Method and apparatus for objective assessment of in-ear device acoustical performance

Abstract

A method and apparatus for objectively assessing acoustical performance of an in-ear device having a passageway extending there through use a dual microphone probe that removably engages the passageway. The acoustical performance of the in-ear device is performed with the in-ear device inserted into the ear canal of the user and a reference sound source. A clip holding the probe in an acoustic near field of the sound source permits real time calibration thereof. The method and apparatus allow on-site and in-situ measurement of a predicted personal attenuation rating of the device, a subject-fit re-insertion test, an acoustic seal test, a rating test, a stability and reliability test, as well as a protection test of the device with an assessment of a filtered predicted exposure level at the ear for a specific noise exposure level. The apparatus may be simply housed along with the sound source for in-field evaluation tests.

Description

where TFOE is the Transfer Function of the Outer Ear, for an unoccluded ear 16 (FIG. 2), and is equal to:

$\mathrm{TFOE}=20{\log }_{10}\left(\frac{P_3}{P}\right)$

In an occluded ear 12 (FIG. 3), the NR is determined by:

$\mathrm{NR}=20{\log }_{10}\left(\frac{P}{P_3^{\prime }}\right)$

It has been clearly demonstrated that the attenuation reported during a REAT measurement may be slightly overestimated (below 500 Hz) due to the masking effect of the physiological noise (PN) on occluded thresholds. It remains that this reported attenuation is a subjective evaluation of the IL and, practically:
REAT=IL+PN

The measured noise reduction (NR_M) measured typically using a dual microphone probe 26 adjacent the in-ear device 12 and measuring the sound pressure levels outside the device 12 being worn by the user and inside the ear canal 14 via the passageway 20 (or sound bore) of the device (see FIG. 1), respectively, is:

${\mathrm{NR}}_M=20{\log }_{10}\left(\frac{P_0^{\prime }}{P_2^{″}}\right)$

Therefore, combining the previous equations, the measured noise reduction NR_M can be linked to the reported attenuation as follows:

$\mathrm{REAT}={\mathrm{NR}}_M+\underset{\underset{\mathrm{COMP}}{︸}}{\begin{array}{c}\mathrm{TFOE}+20{\log }_{10}\left(\frac{P_2^{″}}{P_2^{\prime }}\right)+20{\log }_{10}\left(\frac{P_2^{\prime }}{P_3^{\prime }}\right)+\\ 20{\log }_{10}\left(\frac{P}{P_0^{\prime }}\right)+\mathrm{PN}\end{array}}$
where:

(P″₂/P′₂) stands for the “tube effect” of the microphone probe 26;

(P′₂/P′₃) stands for another “tube effect” of the residual ear canal portion;

(P/P′₀) stands for the diffraction effect of the subject's head and torso.

A compensation term COMP that contains all the above three corrections, the TFOE and the PN masking effect can be defined. This compensation COMP is subject sensitive and, for a large group, distributes as a standard or normal distribution. Therefore, the simultaneous recording of the NR_Mand the REAT for a large number of subjects will determine a global compensation COMP and a corresponding compensation per octave band COMPⁱ (as identified by the indicia ‘i’), respectively. Obviously, the same rationale could be considered by using third of octave bands, twelfth of octave bands or the like without departing from the scope of the present invention.

Knowing the octave band based compensation term COMPⁱ, a corresponding REATⁱ can be obtained. Further knowing that the NRR (slightly modified to correspond to selected octave bands) is obtained by:

$\mathrm{NRR}=10{\log }_{10}\sum _i{10}^{\frac{100+C^i}{10}}-10{\log }_{10}\sum _i{10}^{\frac{100+A^i-\stackrel{\_}{{\mathrm{REAT}}^i}+2{\sigma }_{\mathrm{REAT}}^i}{10}}-3$
where REATⁱ is a statistical average of REATⁱ;

Cⁱ and Aⁱ are octave band weighting factors, and

2σⁱ_REAT is the two-standard deviation factor showing that a 98% confidence level is considered.

