Acoustic acuity

The acoustical performance of a boardroom or video conference room is arguably the most important aspect of the room itself. A controlled acoustical environment within a conference room can lead to more efficient and productive meetings. Auralex Acoustic’s Gavin Haverstick explains.

There are two main obstacles that one is faced with when dealing with boardroom acoustics – sound transmission and sound quality.

Sound transmission occurs when sound leaks in from an adjacent space or vice versa. Common sources of noise that can compromise the isolation of a boardroom are: mechanical rooms, HVAC systems, adjacent rooms, hallways, external noises (traffic, airplanes, trains, etc.), and cooling fans from electrical equipment.

Sound travels much like water – if you imagine filling the boardroom up with water, the places where the water would leak out are places where sound has an easy path to escape or enter the room. For instance, a large air gap below a door leading into the hallway can be the weak link in the isolation of the room and can easily allow outside noise to disturb and interrupt a meeting in progress. Using weather-stripping tape and a quality door sweep can minimize this interference.

In order to decrease the amount of sound that travels in or out of the room through the walls, ceiling or floor one must increase the mass of the system. This typically requires a construction approach where additional layers of building materials are added to the structure. The more mass that is included in the system, the better the results will be.

If a mechanical room is adjacent to a meeting space, it is beneficial to isolate the mechanical room with additional mass and make sure that the room is sealed properly. During the planning stages of a new construction project, it is important to determine where sound sensitive areas (such as a boardroom) are to be located in relation to rooms that will generate significant noise. Many of the discussed problems can be avoided during the planning stage if you have that luxury.

Noise that is caused by HVAC systems can be reduced by using flexible ductwork as opposed to metal ductwork. If metal ductwork exists, you can line the inside of the duct with “ductboard”, an absorptive material that helps to decrease the reflections inside of the duct that would normally carry the sound to adjacent rooms. It is beneficial to have separate HVAC supply and returns for boardrooms so that sound does not travel from adjacent rooms through the ductwork. Another common problem with HVAC systems is improperly sized grills within the room, causing a sound similar to rushing water or a waterfall when the air conditioning is running. This can be cured by having an HVAC specialist properly size the grill for the amount of airflow that is necessary for the room.

Windows can often be the weak link in a wall system. A double-paned window is preferred versus a single pane for the added mass.
Drop-tile ceilings offer a visual barrier for the HVAC and electrical work above, however they are extremely ineffective at stopping sound due to the fact that they are lightweight and porous. If we go back to the water analogy, a drop-tile ceiling has many gaps and spaces throughout the ceiling which easy allows for the sound to leak out. Common office buildings also do not carry the walls all the way up to the floor above – i.e. the walls stop just above the drop ceiling allowing for yet another easy path for sound to travel. Adding thick, dense insulation above each ceiling tile will dramatically improve the isolation qualities of the ceiling.

For additional information on how to properly construct a room to reduce sound transmission, visit

Sound Quality

Boardrooms are typically constructed out of materials such as plaster board, drywall, wood, glass, steel, etc. These common building materials are “acoustically hard” and they reflect sound easily. Too many reflections inside of a room will cause speech to be unintelligible. It is very important to hear the direct sound coming from a presenter or from the teleconference speaker with minimal interference. The goal is to minimize the amount of reflected energy in order to maximize the “direct-to-reflected” ratio of sound energy within the room.

The reflected sound can be reduced by adding absorptive materials to the walls and ceiling surfaces in a room. This absorptive material is typically in the form of specialized polyurethane foam products or fabric-wrapped fiberglass panels. These soft materials absorb acoustical energy through friction loss and can reduce common acoustical problems such as excessive reverberation, flutter echo and room ring.

Some guidelines for acoustically treating a boardroom are listed below:
• Most boardrooms benefit from approximately 20-40% coverage of the reflective surfaces in the room with absorption treatment. If there is an “acoustically soft” ceiling (such as a drop-tile ceiling), the treatment can be focused on the walls only.
• The goal is to minimize the amount of parallel, untreated wall area in the room. Therefore, if you have a panel on one of the walls, you can offset the panel on the opposite wall so that you are maximizing the efficiency of the treatment.
• Wall panels should be centered at ear level throughout the room. The bottom 24-30 inches of each wall can be ignored due to the fact that there is furniture at that level to help break up the sound.
• Two inch thick polyurethane foam panels or one inch thick fabric-wrapped fiberglass materials are acceptable for boardroom applications – these products handle the speech frequency range very well and thicker treatment would be overkill in most situations.

Room Layout and Design

It is important to consider the layout and orientation of the room as it pertains to sound quality. If you can avoid having the presenter facing a wall of glass or a large dry erase board, you will minimize the amount of harsh reflections that would return to the listeners and reduce speech intelligibility. If possible, it is beneficial to have the presenter facing a wall that could potentially have acoustical treatment applied to it. Since the majority of the acoustic energy is being directed at this wall, acoustical treatment will be most effective at this spot in order to kill reflections before they have a chance to have a negative effect on the room’s acoustics.

The room dimensions and surface materials will dictate how the room sounds. If possible, during the design stage, choosing dimensions that are not divisible by the same number or each other will allow for the room to have more pleasing acoustical properties. For instance, a room that is 6m x 3m x 3m will have severe acoustical problems compared to one that is 5m x 4m x 3m. This phenomenon has to do with frequency wavelengths and how they interact with the room dimensions. If the rooms’ dimensions are multiples of each other as in the first room example, acoustical anomalies that are occurring in one direction will also be occurring in the other directions, thus compounding the issue.

Surface materials such as marble, concrete, glass, and stone can be visually stunning. These same materials can also render a room unusable for its intended purpose. A mixture of “acoustically hard” and “acoustically soft” materials in the room can strike a balance between aesthetics and sound quality.

Locating microphones or teleconferencing equipment as far away from noise sources will reduce the amount of interference that you will experience. For example, if there is a loud cooling fan on a projector, it will be helpful to move the microphones away from this unit. Keep in mind that what may not be distracting within the room, can be very disruptive on the other end of a conference call.

With the advances in audio and video technology in recent years, the limiting factor in how effective these products can be is the room that they are being used in. Acoustical treatment can be the difference between effective, productive meetings and a lack of understanding which leads to wasted time and resources.

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