Loudspeaker Cabinet Research Articles

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.

3D shape optimization of loudspeaker cabinets for uniform directivity

3D shape optimization of loudspeaker cabinets for uniform directivity

3D shape optimization of loudspeakers

Improving the performance of loudspeaker units and cabinet designs traditionally relies on a combination of trial and error, sometimes based on a lumped parameter modelling approach. During the last decades, however, large-scale numerical simulations are playing a growing role as a means of improving performance of complex engineering devices such as loudspeakers. However, a numerical model still relies on the experience of the operating engineer to make the appropriate design changes. This can be a difficult task. The use of numerical simulations combined with optimization has a huge potential for further guiding the design process of advanced industrial products where intuition alone is not sufficient. Nevertheless, broadband acoustic simulations are still very time consuming. In this work, we explore the efficiency of a newly proposed semi-analytical adjoint sensitivity approach based on the boundary element method in combination with a lumped parameter model. The sensitivity analysis is used to shape optimize the cabinet of a loudspeaker using free form deformation. The objective of the optimization is to improve frequency responses and directivity patterns.

A Methodology for the Robust Estimation of the Radiation Pattern of Acoustic Sources

We propose a novel methodology for estimating the radiation pattern of acoustic sources, which is general enough as to be suitable for a wide variety of sources without the need of anechoic conditions of operation. Multiple plenacoustic cameras (which can be thought of as arrays of acoustic cameras) scan the source while keeping reflections and interferers at bay through deconvolution and windowing of the measured response. In the case of a moving source (e.g. a musical instrument while it is being played), the plenacoustic cameras are also used for tracking the position of the source. As for its orientation, we propose practical solutions for tracking that as well, whenever such information is not known in advance. Two experiments are conducted in order to validate the proposed solution. The former focuses on a commercial loudspeaker cabinet, whose radiation pattern is known in advance and can be used as groundtruth. The latter concerns violins, which exhibit an extremely rich and hard to predict acoustic behavior, due to their inherent structural and constructional complexity. Our method allows us to capture the radiation pattern of the instrument while it is being played, thus returning data corresponding to the natural timbre of the instrument, including the unavoidable acoustic shadow of the violinist's head. Experimental results confirm a relevant improvement in accuracy and robustness afforded by the adoption of dynamic plenacoustic solutions with respect to state-of-the-art techniques.

Sound field reconstruction using multipole equivalent source model with un-fixed source locations.

The equivalent source methods (ESM) that have been developed to this point can generally be classified into two categories: one in which a relatively large number of lower order sources are fixed at various locations, and one in which a series of higher order sources are fixed at one location. The present work started with a model in the latter category, but the individual sources were then allowed to move separately to locations which were determined by using a nonlinear optimization procedure based on the measured sound field data. To test this approach, experiments were conducted using a small loudspeaker cabinet; measurements were made using an array of microphones on all sides of the loudspeaker. It was found that by allowing the source components to move, the sound field representation in both the near and far fields was improved, particularly at high frequencies, compared to the model with fixed source locations. By comparison with results obtained from boundary element calculations based on laser vibrometer measurements of the loudspeaker's diaphragm and tweeter velocities, it was found that the proposed ESM can also be used to accurately predict the sound pressure distribution on the source surface.

On Sparse Reconstructions in Near-Field Acoustic Holography Using the Method of Superposition

The method of superposition is proposed in combination with a sparse [Formula: see text] optimization algorithm with the aim of finding a sparse basis to accurately reconstruct the structural vibrations of a radiating object from a set of acoustic pressure values on a conformal surface in the near-field. The nature of the reconstructions generated by the method differs fundamentally from those generated via standard Tikhonov regularization in terms of the level of sparsity in the distribution of charge strengths specifying the basis. In many cases, the [Formula: see text] optimization leads to a solution basis whose size is only a small fraction of the total number of measured data points. The effects of changing the wavenumber, the internal source surface and the (noisy) acoustic pressure data in general will all be studied with reference to a numerical study on a cuboid of similar dimensions to a typical loudspeaker cabinet. The development of sparse and accurate reconstructions has a number of advantageous consequences including improved reconstructions from reduced data sets, the enhancement of numerical solution methods and wider applications in source identification problems.

