A cancer treatment and research center is undergoing a renovation to replace wood flooring with terrazzo. The reverberation in this space has already raised some complaints, and the more reflective floor covering is expected to create more. These issues are most noticeable during events hosted in the atrium with amplified loud speakers.
Moffitt Hospital Acoustic Consulting
A reverberation test was set up in the main atrium to determine the reverberation at A-weighted frequencies and speech frequency ranges.
Other Acoustic Testing and Consulting Services
Test Method:
3 different impulse noises were used as the noise source. First, a loud speaker with white noise was cut off to allow measurement of reverberation. Secondly, hand claps were used as an impulse. Both methods failed to produce conclusive readings in the frequencies below 1000 Hz. Finally, 2”x4” wood studs were clapped together to create the noise source. The results were averaged together to yield the RT60 (“reverberation time”) value at each location.
A Type 1 SPL (Sound Pressure Level) meter was used to capture the amount of time it took the initial noise to decay by 60 dB at each frequency range. These results are displayed below in Table 1.
Test Results:
Location | 800 Hz | 1 kHz | 1.25 kHz | 1.6 kHz | 2 kHz | 2.5 kHz | 3.15 kHz | 4 kHz | 5 kHz | 6.3 kHz | RT60 |
Point 1 | 3.41 | 3.16 | 3.21 | 2.97 | 2.78 | 2.42 | 2.27 | 2.3 | 1.89 | 1.44 | 2.8 |
Point 2 | 3.51 | 3.13 | 2.67 | 2.58 | 3.14 | 2.33 | 2.04 | 1.88 | 1.73 | 1.26 | 2.67 |
Point 3 | 2.71 | 2.62 | 2.48 | 2.53 | 2.25 | 2.04 | 2.11 | 2.01 | 1.6 | 1.39 | 2.39 |
Point 4 | 3.95 | 3.9 | 2.48 | 2.61 | 2.46 | 2.25 | 2.13 | 2.11 | 1.75 | 1.5 | 2.47 |
Point 5 | 3.68 | 2.82 | 2.97 | 2.75 | 2.37 | 2.28 | 2.13 | 2.03 | 1.78 | 1.34 | 2.59 |
Average Reverb | 2.58 |
Table 1: Reverberation Results
Figure 1: Reverberation Test Locations
Figure 2: Reverberation Criteria with Various Venues
Recommendations:
In order to achieve a desired reverberation time of 1.45-1.9 seconds for a multi-purpose auditorium or venue, additional absorption materials will need to be added to the space.
After discussion with the client, it appears that installing these closer to the floor will yield significant savings due to the 56’ height of the room.
Using a simple Sabins calculation, the use of 48 panels at 2’x4’x2” thick, with an absorption factor of 1.05 NRC, will be sufficient to reduce the reverberation down to acceptable levels. While this characterization may be over-simplified due to the cavities and non-parallel surfaces in the space, it has been normalized to the readings taken in the field.
