, which is incorporated herein by reference for all purposes. One may also refer to the paper “Stress Analysis of Viscoelastic Composite Materials,” in the J. of Composite Materials, V. 1, No. 3, July 1967, which is incorporated herein by reference for all purposes. Moreover, specification ASTM D 5992.96 describes dynamical mechanical properties versus temperature from which modulus master curves and time-temperature superposition curves may be obtained, and which is incorporated herein by reference for all purposes.
Design optimization of a microphone isolation system 200 thought to be capable of yielding a high radial-to-normal compliance ratio can be pursued with the aid of a formula related to the deflection of curved beams under various boundary conditions. Matlab mathematical software can be used to optimize the microphone isolation system's parameters. For example, analysis may yield an effective or lumped “planar compliance” in the radial direction for the combined eight compliant members 304 of Cp=0.0031 m/N and a lumped “normal compliance” of Cn=0.0080 m/N, both at 100 Hz and 40 C operation (note that this is the beams' compliance, not that of the material). It is noteworthy that, because of beam orthogonality and linearity, Cp is the same for any planar angle of excitation over 360 degrees. In one embodiment, it is contemplated that Cp is equal to Cn. However, Cp can be greater than or less than Cn.
One may consult the text “Roark's Formulas for Stress and Strain,” 6th Ed, McGraw-Hill by Warren C. Young, which is incorporated herein by reference for all purposes, for detailed formulas to help calculate the mechanical compliance and deflections of curved beams. Specifically, for excitation in the plane of curvature, see Table 18, Case 13, with both 5c radial loading and with 5d tangential loading. For excitation in the plane normal to the curvature, see Table 19, Case 1e.
It is noteworthy that the curvature and small width, W, of the compliant members 304 increases Cp by about two orders of magnitude so as to yield a low vibration cutoff frequency, fc. Furthermore, normal compliance, Cn, is maintained as small as possible (via a large H value), yielding a relatively high Cp/Cn ratio of 0.39 in one preferred embodiment. A smaller Cn is preferred because the smaller Cn represent the minimization of initial elastic deflection and creep over time-temperature accelerated time, t*.
In further keeping with embodiments of the present invention, it is desired that vibration velocity-to-velocity transmissibility be minimized. That is, a steady-state vibration velocity of the sidewall 312, Us, should yield a much lower isolation member 300 velocity, Ui. The transmissibility, Tv, is thus defined as 20 log (Ui/Us) in dB. However, it is desired that Tv be negative. Since the electret microphone 202, which is cylindrical in shape with its moving diaphragm in a plane normal to the axis of the cylinder, is placed on the isolation member 300 on its side, then the radial or “planar” vibrations caused by the sidewall 312 are most troublesome. To obtain a desired cutoff frequency (fc) in the planar mode (fcp), defined by an attenuation of 10 dB relative to the use of no isolator, lumped parameter simulation (using equivalent circuit techniques) reveals that additional metal mass, the weight 208 (
Referring now to
The exemplary base unit 210 is illustrated in
Furthermore, the base unit 210 has four gaps 502, although alternative numbers of gaps 502 may be utilized. The gaps 502 facilitate the attachment of the base unit 210 to the top unit 206. The extended areas 310 (
The base unit 210 further includes four stilts 504. The stilts 504 fit behind the sidewall 312 (
It is also noteworthy that terminal connector 508 defines aperture 510. The aperture 510 allows for access to a connection to wire leads 512.
Referring to
In further keeping with exemplary embodiments of the present invention, it is desirable that the electret microphone 202 and the isolation member 300 (
However, very compliant spring members will generally deflect, and/or “creep” (i.e., move over time) due to viscous deformation caused by superposed time and elevated temperature in service. If the normal deflection of the isolation member 300 causes the isolation member 300 to come into contact with any portion of the isolation system 200, then the isolation properties of the isolation member 300 could be hampered. This poses a major obstacle in the design of a small microphone isolation system 200 for a consumer product.
Referring to
The relatively large Cp/Cn inherent in this exemplary system hence achieves vibration isolation down to a very low cutoff frequency fcp, suitable for wideband communications. Critical for practical application of the microphone isolation system 300 (
The microphone isolation system 200 can be implemented in various systems and devices. Referring to
Therefore, an improved microphone isolation system 200 has been shown and described. It is noteworthy that some embodiments according to the present invention are not limited to a microphone isolation system. These embodiments may include a vibration isolator in general, which can be used for various applications.
The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be construed in view of the full breadth and spirit of the invention as disclosed herein.
This application is a continuation of co-pending U.S. Ser. No. 10/155,271 filed May 23, 2002 and entitled “Microphone Isolation System,” which claims priority from U.S. Provisional Patent Application Ser. No. 60/374,175 filed Apr. 19, 2002 and entitled “Microphone Isolation System.” The benefit of priority of Ser. Nos. 10/155,271 and 60/374,175 under 35 U.S.C. § 120 and 35 U.S.C. § 119(e) is hereby claimed. The contents of the foregoing applications are incorporated herein by reference for all purposes.
Number | Date | Country | |
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60374175 | Apr 2002 | US |
Number | Date | Country | |
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Parent | 10155271 | May 2002 | US |
Child | 11671968 | Feb 2007 | US |