Then the PAR can be derived as follows:

$\mathrm{PAR}=10{\log }_{10}\sum _i{10}^{\frac{100+C^i}{10}}-10{\log }_{10}\sum _i{10}^{\frac{100+A^i-{\mathrm{REAT}}^i}{10}}$

Also, the computation of a single number for the rating of a P-PAR using the in-ear device 12, or global personal attenuation rating, is statistically derived from the normalized (N) averaged compensation term COMPⁱ and individual noise reduction NR_indⁱ as being:

$P-\mathrm{PAR}=\stackrel{\_}{\stackrel{\_}{\mathrm{PAR}}}\equiv {\mathrm{NR}}_{\mathrm{ind}}^i+\aleph \left(\stackrel{\_}{{\mathrm{COMP}}^i},{\sigma }_{\mathrm{COMP}}^i\right)$
to give:

$P-\mathrm{PAR}=\stackrel{\_}{\stackrel{\_}{\mathrm{PAR}}}=10{\log }_{10}\sum _i{10}^{\frac{100+C^i}{10}}-10{\log }_{10}\sum _i{10}^{\frac{100+A^i-\stackrel{\_}{{\mathrm{REAT}}^i}}{10}}$

This permits the identification of physical and mechanical properties of one's ear canal from an acoustical measurement.

More specifically, the present invention teaches a method for assessing in-situ an acoustic seal of an in-ear device 12 using an apparatus 10 having a sound measurement device 28 connected thereto, as shown in the simplified flow diagram of FIG. 4 in which all steps, including optional ones, are illustrated. The method comprises:

• • a) calibrating the sound measurement device 28 by measuring a reference sound level with the sound measurement device 28 when being submitted to a sound source 24 and when being located in a close relationship relative thereto;
  • b) measuring a first sound level outside the ear canal 14 with the sound measurement device 28 when submitted to the sound source 24 and when located in a close relationship relative to the in-ear device 12 and outside the ear canal 14;
  • c) measuring a second sound level inside the ear canal 14 with the sound measurement device 28 when submitted to the sound source 24 and when engaged into and occluding the passageway 20 with the in-ear device 12 inserted inside the ear canal 14; and
  • d) assessing the acoustic seal of the in-ear device 12 by subtracting said second sound level from said first sound level.

The method further includes:

• • a1) assessing validity of said reference sound level by determining that the reference sound level is within a predetermined sound level amplitude range, if not step a) is repeated.

Typically, steps b) and c) are simultaneously performed using first 28 and second 30 sound measurement devices, respectively, preferably using the dual microphone probe 26 or the like. Accordingly, step a) includes calibrating first and second sound measurement devices by measuring first and second reference sound levels with the dual probe 26 when being submitted to a reference sound source and when being located in a close relationship or in an acoustic near field relative thereto. Step a) further includes determining a transfer function between the first and second reference sound levels.

Then, step a1) further includes assessing validity of the first and second reference sound levels by determining that the transfer function is within a predetermined sound level template range.

Step d) further includes indicating presence of acoustic seal when attenuation between the first and second sound levels is equal to or larger than a predetermined threshold value within a predetermined frequency range. As an example, the predetermined threshold value could be 11 dB (the NR, ANSI S3.19 test, within the 98% percentile) at about 250 Hz.

Typically, steps b) and c) are also simultaneously performed using first 28 and second 30 sound measurement devices, respectively. And step d) includes:

• • d1) assessing validity of the first and second sound levels by determining coherence there between preferably within a predetermined frequency range, if not steps b) and c) are repeated.

Determining coherence between the first 42 and second 44 sound levels includes determining that the second sound level 44 substantially linearly follows a contour of the first sound level 42, as schematically depicted in FIG. 1. For example, if the user happens to talk, cough or even swallow during the measurement of the second sound level 44, the latter would show acoustic noise induced by the user's voice, thereby not linearly following the contour of the first sound level 42, leading to a non-coherence between the two.

Furthermore, step d) includes assessing the acoustic seal of the in-ear device 12 by subtracting the second sound level 44 from said first sound level 42 and using the transfer function.

As described hereinabove, the assessment of the acoustic seal of the in-ear device 12 further includes using a compensation term (COMP) that relates to the type of in-ear device 12.

The calibration is typically performed before each test to ensure proper functioning of the dual probe 26 as well as the real-time reassessment of the transfer function thereof for accurate measurements.

The above detailed acoustic seal test ensures that the in-ear device 12 or earplug fits properly inside the ear canal 14 of the user, thereby providing a good acoustic seal.

A stability and reliability test that simply monitors the coherence of the transfer function (between external 28 and internal 30 microphones) in the 125 Hz octave band for example is easily performed by the apparatus 10 using the above method.

