It would be great if all that a presenter had to do were to talk louder to make sure that everybody can hear. But hearing a loud voice that travels back into the room is unusual. If they did, the people at the front of the room would probably be disturbed with too much loudness. However, the volume is not the only thing that affects audio quality. A variety of factors influence the sound quality, but two primary considerations are as follows:
- Distance between the audience and the speaker
- Noise from the room such as whispers from people, HVAC systems, and shuffling paper
Such factors make it hard for people to hear, no matter how loud the presenter is trying to speak.
We do have to contend with noise, in addition to distance. All the rooms are soundproof. There are a variety of items that produce this noise: projector or computer fans, building systems (HVAC, plumbing), people moaning or shuffling papers, outside noise (traffic, construction), etc. The mixture of such sounds is called background noise or ambient noise.
The loudness of the voice needs to be substantially above the noise of the room for proper hearing. An adequate distancing between speech and background noise is around 15dB. Let’s assume, for example, the ambient noise level in a meeting room above is 45dB. The narrator talks at 60dB, and her voice is 15dB higher than the noise in the room, which makes everyone to understand her speech.
The house, though, has noisy fans that just turned on, so the ambient noise is 50dB now. Now with just 10Bb of separation to the speaker from the background noise, intelligibility is starting to suffer. At this point, while the people at the front, close to the speaker, would be able to hear, it would be tough for the people seated 16 feet from the presenter in the previous example to understand. That’s because being farther away from the speaker; the speech will begin to mix in with the background noise. It is similar to sitting in a crowded restaurant so that you can hear the person next to you, but you have trouble understanding people around a bigger table.
The installation of sound-absorbing materials such as ceiling tiles and wall panels will reduce the room noise. But this can be a costly endeavor. The best way to counteract the effects of distance and room noise in many multipurpose rooms is by a minor amplification of sound.
In physics, the Inverse Square Law says that every time the distance from the speaker to the listener doubles, sound decreases by 6 decibels (dB). The standard presenter’s voice measures 60dB from the listener at a distance of 4 feet. Double the distance to 8 feet, and reduce the volume to 54dB. The capacity is 48dB, at 16 feet. The distance effect on the sound is the reason we huddle around speakerphones and try to get closer to the speaking person. But that isn’t a feasible option at a large group conference.