阅读说明：本技术 测量扬声器的非线性和不对称性 (Measuring non-linearity and asymmetry of a loudspeaker ) 是由 B·K·迈尔斯 J·L·墨菲 于 2020-01-10 设计创作，主要内容包括：扬声器参数是使用测试信号(120、130、140)针对各种前向和后向的音盆位移独立测量的,该测试信号允许在前向或后向的音盆运动的不同程度上测量参数。测试信号使用短暂的扫频信号(122/124、132/134、142/144),如对数扫频信号,与基频低于例如10Hz的极低频(VLF)音频音调(126、136、146)相结合。极低频音频音调可以有正弦波形状(126)、方波形状(136)或削波正弦波形状(146)。(Loudspeaker parameters are measured independently for various forward and backward cone displacements using test signals (120, 130, 140) that allow the parameters to be measured at different degrees of forward or backward cone movement. The test signal uses a short-lived swept frequency signal (122/124, 132/134, 142/144), such as a logarithmic swept frequency signal, in combination with a Very Low Frequency (VLF) audio tone (126, 136, 146) having a fundamental frequency below, for example, 10 Hz. The very low frequency audio tone may have a sine wave shape (126), a square wave shape (136), or a clipped sine wave shape (146).)

1. A method of testing a speaker, comprising:

applying a test drive signal to the loudspeaker, the test drive signal comprising a brief sweep frequency signal in combination with a very low frequency audio tone having a fundamental frequency below 10 Hz;

determining a first response parameter of the loudspeaker associated with a first drive signal at a first cone offset;

determining a second response parameter of the loudspeaker associated with the first drive signal at a second cone offset; and

comparing the first response parameter and the second response parameter to determine whether their difference exceeds a target threshold.

2. The method of claim 1, further comprising:

determining that at least one characteristic of the speaker is unacceptable in response to determining that the difference value of the first response parameter and the second response parameter is greater than the target threshold.

3. The method of claim 1, further comprising:

determining that at least one characteristic of the speaker is acceptable in response to determining that a difference value of the first response parameter and the second response parameter is less than the target threshold.

4. The method of claim 1, wherein the very low frequency tone has a fundamental frequency below 5 Hz.

5. The method of claim 1, wherein the very low frequency tone has a fundamental frequency below 1 Hz.

6. The method of claim 1, wherein the very low frequency tone has a shape selected from the group consisting of a sine wave shape, a square wave shape, and a clipped sine wave shape.

7. The method of claim 1, wherein the low frequency tones are generated at a plurality of amplitudes.

8. The method of claim 1, wherein the swept frequency signal is a logarithmic swept frequency signal.

9. An apparatus for testing a speaker, comprising:

an audio band output having an electrical terminal for connection to the speaker;

an audio band input section;

at least one processing unit; and

a memory containing program code configured to be executed by the at least one processing unit for:

outputting a test signal to an electrical output terminal, wherein the test signal comprises a very low frequency tone having a fundamental frequency below 10Hz,

receiving the measured signal at the audio band input, an

The test signal and the measured signal are compared and speaker parameters are extracted.

10. The apparatus of claim 9, further comprising an audio power amplifier, wherein the extended low frequency response is about 0.2 Hz.

11. The method of claim 1, wherein the very low frequency tone has a fundamental frequency below 5 Hz.

12. The method of claim 1, wherein the very low frequency tone has a fundamental frequency below 1 Hz.

13. The method of claim 1, wherein the very low frequency tone has a shape selected from the group consisting of a sine wave shape, a square wave shape, and a clipped sine wave shape.

14. The method of claim 1, wherein the low frequency tones are generated at a plurality of amplitudes.

15. A program product, comprising:

program code configured to

Generating a test drive signal for application to the loudspeaker, the test drive signal comprising a brief sweep frequency signal in combination with a very low frequency audio tone having a fundamental frequency below 10 Hz;

determining a first response parameter of the loudspeaker associated with a first drive signal at a first cone offset;

determining a second response parameter of the loudspeaker associated with the first drive signal at a second cone offset; and

comparing the first response parameter and the second response parameter to determine if their difference exceeds a target threshold; and

a computer recordable medium carrying the program code.