Calculation of Loudspeaker Cabinet Diffraction and Correction

A method of calculating the cabinet edge diffractions for loudspeaker driver when mounted in an enclosure is proposed, based on the extended Biot—Tolstoy—Medwin model. Up to the third order, cabinet diffractions are discussed in detail and the diffractive effects on the radiated sound field of the loudspeaker system are quantitatively described, with a correction function built to compensate for the diffractive interference. The method is applied to a practical loudspeaker enclosure that has rectangular facets. The diffractive effects of the cabinet on the forward sound radiation are investigated and predictions of the calculations show quite good agreements with experimental measurements.

Sound radiation from a resilient spherical cap on a rigid sphere

It has been argued that the sound radiation of a loudspeaker is modeled realistically by assuming the loudspeaker cabinet to be a rigid sphere with a resilient spherical cap. Series expansions, valid in the whole space outside the sphere, for the pressure due to a harmonically excited cap with an axially symmetric velocity distribution are presented. The velocity profile is expanded in functions orthogonal on the cap, rather than on the whole sphere. As a result, only a few expansion coefficients are sufficient to accurately describe the velocity profile. An adaptation of the standard solution of the Helmholtz equation to this particular parametrization is required. This is achieved by using recent results on argument scaling of orthogonal (Zernike) polynomials. The approach is illustrated by calculating the pressure due to certain velocity profiles that vanish at the rim of the cap to a desired degree. The associated inverse problem, in which the velocity profile is estimated from pressure measurements around the sphere, is also feasible as the number of expansion coefficients to be estimated is limited. This is demonstrated with a simulation.

Loudspeaker enclosure with damping material laminated within internal shearing brace

A loudspeaker cabinet with a laminated internal brace which has a first rigid layer coupled to a first exterior panel of the cabinet, a second rigid layer coupled to an a second exterior panel of the cabinet, and a damping layer affixed between the rigid layers where they overlap. Vibration, flexure, and expansion/contraction of the cabinet are damped by shearing forces applied to the damping layer as the rigid layers move in opposite, parallel directions.

ACOUSTIC EQUATIONS IN THE PRESENCE OF RIGID POROUS MATERIALS ADAPTED TO THE FINITE-DIFFERENCE TIME-DOMAIN METHOD

Finite-difference time-domain (FDTD) method has been successfully developed to model electromagnetic systems in recent years. Since acoustics and electromagnetism share certain undulatory properties, a natural adaptation of this technique has been developed too. Several acoustics problems, such as room acoustics, require the use of fibrous tangles to attenuate the propagation speed of sound waves. Notwithstanding, although free air acoustic propagation is known, FDTD technique is not developed yet to model fibrous materials. To characterize this behavior, only a few and measurable set of parameters must be considered. In this paper, a new approach for modeling fibrous materials analysis using FDTD is presented and validated. A set of simulations covering various packing densities of a real fibrous material is performed. Loudspeaker cabinets, virtual acoustics and room acoustics are situations in which this method can be applied.

Thermal chimney equipped audio speaker cabinet

A thermally conductive chimney tube extends through a loudspeaker cabinet that encloses a volume of air heated by a speaker driver. The open ends of the chimney are outside the cabinet. A column of air within the chimney is in contact with the external ambient air, but sealed off from the enclosed volume of air. As the speaker driver heats the enclosed volume of air, the material of the chimney transfers the heat to the column of air, which rises and carries the heat away into the external ambient air, cooling the inside of the loudspeaker cabinet and thus cooling the speaker driver.

