Determining proper acoustics for high-rise buildings involves: the intention of the space, speech privacy, background noise and sound masking. The goal is to select acoustical finishes that will meet the visions of the owner and the architect while providing a comfortable work-space.
Lobby acoustics depend on how the space will be used. Will it be a meeting and gatherings space where people want to converse or is it a pedestrian corridor?
Union Station in Washington D.C. is a great example of a grand and beautiful space–but hold a meeting or have more than a quick chat over coffee in the space? No way! It is too loud and too reverberant for conversation. The food court /lobby /atrium at the CNN Center in Atlanta is completely opposite: the level of volume lends itself to conversation. Both spaces are successful but with a different acoustical requirement. In the case of GSA SF, the lower lobby is the transitioning space with the upper skip-stop lobbies (one every three floors) designed as meeting and conversation spaces.
Speech privacy is another issue within office buildings, including individual workspaces, inside conference centers and between offices. It effects the quality of work in the adjacent office – we have all overhead too much information from a coworker, however; the distractions of phones, multi-media computers and conversation directly impact productivity. In the acoustical design for GSA buildings, where spaces for counseling, attorney/client conference rooms, Social Security and medical care guidance, a high level speech privacy is vital .
Background noise can also adversely impact the work-space. Too little background noise and speech privacy is reduced, letting you hear what is going on not only one work-space away but also two and three away. Too much background noise and you cannot concentrate on your work. Noise can come from the person next to you, from traffic outside the office or from the equipment within the building. The goal is to provide a uniform background sound level that is not too loud or too quiet. The central core of the building is usually loudest, the center of the work-spaces is quiet and the area around the windows is louder. Raising the sound levels in the center of the building helps mask the other areas. A green building like GSA SF that relies on natural ventilation is a challenge since there are no HVAC noises. The height of the building also reduces outdoor noise levels. This is a perfect example of when sound masking should be used in an office building.
Sound masking systems are designed to mask over phone conversations and other general office noise. Large open plan offices with workstations that are more than 50 feet away from the core areas are typically too quiet.
Sound masking blends the building systems’ noise levels and the exterior noise levels with an electronic system in the middle. Designing a multi-zone system that is properly adjusted is key to getting the most successful operation. Furniture vendors have often provided a “one solution fits all” that is not reviewed by an acoustician nor can they be properly adjusted to meet the needs of the space. Similar systems have been proposed to start generating a babbling sound when a person picks up a phone to cover what they are saying. When pre-manufactured boxes and cans are installed, they cannot be adjusted and are usually turned off. When a properly adjusted system has been installed, it just runs and runs–TA has one system that has been in operation for over 15 years!
Traditional sound masking systems are located in loudspeakers above the ceiling. The loudspeakers are typically laid out in stereo zones. Zones are further segregated into different open plan areas, conference areas and other spaces for better control of the background sound level.
An acoustical engineer must commission background sound systems. Do not rely on system manufacturers or contractors. The key issue for the GSA SF building was the thermal mass slab. Without the benefit of an acoustical tile ceiling to help diffuse the sound, a design was developed where the sound -masking loudspeaker was installed as part of the indirect lighting fixture. This approach allowed for the correct number of loudspeakers needed for coverage and benefited from the slab’s reflection–just as the indirect lighting system does–providing a truly uniform and non-directional sound field.
A comfortable and productive work-space greatly depends upon its acoustics. Those acoustics are controlled by a good design with extensive knowledge on the use of the space, how much speech privacy is desired, what the background noises are and a properly adjusted sound masking system.