05 Oct Smart Acoustical Design Helps Listeners with Impaired Hearing
When designing your care facility, rest home, classroom, university lecture hall, amphitheatre or house of worship, consider incorporating acoustical design solutions that can improve how voices are heard within the room, especially for listeners with impaired hearing. According to Statistics Canada, 1.2 million Canadians reported hearing limitations in a 2006 survey—that’s almost 5 per cent of our population. Hearing often diminishes with age, a condition known as presbycusis, but other factors can lead to impaired hearing: long-term exposure to high noise levels, head trauma, aural disease and acoustic trauma, that is, exposure to a single loud noise event.
Speech Intelligibility for People with Hearing Limitations
To assess hearing impairment, audiologists test a person’s hearing ability at certain thresholds and compare the results with levels that are considered normal. Gauging speech intelligibility is more difficult.
“Background noise levels in care facilities should be similar to those in television or recording studios”
Speech intelligibility is a listener’s ability to recognize and comprehend speech. Room size, reverberation times and background noise levels can all affect speech intelligibility. A strong signal-to-noise ratio, which is the difference between a speaker’s voice and any existing background noise, is particularly important in discerning speech. When a low signal-to-noise ratio is combined with a reverberant room, speech intelligibility becomes even more challenging. For the elderly, limited speech intelligibility can bring about feelings of isolation and loneliness, and even lead to social withdrawal.
To support ideal speech intelligibility, care facilities should meet a noise criteria rating of 20 (NC20). In other words, background noise levels in care facilities should be similar to those in television or recording studios. Unfortunately, most care facilities don’t incorporate acoustical design solutions for listeners with impaired hearing.
Hearing aids can help, but most can’t distinguish useful sounds, like speech, from ambient noise. They increase the overall noise level but don’t improve the signal-to-noise ratio. Also, for listeners who wear a single hearing aid or have limited hearing in only one ear, locating the source of speech can be difficult, and this further affects speech intelligibility. Algorithms that distinguish ambient noise from speech have been developed, but hearing aids that feature such algorithms have yet to become widely adopted.
Acoustical Design Solutions for Better Speech Intelligibility
We recommend that room sizes be kept small to reduce competing sounds and ambient noise. Rooms should minimize bare walls and feature sound-absorbing elements including quality carpet and underlay, thick curtains or wall panels, and sound-absorbing ceiling tiles. In addition, signal-to-noise ratio can be further improved by installing voice-enhancing reflective surfaces; controlling building noise such as HVAC, elevators, electrical and plumbing; and limiting exterior noise with acoustically designed windows, doors and roofing tiles.
If possible, care facilities should avoid a central sound system, and instead employ an assistive listening system. When room size can’t be limited, create a setting that promotes small group conversations and separate each group with noise-absorbing dividers positioned at a minimum of 40 cm above ear level.
These solutions aren’t specific to care facilities, of course. To create better listening environments for people with hearing limitations, BKL consults on acoustical design for everything from houses of worship to conference centres. We’ve also developed resources for Public Works Canada, BC Family Hearing Resource Centre, UBC and other Canadian universities.
Our experienced acousticians can, when appropriate, develop universal, barrier-free access and follow guidelines such as the Canadian Hard of Hearing Association Guidelines for Persons with Hearing Loss. Regardless of the project, we work with clients to deliver comprehensive acoustical design solutions—and help bring a clear voice to listeners with impaired hearing.