Adding absorptive wall materials, ceiling tiles and flooring reduces the energy and, therefore, the volume of sounds reflected off their surfaces back into the office space.
Because the ceiling is usually the largest unbroken surface in a facility, a good absorptive tile helps lessen the distance over which workplace noise and conversation can be heard. Offices should invest in the best tile they can afford and ensure consistent coverage throughout the facility. Any partial acoustic treatments in a space will decrease the possibility for complete acoustic control.
Ceiling absorption is often rated using Noise Reduction Criteria (NRC), which ranges from 0 (0% absorption) to 1.00 (100% absorption). The higher the NRC, the better. In decreasing order of acoustic performance, ceilings typically rank as follows: fiberglass tile, mineral tile, perforated metal tile, no dropped ceiling, drywall and solid metal tile. The last four types usually exhibit a significant decline in acoustic comfort; however, there are mineral and perforated metal products that demonstrate better-than-average NRC ratings.
The thickness of a mineral or fiberglass tile affects its acoustic performance. Generally, the thinner the tile, the more transparent and less absorptive it is. Foil backing on a fiberglass tile helps contain noise within closed offices. Foil also increases the dispersion of a sound masking signal, ensuring greater consistency in sound masking levels throughout the space. Placing fiberglass insulation above the ceiling tiles affords only marginal acoustic control and hinders access to the ceiling.
Lighting components can increase the acoustic reflectivity of the ceiling because they replace these absorptive ceiling materials with hard surfaces. In order to limit the lighting system’s impact on the absorptive performance of the ceiling, select lighting that incorporates a minimum number of ceiling fixtures while still meeting the specified lighting requirements. From an acoustic control perspective, indirect lighting systems are best because they are suspended from the ceiling and maintain the maximum surface area of the acoustic ceiling tiles. When it is not possible to install an indirect system, consider using a deep parabolic lens instead of the traditional solid plastic lens. Standard acrylic lenses are highly reflective and, because they can take up to 20% of the ceiling, they have an obvious effect on sound transmission.
Though they are used less frequently than acoustical ceilings, absorptive wall materials can also play a significant role toward achieving office privacy. Absorptive panels are effective when applied to large vertical surfaces and to key reflective locations - such as atrium walls or walls that reflect office noise from the foyer up into the office space. They can also be used in areas where the ceiling treatment is not absorptive.
Workstation partitions can also perform an absorptive function. To reduce sound paths, minimize openings between and around the workstation panels, as well as underneath them if carpeting has not been used. Also minimize the number and size of reflective surfaces - such as glass, metal and drywall components - in the workstation because they increase the reflection of workplace noise and conversation, causing them to be heard over greater distances.
Absorption and the reduction of footfall noise are the main acoustic control considerations when selecting flooring. Hard flooring is highly reflective and results in a more reverberant environment. Carpeting greatly reduces footfall noise, but typically provides only minimal absorption of frequencies in the range of human speech. Flooring will have a greater absorptive effect when special under-padding is used.
While the inclusion of absorptive materials in the office is necessary, their use lowers the ambient or background sound level, actually making the environment sound noisier and reducing speech privacy. Conversations will be more distinguishable and intelligible. In other words, absorption addresses some acoustic problems while worsening others.