When it comes to setting up the audio and video infrastructure in the classroom for these applications, there are several factors that need to be taken into account-especially when it comes to the audio.
In secondary education, there are typically two classroom environments: large auditoriums that accommodate hundreds of students, and smaller traditional classrooms with reconfigurable tables designed for 20 to 30 students. In terms of A/V infrastructure, auditoriums give instructors much more to work with. They are far more likely to feature a production system with a technician managing the microphones and video conferencing systems. In addition, components are generally permanently installed, with wires hidden away in walls and ceilings for a clean look.
Conversely, the infrastructure in traditional classrooms tends to be of a more ad hoc and portable nature. It is very unlikely there will be a production system, and if video conferencing is being used, it most often comes in the form of a mobile video cart that is rolled in and parked at the front of the room. However, for all their differences, both classroom environments have the same basic hardware requirements for video conferencing and webcasting: cameras to capture video and microphone systems and speakers to provide the accompanying audio through sound reinforcement.
Camera placement in auditoriums and traditional classrooms is fairly straightforward. Both should have at least two motorized pantilt- zoom (MPTZ) cameras: one in the back of the room to record the presenter and another in the front to record the class. In auditoriums (and in traditional classrooms if there is room), the cameras should be centered over displays located at the front and back of the room.
These displays show what is being transmitted and recorded, and by placing the cameras over them, students and the presenter will be looking directly at the viewers on the far end of the video conference. The only major factor when installing cameras is lighting. Ceiling lights must be out of the camera's field of view, or else they will trigger the camera's automatic gain control (AGC) to reduce the amount of light collected, which will result in a dark signal. This can be easily avoided by placing cameras higher on the wall and tilting them down.
Audio in the classroom, however, is much trickier. In auditoriums, wired ceiling microphones can be used over podiums to amplify the presenter's voice. However, before running microphone cable through the ceiling, there are a few things to consider.
Most importantly, installing ceiling microphones near heating or air conditioning vents will lead to audio noise and interference, which is a serious distraction in any learning environment. If there are any vents nearby, of course, a ceiling microphone is no longer an option. And even if the area is free of vents, with a ceiling microphone the presenter is tied to the podium for the entire class. To give them the ability to move about freely, the presenter should always have a wearable wireless microphone, even if there is already a ceiling microphone over the podium. The mixer in the auditorium should be able to switch between the two, or a push-to-talk/push-to-mute wireless microphone can be used.
Of course, the presenter won't be the only one talking during class. Students will also need to be heard when asking or answering questions, and it's not ideal to pass a handheld microphone around or to have students taking turns walking up to the podium. As a result, microphones will need to be distributed throughout the auditorium. It's easy to underestimate how many microphones will actually be required, but it helps to keep in mind that for optimal audio a microphone needs to be as close to the speaker as possible. Realistically, in a large auditorium it's going to take quite a few microphones to ensure that every student can be heard from where they sit.
If wired microphones are used for students, the focus is going to quickly shift from providing the best audio quality to restrictions on where cable for all of these microphones can be run. Wireless microphones are a better solution, because they can be placed where needed-not simply where it's easiest to install them. More specifically, push-to-talk/push-to-mute wireless microphones are ideal. Any time more than one microphone is active, the possibility for picking up unwanted noise increases. With push-to-talk/push-tomute microphones, all microphones in the auditorium will be muted except when they are being actively used.
To distribute audio throughout the auditorium, ceiling speakers are the best solution. These will typically have a 45-degree cone shape, so the height of the ceiling will determine how many speakers are needed to cover the room. To ensure total coverage, additional wall speakers can be installed in the room's corners. The audio level in any given area of the space should be 70 decibels (dB), which is a comfortable level for everybody. Any lower and students will have to strain to hear; any higher and it will seem loud. If the class is simulcast via video conferencing, the far-end and near-end audio levels should be equivalent in the mixer, allowing the local amplifiers to control the gains. For example, if the far-end's mics are louder, the mixer on the near end should have AGC to bring the volume level down for the room.
While traditional classrooms are smaller than auditoriums, sound reinforcement is still recommended for the presenter, as the acoustics of the room may not be very good-especially in rooms with low ceilings. Furthermore, instructors will appreciate the help it gives their vocal chords after a few hours of lecturing. A dual speaker located in the front of the room, with an amplifier to push the audio into the classroom, will do the trick. Ceiling microphones can be utilized in these spaces, but again, wireless microphones are preferred for their flexibility. In addition, mobile video conferencing systems that are rolled in will need to tie into the microphone system in the room. A wireless system makes for a nice easy installation without the mess created by wires.
When selecting wireless microphones for auditoriums or traditional classrooms, it's important to remember that while RF microphones are popular, they can also be impacted by interference. The UHF and VHF bands are crowded, subjecting wireless microphones using these frequencies to unacceptable levels of interference. An alternative is Wi-Fi microphones, which have several channels available to them at 2.4 GHz and 5 GHz. However, note that these frequencies are also crowded with 802.11 network wireless access points, so interference can still be an issue.
A better choice for a number of reasons is DECT. Wireless microphones utilizing this standard operate between 1.88 GHz to 1.90 GHz in a digital spread spectrum space. DECT microphones also provide exceptional ease of use, requiring minimal training for instructors and students. Unlike UHF and Wi-Fi products that need to be manually recalibrated to a new frequency when they encounter interference, DECT microphones automatically look for and change frequencies themselves.
A final consideration is the audio quality provided by the microphone system. Just because a system is wireless does not mean it has to compromise on audio quality. Solutions are available that not only provide HD audio, but also offer immunity to GSM noise from other wireless electronic devices that students will certainly have on hand, such as smartphones.
Unfortunately, audio often tends to be an afterthought in classroom video conferencing and recording. Keep in mind, however, that without video, viewers on the far end still have the audio to rely on. Without the audio, though, they are essentially left with nothing. It is worth taking the time to think through the type of microphone system to be used and microphone placement throughout the space, ensuring that participants on the far and near end of the lecture can hear every word comfortably.
is CTO and executive vice president of new business development for Revolabs, a leading provider of wireless audio solutions for unified communications, enterprise collaboration, and professional audio applications. He can be reached at email@example.com.