Communication quality : a conceptual approach focusing on classroom assistive listening devices

Sammanfattning: In a classroom an assistive listening device (ALD) is a system of external microphones that transmit sound from a sound source directly to students' hearing aids. An ALD can be a microphone close to the mouth which transmits a voice directly to listeners' hearing aids. An ALD can also be a microphone placed centrally and used by several persons at the same time. Sound quality of a listening device can be described as sound-transmission quality where maximal quality is no difference between input and output. From a wider perspective, this output can be the perceived quality of speech where a high speech quality matches given expectations, demands and necessaries. A focus on participatory learning environment in Swedish hearing impaired classes has brought out new perspectives on ALD solutions. The purpose of the studies reported in this thesis was to develop a methodical framework for the evaluation of classroom ALDs. As a basis for the evaluation of ALD communication quality is suggested. Communication quality is an extension of the sound quality concept which emphasizes student participation and peer interaction. As a pedagogical parallel, sound quality emphasizes a more cognitive view of learning whereas communication quality emphasizes participatory learning. By using room acoustic modelling and auralization in listening tests it was possible to evaluate aspects of room acoustics, signal processing techniques, speech and masking signals, and binaural advantage. A self-assessment approach was also used and a questionnaire was developed based on the Speech, Spatial and Qualities of Hearing Scale (SSQ). The studies found that students in hearing impaired classes prefer using only their hearing aids over using an ALD. Retrieving information about the acoustic environment was important aspects. Also observed was that when comparing different ALD solutions microphone distance is of importance. Listening effort correlates with hearing loss rather than with using different technologies. Today's hearing aids offer the best communication quality but it is also apparent than ALDs are preferred by students in some situations. Determining the combination of design and ALD function which can best benefit students is needed. The methodological framework described is promising for continuous studies developing and assessing classroom ALD.