AES London 2010
Poster Session P7

P7 - Loudspeakers and Headphones

Saturday, May 22, 16:30 — 18:00 (Room C4-Foyer)
P7-1 Theoretical and Experimental Comparison of Amplitude Modulation Techniques for Parametric Loudspeakers—Wei Ji, Woon-Seng Gan, Peifeng Ji, Nanyang Technological University - Singapore
Due to the self-demodulation property of finite amplitude ultrasonic waves propagating in air, a highly focused sound beam can be reproduced. This phenomenon is known as the parametric array in air. However, because of the nonlinearity effect of ultrasonic waves, the reproduced sound wave suffers from high distortion. Several amplitude modulation techniques have been previously proposed to mitigate this problem. Currently, no comprehensive study has been carried out to evaluate the performance of these amplitude modulation techniques. This paper attempts to provide theoretical and experimental studies of the effectiveness in mitigating the distortion from different amplitude modulation techniques. Objective measurements, such as sound pressure level and total harmonic distortion are used to compare the performance of these techniques.
Convention Paper 8006 (Purchase now)

P7-2 Improvement of Sound Quality by Means of Ultra-Soft Elastomer for the Gel Type Inertia Driven DML Type Transducer—Minsung Cho, Edinburgh Napier University - Edingburgh, UK, SFX Technologies Ltd., Edinburgh, UK; Elena Prokofieva, Edinburgh Napier University - Edingburgh, UK; Jordi Munoz, SFX Technologies Ltd. - Edingburgh, UK; Mike Barker, Edinburgh Napier University - Edingburgh, UK
Unlike standard DML transducers, the gel-type inertia driven transducer (referred to as the gel transducer in this paper) designed as a mini woofer DML-type transducer, transfers its pistonic movement to a panel through the gel surround, thereby generating a transverse wave. This mechanism induces maximum movement of a magnet assembly, which boosts the force of the moving voice coil so that sound pressure level increases as the acceleration of the panel increases. This effect is proportional to sound pressure level at low and medium frequencies in the range 50 Hz to 1000 Hz. Furthermore it is found that the gel surround prevents reflected transverse waves from the panel into interfering with the pistonic waves generated by the transducer. Results of the stiffness testing of the gel surround are presented together with data for the displacement and acceleration of the panel with the gel transducer attached. These data are compared to acoustical outputs.
Convention Paper 8007 (Purchase now)

P7-3 Electrical Circuit Model for a Loudspeaker with an Additional Fixed Coil in the Gap—Daniele Ponteggia, Studio Ing. Ponteggia - Terni, Italy; Marco Carlisi, Ing. Carlisi Marco - Como, Italy; Andrea Manzini, 18 Sound - Division of A.E.B. S.r.l. - Cavriago, Italy
A previous paper by some of the authors investigated a solution to minimize the loudspeaker inductance based on an additional fixed coil positioned in the gap with two additional terminals. This device is referred as A.I.C. (Active Impedance Control). In this paper a suitable electrical circuit model for such loudspeaker with four terminals and two coils is proposed.
Convention Paper 8008 (Purchase now)

P7-4 Measurement of the Nonlinear Distortions in Loudspeakers with a Broadband Noise—Rafal Siczek, Andrzej B. Dobrucki, Wroclaw University of Technology - Wroclaw, Poland
The paper presents application of digital filters for measurement of nonlinear distortion in loudspeakers using Wolf’s method and broadband noise as the exciting signal. The results of simulation of the measurement process for loudspeaker with various nonlinearities of Bl factor and suspension stiffness are presented. The influence of various exciting signals, e.g., white and pink noise as well as the parameters of digital filters have been tested. The results of measurement of an actual loudspeaker are also presented.
Convention Paper 8009 (Purchase now)

P7-5 The Fundamentals of Loudspeaker Radiation and Acoustic Quality—Grzegorz P. Matusiak, New Smart System (AC Systems) - Poznan, Poland and Smørum, Denmark
The loudspeaker designer faces many challenges when designing a new loudspeaker system. The proposed solution is to replace the mathematically complicated series circuit of the radiation impedance by a new one, that can easily be introduced into a loudspeaker circuit in the whole frequency range. It facilitates a designing process and enables to learn more about the loudspeaker. The fundamental resonance in air is lower than in vacuum and depends on the radiating surface, as ACOUSTIC QUALITY, which also depends on frequency. 1/QT=1/QE+1/QM+1/QA. The parameters affect the SPL and efficiency response. Investigated structures: pulsating sphere, baffled circular, square and rectangular piston, infinite strip, unflanged pipe-piston, finally horn (0-infinity Hz).
Convention Paper 8010 (Purchase now)

P7-6 Analysis of Low Frequency Audio Reproduction via Multiple Low-Bl Loudspeakers—Theodore Altanis, John Mourjopoulos, University of Patras - Patras, Greece
Small loudspeakers with low force factors (Bl) behave as narrow bandwidth filters with high quality factors and can be tuned at low resonance frequencies. It is possible to optimize low frequency reproduction (in the sub-woofer range) using a number of such drivers. This paper employs a set of such low Bl loudspeakers with different eigenfrequencies to achieve efficient reproduction of low frequency signals and examines the aspects of such implementation comparing the results to an ideal sub-woofer system and also via perceptual evaluation of these systems.
Convention Paper 8011 (Purchase now)

P7-7 Circular Loudspeaker Array with Controllable Directivity—Martin Møller, Martin Olsen, Finn T. Agerkvist, Technical University of Denmark - Lyngby, Denmark; Jakob Dyreby, Gert Kudahl Munch, Bang & Olufsen A/S - Struer, Denmark
Specific directivity patterns for circular arrays of loudspeakers can be achieved by utilizing the concept of phase-modes, which expands the directivity pattern into a series of circular harmonics. This paper investigates the applicability of this concept applied on a loudspeaker array on a cylindrical baffle, with a desired directivity pattern, which is specified in the frequency interval of 400–5000 Hz. From the specified frequency independent directivity pattern filter transfer functions for each loudspeaker are determined. The sensitivity of various parameters, related to practical implementation, is also investigated by introducing filter errors for each array element. Measurements on a small scale model using 2 inch drivers are compared with simulations, showing good agreement between experimental and predicted results.
Convention Paper 8012 (Purchase now)