Loudspeaker Design Research Articles

Multimodal Loudspeaker Based on a Dielectric Elastomer Roll Actuator

A novel loudspeaker design integrating lightweight and efficient acoustic transducers derived from dielectric elastomer films is presented. This innovation centers on core-free dielectric elastomer roll actuators, functioning akin to artificial muscles, altering shape upon the application of an electric field. The actuators serve two roles: propelling acoustically radiating surfaces and emitting sound themselves. The paper provides a model that describes the axial vibration behavior via electromechanical and acoustic networks, facilitating understanding and comparability with electrodynamic loudspeaker systems without the need for extensive background knowledge of dielectric elastomer technology. Based on established methodologies, the design process and adaptability to diverse applications is evident. A demonstrator developed as a proof of concept with the aim of creating a broadband speaker for speech reproduction was designed, constructed, and examined utilizing the established methodology. It shows promising practicality and, in certain aspects, technological superiority over electrodynamic counterparts. Notable features, such as increased efficiency, significant weight reduction, and wide radiation pattern make this speaker viable and particularly attractive for mobile PA applications such as those found in trains and aircraft. Furthermore, the underlying principle and modeling framework allow the future creation and adaptation to a broad spectrum of applications, promising further innovation in the field.

An experimental parametric analysis of the acoustic response in dielectric elastomer loudspeakers

This article presents an experimental parametric analysis of dielectric elastomer (DE) loudspeakers, which generate sound by means of soft lightweight electroactive polymer membranes, with no need for electromagnetic actuators. Attention is set on a simple topology, which consists of a DE actuator membrane deformed out-of-plane in a conical shape between fixed frames. Different scaled replicas of the system were built, featuring different diameters and elastomer membrane thickness, with the aim of highlighting the dependence of the acoustic response on the design parameters. An experimental analysis of the effect of different electrical and mechanical pre-loads was also carried out. Results suggest that the acoustic response is affected by both geometrical factors, possible effects of aero-elastic interactions, and the level of mechanical stress acting on the DE membrane. These findings provide valuable insights for the optimisation of DE loudspeaker design and operational parameters.

Non-linear Acoustic Problems in Loudspeaker Design

The article deals with the issues of non-linear acoustics. A mathematical model of non-linear distortions of the acoustic path has been compiled in relation to the operation of a loudspeaker in a piston mode. The results of experimental measurements are presented and analyzed. Recommendations are given to reduce distortion in the construction of high-quality acoustic systems.

On the Design and Modeling of a Full-Range Piezoelectric MEMS Loudspeaker for In-Ear Applications

On the Design and Modeling of a Full-Range Piezoelectric MEMS Loudspeaker for In-Ear Applications

Loudspeaker cabinet design by topology optimization

Using material distribution-based topology optimization, we optimize the bandpass design of a loudspeaker cabinet targeting low frequencies. The objective is to maximize the loudspeaker’s output power for a single frequency as well as a range of frequencies. To model the loudspeaker’s performance, we combine a linear electromechanical transducer model with a computationally efficient hybrid 2D–3D model for sound propagation. The adjoint variable approach computes the gradients of the objective function with respect to the design variables, and the Method of Moving Asymptotes (MMA) solves the topology optimization problem. To manage intermediate values of the material indicator function, a quadratic penalty is added to the objective function, and a non-linear filter is used to obtain a mesh independent design. By carefully selecting the target frequency range, we can guide the optimization algorithm to successfully generate a loudspeaker design with the required bandpass character. To the best of our knowledge, this study constitutes the first successful attempt to design the interior structure of a loudspeaker cabinet using topology optimization.

Measurement of Compound Sound Sources with Adaptive Spatial Radiation for Low-Frequency Active Noise Control Applications

The proposed compound sound sources for low-frequency noise control applications are composed of dipole sources. Their spatial radiation, which is critical in the modal field of small, closed spaces, is intended to be controlled with independent driving signals of each dipole. The need for small and efficient low-frequency elementary monopole sources led to the proposed vented sub-woofer loudspeaker design with low force factor (low-Bl) drivers. The investigated sources are set up in quadrupole configurations and measured in terms of polar near field response patterns to verify the theoretical predictions. The measurement results consist of the validation of the proposed compound sound sources on the implementation of active noise control problems in the low-frequency range. Also, their small size and modular construction make them interesting for use in other applications.

