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Teleconferencing Acoustics

Dec 8, 2010 10:58 AM, By Russ Berger

Considerations for successful teleconferencing.

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Frequency ranges of noise sources that are common disturbances in conference room setups.

This chart shows the frequency ranges of noise sources that are common disturbances in conference room setups. Measures must be taken to treat or attenuate the noise sources that can’t be removed from the space. See larger version.

The Mechanics

For teleconferencing, architectural and acoustic design must prevent noise from counteracting the function of echo-canceling electronic algorithms. Controlling noise protects the performance of the electronic communication, reinforcement, and conferencing systems. The two goals in creating quiet are 1) sound isolation (keeping out noise from traffic, adjacent rooms, etc.), and 2) noise control (minimizing the generation or introduction of unnecessary noise in the conference space from HVAC, computers, cooling fans, projectors, ice makers, occupants, etc.).

Sound isolation requires the proper design of walls, ceiling, floors, doors, and windows. Mass is our friend and the main component in effective sound isolation, but it must be coupled with other important factors to achieve adequate sound isolation. The stiffness of a partition plays a role in low-frequency sound isolation, as does damping to remove unwanted resonance, decoupling to achieve mechanical isolation, and cavity absorption to improve the overall sound transmission loss performance of multipanel wall and ceiling construction.

Flanking paths (e.g., sound leaks, mechanical coupling, and structure-borne vibration) can easily ruin the best of sound isolation efforts. Leaks through electrical boxes, ducts, plumbing, and piping carelessly cut into walls, ceilings, and floors can transmit sound around and through the untreated opening. If not sealed air-tight, sound will pass through the gaps that remain at the intersection and termination of partitions at window mullions, common walls, and floor/ceiling terminations. Flanking can occur where a wall terminates at a continuous gypsum board ceiling or outside wall. Wall terminations, especially at window mullions, are typically a problematic area of sound control weakness as well.

Bridging through a shared mechanical connection can also defeat sound isolation performance. Double-stud construction provides sound transmission loss benefits over single-stud construction because of mechanical isolation and the increased air cavity. Mechanically shorting out independent floating construction can occur with careless penetrations, internal connections, and nonresilient bracing, rendering our best sound-isolation efforts ineffective.

Structure-borne vibration can also reduce room-to-room sound transmission loss. When sound is introduced and transmitted mechanically through the structure and reradiated as unwanted sound into an adjacent space, it can be a performance killer. This type of flanking is not limited to just adjacent spaces, but it can cause problems in remote parts of the building, sometimes many floors away.

To be effective, noise control measures must either address the source of the noise or the path it takes, or deal with it at the receiving end. It is best to eliminate internal noise sources where possible by removing them from the space. After that, measures must then be taken to treat or attenuate the noise sources that remain. This could take the form of equipment enclosures or simply selecting quieter equipment. An example of a simple solution to a common problem might be adding carpet to reduce the noise from shuffling feet and scraping chairs. And please, get the noisy ice maker out of the executive conference room.

Noise is most cost-effectively addressed during the design process, not after there is a problem. HVAC noise is often the most common disturbance in conference room situations. Selecting a location in a quiet space away from noisy equipment is a great first start. It is the most effective method to ensure a low noise environment, but it is too often overlooked in early facility design.

Design air handling equipment to be quiet from the start. Limit vibration introduced into building structures to avoid expensive corrective measures in sound isolation construction. Reduce turbulence at the source to make it easier to achieve low noise results downstream.

Duct attenuating devices should be used where appropriate. This includes internal duct absorption, engineered sound attenuators, and plenums. Other design-related noise control measures include limiting noise generated in ducts through turbulence related to velocity. High velocity equals noise. Turbulence noise can effectively be improved during design by controlling the geometry of HVAC duct fittings and transitions.

Volume dampers and other obstructions in the ducted air path are also sources of noise, as are diffusers and grilles if not selected for appropriate acoustical performance and configured appropriately. Air supply and return paths are equally critical in reducing transmitted and regenerated duct-borne noise. Simply locating air diffusers and grilles away from microphones can make a significant improvement in overall performance of a conferencing system.

All of these considerations are outside the realm of the conferencing electronic equipment, because there is no electronic substitute for appropriate acoustics. The room, mic, and loudspeaker form an inseparable, interactive, and interdependent system. Small changes in the location of either loudspeaker or mic can have significant consequences in listening quality. Once you’ve bound a space with walls, a floor, and a ceiling, you’ve committed acoustics. Until ear buds are surgically implanted and lavalier mics are clipped to the lip, acoustics will remain the final link between talker and listener.

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