Open-plan office case study

Validation Study conducted by Myrra, in co-operation with Treble, Reykjastræti, and Landsvirkjun.

Abstract

Treble Technologies in co-operation with Reykjastræti, Landsvirkjun and the acoustic consultancy Myrra hljóðstofa conducted a validation study for the Treble Acoustic Simulation Suite. Measurements were performed in an open plan office in Reykjavík and compared to simulations in Treble Acoustic Simulation Suite.

The users of the office space had been complaining about bad acoustics and requested improvement. An acoustical model was set up in Treble to estimate the benefit of the acoustical improvements. It was decided to perform measurements prior to the acoustic improvements mainly for calibration of the acoustical model. Finally, the reverberation time was measured afterwards and compared to the simulations.

1. Initial condition

The space is a very large open office, about 450 m2 and 1400 m3. Exterior walls are glass-systems, ceilings are of concrete with visible technical systems and floors are mostly covered with carpet-tiles although walking-paths are linoleum floorings. The office is furnished with desks, chairs, and floor screens. The initial state of the space was therefore mainly sound absorbing on the high frequencies.

2. Measurements

Measurements were made before and after the acoustic improvements in the area. All measurements were performed in accordance with the IS0 3382-2 standard, Measurement of room acoustic parameters – Part 2: Reverberation time in ordinary rooms. Measurements were carried out in two areas of the office space. Measurements were conducted in the frequency range of 125 to 4000 Hz. Measurements results between spaces were similar.

2.1 Initial state and simulation calibration

A Sketch-up model of the open office was conducted and uploaded into Treble Acoustic Simulation Suite, seen in figure 1. The measurement results were then used to calibrate the Treble model. In figure 2 the comparison of measured reverberation time and simulation results from the calibrated model can be seen.

Fig. 1 Treble Acoustic Simulation Suite model of the open office space.

Fig. 2 Initial state measurement results and simulations results from calibrated Treble model.

2.2 Simulations

In consultation with the office owners, it was decided to look for solutions that had a short delivery time, could be installed quickly and without much disruption. It was therefore decided to use panels that would be mounted directly onto the concrete surface. Since there is a lot of technical equipment in the ceilings the acoustic panels would be distributed evenly throughout the space. The acoustic panels chosen are in sound absorption class A, with αw = 1,0, but as they are 50 mm thick the absorption at 125 Hz is limited. Around 120 m2 of sound-absorbing panels were purchased. For the simulations an estimate was made for the ceiling. Instead of drawing each panel the acoustic properties of the ceiling were calculated as a combination of 27% acoustic panels and 73% concrete. Simulations were carried out in the same area of the office space as the measurements. Positions of sources and receivers in the simulations can be seen in figure 3.

Fig. 3 Position of sources (green) and receivers (blue) in the simulations.

The following figure 4 shows the results of the simulations in Treble Acoustic Simulation Suite using two different transition frequencies, 250 Hz and 500 Hz, compared to the initial state.

Fig. 4 Simulations results from Treble model with 27% ceiling absorbtion.

3. Comparison of simulations and measurements

Following the acoustical improvments measurements were repeated and compared to the simulation results. In figure 5 the comparison of simulations and measurements can be seen.

Fig. 5 Comparison of simulated Treble results and measurement results with 27% of ceiling absorbtion.

As can be seen, there is quite a good agreement between simulations and measurements except at 125 Hz.