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100 Things #67: Measuring Active and Passive Noise Cancellation for Hearing Protection

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SoundCheck makes testing to standards simple by automating precise measurements into a single sequence. In this test sequence hearing protection devices can be tested to the ANSI S3.19-1974 standard to find their NRR rating. Sequences in SoundCheck make testing simple, with message steps instructing operators when interaction is needed with removing or placing hearing protection DUTs, for example. ListenInc.com features an extensive list of pre-written test sequences for any application including noise protection devices, hearing aids, bluetooth devices, and more.

Measuring Active and Passive Noise Cancellation for Hearing Protection

Try our hearing protection sequence for yourself

The hearing protection measurement sequence featured in this video is available in our sequence library.

Video Script:

Did you know that you can test hearing protection devices to industry standards using SoundCheck? Let’s take a look. 

Hearing protection devices are often measured to the ANSI S3.19-1974 standard which measures the Noise Reduction Rating or NRR of the device. This rating is a numerical representation of the device’s sound attenuation.

Our test sequence first measures the response spectrum of the unoccluded hearing protector test fixture, then makes a second measurement with the hearing protection DUT affixed. SoundCheck’s signal generator generates the pink noise stimulus while its Real Time Analyzer simultaneously records the A and C weighted noise spectrums. The unoccluded and occluded measurements are analyzed with a series of post-processing steps according to the ANSI S3.19-1974 standard. The final display shows the NRR numerical value, RTA spectra of the left and right side of the unoccluded and occluded hearing test fixture, average attenuation level of the DUT, and the standard deviation of the DUT on the test fixture.  The sequence prompts the user to recall previously saved unoccluded measurements and standard deviation values, saving time if the test fixture and DUT have been measured previously. When a new unoccluded measurement is taken, the user can save these measurements for a future data recall. 

We have many SoundCheck test sequences written by experts to  save hours of time writing them yourself. Most of these, including this NRR sequence, are free to use and come with well written step-by-step instructions.

Hearing Aid Frequency Response Test Sequence

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This sequence follows the ANSI S3.22-1996 standard method for testing the frequency response of a hearing aid. An equalized stepped sine sweep from 8 kHz – 200 Hz is played at a level of 60 dBSPL through the anechoic box speaker, and the output of the hearing aid is analyzed with the Heterodyne algorithm to produce a frequency response. Next, the HFA (High Frequency Average) is calculated by averaging the response values at three frequencies (1000, 1600, 2500 Hz). The HFA is then subtracted by 20 dB. Two post processing steps are used to find the upper and lower frequency points at which the response curve intersects this calculated value (HFA – 20 dB). These are the high and low frequency cutoff points.

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Hearing Aid OSPL 90 Test Sequence

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This sequence follows the ANSI S3.22-1996 standard method for measuring the OSPL curve, the HFA value, and the Max OSPL value for a hearing aid. An equalized stepped sine sweep from 8 kHz – 200 Hz is played at a level of 90 dBSPL through the anechoic box speaker, and a broadband response curve is analyzed through the hearing aid. Next, the HFA (High Frequency Average) is calculated by averaging the values at three frequencies (1000, 1600, 2500 Hz), and this value is checked with a limit step. The Max OSPL is calculated by finding the maximum point on the broadband response. A limit is also applied to this value.

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Release Time Hearing Aid Test Sequence

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This sequence follows the ANSI S3.22-1996 standard method for testing the release time of AGC (automatic gain control) hearing aids. A 2 kHz sine tone is played at 90 dBSPL for 1 second and then immediately drops to 55 dBSPL for 2 more seconds. A band limited time envelope (1.5-2.5 kHz) is created and then run through a post processing step, which calculates the release time. It does this by calculating the time it takes the device to stabilize within 4 dB of its steady level.

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