Subject Product - Disability Access Analysis
2.4. Accessibility Analysis
2.4.1. Accessibility for Hearing Loss
Because the primary purpose of the Subject Product is to receive and deliver auditory information, accessibility for people with hearing loss is the primary accessibility issue for this product.
Providing volume control is the first accommodation for people with mild hearing loss. Section X.Y.Z of the Subject Product Specification requires that receive volume be adjustable in 3 dB steps from the nominal. Section X.Y.Z.2 specifies a 24 dB dynamic range for the receive volume, ±12 dB from the nominal setting. This meets the FCC Hearing Aid Compatibility requirement of an adjustable volume with a maximum of +12-18 dB over nominal. However, it falls short of the +20 dB advocated by some consumer groups and supported by the Access Board in its Rulemakings for Section 255 and 508. The FCC overturned this requirement for Section 255 and the Section 508 requirement does not directly apply to this product.2
Recommended Action: Additional volume adjustment is probably not technically feasible in a product of this type. However, if a means to provide additional volume range, up to +20 dB, were feasible, it would be a very appealing accessibility feature.
Of equal importance to volume adjustment is the issue of auditory coupling to the ear. While people with hearing loss require additional volume in order to hear, coupling the existing volume level more effectively into the ear can accommodate them just as well. Acoustic engineers know that effective increases of 10-20 dB are to be gained through acoustic coupling, totally independent of the raw sound power.
Recommended Action: The effectiveness of the acoustic design of the product and its coupling loss as compared with similar products should be documented and presented as part of the product’s accessibility analysis.
The noise cancellation specification, Section X.YY.A, X.YZ.B and X.ZA.A is a positive feature for people with hearing loss. It is common for people with hearing loss not only to loose amplitude sensitivity but also dynamic range. This is commonly caused by the loss of the function of the hairs in the inner ear, which contribute significantly to extending the dynamic range of human hearing. These hairs actually change position with sound amplitude, either increasing or decreasing the sensitivity of hearing. The effect of the loss of dynamic range is to reduce a person’s ability to understand conversation in the presence of noise. Hence, features which improve the signal to noise ratio will provide a benefit to people with hearing loss.
For users with hearing loss which volume adjustment cannot accommodate, compatibility with hearing aids and assistive listening devices is required. ANSI C63.19 establishes tests
2 Throughout the report recommended actions and items requiring further investigation are highlighted like the item below. Each recommendation is thus highlighted when it first appears but it may be amplified or more fully explained in succeeding sections of the report. All of the recommendations and follow-up items are summarized at the end of the report.
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