Page 30 - Winter 2011

Fig. 2. High background noise levels at the Lobby Level can be traced to the use of hard, reflective surfaces including the terrazzo floor, the glass curtain walls, and the exposed concrete seating structure. Sound isolation was poor at the south side of the Lobby where traffic noise was transmitted through the glass curtain wall. This was the main cause for the high background noise levels.
were being added on the level beneath the bowl, creating a common need for noise control—so the worship service wouldn’t disturb them and they wouldn’t disturb the worship service. The new barrier was designed to serve triple duty in achieving acoustical separation from the occupied areas below, attenuation of mechanical noise transmitted through the return air path, and (most importantly) low-frequency absorp- tion in the main worship space.
A section typical of the concrete seating risers can be seen in Fig. 4. This shows the location of the slots through the concrete and the rela- tionship to the new plenum feeding the HVAC return air path. Lined with acoustical absorption, the tuning of the slot and plenum combination falls within the range of the problem- atic low frequency reverberation and provides much needed narrow band absorption. The result can be seen when comparing the average Values After Modifications curve with the Average of Measured Values Before Modification on the graph in Fig. 5. Taken together, the acoustical modi-
fications helped to smooth out the room’s response to desirable levels.
Mechanical noise and vibration isolation were other obstacles addressed to insure suitable perform- ance. A new central mechanical plant was designed to serve both the arena and the new five-story structure next door that houses the television pro- duction and broadcast center. All the pumps and chillers had to be physi- cally isolated from the building struc- ture using a series of techniques including floating concrete slabs, iso- lated inertia bases, and vibration iso- lation mounts on each piece of equip- ment. The existing air delivery sys- tems were extremely noisy. When this building was used for hockey or bas- ketball, hearing the score through the crowd noise was the only require- ment. Now, intelligibility and articu- lation of speech and music during a worship service are essential. Through geometry, extensions of the existing ductwork, and supplemen- tary attenuation, the background
noise levels were reduced to appropriate levels. Overall, the efforts achieved 20 dB of noise reduction in the new sanctuary as part of the renovation.
One of many examples of noise and acoustical issues arising from unique features in the space is the sanctuary’s waterfalls. (see Fig. 6.) Lakewood augmented the intimacy of their worship experience with the unprecedented inclusion of waterfalls on either side of the choir area. It’s usually not a
Fig. 3. Seating in the Compaq Center consists of upholstered fabric seats and backs that are useful in decreasing midfrequency reverberation times to suitable lengths. Many large ventilation slots are visible in the concrete seating structure and con- tribute to poor sound isolation between the main bowl and the Lobby Level.
26 Acoustics Today, January 2011