Spectral analysis of acoustic plane waves in ductworks with uniform and varying cross-section waveguides

The problem of low-frequency sound propagation in ducts involving varying cross-sections is analyzed. Spectral finite element formulations for the dynamic analysis of varying cross-section ducts are presented as tapered spectral elements. These elements can be used in connected waveguides through dynamic stiffness relations. Linear and polynomial duct types are considered. The elements’ shape functions are established as well as the dynamic stiffness matrices describing the spectral relation between the acoustic pressure and the volume velocity. The presented spectral approach describes the acoustic wave motion at any position along arbitrary multiply connected duct waveguides within the one-dimensional plane-wave assumption. The derived expressions are verified experimentally, and by comparison with 3-D finite element solutions. The modeling of varying cross-section duct waveguides can play an important role in the design of acoustic excitation devices and horn-type loudspeakers. The advantage of the presented formulations lies in the low computational cost when compared to the finite element approach.

Scenarios for Ecodesign in loudspeaker’s motor

The worldwide loudspeaker market follows the growing tendency of electronic entertainment technologies both in quantity and variety. Consequently, the environmental impacts caused during the life cycle of loudspeakers increase in the same proportion, going in the opposite direction to what is determined by world environmental laws and regulations and global market tendencies. Even so, the environmental performance of this type of product is not considered in the decision-making process for technological updates in loudspeaker design. In this sense, Ecodesign is the most adequate Life Cycle Engineering tool applied in the design of a product since the environmental performance is considered throughout the different design stages. However, the feasibility of Ecodesign in products requiring complex production chains relies on splitting the product into subsystems and components. Thus, the present work focuses on evaluating the environmental performance of a classic loudspeaker motor, which is composed of a magnet, coil, and coil former. Eight raw material substitution scenarios are proposed and analyzed, which allowed the proposal identification with the best environmental performance within the current technologies. This represents an initial step toward the complete Ecodesign of a loudspeaker and sets the procedure to be followed with the other constitutive parts.

Genetic algorithm application for electrodynamic transducer model identification

Research object: the adaptation and application of the genetic algorithm for electrodynamic transducer model parameters identification.
 Investigated problem: to formulate loudspeaker identification task as an optimization problem, adapt it to the genetic algorithm framework and compare obtained results with classical identification method using added mass.
 Main scientific results: the complete genetic algorithm loudspeaker identification procedure is presented, including:
 – data acquisition scheme, where the directly measured values for the algorithm application are: voltage at loudspeaker terminals, current through the voice coil and displacement of the moving part
 – selection of an appropriate set of genes of an individual
 – derivation of the fitness function for assessing the quality of the identified parameters, which can also be used to identify other types of electroacoustic transducers
 Also, the advantages of this method in comparison with the classical method of identification using added mass are considered, that are its versatility and ability to quickly configure and adapt for research and experimentation with different loudspeaker models and different types of transducers used in acoustics.
 Area of practical use of the research results: the proposed genetic loudspeaker model identification scheme can be directly applied on practice to speed up research and development tasks in electroacoustics and other related fields that require frequent experimentation with different types of transducer models.
 Innovative technological product: genetic algorithm based loudspeaker identification scheme that can be applied to identify various model of electrodynamic transducers.
 Scope of application of the innovative technological product: electroacoustics, loudspeaker design, audio systems

Broadband monopole emission enhancement using a dual acoustic grating

The enhanced broadband emission of monopole source is achieved by a dual acoustic grating with anisotropic mass density. The exact expressions among the enhanced efficiency and all the structural parameters of the dual acoustic grating are obtained through rigorous analytical model based on the radiation impedance theory. The results show that the enhanced broadband monopole emission can be realized in the dual acoustic grating through the coupling of the first and the second resonance modes. Considering the thermo-viscous dissipation, the broadband monopole emission can be enhanced through parameter optimization and the sound pressure level (SPL) gain is above 11 dB. Its bandwidth is 1060-1920 Hz and the fluctuation of the SPL gain in the frequency band is 3 dB. The sample is further fabricated and the enhanced broadband emission of monopole sources by the dual acoustic grating is experimentally verified. The study of this letter could have potential application for loudspeaker design and acoustic communication.

