Active increase of sound transmission loss of partitions based on utilizing EMFi panel actuators

Abstract

Active noise control (ANC) has been a promising method for noise control and also for other applications such as active increase of absorption and active increase of sound transmission loss of partitions. However, only a few applications have been commercially attractive. At the Technical Research Centre of Finland (VTT) a method to manufacture thin, flat acoustic sensors and actuators (flat microphones and loudspeakers) utilizing ElectroMechanical Film (EMFi) technology has been developed. Flat sensors and actuators can be implemented in ANC applications, where large surfaces should be covered with sensors or anti-sound producing elements. EMFi sensors and actuators are typically 4- to 10-mm-thick elements. They can also be collocated, forming an advanced sensor–actuator combination. Results of research focusing on the use of EMFi technology to increase the sound transmission loss of partitions by active means are presented. By active means the sound transmission loss of the partitions against broadband noise could be increased up to 10 dB in the frequency range 100–350 Hz. Results are new and of great importance, because new ANC technology is being developed. The commercial production of EMFi panel actuators will start in the middle of the year 2000.

Microstorms in Cellular Polymers: A Route to Soft Piezoelectric Transducer Materials with Engineered Macroscopic Dipoles

“…In a large flat-panel loudspeaker with dimensions of 1.5 to 1.8 m, the sound-pressure level measured at a distance of 3 m can be well above 100 dB between 500 Hz and 8 kHz, [56] as demonstrated in Figure 19.…”

“…Thereby antisound waves are generated to cancel the noise of vibrations, as demonstrated recently with two-layer stacks of cellular polypropylene films. [62] With cellular polymers, the noise-generating vibration may be detected and cancelled with flat microphones and flat-panel loudspeakers [56,63] at mid-and high-frequency levels. The sensitivity in all the applications described above can be enhanced by stacking the foams.…”

“…[27,47,55] In such a flat-panel loudspeaker, charged and nonmetallized cellular electret films are used, [27,56] as depicted in Figure 18. The structure allows a large elongation of the polymer films and therefore high radiated sound-pressure levels.…”

Voided polymer electrets - new materials, new challenges, new chances

“…Flat loudspeaker panels are, however, uniquely suited to active sound control in all kinds of enclosures such as rooms, automobiles, rail cars, airplanes, boats, etc. [74,75]. If thermally stable polymer-foam electrets of high piezoelectric sensitivity can be developed the concept of an "intelligent" (i.e.…”