Acoustic resonance

Summary

Acoustic resonance is a phenomenon in which an acoustic system amplifies sound waves whose frequency matches one of its own natural frequencies of vibration (its resonance frequencies). The term "acoustic resonance" is sometimes used to narrow mechanical resonance to the frequency range of human hearing, but since acoustics is defined in general terms concerning vibrational waves in matter, acoustic resonance can occur at frequencies outside the range of human hearing. An acoustically resonant object usually has more than one resonance frequency, especially at harmonics of the strongest resonance. It will easily vibrate at those frequencies, and vibrate less strongly at other frequencies. It will "pick out" its resonance frequency from a complex excitation, such as an impulse or a wideband noise excitation. In effect, it is filtering out all frequencies other than its resonance. Acoustic resonance is an important consideration for instrument builders, as most acoustic instrument

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Nowadays, requirements for acoustic treatments in rooms are ever more demanding in terms of performance and compactness. A recurring issue in closed spaces is the occurrence of standing waves and acoustic interferences at low frequencies. These unwanted phenomena are likely to affect the frequency response of rooms such as offices, concert halls or home theaters. Unfortunately, state-of-the-art soundproofing solutions cannot efficiently dissipate sound energy, or their embodiments are so bulky that they become almost impracticable. To that purpose, electroacoustic absorbers employing direct-radiator loudspeaker systems can be used to improve listening quality and meet the specifications. Electrodynamic transducers are obvious candidate for this type of noise control application. They are controlled by the resistance around the mechanical resonance, typically of the order of a few tens of Hertz, which also lies in the frequency range of acoustic modes to be damped. This results in a strong interaction between both dynamic systems from which part of the incident acoustic energy of the sound field can be dissipated. A specific electrical load is also connected across the transducer terminals in order to further improve the passive dissipation through the internal damping within the loudspeaker. This paper investigates an optimized placement of electroacoustic absorbers in a reverberant room in order to damp the lowest acoustic resonances.

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An Efficient Piezoelectric Energy Harvesting Interface Circuit Using a Sense-and-Set Rectifier

Yimai Peng

Piezoelectric energy harvesters (PEHs) are widely deployed in many self-sustaining systems, and proper rectifier circuits can significantly improve the energy conversion efficiency and, thus, increase the harvested energy. Various active rectifiers have been proposed in the past decade, such as synchronized switch harvesting on inductor (SSHI) and synchronous electric charge extraction (SECE). This article presents a sense-andset (SaS) rectifier that achieves maximum-power-point-tracking (MPPT) of PEHs and maintains optimal energy extraction for different input excitation levels and output voltages. The proposed circuit is fabricated in the 0.18-μm CMOS process with a 0.47-mm 2 core area, a 230-nW active power, and a 7-nW leakage power. Measured with a commercial PEH device (Mide PPA-1022) at 85and 60-Hz vibration frequency, the proposed circuit shows 512% and 541% power extraction improvement [figure of merit (FoM)] compared with an ideal full-bridge rectifier (FBR) for ON-resonance and OFF-resonance vibrations, respectively, while maintaining high efficiency across different input levels and PEH parameters.

IEEE2019

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In closed spaces, standing waves occur at low frequencies, thus creating annoying acoustic resonances. Such unwanted phenomena are likely to affect the annoyance of noise sources in the low frequency range. Up to date, low-frwquency treatments are mainly based on bulky devices, such as heavy enclosures. To alleviate this problem, electroacoustic absorbers, namely loudspeakers with shunt synthetic electric loads, can be used to damp room modes and then meet noise reduction specifications. Electrodynamic loudspeakers are good candidates for this type of noise control applications. Their mechanical resonance, typically of the order of tens of Hertz, is within the frequency range where acoustic modes to be controlled. The interactions between these dynamic systems are significant, and a consequent amount of the acoustic energy in the room can be passively dissipated through internal losses in the loudspeaker. This paper investigates the design techniques and experimental validation of electroacoustic absorbers with a view to damp the low-frequency acoustic resonances, in the context of the low-frequency noise reduction in inhabitations.

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