A similar method for assessing an acoustical performance of an in-ear device 12 using an apparatus 10 is shown in the simplified flow diagram of FIG. 5 in which all steps, including optional ones, are illustrated. The passageway 20 of the in-ear device 12 is typically adapted to receive an acoustic damper 46 therein, preferably inside a predetermined section or chamber 47 thereof having an enlarged diameter or the like. The acoustic damper 46 typically has a predetermined acoustic attenuation thereof. The method comprises:

• • a) calculating an acoustical performance of the in-ear device 12 with the acoustical damper 46 inserted in the passageway 20 thereof from a measured blocked acoustic attenuation obtained with the passageway 20 being occluded using a sound measurement device 30 selectively engaged therein and the predetermined damper acoustic attenuation.

Typically, the method further includes, before step a), the step of:

• • measuring a blocked acoustic attenuation of the in-ear device 12 with the passageway 20 being occluded using the sound measurement device 30 being selectively and alternately engaged therein and disengaged therefrom (or using a second sound measurement device 28 in the environment).

The predetermined damper acoustic attenuation is typically obtained through the following steps:

• • submitting a user wearing the in-ear device 12 with the passageway 20 thereof being occluded to a gradually increasing or decreasing a volume of a sound level of a predetermined frequency range to determine a first sound level threshold value at which the user start or stop hearing the sound;
  • submitting a user wearing the in-ear device 12 with the acoustic damper 46 inserted in the passageway 20 thereof to a gradually increasing or decreasing a volume of a sound level of a predetermined frequency range to determine a second sound level threshold value at which the user start or stop hearing the sound; and
  • calculating the predetermined damper acoustic attenuation from a difference between the first and second sound level threshold values or preferably, from a difference between first and second average sound level thresholds obtained from a statistically significant number of the first and second sound level threshold values, respectively.

Alternatively, the predetermined damper acoustic attenuation may be typically obtained through the same steps with reference to first and second sound threshold values determined with a gradually increasing or decreasing a frequency of a sound level of a predetermined volume range at which the user stop or start hearing the sound.

As the in-ear device 12 is typically for being worn by a user subjected to an environment with a predetermined noise exposure level, the method further includes:

• • b) calculating a filtered exposure level at an ear of the user would be subjected to when protected by the in-ear device 12 with the acoustic damper 46 inserted in the passageway 20 thereof inside the environment from the calculated acoustical performance and the predetermined sound exposure level.

Since a plurality of acoustic dampers 48, each having a respective predetermined damper acoustic attenuation thereof, may be considered, the method would, after calculating respective filtered exposure levels with the different dampers 48, further includes:

• • c) selecting one of the plurality of acoustic dampers 48 providing a corresponding filtered exposure level within or closest to a predetermined optimal exposure level range, typically between about 75 dBA and about 80 dBA.

Similarly, an exposure level range between about 70 dBA and about 75 dBA or between about 80 dBA and about 85 dBA would be considered acceptable. An exposure level above 85 dBA would be considered unacceptably insufficient and dangerous to the user for over exposure, while an exposure level below 70 dBA would be unacceptably overprotecting and also dangerous because speech and warning signals would essentially not be heard by the user.

To be more practical, similarly to the quasi-subjective evaluation of the REAT made to get the compensation term COMP and the PAR, an evaluation of the attenuation of an in-ear device in a full-block configuration (ATT_Full-block) with the passageway occluded with a plug 50 or the like and in a filtered or “combo” configuration (ATT_Combo) with predetermined acoustic dampers 48, such as plastic pieces of different densities or the like, occluding the passageway can be made to statistically assess the difference between the two configurations and therefore get the attenuation of the damper as follows:

${\mathrm{ATT}}_{\mathrm{Damper}}=-20{\log }_{10}\left({10}^{\frac{-{\mathrm{ATT}}_{\mathrm{Combo}}}{20}}-{10}^{\frac{-{\mathrm{ATT}}_{\mathrm{Full}-\mathrm{block}}}{20}}\right)$

As shown in FIG. 6, the above-described prediction of an in-ear device attenuation filtered with acoustic dampers 48 is obtained from the an in-situ assessment of the acoustic seal performance of the device 12 and the knowledge of the attenuation of the dampers 48 illustrated above.

For the filter selection, once the earplug 12 has been tested successfully, an acoustical filter 46 can be placed into the inner bore 20 (since the microphone probe has been removed) to let more sound get through. The filters 48 are, but not limited to, pure acoustical dampers that are properly selected according to some guiding rules where the protected exposure level is computed from the estimated attenuation of the passive earplug 12 and the time weighted exposure level of the subject.

