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US6970568: Apparatus and method for analyzing an electro-acoustic system

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Filing Information

Inventor(s) Dwight H. Freeman · Dennis Lynn Griffiths ·
Assignee(s) Electronic Engineering and Manufacturing Inc. ·
Attorney/Agent(s) Dorsey & Whitney LLP ·
Primary Examiner Ping Lee ·
Application Number US9406203
Filing date 09/27/1999
Issue date 11/29/2005
Predicted expiration date 09/27/2019
U.S. Classifications 381/58  · 381/303  · 381/59  ·
International Classifications --
Kind CodeB1
International Classifications 381103 · 381303 · 381 58 · 381 59 · 381108 ·
67 Claims, 8 Drawings


Abstract

An analysis system for accurately measuring the time-of-flight of an audio signal generated in response to a stimulus signal by an electro-acoustic transducer of an electro-acoustic system, such as an audio loudspeaker, to a point of measurement. The measurement is made by correlating the audio signal to a second signal having the same characteristics as the stimulus signal, but is delayed with respect to the stimulus signal. The measurement identifies the total overall delay from the time the stimulus signal is generated to the time the resulting audio signal is detected. Thus, any system delays, such as those due to signal processing, have already been accounted for by the measurement. Some or all of the measurement process may be automated through software programming in order to minimize measurement time. The time-of-flight is the delay time corresponding to when the stimulus signal, or the delayed second signal, and the resulting audio signal reach peak correlation. The distance of the acoustic center of the transducer can be calculated from the measured time-of-flight. The resulting comparison between the audio signal and the delayed second signal may also be used to determine the polarity of the transducer with respect to the stimulus signal.

Independent Claims | See all claims (67)