16. The method of claim 15, wherein the very low frequency tone has a fundamental frequency below 5 Hz.

17. The method of claim 15, wherein the very low frequency tone has a fundamental frequency below 1 Hz.

18. The method of claim 15, wherein the very low frequency tone has a shape selected from the group consisting of a sine wave shape, a square wave shape, and a clipped sine wave shape.

19. The method of claim 15, wherein the low frequency tones are generated at a plurality of amplitudes.

Technical Field

The present application relates broadly to loudspeakers and in particular to testing loudspeakers for defects that may lead to resulting sound distortion.

Background

Loudspeakers vary widely in part and composition, most commonly using a lightweight diaphragm (or "cone") connected by a flexible suspension to a rigid basket (or "frame") that constrains a thin wire coil ("voice coil") from axial movement in a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, the current in the voice coil creates a magnetic field that makes it a variable electromagnet. The voice coil and the magnetic system interact, generating mechanical forces that move the voice coil (and thus the attached cone) back and forth, reproducing sound under the control of an applied electrical signal.

Despite significant advances in the materials used to fabricate the speaker, as well as advances in the structure of the speaker itself, the speaker remains an electromechanical device that is prone to failure and performance inefficiencies. Failure of the speaker may be due to misalignment of the magnetic system of the speaker, but often occurs after introduction of a foreign object in the speaker (e.g., between the voice coil and the gap), reducing the ability of the voice coil to move back and forth. Such foreign matter may include dust, ferrous debris, non-ferrous debris, and general debris present in various environments. Failure of the speaker can in turn entail significant maintenance costs, since the speaker is already ubiquitous in automobiles, computers, telephones and any other device that generates or transmits sound, but is generally considered to be the most stable and therefore placed in a location that requires a great deal of labor to reach.

Accordingly, speakers are often tested for defects prior to installation to reduce the likelihood of replacement due to foreign objects introduced into the speaker by manufacturing, storage, or some other condition. Conventional speaker testing involves connecting a speaker to an electrical signal and audibly measuring the sound produced thereby with a microphone. If the sound from the speaker is sufficiently clear (e.g., the sound does not exhibit too much distortion), the speaker passes the test and can be used. Conversely, if the sound from the speaker exhibits too much distortion, the speaker is considered unsuitable for use and is rejected for poor quality.

Testing a loudspeaker in this manner, however, tends to be very time consuming because various tones must be produced for the test device and there is little way to account for the distortion introduced by the microphone. In addition, failure of the speaker often takes time to manifest due to contamination by foreign matter. Specifically, foreign objects may not significantly degrade the quality of sound from the speaker when first introduced, but as the speaker is used, foreign objects degrade the quality of the components of the speaker until the sound from the speaker is unacceptable.

The Dayton Audio Test System (DATS) sold by the assignee of the present application drives the speaker with a very short (0.7 second) logarithmic sweep signal to perform high resolution impedance measurements. This swept test signal 100 is shown in figure 2. Using the output when driving the loudspeaker by means of a swept frequency test signal, the DATS software can derive very detailed parameters that describe the characteristics of the loudspeaker in a standard way, which is useful for anyone who is interested in loudspeaker specifications and performance.

The DATS drives the speaker once with a frequency sweep to measure the free air properties and parameters of the speaker, and then repeats the frequency sweep to measure various speaker electromechanical parameters, such as Fs (resonant frequency), Qts (total Q of the speaker at Fs), and Vas (equivalent volume of the speaker). Before the second frequency sweep, the user is typically required to place the speaker in a test box or add a test mass to the cone in order to allow parameter measurements to be made.

Small signal measurement systems like DATS can be used to perform basic large signal analysis of the speaker by adding a power amplifier to the output of the DATS system to drive the speaker under test. This may cause the speaker to be driven to even possibly beyond the limits of normal use. In this way, generating test sweeps at higher and higher amplitudes, it is possible to measure the complete set of loudspeaker parameters at each tested power level. This method provides a measure of the parameter variation as the drive level of the loudspeaker is increased.

Fig. 3 shows a test frequency sweep 110 generated at increased signal levels 112, 114, 116 according to the method described above. The signal level shown in fig. 2 is the output voltage from the power amplifier driving the speaker under test. (the DATS measurement software can convert the drive voltage to input power or cone offset, as desired by the user).

