BACKGROUND NOISE:

Anything that interferes with the reception of the signal which may include people talking, heating or cooling systems, computers, traffic, televisions, playground noises, hallway noise, wind etc.

SIGNAL TO NOISE RATIO:

The relationship between the input signal (the important signal such as speech) and the background noise.

Individuals with normal hearing abilities need a signal to noise ratio of +6 dB for reception of intelligible speech (Flexer, 1994).

Individuals who present with hearing impairment need a signal to noise ratio of +20 dB for the reception of intelligible speech (Flexer, 1994).

Due to reverberation, noise and changes in the teacher’s position, the average classroom presents with a signal to noise ratio of approximately +4 or +5 dB. This can even get as low as 0 dB which is even less than what is suitable for normal hearing children (Ross, 1992).

IMPROVING CLASSROOM ACOUSTICS

Modifications to reduce noise levels:

Classroom Modifications

1. Room dimensions

• floor/ceiling areas (enormous impact on noise levels in the class- Ross, 1991)
• ceiling < 12 ft height?
• acoustical tiling or plain plaster
• carpeting, wood, tiled floors, linoleum
• walls - brick, plaster, wood
• windows - draperies?
• chalkboards, corkboards
• other surfaces, ie. Felt
• doors- solid, sealed with weather stripping and well maintained

2. Classroom Location

• on opposite side of school from gymnasium, cafeteria, bathrooms
• away from playground, traffic, train tracks, etc

3. Classroom Style

• closed concept
• open concept
• split grade
• portable classroom

4. Soundfield Amplification?

5. Classroom composition

• numbers of children
• make up

 6.  Use assistive listening devices

• can reduce noise and reverberation, and important to improve signal to noise ratio and reduce effects of distance
• distance effects are reduced with FM transmitter microphone placed 4-6 inches from the teacher's mouth
• placement of microphone is critical
• this improves the signal to noise ratio as the teacher's voice will be louder than the classroom noise
• the signal will be 15-20 dB more intense through the transmitter microphone than through the hearing aid microphones. 

NOTE: FM systems allow for the presentation of FM signal only, hearing aid only (FM off) or HA + FM. The child's hearing aids should always be on (HA/FM) -- this is the only way the child is able to hear him/herself and monitor his/her own productions and maintain contact with his/her environment (importance of social learning).

• different systems would be recommended for different cases, however the overall goal is to improve the auditory signal for the listener

note: FM systems do not remove background noise; they provide the salient signal at levels more intense than the noise

Why use an FM System?

• to improve the ability to receive auditory information
• we know that a hearing loss precludes the perception of some speech sounds
• distance from the speaker, noise in the classroom and reverberation will all decrease the auditory information available
• the child will probably have some language delay that interferes with the ability to comprehend the speech that is heard

A child with any degree of hearing loss who must function under aversive listening conditions needs an assistive listening device.

Every attempt must be made to improve listening in the auditory-verbal learning environment of the classroom.

• the acoustical considerations of the classroom and the child must be managed by an audiologist or a professional knowledgeable in FM system devices and children who have a hearing loss.

Maximizing Amplification and Assistive Listening Devices in the Classroom

The audiologist should be involved in the team. This is critical for optimal use of the technology

1. Understand the child's hearing aids and assistive listening devices.

• switches-

m/t/o (m=on/t=on, telephone setting/o=off)
1T2 (1=program 1/T=telephone/2=program 2)

• how should they be set? On/off for FM use. Boot switches.
• volume setting (set by audiologist-always the same)
• batteries where?
• FM batteries/charging

2. Learn basic trouble shooting techniques.

• over 50% of amplification devices are not working at any given time.
• perform the LING 6 sound test
• do a listening check of the system with a stethoscope every morning
• ensure the signal is strong, free from distortion and free from interference (be aware of interference from cellular phones and pagers; be aware of other children in the school who may be using an FM and ensure it's a different transmitting frequency)
• know to charge FM batteries at end of the day or teach the child to be responsible (easy/foolproof)
• have equipment to troubleshoot
• stethoscope
• battery tester
• earmold tubing blower
• have spare equipment available(boots, cords, FM System etc.)if something breaks down (again critical to maintain relationship with audiologist)

3. Feel comfortable with the hearing aids and assistive devices and know how to use them appropriately.

• Know when to turn the FM on or off.
• Know where to place the microphone. (If a boom microphone is used, this step is not necessary)
• implement a strategy or preliminary test when the child puts the equipment on to determine if it’s on (Get the child's attention by calling his/her name and then ask a simple question such as where do you live? Avoid asking yes/no questions).
• maintain contact with an audiologist and/or the child's therapist who may be available to assist with troubleshooting over the phone.