中文摘要 / Summary in Chinese
Lecturers around the world have long resorted to technology in order to make their voices heard across a classroom without hurting their vocal cords. The use of portable sound systems is common. Such modestly-priced devices often have many additional capabilities, and a long battery life, allowing smooth communication and providing clear sound output, and low levels of audio feedback.
Portable sound systems are particularly useful for those lecturers needing to demonstrate the use of computer software during lab sessions. While wired microphones might seem an obvious option for most lecturers, those who teach in a computer lab are often busy handling a mouse, a keyboard and a touchscreen, while demonstrating to students how to use particular software applications. As a result, wireless sound systems might be a better choice for those lecturers.
Many outsiders might think a clip-on microphone would be useful in such a scenario. But an even better choice is a portable ultra-high frequency (UHF) wireless system, since the microphone can be adjusted and placed much nearer to the lecturer’s mouth, and the respective voice amplifier can be placed closer to the students than normal classroom speakers. In Chinese, a device of this kind is colloquially known as a ‘small bee’ (小蜜蜂).
This type of system supports easy and uninterrupted pairing of both devices involved (Figure 1) regardless of each device’s location in the classroom. It is also helpful in reducing audio feedback, as it is easier to position the loudspeaker away from the microphone.
Generally speaking, an audio feedback loop occurs when a microphone gets too close to a loudspeaker to which it is connected, as the sound emitted by the speaker is passed into the microphone again, amplified even further and then passed back into the microphone, creating unpleasant sounds. High-quality sound systems should already include features to reduce the level of audio feedback.
A UHF system was put into use for 2 weeks at a 100 square-metre computer lab at IFT, under normal classroom conditions (Figure 2). The result was satisfactory because lecturers could use both hands to perform demonstrations while the sound output was crystal clear and noise free. The system’s battery ensured at least 3 hours of uninterrupted voice transmission and output before recharge was required.
A portable device like this could be a godsend for the vocal cords of lecturers engaged in back-to-back lectures. After the testing of the ‘small bee’ sound system in a lab classroom, the author has noted its performance, and the pros and cons are summarised as follows:
|Crystal clear voice.||—|
|Highly portable; lightweight.||Could introduce extra physical stress to the user, namely on the back of both ears, especially for teachers who wear glasses, after usage periods of 2 or more hours.|
|Battery can last for at least 3 hours for uninterrupted use.||Battery charging up to its full capacity may require 2 to 3 hours for each unit.|
|Loudness is acceptable when the volume is turned to the maximum.||The maximum volume may not be high enough for the lecturer to be heard across the classroom if many students start to talk among themselves.|
|Feedback is reduced to a minimal level, even if the microphone gets too close to the amplifier speaker.||—|
By IFT Lecturer Simon Lei