The DATS software can automatically measure parameters in this manner using a continuous sweep at progressively larger amplitudes at several signal levels. The measurement results may then be presented to the user in the form of a table showing the driver parameters for each drive level. In addition, each loudspeaker parameter may be plotted as a function of drive voltage, input power, or average cone excursion to show how the parameter varies with drive level. It should be noted that the above-described method of increasing the signal amplitude does not take into account the polarity of the cone displacement.

Another historically known method for measuring large signal speaker parameters is to forcibly displace the cone during testing. There are several methods that can be used to displace the cone, including applying air pressure to the cone in a pressure/vacuum chamber, coupling an accessory to the cone to apply a force to displace the cone, or applying Direct Current (DC) to the voice coil. Cone displacement may be measured directly (e.g. with a scale) or by using a separate laser-based instrument. After displacement of the cone, the impedance may be measured and parameters extracted from the impedance measurement by a computer software routine. A well-known source of such a non-linear testing device is Klippel GmbH (cleppel ltd) in germany.

Although the above methods exist, none of them are entirely satisfactory for testing speakers in large signal operation. The method using DATS involves multiple signal generation and mapping steps and does not take into account the polarity of the cone displacement. The method involving forced displacement of the cone requires that the speaker be used in a manner different from conventional operation, either by additional external pressure or displacement, or using Direct Current (DC) current.

Thus, there remains a need in the art for a way to test speakers for defects that does not suffer from the above-mentioned disadvantages.

Disclosure of Invention

Embodiments consistent with the present application include a method, apparatus and program product for independently measuring speaker parameters for various forward and backward cone displacements. The independent measurement of parameters for forward and backward cone displacement will reveal asymmetries for Bl (magnetic field strength of coil gap), CMS (compliance), FS (resonant frequency), QTS (total Q value of the loudspeaker at FS), LE (voice coil inductance) and other parameters, helping driver designers to optimize their drivers to obtain maximum sound output capability from the driver before overload distortion begins.

In accordance with the principles of the present application, a new test signal is used to measure parameters of various degrees of forward or backward cone motion. The test signal uses a short-lived swept frequency signal, such as the logarithmic swept frequency signal currently used in DATS, in combination with a Very Low Frequency (VLF) audio tone with a fundamental frequency below 10 Hz.

In detailed embodiments, the very low frequency tone may have a fundamental frequency below 5Hz, or below 1Hz, and in one embodiment, the tone may have a fundamental frequency of 0.1 Hz. In detailed embodiments, the very low frequency audio tone may have a sine wave shape, a square wave shape, or a clipped sine wave shape.

In a particular embodiment, the test signal further comprises a log swept frequency signal combined with the very low frequency tone. Furthermore, very low frequency tones may be applied at multiple amplitudes.

In other aspects, the application features a test apparatus for testing a speaker including an audio band output having an electrical display terminal for connection to the speaker, an audio band input, at least one processing unit, and a memory containing program code configured for execution by the at least one processing unit to output a test signal to the electrical output terminal, wherein the test signal includes a very low frequency tone to receive a measured signal at the audio band input, and to compare the test signal to the measured signal and extract speaker parameters.

In a specific embodiment, the test device employs an audio power amplifier, wherein the extended low frequency response is to about 0.2 Hz.

In other aspects, the application features a program product including program code configured to perform the method and activate the testing device to test a speaker. The program code causes the processor to generate a test signal comprising the very low frequency tone, receive a measured signal representative of sound produced by the speaker, and extract parameters of the speaker for various different degrees of forward and backward cone excursion.

The present application thus allows testing of the non-linearity of a loudspeaker at various drive levels, and performing the test in different situations of forward cone movement and backward cone movement in such a way that a excursion of the loudspeaker cone is caused by a test signal comprising an extremely low frequency tone applied at an electrical terminal of the loudspeaker.

Drawings

The foregoing aspects and detailed embodiments of the present application will be further understood by reference to the drawings attached hereto, wherein:

FIG. 1 is an illustration of a test system consistent with an embodiment of the present application.

FIG. 2 is a graphical representation of a log swept test signal.

FIG. 3 is a graphical representation of a series of log swept test signals with increasing amplitude.

FIG. 4 is a graphical representation of one embodiment of a novel test signal including a very low frequency sine wave combined with a frequency sweep signal in accordance with the principles of the present application.

FIG. 5 is a graphical representation of a second embodiment of a novel test signal including a very low frequency sine wave combined with a frequency sweep signal in accordance with the principles of the present application.

