Patent Application
20180213340
The present invention relates to high throughput test apparatus for acoustic vent structures such as, but not limited to, protective covers and membranes.
Electronic devices such as cellular phones, pagers, radios, hearing aids, headsets, barcode scanners, digital cameras, etc. are designed with enclosures having small openings located over an acoustic transducer (such as a bell, speaker, microphone, buzzer, loudspeaker, etc.) to allow sound transmission. Protective acoustic vent structures such as acoustic covers are placed over openings to protect the transducer from damage from dust and water intrusion.
Known protective acoustic covers include non-porous films and micro-porous membranes, such as expanded PTFE (ePTFE). Protective acoustic covers are also described in U.S. Pat. No. 6,512,834 and U.S. Pat. No. 5,828,012.
Membranes for acoustic protective covers must be capable of protecting an enclosure from intrusion, e.g., from foreign contaminants like water or dust, while also adequately conveying sound. While test protocols exist for many facets of acoustic vent structure testing, there exists a need for improved apparatuses and methods to conduct high throughput testing on acoustic vent structures across a range of frequencies, especially at high frequencies.
Some test apparatuses for acoustic devices are disclosed in the following references. For example, U.S. Patent Pub. No. 2008/304674 discloses a hearing device test adapter that connects a hearing device to a test microphone. Similarly, U.S. Pat. No. 8,194,870 discloses a system and method for open fitting hearing aid frequency response sound measurements; U.S. Pat. No. 4,038,500 discloses a microphone coupler for use in performing frequency response tests on earphones; U.S. Pat. No. 3,876,035 discloses a testing apparatus for hearing aids and the like; and U.S. Pat. No. 2,530,383 discloses microphones, e.g., by way of an acoustic coupler that couples the microphone to be tested to a source of acoustic energy. However, the aforementioned publications do not describe apparatuses or methods for conducting high throughput testing on acoustic vent structures.
According to some embodiments, the present disclosure provides a testing apparatus for high throughput quality control testing for acoustic vent structures, e.g., for testing protective acoustic covers or microphone covers, membranes, and the like. In one embodiment, the vent structure comprises at least one membrane. Some embodiments include a near field testing apparatus for measuring acoustic insertion loss of acoustic vent structures including a first element and second element. In some embodiments, an acoustic phase may be measured instead of or in addition to acoustic insertion loss. The second element is removably connectible to the first element, and the first and second elements define at least one closed acoustic chamber when the first and second elements are connected. The first element has at least one acoustic cavity, one or more first alignment features, and at least one sound source capable of generating sound within each of the at least one acoustic cavities. The second element has one or more second alignment features arranged to connect with the one or more first alignment features, a plurality of microphones configured to detect acoustic signals, a plurality of ports that each define an acoustic channel between one of the at least one closed acoustic chamber and one of the plurality of microphones, and one or more sample holders for a plurality of acoustic vent structures to be positioned over at least one of the plurality of microphones. Each cavity of the at least one acoustic cavity is aligned with a respective port of the plurality of ports when the second element is connected with the first element.
According to some embodiments, the sound source is capable of generating sound within each of the at least one acoustic cavities through some or all of the range of 10 Hz to 30 kHz, e.g., in the range of 10 Hz to 20 kHz, in the range of 20 Hz to 20 kHz, in the range of 100 Hz to 20 kHz, or in the range of 100 Hz to 10 kHz. In one embodiment, the testing apparatus is particular useful for testing higher frequencies over 10 kHz that tend to be more difficult to measure. The plurality of sample holders can include at least one plate containing the plurality of ports therethrough, wherein the plurality of microphones is positioned on a first side of the plate opposite the closed acoustic chamber; and a second side of the plate facing the closed acoustic chamber is configured to receive the plurality of acoustic vent structures. According to some embodiments, the at least one plate is removable from the second element (i.e. for removing or replacing microphones from the sample holder). According to some embodiments, each microphone of the plurality of microphones is a MEMS (Micro-Electrical-Mechanical Systems) microphone. The plurality of MEMS microphones may be arranged in a planar array to measure acoustic insertion loss or acoustic phase, and may also include one or more reference microphones. Reference microphones may also be MEMS microphones.
According to some embodiments, the acoustic cavity is at least partially filled with a passive damping material. The passive damping material may be selected from a group comprising foamed synthetic resins, felts, non-woven fabrics, synthetic resin fibers, and mineral fibers. In some specific embodiments, the passive damping material is fibrillated foam.
