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Introduction: What do educational audiologists do?
When polling people outside the field of hearing and speech about what they think audiologists do, the most common response is that they do something similar to speech therapy. The second most common response is that audiologists do “those beep tests”.
While school hearing screening is one of the many jobs an educational audiologist may do, they also perform a variety of other jobs related to serving students with hearing loss and sometimes those with normal hearing. Responsibilities can range from identifying hearing loss and making recommendations for hearing assistive technology to developing and executing hearing conservation programs or plans for improving classroom acoustics.
To mark Better Hearing and Speech Month, here we will discuss characteristics of acoustically good, bad, and ugly spaces in schools and classrooms. We will also offer occupational therapists, physical therapists, speech language pathologists and educators some suggestions to improve auditory access for students with and without hearing loss.
I can’t even hear myself think! Acoustical Challenges and the worst room in the school
If you were to tour a school, the loudest and most acoustically challenging room would likely be the lunchroom followed by the auditorium or gymnasium. These spaces are typically large and filled with hard surfaces like plastic or metal tables and chairs, wood or tile flooring, windows, etc.
The upside of the lunch room (for example) is that it can hold many students simultaneously and the hard surfaces are easy to clean and disinfect in the event of flying food. The downside is that the acoustic properties of the room (i.e., the factors or physics determining how sound is transmitted within a space) are highly unfavorable for speech perception.
Reverberation and noise can dramatically impair speech perception whether it be while talking to a neighbor at the lunch table or listening to the teacher in class. Reverberation refers to the amount of time (seconds) it takes for sound reflections to dissipate and become inaudible. Reverberation time is related to the size of the space so in larger spaces it takes longer for sound reflections to become inaudible.
Reflected sound can combine and interfere with incident sound (i.e., sound coming directly from a source or speaker), and this can adversely affect speech understanding.
The material contained within the space also plays a key role since sound is less likely to be absorbed when it strikes harder (think concrete block) compared to softer (think curtains or carpet) surfaces. Softer materials have a higher absorption coefficient, which is inversely related to reverberation time and positively related to speech perception.
Summary Point # 1: SMALLER SPACE + SOFT MATERIALS = LESS RELATIVE REVERBERATION = BETTER SPEECH PERCEPTION
Note: Sound absorbing materials such as acoustic tiles can help improve acoustics in spaces like the cafeteria or auditorium by reducing reverberation thus improving speech understanding.
Next, let’s address another factor known to dramatically affect speech perception – noise. There is a well-documented negative effect of noise on speech understanding and a synergistic effect of noise and reverberation together (e.g., Finitzo-Hieber & Tillman, 1978). The list of potential noise sources in schools is vast, but can be loosely classified into one of two categories – energetic or informational maskers.
Energetic maskers include fan or HVAC noise, chairs moving, paper crunching, etc. These maskers are believed to affect understanding by interfering with target signal encoding in the periphery. For example, if you are receiving important instruction while standing next to a generator, your brain wants to understand the message, but there’s too much energy in the noise and too little in the instruction for it to be heard. This masking is believed to arise from overlapping excitation on the basilar membrane in the inner ear.
The other type of noise competition, informational masking noise, is believed to have both peripheral (inner ear) and central (brain) contributions. It is thought to arise not only from physical interference, but also from difficulty separating out the signal of interest from the competing background and selectively attending to the wanted signal while ignoring the irrelevant masking noise (e.g., Brungart, 2001). An example of this is when you are trying to have a conversation in a space with a few other talkers nearby. Although both types of masking impact speech understanding, informational masking (when speech is both the target and the noise) can be more disruptive, especially in younger children (e.g., Hall, Grose, Buss & Dev, 2002; Leibold, Hillock-Dunn, Duncan, Roush & Buss, 2013).
Summary Point # 2:
NOISE = POOR SPEECH PERCEPTION
REVERBERATION = POOR SPEECH PERCEPTION
NOISE + REVERBERATION = POOREST SPEECH PERCEPTION
Summary Point # 3: All noise was not created equal and some noise sources can be eliminated very economically… Ask your neighbor to stop talking when the teacher is speaking!