FIG. 6 is a graphical representation of a third embodiment of a novel test signal in accordance with the principles of the present application including a very low frequency waveform in the form of a clipped sine wave in combination with a sweep signal during clipped peaks of the very low frequency waveform.

Fig. 7 is a flow chart illustrating a sequence of operations for providing drive signals for the loudspeaker of fig. 1 consistent with embodiments of the present application.

Fig. 8 is a flow chart illustrating a sequence of operations for determining whether the speaker of fig. 1 is acceptable based on various impedances or resistances of the speaker determined from corresponding drive signals.

Detailed Description

FIG. 1 is an illustration of a test system 10 consistent with an embodiment of the present application. In particular, the test system includes a computer 12 connected to test equipment 14, the test equipment 14 configured to provide one or more signals to a speaker 18 through an electrical output terminal 16. The test device 14 is further configured to measure the characteristics of one or more audio band signals produced by the loudspeaker via the connection 20.

In particular, computer 12 may include at least one computer, computer system, computing device, server, disk array, or programmable device such as a multi-user computer, single-user computer, hand-held device, networked devices (including clustered computers), or the like. The computer 12 includes at least one central processing unit ("CPU") 22 coupled to a memory 24. The CPU 22 is typically implemented in hardware using circuit logic disposed in one or more physical integrated circuit devices or chips and may be one or more microprocessors, microcontrollers, field programmable gate arrays, or ASICs, while the memory 24 may comprise Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), flash, EEPROM, and/or other digital storage media and is typically implemented using circuit logic disposed in one or more physical integrated circuit devices or chips. Thus, memory 24 may be considered to include memory storage physically located elsewhere in computer 12, e.g., any cache memory in at least one CPU 22, as well as any storage capacity used as virtual memory.

The computer 12 is under the control of an operating system (not shown) and executes or otherwise relies upon various computer software applications, components, programs, files, objects, modules, etc. (illustrated as "applications" 26). The application 26 is then configured to control the test equipment 14 to send signals to the loudspeaker 18 and to measure characteristics of the signals from the loudspeaker 18. Test equipment 14 may be connected to computer 12 via a universal serial bus ("USB"), and in a particular implementation, may be a Dayton Audio Test System (DATS) speaker tester distributed by Parts Express International, Inc. of Springboro (Spulin Boler), Ohio. In a specific implementation, application 26 may be DATS software, also distributed by Parts Express, Inc., and configured to interoperate with test device 14 when the test device is a DATS speaker tester.

FIG. 2, discussed above, shows a log swept test signal 110, which may be used herein as an integral part of the present application.

FIG. 4 is a graphical representation of one embodiment of a novel test signal 120 generated by system 10 in accordance with the principles of the present application including a very low frequency sine wave 126 in combination with swept frequency signals 122, 124. In this signal, the logarithmic sweep signals 112 and 124, conventionally used for DATS, are of very short duration (0.7 seconds), combined with a Very Low Frequency (VLF) tone 126, so that the combined tone can then be used to measure the impedance at the independent positive and negative peaks of the VLF tone. Impedance measurements sufficient to extract speaker parameters are performed independently at the positive and negative peaks of the monocycle VLF waveform. Using this "swept frequency plus VLF tone" approach, the system 10 can calculate driver parameters independently for each signal polarity over a wide range of VLF levels and corresponding cone offsets. By varying the VLF signal level, the system 10 can control the cone displacement at the time of measurement and thereby measure the driver parameters for various forward and backward cone displacements.

In the illustrated case, the Very Low Frequency (VLF) tone is a 0.1Hz sine wave 126 with a period of 10 seconds. VLF wave 126 has positive and negative peaks that are long enough to generate and acquire sweeps 122 and 124 at each peak of the VLF tone. The sweep may be repeated as the VLF amplitude increases, producing a series of measurements that capture the impedance response of the loudspeaker over a range of cone displacements. The application 26 then analyzes each captured impedance sweep and calculates the parameters for that particular offset and polarity.