Loudspeaker with differential flow vent means

Differential flow vents allow airflow within a vent to be preferential. A flange disposed within a vent introduces non-linearities and causes a preferred direction of airflow into an expanding volume. The differential flow vents are used in conjunction with the natural motion of the loudspeaker cone acting as a pump to cool the loudspeaker cabinet enclosure without having to directly cool the woofer magnet structure. In one embodiment, at least one pair of opposed differential flow vents within the cabinet enclosure provide fresh air to be preferentially circulated to cool the interior of a loudspeaker system. In another embodiment, by providing an odd number of opposed differential flow vents within the cabinet enclosure, positive air circulation also results. By making either the pairs or odd number of differential flow vents to be asymmetrical, dynamic woofer offset is compensated. By placing the differential flow vents in the backplate of the woofer magnet structure and using the natural motion of the woofer speaker cone acting as a pump, cabinet enclosed air may be preferentially pumped into the magnet structure for cooling heated components. By providing the differential flow vents in both the cabinet enclosure and in the backplate of the woofer magnet structure, maximal cooling is achieved. Where system linearity is not an issue, pairs of opposed symmetrical differential flow vents may be used in the cabinet enclosure and or woofer magnet structure for cooling.

Surround sound loudspeaker system

The generation of skewed hypercardioid sound energy fields (in polar diagrams) from right front and left front "surround" loudspeakers with the principal nulls directed at the expected listener location produces the effect of sidewall and rearwall loudspeakers in a home theater setting without any actual sidewall or rearwall loudspeakers. The effect is enhanced by secondary nulls that are directed so as to "reflect" off the front wall of the room toward the expected listener location. Each surround loudspeaker contains an antiphase driver and circuitry including a delay network that powers the drivers to create the skewed hypercardioid sound energy field. The invention is independent of electrical mixing and interaction of two or more input channels. Rather the channels are assumed to be independent and the invention concerns the unique directional sound energy radiation pattern generated from each channel considered independently. An important feature of the skewed hypercardioid sound energy field according to the invention is the insensitivity of the principal null direction to frequency over a range of 120 H z to 4 kH z . Also important is a surround sound effect more pronounced in miniature (close range) speaker configurations because the energy gradient between the right and left ears is steeper with the skewed hypercardioid at close range. The invention provides a generalized method of handling direct and reflected sound in an enclosed listening space, since the parameters are variable with delay in the circuitry, the angular relationship of the drivers in the loudspeaker cabinet and the shape of the cabinet. In some listening configurations only the surround loudspeakers are necessary for superior sound reproduction.

Bass-reflex loudspeaker

A bass-reflex loudspeaker system includes a number of ports configured to reduce acoustic depth mode re-radiation associated with the loudspeaker cabinet during use. The length of a first port is dependent upon the interior depth of the loudspeaker cabinet and the first port is configured such that the half-wavelength resonance of the first port coincides with the half-wavelength depth mode resonance of the loudspeaker cabinet. The length of a second port is less than the length of the first port and the cross sectional area of the first port is approximately equal to the cross sectional area of the second port.

Vibration patterns of the front panel of the loudspeaker system: Measurement conditions and results.

This paper is concerned with an experimental modal analysis of a loudspeaker system. Based on Frequency Response Functions (FRFs) measured in about 500 points uniformly spaced on the front panel of the loudspeaker system several vibrations modes of the loudsneaker membranes have been found. Then, the vibrations of the loudspeaker membranes were compared with vibrations of the cabinet of the loudspeaker system. It has been shown that the vibrations of the loudspeaker case were very small relative to the vibration of the loudspeaker membranes. Thus, the loudspeaker cabinet, which may be considered as a set of vibrating plates, is rather a source of a very weak sound and may be neglected. It does not influence significantly on the acoustics field radiated by the loudspeaker system.

