This article will cover some general concepts around audio and acoustics. Generally we will examine reverberation and some general rules of thumb when it comes to optimizing your space before you start thinking about specific technologies to implement.
We will covers general audio concepts including:
- Acoustics (Reverb Issues)
- Signal to Noise Ratio (Noisy Rooms)
- Microphone Concepts
- Speaker Concepts
- Acoustic Treatment Specialists
For information regarding Audio Processing and Acoustic Echo Cancellation, please refer to the Zoom Rooms Audio Guidelines with specifics around Zoom Rooms and technical processing.
Acoustics (Reverb Issues)
Acoustics is a very important aspect for any conference room. Reverberation in a room will always degrade the sound quality and intelligibility of a conference participant. Treatment (adding soft and non-flat surfaces) will allow the microphones to hear the source more directly and diminish the sound artifacts that may be residual in the room because of reverberation caused by hard surfaces such as walls, ceilings, glass windows or conference room tables. RT60 is a measurement expressing the time during which a sustained sound drops by 60dB after the sound stops. A general rule of thumb is to make sure that there is no more than half of a second of reverb time based on RT60.
If the reverb time is higher than half of a second in a space, another calculation can be applied for room treatment. Take the square footage of the floor of the room with an average ceiling height. 40% of that square footage should be the general square footage of treatment or non-hard surfaces in the space. There are many manufacturers of acoustic paneling, ceiling baffles etc. that can be placed on the wall to mitigate reverberation. This tends to be expensive depending on how heavily a space needs to be treated which may be the case. Before consulting a specialist, think about soft objects you can add to a troublesome space such as book cases, overflow soft seating, carpeting, canvas artwork or plant life which will all dampen reverberation.
Signal to Noise Ratio (Noisy Rooms)
Signal to Noise Ratio is the relationship between the noise floor or ambient state of the room as compared to the actual volume of the desired audio we are trying to capture and transmit. Ideally, the noise floor in any space is no louder than about 40 dB SPL A-weighted. If we assume that a normal speaking voice is about 70 dB SPL A-weighted, then our signal to noise ratio is 70 minus 40, equaling 30 dB which would classify this room as an optimal candidate for conferencing. The noise floor in a conference room can be affected by things like heating, air conditioning & ventilation (HVAC), elevators, building mechanics, open sales offices or trading floors, traffic, trains, planes etc. What action can you take? When designing room layouts and you can anticipate issues, absorption and sound-proofing materials will be the best approach.
- Double-paned glass between a room and a busy street
- Heavier wall and ceiling tiles with a higher transmission coefficient
- Wall construction from floor to infrastructure ceiling (above ceiling grid)
- Sound absorbing ceiling tiles
Microphones take energy and convert it from one form to another. This is also known as a transducer. In our scenario, we are taking acoustic energy and turning it into electrical energy to produce digital data. In a video conferencing scenario, there really are two different use cases when it comes to audio capture in a space.
There are a few mic configuration varieties:
- (a) All microphones are part of the room listening experience with some processing to optimize the experience
- (b) Presentation microphones are prioritized for local voice lift and primary audio into the conference system. Additional room mics may exist alongside in this scenario
- (c) is a hybrid of the two typically seen in boardrooms with long gooseneck microphones for each seated participant utilizing the 3 to 1 rule where for every participant to mic distance of one there will be a relative distance of three between mics. This invasive model is a bit outdated.
Generally, it is desired that the video experience be seamless and invisible. Ideally participants do not know the technology is there. (a) for conference rooms and (b) for presentation spaces are the preferred design approach.
In the conference room, new array microphone technologies can now simplify and steer microphone pickup with more directive technology and allows the microphone experience to be unnoticed instead of invasive. Close proximity to microphones is not usually preferred. More and more that scenario is not beneficial with typing, whispering, eating as a factor. If I am in a conference room, the last thing I think I would want is to put my ears right in front of everyone’s computer keyboard, tapping fingers etc. I would rather hear the room as a whole. This is a more natural room listening experience.
Speakers are another transducer that takes the digital data, converted to electrical energy and converts it back into acoustic energy so that we can hear it. Speakers should be thought of as the mouths of the video participants.
The conference phone in the center of the table has historically been the point of focus. This has translated into some room designs as a speaker/mic on the table with video participants on the wall. This is an unnatural experience, but in most all cases, the mic/speaker must function as both for it to work properly as those devices (such as Poly Trio, Crestron Mercury, Logi Group etc.) have their own internal processing.
In a lot of Zoom designs, we try to put speakers as close to the people on video as possible as that is where we aim our attention. We are, after all, talking and listening to a face on-screen which are just a recreation of their image captured by a camera. The technology becomes invisible. With that, we need to create a natural environment. In smaller huddle rooms, an all in one soundbar emits sound nicely while combining microphone and camera. In a standard conference room, a pro soundbar mounted near the displays works best. For larger conference rooms, we run into the issue of lacking uniformity of the sound system in the space which can be problematic. In much larger systems we it is preferred to distribute the audio so that all participants continue to have a good experience listening without great volume fluctuation depending on the seat location.
Acoustic Treatment Specialists
Here is a small list of companies that will assist you with sound treatment in your space to optimize the Zoom Rooms experience. Please feel free to reach out directly for consultation.