To implement this method, the test equipment 14 contains a power amplifier that can reliably deliver a specified VLF test signal to the speaker. Experience with analog power amplifiers has shown that when the high power signals used to drive them are well below 20Hz, the result can be excessive heat dissipation and potential failure. Therefore, a power amplifier that can operate at a frequency well below 20Hz without failure must be selected. Off-the-shelf audio power amplifiers are suitably modified to extend their response below 0.1Hz (since most audio amplifiers are limited to around 5-10 Hz). If the switch transient state is not well processed, the low-frequency response with large extension degree can cause potential safety hazard to the tested unit. To minimize the safety issues of the driver, the low frequency bandwidth of the amplifier should only be extended to the low level required to deliver the test signal.

The VLF sine wave shown in fig. 4 moves slowly between the peak displacement levels of the sweep. Long-lasting VLF periods have a lower fundamental frequency and require power amplifiers with similar or lower cut-off frequencies. To improve this low frequency cutoff, the VLF period (cycle time) can be made as short as possible while the test sweep is acquired cleanly.

Fig. 5 is a graphical representation of a second embodiment of a novel test signal 130 in which the very low frequency is a square wave 136 combined with swept frequency signals 132 and 134 in accordance with the principles of the present application. This VLF signal 136 transitions between peak levels (peak cone excursions) much faster than the sine wave shown in fig. 4, but may produce a very loud and rough "click" sound at each vertical segment of the waveform.

Fig. 6 is a diagram of a third embodiment of a novel test signal 140 in accordance with the principles of the present application, including a very low frequency waveform in the form of a clipped sine wave in combination with sweep signals 142 and 144 during clipped peaks of the very low frequency waveform. This VLF waveform uses sinusoidal bands at the beginning, center and end of the waveform to achieve a fast but smooth transition between the base levels of the test signal, but the shape of the sine wave is clipped to a maximum and minimum. This VLF period is much shorter than the sine wave of fig. 4 and is almost as short as the square wave of fig. 5, but without an annoying loud clicking sound.

Using the VLF and swept frequency signals described herein, comprehensive testing of the speaker can be performed efficiently. More specifically, test equipment 14 is configured to provide a plurality of drive signals (e.g., VLF signals for a frequency sweep and a plurality of voltage levels) to speaker 18 and to measure the voltage provided from speaker 18 in response to these drive signals. The test equipment 14 or application 26 then calculates the complex impedance or resistance of the loudspeaker 18 for each particular drive signal based on the data for the voltage and/or current from the loudspeaker 18 at that drive signal level. Application 26 then determines whether the resonant frequency or resistance at the various drive levels shifts unacceptably with changes in drive level, or whether the peak value of the resonant frequency or resistance at the various drive levels increases or decreases unacceptably with changes in drive level.

For example, a shift in the resonant frequency of the complex impedance above a frequency threshold or a shift in the peak of the complex impedance above a peak threshold indicates that the speaker 18 may not be operating properly. Such drift may be caused by improper alignment of components of the speaker 18, failure of components of the speaker 18, or improper components for the speaker 18, but is generally caused by foreign objects introduced into the speaker 18. These foreign objects may cause buzzes and rubs in the sound produced by the speaker 18, but may not be audible or detectable using conventional testing methods. However, foreign objects in the speaker 18 also often change the resistance and complex impedance of the speaker 18 at its resonant frequency.

Thus, embodiments of the present application determine the resonant frequency of the speaker 18 at various drive levels and determine the corresponding complex impedances, which are then analyzed to determine speaker parameters and whether the speaker 18 is acceptable.

In an embodiment, the application 26 may be configured to reject the speaker 18 when the shift in the resonant frequency of the drive level exceeds a target frequency threshold. In some embodiments, the target frequency threshold may be set at about 500% more or less than the resonant frequency of the drive signal at 0 dBu. However, in alternative embodiments, the target frequency threshold may be set lower, for example from about 30% to about 40%, which provides an acceptable range in which the resonant frequency of the complex impedance of the various drive signals may vary. In a further alternative embodiment, the shift in resonant frequency at a particular cone excursion may be determined relative to the resonant frequency of a previous or subsequent drive signal. In these embodiments, the speaker 18 may be rejected when the shift in resonant frequency from the first drive signal to the second drive signal meets or exceeds the target frequency threshold. One of ordinary skill in the art will appreciate that the target frequency threshold may be user defined and thus include different ranges or values than those disclosed above.