Such an acoustic protection test verifies what protection the earplug 12 offers and allows to adapt this amount of protection to match the user's needs, in terms of providing the filtered predicted exposure level (F-PEL) of the individual with the earplug 12 when subjected to the specific noise environment.

The present invention further refers to a method for assessing an acoustical performance of an in-ear device 12 using an apparatus 10, as shown in the simplified flow diagram of FIG. 7 in which all steps, including optional ones, are illustrated. The method comprises:

• • a) measuring a first sound level outside the ear canal 14 with the sound measurement device 28 when submitted to the sound source 24 and when located in a close relationship relative to the in-ear device 12 and outside the ear canal 14;
  • b) measuring a second sound level inside the ear canal 14 with the sound measurement device 28 when submitted to the sound source 24 and when engaged into and occluding the passageway 20 with the in-ear device 12 inserted inside the ear canal 14 after being fitted thereto and before removal therefrom;
  • c) measuring a third sound level inside the ear canal 14 with the sound measurement device 28 when submitted to the sound source 24 and when engaged into and occluding the passageway 20 with the in-ear device 12 inserted inside the ear canal 14 after removal therefrom and reinsertion therein by the wearer thereof;
  • d) assessing a reference acoustic seal of the in-ear device 12 by subtracting the second sound level from the first sound level and an actual acoustic seal of the in-ear device 12 by subtracting the third sound level from the first sound level; and
  • e) assessing a rating of the in-ear device 12 by comparing the actual acoustic seal relative to the reference acoustic seal.

Step d) includes indicating presence of acceptable acoustic seal when the actual acoustic seal is within a predetermined range from the reference acoustic seal, for example within about 3 dB.

Step e) typically further includes comparing the obtained rating to a standardized rating value (NRR) corresponding to a type of the in-ear device 12.

When using the dual microphone probe 26, steps a) and b) are simultaneously performed using first 28 and second 30 sound measurement devices, respectively. Then step c) includes measuring a third sound level inside the ear canal 14 with the second sound measurement device 30 when submitted to the sound source 24 and when engaged into and occluding the passageway 20 with the in-ear device 12 inserted inside the ear canal 14 after removal therefrom and reinsertion therein by the wearer thereof, and measuring a fourth sound level outside the ear canal 14 with the first measurement device 28 when submitted to the sound source 24 and when located in a close relationship relative to the in-ear device 12 and outside the ear canal 12. The reference acoustic seal of the in-ear device 12 is assessed by subtracting the second sound level from the first sound level, and the actual acoustic seal of the in-ear device 12 by subtracting the third sound level from the fourth sound level.

Typically, the method includes, before step a), the step of:

• • simultaneously measuring first and second reference sound levels with the first and second sound measurement devices 28, 30, respectively, when being submitted to a reference sound source 24 and when being in an acoustic near field relative thereto, and determining a transfer function between the first and second reference sound levels.

Then, assessment of the reference acoustic seal of the in-ear device 12 is made by subtracting the second sound level from the first sound level and using the compensation term (COMP) and the transfer function, and the actual acoustic seal of the in-ear device 12 is made by subtracting the third sound level from the fourth sound level and using the compensation term and the transfer function.

A quick re-insertion test, corresponding to the post-curing sound level measurements minus the subject-fit P-PAR measurements, is also performed by the present apparatus 10 in order to assess the quality of the reinsertion of an in-ear device 12 from objective measurements before removal of the fitted device 12 and after re-insertion thereof by the user himself.

The above rating test of the apparatus 10 ensures that the earplug 12 offers at least the corresponding published NRR; thereby ensuring that the earplug 12 does not need to be derated (typically by a factor of two for earplugs, according to Occupational Safety and Health Association (OSHA) to account for discrepancies between in-field performance and laboratory certification measurement tests). For example, if the P-PAR (at 84% confidence level) is larger than the published NRR (about 17 dB for example), then the user belongs to the 98% percentile category of people having standard minimal required hearing protection and therefore not subjected to any derating rule factor.

Alternatives

As shown in FIG. 1, a simple apparatus 10 of the present invention could be used to quickly perform on-site in-situ acoustic seal performance test of in-ear devices 12 with simple handheld devices with simple user interface 32 as controllers 22′ instead of more versatile computers 22 that could allow to perform multiple different tests and measurements for different in-ear devices 12 with known normalized data stored therein.

