Saturday, May 20, 09:00 — 12:30 (Salon 2+3 Rome)
Aki Mäkivirta (Chair)
P02-01 Active Vibration Control of Breakup Modes in Loudspeaker Diaphragms
William Cardenas (Presenting Author)
One of the factors that contribute to the degradation of the sound quality of the loudspeakers are the breakup modes of the membrane since they cause complex directivity patterns, peaks, and deeps in the frequency response. This paper presents an active vibration control simulation applied to a 2D Finite Element model of a loudspeaker loaded by a fluid domain to demonstrate an innovative alternative to reduce the amplitude of the breakup modes of loudspeaker diaphragms, improving substantially the mechanical and acoustical performance. The benefits of the controlled system are demonstrated in terms of the acceleration response of the cone and the acoustic directivity.
Convention Paper 9693
P02-02 An Acoustic Radiator with Integrated Cavity and Active Control of Surface Vibration
Arthur Berkhoff (Presenting Author), Farnaz Tajdari (Author)
This paper presents a method to realize an acoustic source for low frequencies with relatively small thickness. A honeycomb plate structure that is open on one side combines the radiating surface and the major part of the air cavity. The vibration of the plate is controlled with a decentralized feedback controller. The fundamental resonance is controlled, as well as higher-order bending modes, while avoiding possible instabilities due to the fluid-structure interaction. The smooth and well defined frequency response enables robust feedforward control for further response equalization. The influence of different actuation principles on the overall system efficiency is compared.
Convention Paper 9694
P02-03 The Acoustic Design of Minimum Diffraction Coaxial Loudspeakers with Integrated Waveguides
Aki Mäkivirta (Presenting Author), Thomas Lund (Author), Ilpo Martikainen (Author), Siamäk Naghian (Author), Jussi Väisänen (Author)
Complementary to precision microphones, creating an ideal point source monitoring speaker has long been considered the holy grail of loudspeaker design. Coaxial transducers unfortunately typically come with several design compromises, such as adding intermodulation distortion, giving rise to various sources of diffraction, and resulting in somewhat restricted maximum output performance or frequency response. In this paper we review the history of coaxial transducer design, considerations for an ideal point source loudspeaker, discuss the performance of a minimum diffraction coaxial loudspeaker and describe novel designs where the bottlenecks of conventional coaxial transducers have been eliminated. In these, the coaxial element also forms an integral part of a compact, continuous waveguide, thereby further facilitating smooth off-axis dispersion.
Convention Paper 9695
P02-04 Root Cause Analysis of Rocking Modes in the Nonlinear Domain
Andreas Schwock (Presenting Author), William Cardenas (Author), Mattia Cobianchi (Author), Wolfgang Klippel (Author)
Rocking modes are caused by small imbalances in the distribution of stiffness, mass, and force factor. A measurement technique to determine these root causes, using laser vibrometry, parameter identification, and root causes analysis has been presented in a previous paper. This paper focuses on the application of this technique to examine rocking modes in nonlinear domain. An incremental DC-offset is applied to the loudspeaker to examine changes of the root causes of the rocking throughout the working range of the loudspeaker.
Convention Paper 9696
P02-05 Nonlinearity of Ported Loudspeaker Enclosures
Juha Backman (Presenting Author)
This paper presents the results of a computational fluid dynamics analysis of an unlined ported enclosure, focusing on the behavior around the tuning frequency. The work presents results for the amplitude dependence of the behavior and the time development of the sound field. The results indicate that the vortex formation around the port ends has a significant effect already at a relatively low flow velocities, and that the nonlinearity of the port is clearly visible in the acoustical load seen by the driver at the resonance frequency.
Convention Paper 9697
P02-06 Efficiency Investigation of Subwoofer Driven Around Resonance Frequency
Tobias Thydal (Presenting Author), Niels Elkj'r Iversen (Author), Arnold Knott (Author)
The need for efficient portable speaker systems has increased tremendously over the past 10 years. The batteries, amplifiers, and filtering has all seen great improvements in efficiency leaving the speakers’ units as the most inefficient part of the system, mainly due to the large amounts of current drawn that ends up being dissipated as heat in the voice coil. This paper will look at how you can design a speaker system to take advantage of the resonance of a speaker unit, since that is where the unit is most efficient and draws the least current. A subwoofer speaker system will be designed with focus on only driving the speaker units near their resonance frequency. The tests found that with modern DSP it was rather simple to design a speaker system that operates in a very narrow frequency band around the speaker units’ resonance frequencies, which in turn ensured a very small current draw. This greatest drawback of this method is the increase in components needed, which drives up cost and complexity.
Convention Paper 9698
P02-07 An Analytical Approach for Optimizing the Curving of Line Source Arrays
Florian Straube (Presenting Author), David Albenés Bonillo (Author), Frank Schultz (Author), Stefan Weinzierl (Author)
Line source arrays (LSAs) are used for large-scale sound reinforcement aiming at the synthesis of homogeneous sound fields for the whole audio bandwidth. The deployed loudspeaker cabinets are rigged with different tilt angles and/or electronically controlled in order to provide the intended coverage of the audience zones and to avoid radiation towards the ceiling, reflective walls or residential areas. This contribution introduces the analytical polygonal audience line curving (PALC) approach for finding appropriate LSA cabinet tilt angles with respect to the geometry of the receiver area, and the intended coverage. PALC can be previously applied to a numerical optimization of the loudspeakers’ driving functions. The method can be used with different objectives, such as a constant interaction between adjacent cabinets with respect to the receiver geometry or by additionally considering amplitude attenuation. PALC is compared with typical standard LSA curving schemes. The advantages of the presented approach regarding sound field homogeneity and target-oriented radiation will be shown with the help of technical quality measures.
Convention Paper 9699