Last Updated: 20050401, meiTuesday, May 31, 14:30 — 16:00
Z11-1 Simulation Tools in Electroacoustics: Comparison with Experimental Measurements—Juan Gómez-Alfageme, Beatriz Sanchez-Alonso, Universidad Politécnica de Madrid - Madrid, Spain
This is a continuation of our paper presented at the AES 114th Convention in Amsterdam 2003 (Paper 5758). We have furthered our testing of the proposals set out in that paper. First, a prototype of the band-pass system was made. The acoustic box was designed with variable geometry, so that it can vary the volume of the two internal cavities as well as the disposition and number of the tuning tubes. It is also possible to vary the diameter and longitude of these tubes. Next, different measurements on the band-pass system was made in an anechoic room. Last, comparisons between the measurements and simulations were developed, as described in the previous paper. In conclusion, the results of the comparison are very positive, which allows us to validate the simulations developed and to continue to use them as training tools both in teaching and in prototype developing.
Convention Paper 6516 (Purchase now)
Z11-2 Measurement and Analysis of Subharmonics and Other Distortions in Compression Drivers—Fernando Bolaños, Acústica Beyma S.A. - Valencia, Spain
This paper presents the results of the subharmonic analysis of single suspension loudspeakers such as the compression drivers. The formation, synchronization, and lock-in of the subharmonic frequencies, when working with the analytic form of the pressure signal, have been observed. A parametric or autoparametric (internal resonance) mechanism seems to be the main cause of these subharmonic excitations and responses. The modal shape of the moving assembly including the diaphragm, coil, former, and suspension has an important role in the whole dynamic of these transducers. One of the four analyzed samples presented a bilinear response because of a spontaneous formation of sidebanding when it was excited in specific spectral regions. Another sample showed a combined behavior that was in between the bilinear character and the locked-in subharmonic. This sample exhibited regions in which the spontaneous sidebanding had a fractal structure. The basic control criterion of subharmonic responses is to avoid specific modes whose eigenfrequencies are multiples of each other.
Convention Paper 6517 (Purchase now)
Z11-3 Dome Tweeter and Concave Woofer: Simulation Model Using Ring Elements—Elena Prokofieva, Linn Products Limited - Glasgow, Scotland, UK
A theoretical investigation of conventional speaker radiation has been presented at AES 116 and 117, 2004 (Papers 6154 and 6246, respectively). The concentric ring element was introduced to simulate the speaker’s diaphragm. The technical characteristics of this element were fully described in previous papers. Four approximations of simulation models were developed to predict the behavior of a real cone speaker. Most of the modern tweeters used in multiway loudspeakers are rigid or soft domes. To describe the geometry of a spherical segment, the approximation with truncated cones can be used. Each cone can be presented as a number of ring elements. The approximation of a concave rigid driver with ring elements is provided in the present paper. The same method can be used for rigid dome tweeters.
Convention Paper 6518 (Purchase now)
Z11-4 Influence of Transfer Functions of Transducers Constituting the Loudspeaker with the Direct D/A Conversion on the Performance of the System—Libor Husník, Czech Technical University - Prague, Czech Republic
This paper deals with the problem of signals used for driving transducers with the direct digital-to-analog conversion, which are sometimes referred to as "digital loudspeakers." Many claim elementary transducers, which transmit bit signals, should have ideally flat impulse responses, imposing a very strict demand on them. In this paper analysis of transducers in the field arrangements acting as signal filters is given. Various types of transducer transfer functions are modeled and their influence on digital (rectangular) signal is shown. As a result, types of transducer transfer functions for usage in digital loudspeakers are discussed.
Convention Paper 6519 (Purchase now)
Z11-5 Active Acoustic Absorption and Reflection—Peter Swarte, P.A.S. Electro-Acoustics - Eindhoven, The Netherlands
The subject called "Active Absorption and Reflection" has already been theoretically discussed during one of the scientific sessions in 1986 of the Dutch Acoustical Society (NAG) in Delft, The Netherlands. The idea behind the subject was laid down in a pending US patent. The patent was granted to Philips in Dec. 1987. The principle with the possible applications is described in publication nr 84 of the NAG d.d. April 1987. Many others have investigated the phenomenon: a 2001 search on the Internet delivered all publications of the Drittes Physikalisches Institut of the University of Göttingen, Germany. A lot of these publications had underwater acoustics as application field. It was not an easy matter to give proof of the feasibility of the idea at that time. Nowadays, the technical possibilities to do investigations and to gather convincing results have dramatically improved. With the help of adequate software implemented on a high-quality personal computer and a special acoustical set up, the measurements can be performed in order to collect results that give a convincing support to the theoretical background. Two types of transducers, i.e., a dynamic and an electrostatic (electret) transducer, have been investigated. The transducers are an element of an electronic positive or a negative feedback circuit. The feed back circuit has to adapt the reflecting or absorbing nature of the diaphragms of the transducers to the desired degree of acoustic absorption or reflection. It is obvious that, at the same time, the transmitting properties of the diaphragms are also influenced. This phenomenon was, in fact, not a subject of this feasibility study. But a quick investigation has shown that the transmission of sound is indeed influenced by the feed back control circuit. In this feasibility study, the measurement set up and the results are explained and discussed. The results are encouraging. But this is only the beginning; a couple of investigations must be executed in order to arrive at a manageable product. The products are expected to cover a wide range of acoustic and electro-acoustic applications.