Reduction of loudspeaker polar response aberrations through the application of psychoacoustic error concealment

In a loudspeaker system it is important to have a well controlled polar response: however, with conventional multidriver enclosures off-axis phase cancellation will occur at and around the crossover frequency. To generate a uniform polar radiation pattern from any given imperfect loudspeaker cabinet, it is necessary to reduce the perceived off-axis phase cancellation due to the crossover filters. The paper proposes a correction strategy, which is then evaluated in terms of the perceived improvement. By making use of the psychoacoustic theory of masking, and developing a new strategy for time-varying filters, a creative solution was found whereby the crossover filters cause the phase cancellation to be masked from the listener, rendering it inaudible. The proposed strategy is tested using both auditory models and actual listeners as arbiters of performance. Both test methods confirm that with the proposed strategy an improvement in sound quality at an off-axis position is obtained. The on-axis sound, unaffected, remains the in-phase sum of the loudspeaker driver outputs.

Computational methods for the acoustic modal analysis of an enclosed fluid with application to a loudspeaker cabinet

Computational methods for the acoustic modal analysis of an enclosed fluid are considered. The finite element method is outlined and methods based on the boundary integral equations are reviewed. The discretization of the boundary integral equation results in a non-linear eigenvalue problem. However, through a polynomial approximation with respect to the wavenumber, the non-linear eigenvalue problem is reduced to a standard generalized eigenvalue problem. Methods based on this are applied to the test problems of the axisymmetric three-dimensional cases of a sphere and a cylinder. The physical importance of the interior acoustic resonances of a loudspeaker is discussed. An acoustic modal analysis of an axisymmetric loudspeaker interior is carried out using this method and the results are compared with results from the finite element method and experimental results.

Solid state audio amplifier emulating a tube audio amplifier

A solid state audio amplifier for connection with a loudspeaker cabinet or emulation thereof to provide amplification characteristics emulating in frequency response those of a valve audio amplifier driving a loudspeaker cabinet. The loudspeaker cabinet comprises a loudspeaker drive and its enclosure. The frequency response of the audio amplifier exhibits a low frequency resonant peak in gain representing the fundamental resonance of the loudspeaker cabinet and a monotonic increase in gain at higher frequency associated with the impedance provided voice coil inductance of the loudspeaker cabinet. The audio amplifier comprises an amplifier and gain control circuitry associated therewith. The amplifier comprises a differential amplifier and the gain control circuitry comprises a impedance network connected in feedback. The impedance network comprises a tuned circuit connected to create the low frequency resonant peak in gain and a reactance providing the increase in gain at higher frequency. The tuned circuit comprises a capacitance and a gyrator circuit simulating an inductance and the reactance comprises a capacitance.

Excursion requirements for low-frequency transducers when operated in electrically equalized loudspeaker systems

Electrically equalized loudspeaker systems are found in many professional applications where extended low-frequency response is desired. The maximum amount of equalization which can be applied is usually limited by the driver’s linear excursion. The excursion required is governed by the acoustical loading of the loudspeaker cabinet. It is possible to define the excursion based upon the acoustical parameters of the transducer-box equivalent circuit, using SPICE, for any given set of low-frequency response requirements. It is then immediately seen by the transducer designer whether these linear excursions are possible. Experimental measurements verify the results.

Speaker system with folded audio transmission passage

A loudspeaker cabinet in which an elongated enclosure has a driver mounted internally in one wall thereof in facing, open communication with the exterior of the enclosure and an outlet sound port positioned in spaced relation to the driver in another wall of the enclosure remote from the one wall. An audio transmission passage extends longitudinally at right angles to the axis of the driver and is defined by baffles extending in equally spaced parallel relation to one another to divide the passage into a plurality of communicating folded passage sections extending from open communication with the driver to terminate in the outlet sound port. The total length of the passage through its cross-sectional area is on the order of from 8:1 to 16:1 so that at low frequencies air pulses delivered by the driver will remain in phase throughout the length of the transmission passage.