According to some embodiments the second element can be repeatably aligned with the first element within a tolerance of 0.1 mm. A backing cavity can be arranged on a side of the sample holder opposite to the at least one closed acoustic cavity, the backing cavity including an acoustic dampening material.
The present disclosure will be better understood in view of the appended non-limiting figures.
While the following is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the claims to the particular embodiments described. On the contrary, the description is intended to cover all modifications, equivalents, and alternatives thereof.
Various embodiments described herein address a testing apparatus and methods for high throughput testing for acoustic vent structures, such as but not limited to membranes used in acoustic protective covers or related applications. A high throughput testing apparatus for acoustic vent structures has capacity to subject test samples of acoustic vent structures to an acoustic signal across a range of frequencies and/or across a range of amplitudes, and detect an insertion loss across the test samples in a short period of time. Detecting the insertion loss involves detecting the test acoustic signal that is passed through the acoustic vent structures. The test acoustic signal can be processed, e.g., by a computer, to compare the test acoustic signal to a predetermined baseline acoustic signal to detect, and/or quantify an insertion loss, i.e. a loss in acoustic pressure or sound pressure level (SPL loss), or in some embodiments to detect a change in acoustic phase.
The apparatuses and systems disclosed herein may be used to test a wide range of acoustic parameters of acoustic vent structures and protective layers. For example, some additional acoustic quality metrics that can be measured include but are not limited to: total distortion, total harmonic distortion, intermodulated distortion, difference frequency distortion, acoustic rub, acoustic buzz, perceptual acoustic rub, perceptual acoustic buzz, or signal to noise ratio. Total distortion can be characterized by a power sum of all selected or evaluated harmonics. Total harmonic distortion (THD) can be characterizes as an amount, e.g. by way of a percentage or by way of a dB value, effected by harmonically related distortion for a given fundamental excitation signal, and in some cases can include only harmonics below the 10th harmonic. A value of total harmonic distortion plus noise (THD+noise) can be characterized as the total harmonic distortion with the added inclusion of one or more non-harmonically relates signals. Rub and buzz can be characterized in the same manner as total harmonic distortion, e.g. as a percentage or a dB value, effected by harmonically related distortion for a given fundamental excitation signal that includes only harmonics greater than a floor value, typically the 10th harmonic and also typically less than the 35th.
Analysis of acoustic signals obtained by the methods herein disclosed can be performed by way of a variety of acoustic analysis algorithms. For example, a Fourier-transform based analysis algorithm, like a fast Fourier transform (FFT) algorithm, can be used to assess a typical signal channel response spectrum to monitor background or baseline sound pressure in a microphone. Transfer functions may be applied to perform frequency response analysis for acoustic signal magnitude, phase, distortion, coherence, and related parameters. A real-time analysis algorithm can allow for frequency response analysis while also providing octave and band analysis capability. In one particular example, the FFT-based HARMONICTRAK algorithm (Listen, Inc.) can be used to obtain similar analytical results as a transfer function algorithm based on a sweep stimulus frequency or similar excitation.
The first element 102 includes a first substrate 104 that defines an acoustic cavity 106, the acoustic cavity 106 being defined by a void 110 in the first element 102. The first substrate 104 may be any suitable structural material, such as a plastic or metal, and preferably a material that impedes propagation of sound. The first element 102 also includes alignment features 120, such as posts, pins, holes, or other suitable features which enable the first element 102 to be repeatably aligned with the second element 130.
The acoustic cavity 106 is positioned adjacent to an acoustic source 114, which may be any suitable device for generating acoustic energy toward the acoustic cavity 106. Preferably, the acoustic source 114 comprises a speaker or other suitable audio transducer 116 which is capable of generating directional sound. The acoustic source 114 is capable of directing acoustic energy into the acoustic cavity 106, e.g., by having a transducer 116 oriented toward the acoustic cavity. It will be understood that non-directional sound sources, or sound sources that direct acoustic energy over distance may be used instead provided that they produce a repeatable acoustic signal in the acoustic cavity 106.
For purposes of testing, the source is able to generate repeatability between testing within 1 dB over the frequency range of 10 Hz to 30 kHz, e.g., over the frequency range of 10 Hz to 20 kHz. Source characteristics should be such that pressure equalization within 1 dB can be achieved over the same frequency range. The source is driven at a sound pressure level such that signal/noise ratio is 20 dB or greater.