Finite Element Simulation and Shape Optimization of Acoustic Horn

Horn refers to the tube with continuous change of cross-sectional area, which can improve the matching of diaphragm and air load, so as to improve the electro acoustic conversion efficiency. For long-distance strong sound equipment, the purpose of using horn is to pursue higher sound pressure level, and control directivity and smoothness of sound pressure level response. In order to obtain higher sound pressure level and sharper directivity, parametric curve expressions of conical, exponential, hyperbolic and parabolic horn were derived. By using COMSOL multiphysics software, two-dimensional axisymmetric finite element simulation models of conical, exponential, hyperbolic and parabolic horn were established. Combined with if + end if programming function of the software, the effects of different cross-section shapes of horn on far-field sound pressure level and directivity were analyzed. The simulation results show that the parabolic horn can achieve a higher sound pressure level, and the sound pressure level is more than 3dB higher than the other three in the frequency band above 2000Hz. In the aspect of directivity, the beam width of parabolic horn is the smallest and more stable, and the overall directivity is the strongest. By using the shape optimization function of the software and constructing 8-order Bernstein polynomials, based on the parabolic horn, the shape of the horn was optimized for the most sensitive frequency range of 2000-4000hz, and the sound pressure level of the optimized horn was significantly improved in a large frequency range. This paper can provide technical reference for the design and development of horn loudspeaker.

A broadband point source loudspeaker design and its application to anechoic chamber qualification

A broadband point source loudspeaker, referred to as a ‘gap source’, is described. The source is driven by four compression drivers configured as two identical two-way sources connected to two symmetric pipe structures. The sound source radiates from a small gap between the pipe openings, yielding sufficiently powerful omnidirectional radiation in the range 100 Hz–20 kHz for anechoic room qualification in accordance with ISO 26101. For proof of concept, the source performance was compared with that of a commercial omnidirectional loudspeaker for traverses in an anechoic room. Results demonstrate that a single sound source, as described, is sufficient for anechoic room qualification in 1/3-octave bands at and above 100 Hz. The source’s improved adherence to omnidirectionality is shown to be an advantage in detecting an introduced reflection in an anechoic room.

The Evolution and Design of Flat-Panel Loudspeakers for Audio Reproduction

MI. C.. Heilemann, DA. A.. Anderson, S. Roessner, and MA. F.. Bocko, "The Evolution and Design of Flat-Panel Loudspeakers for Audio Reproduction,"

2Pb4-6 Examination of Arrangement of facing ultrasonic transducer arrays for design of omnidirectional loudspeaker

2Pb4-6 Examination of Arrangement of facing ultrasonic transducer arrays for design of omnidirectional loudspeaker

Mechanical and Acoustic Properties of Alkali-Treated Sansevieria ehrenbergii/Camellia sinensis Fiber–Reinforced Hybrid Epoxy Composites: Incorporation of Glass Fiber Hybridization

The intention behind this research work was to analyse the mechanical as well as acoustic behaviour of Sansevieria ehrenbergii (snake grass) / Camellia sinensis (waste tealeaf) fibers with glass fiber (GF) – reinforcement to form the hybrid epoxy composites. Fibers of S.ehrenbergii/C.sinensis were chemically modified for their effective usage as reinforcement in hybrid composites. Five combinations of hybrid composites were fabricated using hand-operated compression molding techniques by changing the percentage weight of snake grass fiber (SGF) and waste tea leaf fiber (WTLF). The results indicated that the mechanical behaviour of SGF/WTLF composites have been substantially enhanced by hybridization with GF. Enhanced mechanical behavior of hybrid composites is observed as an incremental percentage of SGF composition. The experimental findings show that the weight fraction of 25 wt.% WTLF reinforced with SGF shows a strong acoustic absorption coefficient (AAC) of 0.59 in the frequency range of 2000–6300 Hz as well introduces the potential for acoustic sound proofing applications, such as loudspeaker design, perforated panels, sound recording, and reproduction room. The morphological behavior of hybrid composites, such as fiber pullout, matrix crack, void formation, and interfacial bond between the binder and fibers were observed using a scanning electron microscope.

Enhanced Low‐Frequency Monopole and Dipole Acoustic Antennas Based on a Subwavelength Bianisotropic Structure

AbstractHigh‐efficiency sound emission is crucial in practical scenarios, such as sonar system and acoustic communication. However, the efficient emission of the low‐frequency sound source is difficult because of the large acoustic radiation reactance from the ambient medium. Here, a subwavelength bianisotropic hybrid Mie resonator (BHMR) is proposed, which has shown excellent capability in converting a central monopole source into the enhanced monopole and dipole acoustic antennas at low frequency. The simulated acoustic field distributions and far‐field radiations of the BHMR demonstrate that the enhanced omnidirectional and directional antennas are induced by the monopole and dipole resonances, respectively. A BHMR sample is further fabricated and the enhancements of the monopole and dipole acoustic antennas by the BHMR are experimentally verified. The miniature BHMR offers an alternative way to achieve the enhanced low‐frequency monopole and dipole antennas that are highly desirable for loudspeaker design and acoustic communication.