In a further or alternative embodiment, the application 26 is configured to reject the loudspeaker 18 when the peak magnitude of the complex impedance at the resonance frequency of the drive level drifts beyond a target peak threshold. In some embodiments, the target peak threshold may be set at about 100% to about 150% more or less than the complex impedance peak at the resonant frequency of the drive signal at 0 dBu. In a further alternative embodiment, the peak value of the complex impedance of the resonance frequency at a particular cone excursion may be determined relative to the peak value of the complex impedance of the resonance frequency of a previous or subsequent cone excursion. In these embodiments, the speaker 18 may be rejected when the peak drifts from the first drive signal to the second drive signal meet or exceed the target peak threshold. One of ordinary skill in the art will appreciate that the target peak threshold may be user defined and thus include different ranges or values than those disclosed above. In a further embodiment, impedance data from the tested speaker is compared to data from a known good reference speaker. By using data from known good speakers for a first (reference) impedance measurement, the tested speakers can be screened over a single sweep, providing greater efficiency for continuous production testing.

The routines executed to implement the embodiments of the application, whether implemented as part of an operating system or a specific application, component, program, object, module or sequence of instructions being executed by computer 12 or test equipment 14, will be referred to herein as "a sequence of operations," a program product, "or more simply" program code. The program code typically comprises one or more instructions that are resident at various times in various memory and storage devices, and that, when read and executed by one or more processing units, such as CPU 22 of computer 12 or a processing unit (not shown) of testing device 14, cause the computer 12 or testing device 14 to perform the necessary steps to execute steps, elements and/or blocks embodying aspects of the present application using the processor(s) as such.

Those skilled in the art will appreciate that aspects of the present application are capable of being distributed as a program product in a variety of forms, and that the present application applies equally regardless of the particular type of computer-readable signal bearing media used to actually carry out the distribution. Examples of computer-readable signal bearing media include but are not limited to physical and tangible recordable type media such as volatile and non-volatile memory devices, floppy and other removable disks, hard disk drives, optical disks (e.g., CD-ROMs, DVDs, BLU-RAY, etc.), among others.

In addition, various program code described hereinafter may be identified based upon the application or software component within which it is implemented. However, it should be appreciated that any particular program nomenclature that follows is used merely for convenience, and thus the application should not be limited to use solely in any specific application identified and/or implied by such nomenclature. Furthermore, in view of the typically endless number of manners in which computer programs may be organized into routines, programs, methods, modules, objects, and the like, as well as the various manners in which program functionality may be allocated among various software layers that are resident within a typical computer (e.g., operating systems, libraries, APIs, applications, applets, etc.), it should be appreciated that the application is not limited to the specific organization and allocation of program functionality described herein.

Fig. 7 is a flowchart 200 illustrating a sequence of operations for providing drive signals for the speaker 18 consistent with embodiments of the present application. In some embodiments, the sequence of operations of FIG. 7 may be performed by the computer 12, by the test equipment 14 under the control of the computer 12, or independently by the test equipment 14. In any case, when the user selects to begin testing the speaker 18, the computer 12 or the test equipment 14 provides an initial drive signal (e.g., a swept sine wave signal of a particular magnitude swept through a frequency range) (block 202) and measures the impedance or resistance of the speaker 18 to the drive signal (block 204). The computer 12 or the test equipment 14 then determines whether the test is complete (block 206). When the test has not ended ("no" branch of decision block 206), computer 12 or test equipment 14 increases or decreases the magnitude of the drive signal (block 208), and the sequence of operations returns to block 204. When the test ends ("yes" branch of decision block 206), the sequence of operations may end.