Although the present method and apparatus for objective assessment of in-ear device acoustical performance have been described with a certain degree of particularity, it is to be understood that the disclosure has been made by way of example only and that the present invention is not limited to the features of the embodiments described and illustrated herein, but includes all variations and modifications within the scope and spirit of the invention as hereinafter claimed.

Claims

1. A method for assessing in-situ an acoustic seal of an in-ear device using an apparatus having comprising a first sound measurement device and a second sound measurement device connected thereto, the in-ear device having comprising a passageway extending therethrough, the passageway being in fluid communication with an ear canal of an ear when the in-ear device is inserted therein, the first and second sound measurement devices being removably engageable into the passageway, said method comprising:

a) calibrating at least one of said first or second sound measurement devices by measuring a reference sound level with said sound measurement device when being submitted to a reference sound source and when being located in a close relationship relative thereto;

b) measuring a first sound level outside the ear canal with the first sound measurement device when submitted to the sound source and when located in a close relationship relative to the in-ear device and outside the ear canal;

c) simultaneously measuring a second sound level inside the ear canal with the second sound measurement device when submitted to the sound source and when engaged into and occluding the passageway with the in-ear device inserted inside the ear canal;

d) assessing the acoustic seal of the in-ear device by subtracting said second sound level from said first sound level; and

e) assessing validity of said first and second sound levels by determining coherence between said first and second sound levels, and if not coherent, repeating steps b) and c) are repeated.

2. The method of claim 1, wherein step a) includes measuring a reference sound level with said sound measurement device when being submitted to a reference sound source and when being in an acoustic near field relative thereto.

3. The method of claim 1, further including:

a1) assessing validity of said reference sound level by determining that said reference sound level is within a predetermined sound level amplitude range, and if not within the predetermined sound level amplitude range, repeating step a) is repeated.

4. The method of claim 1, wherein step d) includes indicating presence of acoustic seal when attenuation between said first and second sound levels is equal to or larger than a predetermined threshold value within a predetermined frequency range.

5. The method of claim 1, wherein steps b) and c) are simultaneously performed using first and second sound measurement devices, respectively.

6. The method of claim 5, wherein step d) includes:

d1) assessing validity of said first and second sound levels by determining coherence between said first and second sound levels, if not steps b) and c) are repeated.

7. The method of claim 1, wherein step e) includes determining coherence between said first and second sound levels within a predetermined frequency range.

8. The method of claim 1, wherein determining coherence between said first and second sound levels includes determining that said second sound level substantially linearly follows a contour of said first sound level.

9. The method of claim 1, wherein step d) includes indicating presence of acoustic seal when attenuation between said first and second sound levels is equal to or larger than a predetermined threshold value within a predetermined frequency range.

10. The method of claim 1, wherein step d) includes assessing the acoustic seal of the in-ear device by subtracting said second sound level from said first sound level and using a compensation term relating to the in-ear device.

11. The method of claim 1, wherein step a) includes calibrating first and second sound measurement devices by measuring first and second reference sound levels with said first and second sound measurement devices, respectively, when being submitted to a reference sound source and when being located in a close relationship relative thereto.

12. the The method of claim 11, wherein step a) includes simultaneously measuring first and second reference sound levels with said first and second sound measurement devices, respectively, when being submitted to a reference sound source and when being in an acoustic near field relative thereto.

13. The method of claim 11, further including:

a1) assessing validity of said first and second reference sound levels by determining that said first and second reference sound levels are within a predetermined sound level template amplitude range, and if not within the predetermined sound level amplitude range than repeat step a) is repeated.

14. The method of claim 11, wherein step a) includes simultaneously measuring first and second reference sound levels with said first and second sound measurement devices, respectively, when being submitted to a reference sound source and when being in an acoustic near field relative thereto, and determining a transfer function between said first and second reference sound levels.

15. The method of claim 14, further including:

a1) assessing validity of said first and second reference sound levels by determining that said transfer function is within a predetermined sound level template amplitude range, if not step a) is repeated.

16. The method of claim 14, wherein step d) includes assessing the acoustic seal of the in-ear device by subtracting said second sound level from said first sound level and using said transfer function.

17. The method of claim 16, wherein step d) includes assessing the acoustic seal of the in-ear device by subtracting said second sound level from said first sound level and using said transfer function and a compensation term relating to the in-ear device.

18. The method of claim 1, wherein in step a), the sound measurement device is releasably supported by a supporting device mounted onto the reference sound source.