4. Microphone Solutions

For visual communication and collaboration it is a fact that the sound quality is even more critical than the video quality. In fact, it may be possible to have some kind of communication with a far end part experiencing a bad picture quality provided that the sound quality is good. Unfortunately, in the opposite situation with good video quality and bad sound quality it is impossible to have a useful outcome. Therefore, microphone and audio solutions must be considered carefully. As a basic rule one should always remember that microphones are 'stupid' in the sense that useful sound is not separated from useless noise.

Tabletop microphones

When a small group of people are gathered around a table, the most common solution used is a tabletop microphone, as shown in the pictures below.

The tabletop microphone may be a reasonable good solution provided that:

1. there are not too many persons around the table, so that they may all be seated with almost equal distance to the microphone, as demonstrated in the right picture. If the distance becomes too large, there could be used an additional microphone.
2. the microphone is not centered at the table, but instead placed at one of the ends, as demonstrated in the right picture. A tabletop microphone is normally directional , i.e. it is more sensitive in a specified angular section. The input signal from a person behind the microphone may be too low to be detected. The microphone should be placed so that all persons will be covered by it.

However, tabletop microphones introduce challenges with respect to noise. The placement on the tabletop implies sensitivity to different kinds of noise from the surrounding people (irrelevant small talk, paper bending, moving of coffee cups, watches and pieces of jewelry hitting the surface, unconscious knocking with fingers, pens etc.). In the room where the noise is actually made, the people will hardly hear it, as we are more or less accustomed to these kind of sounds. But for people at the far end part the sounds become irritating and often untenable, and the noise may drown out the speech. Some of these problems with mechanical transferred noise from the surface of the table may be reduced by using a small and soft pad under the microphone. The pad should be less than the area of the microphone. However, strong dicipline with respect to own behaviour is essential for people participating in a videoconference.

Ceiling-mounted microphones

Microphones mounted in the ceiling are often used in 'passive' rooms designed for receiving (as opposed to hosting/broadcasting) video lectures, i.e. rooms where students receive lectures by a videoconference. Ceiling-mounted microphones provide an effective method for picking up questions and comments from the audience (all of whom are roughly at the same distance from the microphones), without the hassle of tabletop microphones or wireless mics.

On the left-hand picture we see two ceiling-mounted microphones, which in this case covers a meeting table for 10 - 12 persons. On the right-hand picture one of the microphones is zoomed in.

Ceiling-mounted microphones do have several pitfalls, however: they are susceptible to ambient noise from ventilation systems, lighting armatures, noise from adjacent rooms and stepping sounds from the floor above. Also, if the walls in the room are very acustically reflective, the reflections are easily picked up by the ceiling-mounted microphones. The main challenge with ceiling-mounted microphones is fine-tuning involved to make them pick up sound from the audience, while suppressing unwanted ambient noise from ventilation fans etc. As explained earlier, it is important to realise that sound quality is more important than picture quality in a video conference.

In this picture we see a lecturer standing in front of a whiteboard with a ceiling-mounted microphone over his head. This is not an optimized solution; if a room is designed for hosting/broadcasting lectures, ceiling-mounted (and tabletop) microphones will not pick up the lecturer's voice properly as he is moving around and turning his head in different directions. A lecturer will need to use an auxiliary microphone - a so-called wireless microphone.

Wireless microphones

For a lecturer a wireless microphone is normally the best solution. As shown in the picture below, we see that a wireless microphone system consists of three fundamental parts:

a microphone recording the voice of the lecturer, a transmitter, which is connected to the microphone by a thin cable, and a receiver that receive signals from the transmitter and sends the signal to an audio system or a videoconferencing codec.

There are two types of wireless microphones (often denoted 'lavaliere' microphones):

1. attached to the lecturer's clothes, as demonstrated in the left-hand picture below, and
2. attached to the lecturer's cheek, as shown in the right-hand picture below,

Wireless microphones attached to the cheek work the best, because this type of microphone gives a consistent sound level/quality, no matter how the lecturer's head is orientated. The disadvantage is that this solution might be quite expensive. Wireless microphones attached to the lecturer's clothes are less suitable because the sound level decreases when the lecturer's head turns away from the microphone. This type of microphone is also very susceptible to handling noise (from clothes etc). But this type is often less expensive and, normally, a better solution for a lecturer than a ceiling-mounted or tabletop microphone.

For both types of wireless microphones, the transmitter is attached to the lecturer's belt or pocket, as demonstrated in the left-hand picture below. The cable between the microphone and the transmitter should be hidden inside the shirt to avoid destruction of the cable/microphone/transmitter (see the right-hand picture below).