AES London 2010
Paper Session P5

P5 - Loudspeakers and Headphones: Part 1

Saturday, May 22, 14:00 — 18:00 (Room C5)
Chair: Mark Dodd, GP Acoustics - UK

P5-1 Micro Loudspeaker Behavior versus 6½-Inch Driver, Micro Loudspeaker Parameter Drift—Bo Rohde Pedersen, Aalborg University Esbjerg - Esbjerg, Denmark
This study tested micro loudspeaker behavior from the perspective of loudspeaker parameter drift. The main difference between traditional transducers and micro loudspeakers, apart from their size, is their suspension construction. The suspension generally is a loudspeaker's most unstable parameter, and the study investigated temperature drift and signal dependency. There is investigated three different micro loudspeakers and compared their behavior to that of a typical bass mid-range loudspeaker unit. There is measured all linear loudspeaker parameters at different temperatures.
Convention Paper 7988 (Purchase now)

P5-2 Modeling a Loudspeaker as a Flexible Spherical Cap on a Rigid Sphere—Ronald Aarts, Philips Research Europe - Eindhoven, The Netherlands, Technical University Eindhoven, Eindhoven, The Netherlands; Augustus J. E. M. Janssen, Technical University Eindhoven - Eindhoven, The Netherlands
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 moving rigid spherical cap. Series expansions, valid in the whole space on and outside the sphere, for the pressure due to a harmonically excited, flexible 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. This has the advantage that 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 in orthogonal Zernike polynomials. The efficacy of the approach is exemplified by calculating various acoustical quantities with particular attention to certain velocity profiles that vanish at the rim of the cap to a desired degree. These quantities are: the sound pressure, polar response, baffle-step response, sound power, directivity, and acoustic center of the radiator. The associated inverse problem, in which the velocity profile is estimated from pressure measurements around the sphere, is feasible as well since the number of expansion coefficients to be estimated is limited. This is demonstrated with a simulation.
Convention Paper 7989 (Purchase now)

P5-3 Closed and Vented Loudspeaker Alignments that Compensate for Nearby Room Boundaries—Jamie A. S. Angus, University of Salford - Salford, Greater Manchester, UK
The purpose of this paper is to present a method of designing loudspeakers in which the presence of the nearest three boundaries are taken into account in the design of the low frequency speaker. The paper will first review the effects of the three boundaries. It will then discuss how these effects might be compensated for. The paper will then examine the low frequency behavior of loudspeaker drive units and make suggestions for new alignments, which take account of the boundaries. It will conclude with some simulation examples.
Convention Paper 7990 (Purchase now)

P5-4 Point-Source Loudspeaker Reversely-Attached Acoustic Horn: Its Architecture, Acoustic Characteristics and Application to HRTF Measurements—Takahiro Miura, Teruo Muraoka, Tohru Ifukube, The University of Tokyo - Tokyo, Japan
It is ideal to measure acoustic characteristics by point-source sound. In the case when simultaneous recording of single source by multiple microphones located at under 1 m from the source, it is difficult to regard the loudspeaker as a point-source. In this paper we propose a point-source loudspeaker whose radiation diameter is smaller than 2 cm. The loudspeaker is designed to attach the mouse of hyperbolic horn to the diaphragm of a loudspeaker unit. Directional patterns of the proposed was measured at a distance of 50 cm from the radiation point in anechoic chamber. As a result, the difference of directional intensity at the frequency range of 20 - 700 Hz were within 3 dB at any combination of azimuth and elevation. At the frequency range over 700 Hz, difference of azimuthal directional intensity were within 10 dB while that of the elevational ones were within 20 dB.
Convention Paper 7991 (Purchase now)

P5-5 The Low-Frequency Acoustic Center: Measurement, Theory, and Application—John Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada
At low frequencies the acoustic effect of a loudspeaker becomes simpler as the wavelength of the sound becomes large relative to the cabinet dimensions. One point acoustically acts as the center of the speaker at the lower frequencies. Measurements and acoustic boundary-element simulations verify the concept. Source radiation can be expressed as a multipole expansion, consisting of a spherical monopolar portion and a significant dipolar part, which becomes zero when the acoustic centre is chosen as the origin. Theory shows a strong connection between diffraction and the position of the acoustic center. General criteria are presented to give the position of the acoustic center for different geometrical cabinet shapes. Polar plots benefit when the pivot point is chosen to be the acoustic center. For the first of several applications we consider a subwoofer, whose radiation into a room is strongly influenced by the position of the acoustic center. A second application that we consider is the accurate reciprocity calibration of microphones, for which it is necessary to know the position of the acoustic center. A final application is the effective position of the ears on the head at lower frequencies. Calculations and measurements show that the acoustic centers of the ears are well away from the head.
Convention Paper 7992 (Purchase now)

P5-6 Prediction of Harmonic Distortion Generated by Electro-Dynamic Loudspeakers Using Cascade of Hammerstein Models—Marc Rebillat, LIMSI-CRNS - Orsay, France, LMS (CNRS, École Polytechnique), Palaiseau, France; Romain Hennequin, Institut TELECOM, TELECOM ParisTech - Paris, France; Etienne Corteel, sonic emotion - Oberglatt (Zurich), Switzerland; Brian F. G. Katz, LIMSI-CRNS - Orsay, France
Audio rendering systems are always slightly nonlinear. Their non-linearities must be modeled and measured for quality evaluation and control purposes. Cascade of Hammerstein models describes a large class of nonlinearities. To identify the elements of such a model, a method based on a phase property of exponential sine sweeps is proposed. A complete model of non-linearities is identified from a single measurement. Cascade of Hammerstein models corresponding to an electro-dynamic loudspeaker are identified this way. Harmonic distortion is afterward predicted using the identified models. Comparisons with classical measurement techniques show that harmonic distortion is accurately predicted by the identified models over the entire audio frequency range for any desired input amplitude.
Convention Paper 7993 (Purchase now)

P5-7 Characterizing Studio Monitor Loudspeakers for Auralization—Ben Supper, Focusrite Audio Engineering Ltd. - High Wycombe, UK
A method is presented for obtaining the frequency and phase response, directivity pattern, and some of the nonlinear distortion characteristics of studio monitor loudspeakers. Using a specially-designed test signal, the impulse response and directivity pattern are measured in a small recording room. A near-field measurement is also taken. An algorithm is presented for combining the near- and far-field responses in order to compute out the early reflections of the room. Doppler distortion can be calculated using recorded and measured properties of the loudspeaker. The result is a set of loudspeaker impulse and directional responses that are detailed enough for convincing auralization.
Convention Paper 7994 (Purchase now)

P5-8 Automated Design of Loudspeaker Diaphragm Profile by Optimizing the Simulated Radiated Sound Field with Experimental Validation—Patrick Macey, PACSYS Limited - Nottingham, UK; Kelvin Griffiths, Harman International Automotive Division - Bridgend, UK
Loudspeaker designers often aim to reduce acoustic effects of diaphragm resonance from the frequency and power response. However, even in the domain of simulation models, this often requires considerable trial and error to produce a satisfactory outcome. A modeling platform to simulate loudspeakers is presented, which can automatically cycle through vast permutations guided by a carefully considered objective function until convergence is achieved, and importantly, the entire iterative effort is accommodated by the computer. Experience and knowledge must make an initial evaluation of which factors are important in achieving a desired result a priori. Once prepared, the basis of a rapid loudspeaker development tool is formed that can return a tangible resource profit when compared to successive manual efforts to optimize loudspeaker components.
Convention Paper 7995 (Purchase now)