  1. 1. A method of measuring a system delay time between when a stimulus signal is applied to an input of an electro-acoustic system having at least one acoustic transducer and when a resulting audio signal produced by the at least one acoustic transducer in response to the stimulus signal is detected at a point of measurement, the method comprising: generating a first signal having a repeatable sequence; coupling the first signal to the electronic input of the electro-acoustic system as the stimulus signal, the acoustic transducer generating a resulting audio signal in response; generating a second signal at an initial delay time subsequent to generating the first signal, the second signal having the repeatable sequence of the first signal; converting the resulting audio signal detected at the point of measurement to a corresponding electronic signal; comparing the corresponding electronic signal and the second signal for a plurality of delay times beginning with the initial delay time; generating and recording for the plurality of delay times a corresponding plurality of signed correlation values having magnitudes indicative of the correlation between the corresponding electronic signal and the second signal at the respective delay time; evaluating the plurality of correlation values for a peak correlation value corresponding to the peak correlation between the corresponding electronic signal and the second signal; and selecting the delay time associated with the peak correlation value as the system delay time.
  2. 22. A method of measuring a time-of-flight for an audio signal generated by a selected one of a plurality of acoustic transducers of an electro-acoustic system to reach a W point of measurement, comprising: generating a first pseudo-random noise signal having a repeatable sequence as the stimulus signal applied to the electro-acoustic system; generating a second pseudo-random noise signal at a source delay time subsequent to generating the first noise signal, the second noise signal having the repeatable sequence of the first noise signal; converting an audio signal generated by the selected acoustic transducer in response to the stimulus signal into an electronic signal when the audio signal is detected at the point of measurement; comparing the electronic signal and the second noise signal for a plurality of delay times beginning with the source delay time; generating and recording for the plurality of delay times a corresponding plurality of signed average values having magnitudes indicative of the correlation between the electronic signal and the second noise signal; evaluating the plurality of signed average values for a peak correlation value corresponding to the maximum correlation between the electronic signal and the second noise signal; and selecting the delay time associated with the peak correlation value as the time-of-flight.
  3. 41. A system for measuring a time delay between when a stimulus signal is applied to an input of an electro-acoustic system having at least one acoustic transducer and when a resulting audio signal produced by the at least one acoustic transducer in response to the stimulus signal is detected at a point of measurement, the system comprising: a signal generator to generate first and second signals at first and second signal outputs of the signal generator, respectively, the first signal having a sequence and being applied through the first signal output to the electronic input of the electro-acoustic system as the stimulus signal, the second signal having the sequence of the first signal and being delayed with respect to the first signal by an adjustable delay time determined by the value of a delay control signal; a microphone acoustically coupled to the at least one acoustic transducer of the electro-acoustic system and generating at a microphone output a resulting output signal corresponding to the resulting acoustic signal; a mixer circuit coupled to the microphone output and the second signal output to receive the resulting output signal and second pseudo-random noise signal, respectively, the mixer circuit providing at a mixer output a mixer output signal having a magnitude indicative of a predetermined relationship between the resulting output signal and the second signal; an analog-to-digital converter having an input coupled to the mixer output, the analog-to-digital converter generating at a converter output digital words corresponding to the magnitude of the mixer output signal applied to its input; a memory for recording the digital words; a display for displaying information resulting from the measurement; and a microprocessor coupled to the signal generator for generating the delay control signal, the analog-to-digital converter for receiving the digital words corresponding to the magnitude of the mixer output signal, the memory for recording the digital words, and the display for providing information related the measurement to be displayed, the microprocessor measuring the time delay by: initiating the signal generator to generate the first signal; adjusting the delay control signal provided to the delay circuit to delay the second signal with respect to the first signal for a plurality of delay times; recording for each of the plurality of delay times a digital word generated by the analog-to-digital converter; evaluating the digital words for a selected digital word corresponding to the peak of the predetermined relationship between the resulting output signal and second signal; and causing the display to provide visual information related to the selected digital word.
  4. 51. An analysis system for measuring a system delay time between when a stimulus signal is applied to an input of an electro-acoustic system having at least one acoustic transducer and when a resulting audio signal produced by the at least one acoustic transducer in response to the stimulus signal is detected at a point of measurement, the method comprising: first signal generator means for generating a first signal having a repeatable sequence coupled to the electronic input to provide the first signal as the stimulus signal; second signal generator means for generating a second signal at an initial delay time subsequent to generating the first signal, the second signal having the repeatable sequence of the first signal; microphone means for converting the resulting audio signal detected at the point of measurement to a corresponding electronic signal, the microphone means acoustically coupled to the acoustic transducer; comparison circuit means for comparing the corresponding electronic signal and the second signal for a plurality of delay times beginning with the initial delay time; converter circuit means for generating for the plurality of delay times a corresponding plurality of signed correlation values having magnitudes indicative of the correlation between the corresponding electronic signal and the second signal at the respective delay time; memory means for storing the plurality of signed correlation values and the corresponding plurality of delay times; microprocessor means for evaluating the plurality of correlation values for a peak correlation value corresponding to the peak correlation between the corresponding electronic signal and the second signal, the microprocessor means further selecting the delay time associated with the peak correlation value as the system delay time; and display means coupled to the microprocessor means for displaying information generated by the microprocessor means.
  5. 60. A system for measuring a time delay between when a stimulus signal is applied to an input of an electro-acoustic system having at least one acoustic transducer and when a resulting audio signal produced by the at least one acoustic transducer in response to the stimulus signal is detected at a point of measurement, the system comprising: a first pseudo-random noise generator generating at a first noise output a first pseudo-random noise signal having a repeatable sequence, the first pseudo-random noise signal applied through the first noise output to the electronic input of the electro-acoustic system as the stimulus signal; a microphone acoustically coupled to the at least one acoustic transducer of the electro-acoustic system and generating at a microphone output a resulting output signal corresponding to the resulting acoustic signal; a second pseudo-random noise generator generating at a second noise output a second pseudo-random noise signal having the repeatable sequence of the first pseudo random noise signal, the second pseudo-random noise signal being delayed with respect to the first pseudo-random noise signal by a delay time determined by the value of a delay control signal; a comparison circuit coupled to the microphone output and the second noise output to compare the resulting output signal and the second pseudo-random noise signal, the comparison circuit providing at a comparison circuit output digital words corresponding to the magnitude of correlation between the resulting output signal and the second pseudo-random noise signal; a memory circuit for storing the digital words provided by the comparison circuit; a display for displaying information resulting from the measurement; and a microprocessor coupled to the first and second pseudo-random noise generators for initiating the first pseudo-random noise signal and initiating the second pseudo-random at the delay time, the comparison circuit output for receiving the digital words, the memory circuit for providing the digital words for storage, and the display for providing data related to the measurement to be displayed, the microprocessor measuring the time delay by: initiating the first pseudo-random noise generator to generate the first pseudo-random noise signal, and initiating the second pseudo-random noise generator at an initial delay time thereafter to generate the second pseudo-random noise signal; providing the delay control signal to the second pseudo-random noise generator to adjust the delay value for a plurality of delay times; storing for each of the plurality of delay times a digital word provided by the comparison circuit; evaluating the digital words for a selected digital word corresponding to the peak correlation of the resulting output signal and second pseudo-random noise signal; and causing the display to provide visual information related to the selected digital word.

References Cited

U.S. Patent Documents

Document NumberAssigneesInventorsIssue/Pub Date
US5113447 Electronic Engineering and Manufacturing, Inc. Hatley et al. May 1992
US5555311 Electronic Engineering and Manufacturing, Inc. Reams Sep 1996
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* cited by examiner

Other Publications

DRA Laboratories, “MLSSA Acoustical Measurement System,” Brochure, www.mlssa.com, 8 Pages.
Rife, Douglas D., “MLSSA Maximum-Length Sequence System Analyzer”, Reference Manual, Version 10WI-4, DRA Laboratories, Copyright 1987-2001, pp. i-296.

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