Introduction:

In a normal classroom situation it is pretty safe to say that if a child doesn't hear then they won't learn. Consequently if a child hears poorly then they will learn poorly, or to turn this around "the better they hear, the more they will learn". This is a fairly simple concept but one which has not come to the fore in NZ schools.

Classrooms:

Recent research has shown that our classrooms are not only very noisy places (both full and empty) but acoustically they are poorly designed. The acoustic features (reverberation, noise, and distance) of a room affect the intelligibility of speech and thus the speech perception by the child. A classroom acoustical standard has recently been formulated (AS/NZS 2107:2000), but few classrooms meet this criterion. The level of the teacher's voice in relation to the overall noise in the classroom is known as the signal-to-noise ratio. An acceptable ratio for children with normal hearing, is +15 dB S/N ratio (ie the teacher's voice is 15dB louder than the classroom noise), but for hearing impaired children this ratio needs to be higher. Very few classrooms reach minimal levels.

Learning:

It is obvious that to learn to speak a language fluently one has to hear the language clearly. As children begin to read and write, they learn that the written word is representative of the spoken word. It is now generally understood that the child needs to be able to break down and separate sounds in the spoken word (phonological awareness), in order to read successfully. The spoken sounds therefore have to be heard accurately. For children who are learning in a language which is not their mother tongue, good speech intelligibility is even more critical.

Listening is not something children are born with - it is a learned skill. As children develop they learn to focus on "interesting" acoustic signals and thus to screen out "non interesting" signals. This skill of listening selectively and filtering out unwanted noise improves with age and is fully developed only by the early teens. If a child is put into a situation where there is difficulty in perceiving speech, then long term they develop poor listening skills. When listening becomes a constant effort, then learning ability will be affected.

Children:

Most classrooms have a varied mixture of children who exhibit a range of performance, intelligence, maturity, and neurological status. Within this group will often he found children with fluctuating or permanent hearing loss (including unilateral losses), children with developmental disabilities, children with articulation disorders, children with

language or learning disorders, and children with auditory processing disorders. All these children generally have difficulty in attending to auditory information and many are labelled "poor attenders". Often the inattention stems from the fact that the teacher's voice is masked by surrounding noise or that the voice is not loud enough to reach audibility.

Sound Field Systems:

Sound field FM technology offers a way to amplify classrooms so that the teacher's voice is at a consistently loud level throughout the classroom, no matter where the teacher or the students are positioned. It does this through the use of wall-mounted speakers which are connected to an amplifier. The teacher wears a Madonna-style boom microphone which is wired to a small pocket-sized transmitter carried in a pocket or clipped onto a belt. The teacher's voice travels via a carrier wave to the amplifier; thus teacher mobility is not restricted. Positioning the microphone close to the mouth means the signal-to-noise component is maximised.

Collectively, results of studies carried out on the effectiveness of sound field amplification show significant improvements in the areas of better signal-to-noise ratios, quieter classrooms, less teacher voice strain, less classroom turmoil, improved academic achievement, improved speech reception and greater on-task behaviour. Although these systems are not the great cure-all for all educational problems, they will make the learning and teaching tasks easier.

Wally Potts
AUDIOLOGIST