Exploitable results
New active elements for building acoustics were developed in the SMARTACUS project. In the project there were 9 partners: 3 research institutes and 6 industrial partners, of which four were SMEs. Project was started in the November 1998 and was finished in April 2001.
The main idea in the project was to develop active noise cancelling elements for the use in the building acoustics. There were 3 topic areas:
- Sound absorption,
- Sound insulation,
- Sound insulation with the transparent structures.
This target was approached with a two-way method. First, the basic building blocks for the project were developed. This included the basic actuator types, such as JMC- and shutter blind actuators, as well as basic analog and digital control systems. This phase of the project was called the generic phase. The latter part of the project was the application phase. In the beginning of it, the technology developed in the previous phase was evaluated and the best structures were adopted. This also meant, that some interesting developed technology, such as p/u-microphones and large JMC elements was not further used. The application phase concentrated on the development of solutions for the three topic areas.
Simultaneously with the technical development of the prototypes and tests carried out with them a lot of effort was put on the specifications, modelling, simulation, and optimisation. With the specifications theoretical concepts of the elements to be used were defined and refined, and many new ideas for the noise-treatment elements were developed. The modelling and simulation of the absorption and JMC elements gave very good estimations of the element performance, which was finally achieved. Sound insulation modelling and simulation predicted the behaviour of both single wall and double wall systems. Furthermore, the shutter blind structures were simulated and the final prototype was constructed according to the simulation. In this phase also the locations of the error sensors in the cavity of the active window were optimised and this information was utilised in the final demonstrations, as well.
For the sound absorption application the original idea of the SMARTACUS project was to develop absorbing panels, which could operate in the 3-dimensional sound field. This target was, however, cut back somewhat during the project because more resources were re-allocated to the sound insulation applications. Despite of that, good results with the pressure release and JMC-Zp methods were achieved in the 1-dimensional sound field in the laboratory conditions, and the absorption coefficient of the structure was increased close to 0.8 beginning from the frequency of 150Hz using the broadband excitation.
Active door became the target system in the sound insulation application area. The first, generic element measurement of active sound insulation both with the double structure as well as single panel structure gave improvements of 3dB – 10dB in the frequency range of 100Hz – 500Hz. Second test was with a small, 1/3-section of the door. It gave similar results in the laboratory conditions. A three-section door was constructed based on these results for the final sound insulation prototype.
Active window with the active acoustic shutter blind element was constructed for the active, transparent sound insulation application. The idea was to keep window transparent by using very narrow actuator elements in the window. In the first test with a relatively small window the attenuation was up to 30dB in the narrow band. Based on this a larger window was constructed as the final prototype.
Final sound insulation prototypes (door and window) were installed in the dividing internal wall of the mobile office. The office was presented in the final meeting of the project. This field test gave somewhat mixed results. The acoustic environment was very difficult being small and reverberant. However, the goal of Rw improvement of 4dB and single frequencies attenuation of 12dB was approximately achieved with the door structure. On the other hand, the performance of the large active window was much weaker and it did not fill the expectations, based on the results achieved in the laboratory conditions.
There were several clear benefits in the project. First of all, SMARTACUS project was one of the first projects in field of active noise control for the building acoustics. It had a relatively large scope from the sound absorption to the window structures. It produced a lot of useful information as such, as well as new ways to proceed by introducing new JMC-based structures. Furthermore, the active element building blocks were quite unique and could at least partly be exploited and commercialised by themselves. These blocks include round and rectangular actuators, p/u-microphones, and control systems.
One of the most important benefits of the SMARTACUS project is, however, the demonstration of real active building acoustics elements. Perhaps the most important and best working example of those in this project is an actively sound insulating door, which uses flat actuators and sensors plus relatively simple analog control system to achieve improved sound attenuation. Such a clear and proven concept could be one to be commercialised in a rapid timetable.
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