Fig. 8 is a flow chart 210 illustrating a sequence of operations for determining whether the speaker 18 is acceptable based on various impedances or resistances of the speaker 18 determined from the corresponding drive signals. In some embodiments, the sequence of operations of FIG. 8 may be performed by computer 12, by test equipment 14 under the control of computer 12, or independently by test equipment 14. In any case, computer 12 or test equipment 14 determines the impedance or resistance of speaker 18 and the resonant frequency of speaker 18 associated with the at least two drive signals (e.g., determines the resonant frequency at each drive signal and the peak impedance or resistance at the resonant frequency of each drive signal) (block 212). Computer 12 or test equipment 14 may then determine whether the resonant frequencies of speaker 18 for the at least two drive signals differ by a value that meets or exceeds a target frequency threshold (block 214). When the resonant frequencies of speaker 18 for the at least two drive signals differ by a value that does not meet or exceed the target frequency threshold ("no" branch of decision block 214), then computer 12 or test device 14 may determine whether the magnitudes of the impedances or resistances of speaker 18 for the resonant frequencies of the at least two drive signals differ by a value that meets or exceeds the target peak threshold (block 216). When the magnitudes of the peaks of the resonant frequencies of the speaker 18 for the at least two drive signals differ by a value that does not meet or exceed the target peak threshold ("no" branch of decision block 216), the computer 12 or the test equipment determines that the speaker 18 is acceptable (block 218), and determines that the sequence of operations may end. However, when the resonant frequencies of speaker 18 for the at least two drive signals differ by a value that meets or exceeds the target frequency threshold ("yes" branch of decision block 214), or when the magnitude of the peaks of the resonant frequencies of speaker 18 for the at least two drive signals differ by a value that meets or exceeds the target peak threshold ("yes" branch of decision block 216), computer 12 or test equipment 14 determines that speaker 18 is unacceptable (block 220) and the sequence of operations may end.

In a further embodiment, the resonance frequency or impedance magnitude of the measured loudspeaker for the first cone excursion is compared with the resonance frequency or impedance magnitude of the known good loudspeaker for the second cone excursion or with the average resonance frequency or average impedance magnitude of the plurality of known good loudspeakers for the second cone excursion. These data of the tested loudspeaker are compared with the data of the reference loudspeaker(s). Although it is normal for a single loudspeaker to have a different magnitude of impedance at or near its resonant frequency, the variation caused by imperfections or other problems is typically far outside the range considered normal. For example, for a drive signal of about 100Hz, a loudspeaker typically has a resonant frequency that may vary by + -20% around the resonant frequency of a known-good loudspeaker. Thus, embodiments of the present application may be configured to accept speakers exhibiting normal variations in resonant frequency and reject speakers exhibiting deviations from normal, such as variations of ± 30% around the resonant frequency of a known-good speaker at a particular drive level, or variations of ± 30% around the average resonant frequency of a plurality of known-good speakers at a particular drive level. Generally, some preliminary tests show that rejected loudspeakers show a ± 100% deviation around a known good or average resonance frequency. Accordingly, the impedance magnitude is typically different from speaker to speaker. Thus, embodiments of the present application may be configured to accept a speaker exhibiting a normal change in impedance magnitude for a resonant frequency, and reject a speaker exhibiting a deviation from normal for impedance magnitude at the resonant frequency, such as ± 30% from its impedance magnitude for the speaker resonant frequency, or 130% from the average impedance magnitude for a plurality of speaker resonant frequencies.

In view of the above, loudspeaker imperfections may be determined for multiple sweeps of the drive signal for the same loudspeaker at different cone excursions. Data from one or more of the plurality of frequency sweeps is then compared with data from one or more different frequency sweeps of the plurality of frequency sweeps at different cone offsets to determine whether the tested speaker is acceptable. In addition, the imperfections of the loudspeaker may be determined from a single sweep of the drive signal of the loudspeaker at a particular cone excursion. The data from a single sweep is then compared to data from one or more sweeps of one or more reference speakers (e.g., speakers known to be acceptable or otherwise good) to determine whether the tested speaker is acceptable.

While the present application has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art.

By way of example, computer 12 and test equipment may include more or fewer components than those shown. Also by way of example, although test device 14 is illustrated as being separate from computer 12, one of ordinary skill in the art will appreciate that test device 14 may be internal to computer 12 or otherwise integrated with components of computer 12. Thus, the computer 12 may utilize an I/O interface or specialized hardware to generate the various drive signals and similarly utilize an I/O interface or specialized hardware to measure characteristics of the signals from the speaker 18. In these embodiments, application 26 may be configured to utilize components of computer 12, and in particular embodiments may be TRURTA real-time Audio spectrum analysis software sold by True Audio corporation of Anderson Vill, Tenn. Further, one of ordinary skill in the art may appreciate that computer 12 or testing device 14 may determine that speaker 18 is unacceptable when the difference between the first and second resonant frequencies is equal to a target frequency threshold and/or when the difference between the magnitudes of the impedance or resistance at the two resonant frequencies is equal to a target peak threshold.

The application, in its broader aspects, is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general application concept.