Meeting Room Acoustics - AvNetwork.com

Meeting Room Acoustics

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Meeting space planning tends to focus on the visual element. Poor acoustics — which can negatively impact communication — are typically discovered only after the room is complete. Fixing acoustic problems can be costly and time-consuming.

When planning and equipping meeting spaces, technology managers need to pay
attention to the following guidelines during the design phase.

1. MAXIMIZE SPEECH INTELLIGIBILITY

The energy level and frequency content of sound reflections within a room have a major impact on speech intelligibility. The room should be neither too “dead” nor too “live.” A room that creates no reflections (like an anechoic chamber) makes it difficult to project natural speaking voices from one end of a conference table to the other. If the room’s surfaces create too many reflections, the consonants of speech sounds lose articulation, and communication suffers. In addition, the ability of participants to localize where the speech is coming from is impeded.

Use wall and ceiling finishes that naturally amplify sound within the meeting space, while at the same time reducing reverberation. Rooms with too many hard surfaces like glass, stone, or concrete will have too many reflections, and are likely to suffer poor speech intelligibility.

“RT60” is the time it takes for a noise to dissipate by a factor of 60 decibels. An ideal RT60 for meetings rooms is between 0.8 and 1.2 seconds (depending on the size). An acoustical consultant can help provide the right balance of absorption, reflection, and diffusion, creating an environment of clear communication and free flowing discussion.

2. KEEP OUTSIDE NOISE OUTSIDE

Noise that is generated from outside the meeting room can disturb the meeting and make it necessary for talkers to raise their voices. To minimize the transmission of sound from adjacent spaces and the outdoors, meeting rooms should be acoustically isolated.

Sound Transmission Class (STC) is the rating system used to describe how well building partitions minimize noise from adjacent spaces. STC is a single-number rating of a partition’s ability to resist airborne sound transfer at the frequencies 125 Hz to 4 kHz. In general, a higher STC rating blocks more noise from transmitting through a partition. For meetings rooms, partitions should have an STC of at least 55.

Some general rules of thumb:
• Optimal isolation requires that a wall extend to the structural deck. Walls extending only to a dropped ceiling will result in inadequate isolation.
• Sound will travel through the weakest structural elements, which, many times, are doors, windows, or electrical outlets.
• When the mass of a barrier is doubled, the STC rating increases significantly (approximately 5 dB).
• Installing insulation within a wall or floor/ceiling cavity will improve the STC rating by about 4 to 6 dB.
• Metal studs perform better than wood studs. Staggering the studs or using dual studs can provide a substantial increase in isolation.
• Increasing air space in a wall or window assembly will improve isolation.
• Double glazed windows will provide better protection than single glazing. For high external noise, double windows with a large air gap (25 to 100 mm) are even better.

3. MINIMIZE INSIDE NOISE

Noise inside the meeting room is generally a result of HVAC or other equipment (like projectors) producing noise within the space. A window-mounted air conditioner is the obvious worst offender, and will render meaningful conversation nearly impossible. But even if air handlers and air conditioning equipment is externally located, the type of ductwork into the space can create excessive noise if the supply and return duct system is not properly designed.

One of the most common ways that a room is rated is by using Noise Criteria (NC), which is a single number value that actually refers to a curve of specific sound pressure levels plotted against octave band frequency for eight different octave bands. The criteria curves define the limits of octave band spectra that must not be exceeded to meet occupant acceptance in certain spaces. The larger the NC value, the greater the noise it represents. NC for meeting rooms should be 30 or less, which is the equivalent of a noise level of about 40 decibels (A-weighted).

4. SPECIAL CONSIDERATIONS FOR TELE OR VIDEOCONFERENCING

Room acoustics is just as important — if not moreso — for tele- and videoconferences. Why? Because “far end” participants lack many of the local visual and auditory cues that help determine the actual content of verbal communication. Even the best quality microphones and video cameras lack the advantage of the human brain to help compensate for acoustical problems. Directional cues, body language, eye contact, and subtle facial expressions may be lost entirely when
transmitted via electronic equipment. A room that’s designed with good acoustics can help mitigate some of the disadvantages by preserving good speech intelligibility on both sides of the conference.

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