The first element 102 may also include sealing features 122, such as an O-ring or other comparable sealing member, disposed between the first element 102 and the second element 130 for sealing the acoustic cavity 106 against the second element 130 to create an acoustic chamber. In alternative embodiments, the first and second elements 102, 130 may seal together tightly without further sealing features.
According to some embodiments, the acoustic cavity 106 may also contain a passive damping material 108. The passive damping material can substantially fill the void 110 defining the acoustic cavity 106, i.e., providing an acoustic source clearance 118 to allow acoustic waves to propagate from the acoustic source 114 and test sample clearance 112 to allow acoustic waves to propagate through any test samples. Preferably, the acoustic source clearance 118 is on the order of 2 mm, or within a range of 0.1 to 10 mm. The test sample clearance 112 may be approximately 0.5 mm, but may include ranges from 0.1 to 3 mm. The passive damping material 108 can be selected from a group consisting of foamed synthetic resins, felts, non-woven fabrics, synthetic resin fibers and mineral fibers. In some specific embodiments, the passive damping material 108 is fibrillated foam, e.g., fibrillated foam of polypropylene. The size of the acoustic cavity 106 is proportioned for operating in a near-field mode. For example, the acoustic cavity 106 can have a total depth between the acoustic source 114 and the sample holder 136 from about one wavelength of the lowest frequency-tested distance (i.e. distance at the shortest wavelength) when the first and second elements are assembled. By way of example, suitable frequencies for use can include from 10 Hz to 30 kHz, e.g., from 10 Hz to 20 kHz. Sound in air at the highest frequencies has a wavelength of less than 17 mm, which varies depending on the presence or specific material of passive dampening material 108. The acoustic source 114 can include electrical connections 124 to a signal conditioner (not shown) or other suitable signal source for supplying an amplified acoustic signal.
According to some embodiments, the second element 130 comprises a second substrate 132 that is arranged to repeatably mate with the first element 102, and which can retain a sample holder 136 that is arrange to cover the void 110 to fully enclose the acoustic cavity 106. In some embodiments, the sample holder 136 may be arranged so that a test sample side 144 of the sample holder 136 lays flush across a portion of the first element 102 to enclose the acoustic cavity 106. The sample holder 136 may also, or instead, press into the sealing features 122 to seal the acoustic cavity 106. The second substrate 132 can include second alignment features 150 which can interact with the first alignment features 120 for aligning the first and second elements 102, 130 when they are connected together. In some embodiments, the first and second elements 102, 130 can be aligned to within a tolerance of 0.1 mm or less.
The second element 130 further includes a backing cavity 134 adjacent to a portion of the sample holder 136. In particular, the backing cavity 134 is arranged to accommodate one or more microphones 140 on a microphone side 146 of the sample holder 136. As stated herein, the microphones 140 may be arranged in a planar array for repeatability in testing and loading of samples. The microphone side 146 is opposite the test sample side 144 and facing away from the acoustic cavity 106 when the first and second elements 102, 130 are assembled. The backing cavity 134 is sufficiently deep to accommodate the one or more microphones 140, and can open to a conduit (not shown) for accommodating control and power cords for the one or more microphones 140. The backing cavity 134 contains a backing material 148 which can include any suitable acoustic absorptive material, such as a rubber or polymer foam including, e.g., polyurethane foam or similar sound-absorbing material. Both the acoustic source 114 and microphones 140 are enclosed in structures with noise rejection properties such that internal audible noise is 10 dB less than external audible noise averaged across the test frequency range.
Although the sample holder 136 is generally fixed to the second element 130, and is arranged to engage with and separate from the first element 102 when the second element is affixed with or removed from the first element; the sample holder 136 may also be removable from the second element 130. For example, the sample holder 136 may be sized and/or shaped to align with one or more features of the second substrate 132, e.g., with backing cavity 134, and may be removably attached with the second element 130 by such connectors as screws, bolts, pins, clips, or comparable connectors. The sample holder 136 can be removed, e.g., in order to replace one or more of the microphones 140.
The sample holder 136 is arranged to attach with the second element 130 so that the sample holder is repeatably placed in alignment with the acoustic cavity 106 when the second element 130 is assembled with the first element 102. The sample holder 136 includes multiple ports 138 defining through-holes in the sample holder 136. The ports 138 can be on the order of 1 mm in diameter, but can range from 0.2 to 3.0 mm in diameter. The ports 138 are connected at one side of the sample holder 136 with the test sample side 144, and are connected with the one or more microphones 140 at the microphone side 146, so that sound passing through each one of the ports 138 is picked up predominantly by a respective one of the one or more microphones 140. In various embodiments, the sample holder 136 comprises a substantially flat test sample surface 144 which is capable of both sealing to the first element 102 (i.e. by way of sealing features 122), and which is capable of retaining adhered or otherwise affixed test samples thereon.