Convention Paper 6520 (Purchase now)
Z11-6 Prototype of Parametric Array Loudspeaker on Mobile Phone and its Acoustical Characteristics—Yusuke Nakashima, Takeshi Yoshimura, Tomoyuki Ohya, NTT DoCoMo, Inc. - Yokosuka, Kanagawa, Japan
We introduce the use of a parametric array loudspeaker system on a mobile phone and report the acoustic characteristics of a mobile-phone-size super-directional loudspeaker prototype. The prototype has two sets of parametric array loudspeakers that emit narrow ultrasonic beams that are demodulated into audible frequencies by the nonlinearity of air. We realize audible sound pressures above 90 dBSPL at the distance of 50 cm, and also confirm the high directionality of the sound field; the channel separation between the two ears exceeds 30 dB. The small superdirectional loudspeaker makes it possible to provide a personal sound field for hands-free playback in mobile environments.
Convention Paper 6521 (Purchase now)
Z11-7 Modal Optimization of Distributed Mode Loudspeaker—Shen Xiaoxiang, Shen Yong, Dong Yongzheng, Nanjing University - Nanjing, China
The model of a panel with attached mass is developed and the modes of distributed mode loudspeaker (DML) have been analyzed with Rayleigh-Ritz method in this paper. Distribution of bending wave modes is determined not only by the geometrical and elastic parameters of the panel but also by the mass attached on the panel, which can be predicted by our calculation. Therefore, the mass and position of exciters should be considered carefully by the panel’s optimization program. The optimal result using a generic algorithm (GA) is given in this paper.
Convention Paper 6522 (Purchase now)
Z11-8 Nonlinear Loudspeaker Adaptive Controllers Using Kalman and RLS Adaptive Algorithms—Ricardo Adriano Ribeiro, INESC-ID - Lisbon, Portugal, and Instituto Superior Técnico, Lisbon, Portugal; António Joaquim Serralheiro, INESC-ID - Lisbon, Portugal, and Academia Militar, Lisbon, Portugal; Moisés Simões Piedade, INESC-ID - Lisbon, Portugal, and Instituto Superior Técnico, Lisbon, Portugal
The nonlinear behavior of loudspeakers is responsible for distorting the sound it reproduces. In order to decrease that distortion, nonlinear controllers are used. However, a good knowledge of the loudspeaker parameters is required so that the controllers can be effective. Based both on a simplified nonlinear model of the loudspeaker and a modification to adaptive filers, systems for the estimation of the mechanical and electrical parameters of the loudspeaker where developed. The application of the Kalman and the RLS adaptive algorithms shown that both converge, although the convergence time for the electrical part estimation system was about 15 times slower than for the mechanical one.
Convention Paper 6523 (Purchase now)
Z11-9 Viscoelastic Aspects of Loudspeaker Drivers—Martial Rousseau, B&W Research Centre - Steyning, West Sussex, UK; John Vanderkooy, B&W Research Centre - Steyning, West Sussex, UK and University of Waterloo, Waterloo, Ontario, Canada
Damping materials used in drivers often give rise to changes in resonance characteristics that can affect their acoustic properties. We study with several techniques the properties of the viscoelastic materials used in the construction of loudspeakers, and the effects of these on parameters of the unit. Two different drivers are studied: one is a conventional unit with rubber surround, which has a relatively low loss, and one with a treated fabric surround, with very high loss. Measurements are taken of the resonance characteristics with increasing temperature, force-displacement loops, and temperature of the surround. The lossy unit shows a significant temperature rise of the surround upon exercise, with a concomitant significant change in resonance frequency. Differential scanning calorimetry (DSC) measurements are made of some samples in an attempt to understand the underlying physical behavior.
Convention Paper 6524 (Purchase now)
©2005 Audio Engineering Society, Inc.