Characterization and Comparative Analysis on Mechanical and Acoustical Properties of Camellia Sinensis/Ananas Comosus/Glass Fiber Hybrid Polymer Composites

ABSTRACT During last few decades, the hybrid composites emerged from natural fiber has brought incontestable advantages over synthetic materials. The environmental impact such as toxicity, nonbiodegradable garbage, and noise pollution has led to the identification of new class of fibers and also subsequent failure in critical stiffness and weight sensitivities of fiber-reinforced polymers has initiated magnification of mechanical toughness. In this present paper, fiber-reinforced composite materials are made with Camellia sinensis–Ananas comosus hybridized by glass fiber and epoxy resin matrix. The amalgamated laminates were forged by a compression molding process with the composition of 40% wt. of reinforcing fiber and 60% wt. of epoxy matrix in a constant proportion. A hydrophilic content present inside natural fibers are alkalized by 5% of NaOH to modify as hydrophobic nature for intensifying bonding between fiber and matrix. These hybridized fibers are mechanically, chemically, morphologically, and acoustically analyzed to meet the requirements of mechanical and sound proofing properties. The results shows that 25% wt. fraction of Camellia sinensis amalgamate with unidirectional fiber shows better average acoustical absorption coefficient (AAC) of 0.46 at 2000–6300 Hz frequency range and compared with existing material to establish the potential of using it in sound-proofing acoustical applications such as architectural acoustics, sound recording and reproduction room, noise barrier walls, loudspeaker design, etc.

Dynamics and sound radiation of a dielectric elastomer membrane

This paper investigates sound radiation by an inflated dielectric elastomer membrane. The constitutive equations of the coupled electromechanical system are derived from general mechanical equilibrium equations, from Maxwell's equations, and from thermodynamic considerations. A finite deformation model featuring a hyperelastic constitutive law is written for the case of a thin membrane. The static finite deformation obtained when the membrane is inflated and when a voltage is applied is computed. The linear dynamics around this equilibrium are studied on the modal basis: the mode shapes and eigenfrequencies are computed, as well as the modal forces created by the voltage applied on the electrodes. The radiated acoustic pressure is estimated using a modified Rayleigh integral to take into account curvature effects. All numerical calculations are validated against measurements. The model is shown to be able to predict the linear vibrations, as well as the radiated pressure. The effect of the volume of the cavity on which the membrane is inflated is taken into account in the model. This model can therefore be used to optimize the design of dielectric loudspeakers, in terms of spectral balance for example.

A Comparative Study on Estimation Methods for Statistical Moments of Electromagnetic Performance Functions

A performance moment integration method is proposed to accurately estimate the first two statistical moments, mean and variance, of electromagnetic performance functions in the present of uncertainties. To maximize computational efficiency, its numerical integration is executed not on the input design domain but on the output performance domain, where quadrature points are explored by the first order reliability analysis method. For better understating between statistical moment analysis methods, two different numerical integration schemes of dimension reduction method and performance moment integration method are compared with each other. Finally, a mathematical model and a loudspeaker design model are tested to demonstrate the features of two methods and to examine their numerical accuracy and efficiency.

High-efficiency collimation of airborne sound through a single deep-subwavelength aperture in an ultra-thin planar plate

We propose a mechanism for high-efficiency collimation of airborne sound through an ultra-thin planar structure perforated with a single deep-subwavelength aperture by combining a zigzag-shaped structure with arrays of subwavelength resonators to increase the equivalent refractive index and eliminate high-order diffractive waves simultaneously. Numerical simulations demonstrate that the proposed mechanism enables remarkably enhanced transmission and strong collimation of the transmitted wave, which propagates for a strikingly long distance exceeding 125 wavelengths. Due to its capabilities and flexibility, the proposed design opens up possibilities for novel compact acoustic-steering devices and may have far-reaching impacts in diverse applications such as acoustic communications and loudspeaker design.