Each of the ports 138 is associated with a test sample position 142 of the sample holder 136. In some embodiments, the test sample face 144 of the sample holder 136 can be a smooth polymer surface or polymer-coated surface, e.g., a polyimide coated surface, or other comparable coating. Preferably, the test sample face 144 is smooth and capable of adhering to and fully releasing from an adhesive test sample. In some alternative embodiments, the test sample face 144 can be formed of a smooth polymer or polymer coated layer applied and affixed to a structural part of the sample holder 136. The sample holder 136 can be substantially formed of any suitable structural material such as a rigid polymer or metal. The ports 138 are formed through an entire thickness of the sample holder 136, connecting each microphone 140 with a respective test sample position 142. In some embodiments, the test sample positions 142 denote locations on the test sample face 144 where test samples, e.g., samples of acoustic covers, can be affixed to each fully cover the ports 138. In other embodiments, the test sample positions 142 can designate surface features (not shown) which can further enable test samples to be affixed to the test sample face 144.
In another aspect there is provided an acoustic cover test sample 600 including a test membrane 620 positioned on a sample holder 636, as shown in
Parts of the apparatus described above can be repeated and positioned to increase the number of acoustic test samples that can be assessed simultaneously. In the embodiments of sample holders (e.g., sample holder 136 shown in
To increase the throughput a test apparatus may have a plurality of acoustic cavities in the first element and a corresponding number of sample holders in the second element. The number of acoustic cavities may be from 2 to 10, e.g., from 3 or 8. In one exemplary embodiment, the four acoustic cavities may be employed as shown in
Apparatus 700 has multiple acoustic cavities 706 positioned within a single first element 702 and arranged to align with multiple sample holders 736 of a singular second element 730. The first element 702 also contains multiple acoustic sources 714, each acoustic source facing a respective sample holder 736 across a respective acoustic cavity 706. The alignment features 720 of the first element 702 are arranged to repeatably align the first and second elements 702, 730 together to align each respective acoustic cavity 706 with a respective sample holder 736. The test apparatus 700 shown illustrates an assembly having four acoustic cavities 706 and associated components; however it will be understood that a high throughput test apparatus can have more or can have fewer than four acoustic cavities.
Next, one or more test samples can be positioned at sample positions on the sample holder and enclosed within the closed acoustic chamber in a test configuration (act 908). The plurality of measurement microphones can be exposed to a second acoustic signal while covered by the test samples (act 910). From each acoustic stimulus measured, sound pressure level across the test frequency range of interest should not deviate by more than 6 dB. Then, a test acoustic response can be generated for the plurality of measurement microphones based on the response of each measurement microphone in the test configuration (act 912). An acceptable response range can be generated for each microphone based in part on the baseline acoustic response (act 914) and corrected by reference microphone. In one embodiment, consecutive testing can have a deviation of 1 dB or less, when correction is used, e.g., 0.5 dB or less or 0.3 dB or less.
Next, the test acoustic responses for each microphone can be compared to the baseline acoustic responses for each microphone in order to calculate an acoustic insertion loss for each respective test sample (act 916). If one or more acoustic insertion losses exceeds a predetermined threshold (i.e., if one or more test responses exceeds a suitable predetermined threshold for acoustic loss), the system can generate an indication for presentation to a user that the test has failed. Test method throughput is most preferably 3 parts per minute or greater. Where a reference microphone is provided, a reference signal obtained by the reference microphone can be used, e.g., for noise cancellation, source stability correction, and/or obtaining a phase shift associated with the unimpeded reference port. For example, a phase shift associated with the reference microphone can be detected and compared with a phase shift associated with a measurement microphone to determine a phase shift caused by each respective test sample.
In an example “open” test, an acoustic testing apparatus similar to the apparatus of
In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present invention. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.
Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the present invention or claims.
Where a range of values is provided, it is understood that each intervening value, to the smallest fraction of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Any narrower range between any stated values or unstated intervening values in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of those smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the present invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a filter” includes a plurality of such filters, and reference to “the support member” includes reference to one or more support members and equivalents thereof known to those skilled in the art, and so forth.
Also, the words “comprise,” “comprising,” “contains,” “containing,” “include,” “including,” and “includes,” when used in this specification and in the following claims, are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.
