Improved Directivity of Flat Panel Loudspeakers by Minimizing the Off-Axis Radiation below Coincidence

Benjamin Zenker,Sebastian Merchel,Robert Schurmann,M Ercan Altınsoy

doi:10.3390/app11157001

Abstract

Flat panel loudspeakers are a promising alternative to conventional loudspeakers. In particular, quasi-omnidirectional radiation at higher frequencies is stressed as an advantage of these systems compared to conventional speaker systems. However, this advantage can also be considered a disadvantage. Compared to that from conventional speakers with a flat and smooth on-axis and off-axis response, this wide radiation from flat panel loudspeakers occurs with an inconstant directivity factor, which can cause coloration and unusual spatial artifacts. This paper investigated the root causes of inhomogeneous directivity by using numerical methods. Based on these analyses, specific prototypes with various damping layups were built to overcome this problem. The additional damping layer reduces the off-axis radiation without significantly reducing the pressure level in the listening window. This approach is simple, robust, inexpensive and effective for improving the directivity of flat panel loudspeakers.

Highlights

Flat panel loudspeakers are a promising alternative to conventional loudspeakers.Invisible integration, wide and diffuse radiation and improved room interaction are the advantages of a flat panel loudspeaker design [1]
The previous section explained that damping increases the proportion of traveling waves relative to standing waves
This paper focuses on optimizing the directivity of flat panel loudspeakers below the coincidence frequency by minimizing the off-axis radiation

Summary

Introduction

Flat panel loudspeakers are a promising alternative to conventional loudspeakers.Invisible integration, wide and diffuse radiation and improved room interaction are the advantages of a flat panel loudspeaker design [1]. The moving panel is modeled as a 2D finite element (FE) subsystem with dimensions of 0.3 m2 and a ratio of 2. The boundary element model (BEM) subsystem is used to describe the free-field radiation; it has the outer dimensions of the prototype. The mesh size of the FEA model and the BEM subsystem is chosen to guarantee more than six elements per acoustic wavelength up to 5 kHz according to [19]. The adaptable prototype enables the exchange of different parts of the flat panel loudspeaker for comparison, e.g., different panels with the same boundary conditions. The second prototype featuring bitumen on the frame (BOF) has a damping layer between the frame and the panel, and the panel is decoupled This construction might have similar fixed boundary conditions at lower frequencies, where the bending wavelength is large. No additional mass is attached to the moving panel, and fc should be equal to that of the raw undamped panel

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