To promote good speech understanding, remember the word “SOFT”. Softer materials, equipment, and competing speech will prioritize access to the teacher’s voice and instruction over competing background noise. Now that we’ve established how acoustics and noise influence the fidelity of the signal that’s accessible to students, let’s review the guidelines for creating a better environment for listening and learning and strategies for addressing acoustical challenges.
Top of the Class! Acoustical Benchmarks!
The cafeteria and gymnasium may not win any awards for acoustics, but let’s consider classrooms. Guidelines from the American National Standards Institute (ANSI, 2010) suggest that ambient noise levels in unoccupied classrooms should be 35 dBA or less and reverberation time should be 0.6 seconds or less. Research in occupied classrooms generally finds elevated ambient noise levels (~ 60 – 75 dB A) and longer reverberation times (e.g., Crandell & Smaldino, 2000; Knecht, Nelson, Whitelaw, & Feth, 2002). Higher noise levels tend to be associated with younger grades.
For children with hearing loss, it is recommended that the signal (teacher’s voice) be more than 15 to 20 dB louder than the room noise and that reverberation time be less than 0.6 seconds (ANSI, 2010). However, measurements in real-world occupied classrooms typically show reverberation times exceeding 0.6 seconds and signal to noise ratios (SNR) ranging from – 7 dB to + 4 dB*, conditions that comprise speech understanding and learning (e.g., Knecht, Nelson, Whitelaw, & Feth, 2002; Crandell & Smaldino, 2000).
*SNR represents the level of the signal of interest relative to the background noise; -7 means the teacher’s voice is 7 dB quieter than the competing background, whereas +5 means his/her voice is 5 dB louder.
So what do we do about it!?
Some of the ways we can optimize the educational environment for students with hearing loss is through the provision of hearing technology. Some students wear personal hearing aids which helps audibility, but not necessarily the challenges from noise and reverberation described earlier. Wireless technologies such as FM or ROGER can pick-up the speech signal from a microphone placed within inches of the teacher’s mouth and transmit it to a receiver (coupled to a hearing aid or cochlear implant). That conveys the augmented signal to the device, effectively providing a boost that helps overcomes the noise, reverberation or distance from the teacher.
Strategic seating can also be used to improve visual access to speechreading cues from the lips and face, which can significantly improve speech understanding compared to listening alone (e.g., Macleod and Summerfield, 1987). Closer proximity to the teacher not only allows the student to gain access to visual cues but also reduces degradation of the acoustic signal with increased distance+, which especially impacts children without access to remote wireless technology like FM or ROGER.
Advocacy skills can also be an important tool for students regardless of hearing status. Asking for repetition of a missed message is critical in ensuring understanding of classroom content and teacher instructions.
Finally, as mentioned above room modifications can be considered to improve an acoustically challenging space.
Note: For every doubling of distance, there is a 6 dB reduction in signal intensity.
If you have questions about a space at your school, talk to an audiologist about obtaining measurements and making recommendations for improving acoustics and speech access for enhancing student learning!
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Top 5 Recommendations when working with students to optimize communication:
- Reduce sound ‘competition’= Give instructions in a quieter space such as entrance to the gym instead of inside the gym.
- Promote self-determination and advocacy= Model how to politely ask for repetitions and request noise makers to desist. Begin to encourage students to increasingly advocate for themselves.
- Optimize input= Speak clearly and facing students (not the chalkboard) so they can take advantage of visual cues that assist with understanding.
- If there is an FM/ROGER or loudspeaker system, use it! This means you!! With every doubling of distance, the level of the speech signal drops by 6 dB!
- Add soft materials to acoustically challenging rooms to reduce reverberation and improve understanding!
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Authors:
Andrea Dunn, AuD, PhD, Assistant Professor, UNC, Chapel Hill, NC; Educational Audiology Consultant; NC Department of Public Instruction, Exceptional Children Division
Martha Mundy, AuD, Associate Professor and Coordinator of Au.D. Studies, UNC, Chapel Hill, NC
