AES Berlin 2014
Paper Session P7
P7 - Transducers—Part 1: Loudspeakers
Monday, April 28, 09:00 — 13:00 (Room Paris)
Markus Koch, Bang & Olufsen Deutschland GmbH - Pullach, Germany
P7-1 Small-Signal Loudspeaker Impedance Emulator—Niels Elkjær Iversen, Technical University of Denmark - Kongens Lyngby, Denmark; Arnold Knott, Technical University of Denmark - Kgs. Lyngby, Denmark
Specifying the performance of audio amplifiers is typically done by playing sine waves into a pure ohmic load. However real loudspeaker impedances are not purely ohmic but characterized by the mechanical resonance between the mass of the diaphragm and the compliance of its’ suspension which vary from driver to driver. Therefore a loudspeaker emulator capable of adjusting its’ impedance to a given driver is in need for measurement purposes. This paper proposes a loudspeaker emulator circuit for small signals. Simulations and experimental results are compared and show that it is possible to emulate the loudspeaker impedance with an electric circuit and that its’ resonance frequency can be changed by tuning two resistors.
Convention Paper 9053 (Purchase now)
P7-2 Dynamic Measurement of Loudspeaker Suspension Parameters Using an Active Harmonic Control Technique—Antonin Novak, Orkidia Audio - Ascain, France; Université du Maine, UMR CNRS 6613 - Les Mans, France; Pierrick Lotton, Université du Maine, UMR CNRS 6613 - Le Mans, France; Laurent Simon, Université du Maine, UMR CNRS 6613 - Le Mans, France
A new nondestructive technique to measure the nonlinear suspension parameters (stiffness Kms and mechanical resistance Rms) of a loudspeaker using an active harmonic control technique is presented. The goal of the active harmonic control is to eliminate the higher harmonics from the displacement signal so that a purely harmonic motion of the diaphragm is ensured. The nonlinear stiffness Kms is then measured as a function of instantaneous and peak displacement; the mechanical resistance Rms is measured as a function of velocity. A frequency dependence of these parameters is also discussed.
Convention Paper 9054 (Purchase now)
P7-3 Auralization of Signal Distortion in Audio Systems Part 2: Transducer Modeling—Wolfgang Klippel, Klippel GmbH - Dresden, Germany
A new method is presented for the auralization of selected distortion components generated by regular nonlinearities inherent in loudspeaker systems. Contrary to the generic approach presented in the first part the alternative approach presented here exploits the results of lumped parameter modeling in the state space. A mixing device generates a virtual output signal comprising nonlinear distortion attenuated or enhanced by a user-defined scaling factor. The auralization output can be used for systematic listening tests or perceptive modeling to determine audibility thresholds and to assess the impact on sound quality of the dominant nonlinearities in loudspeakers.
Convention Paper 9055 (Purchase now)
P7-4 Quantifying Acoustic Measurement Tolerances and Their Importance in the Loudspeaker Supply Chain—Peter John Chapman, Bang & Olufsen a/s - Struer, Denmark
Tolerances are attached to any type of measurement, and acoustical measurements are typically associated with relatively large tolerances. Despite this, measurement results are often quoted to a high degree of precision and test limits are regularly set without consideration of the measurement tolerances involved. Quantifying measurement tolerances in manufacturing in general is well documented; however the literature fails to describe the application of suitable analysis methods to the field of acoustical measurements. The paper presents the consequences of the presence of measurement tolerances in classifying parts and also describes the shortfalls of the Gauge R&R study. How to quantify a capable measurement system is described including a simple method for quantifying acoustical measurement tolerances. This is particularly relevant in quality assurance in loudspeaker production and relates strongly to the definition of test limits and loudspeaker specifications in the supply chain.
Convention Paper 9056 (Purchase now)
P7-5 An Investigation of Loudspeaker Simulation Efficiency and Accuracy Using a Conventional Model, a Near-to-Far-Field Transformation, and the Rayleigh Integral—Ulrik Skov, iCapture ApS - Roskilde, Copenhagen, Denmark; René Christensen, iCapture ApS - Roskilde, Denmark
Simulation on loudspeaker drivers require a conventional fully coupled vibroacoustic model to capture both the effect of the loading mass of the air on the moving parts and the geometric topology of the cone, dust cap, and surround. An accurate vibroacoustic model can be time-consuming to solve, especially in 3-D. In practical applications, this results in poor efficiency concerning the decision-making process to move on to the next simulation model. To overcome this the loudspeaker designer can use either a near-to-far-field transformation or post-process structural only results via the Rayleigh integral to reduce or totally eliminate the computationally demanding open air domain in front of the speaker. These simplifications come with the cost of a frequency dependent inaccuracy. This paper compares for three different drivers (a totally flat, a concave cone, and a convex dome) the efficiency and accuracy of a conventional fully-coupled vibroacoustic model where the measurement point is included in the computational FEA domain with respectively, a reduced air domain model having the measurement point outside the computational FEA domain obtained by a near-to-far-field transformation, and a model relying on the structural only Rayleigh integral post-processing.
Convention Paper 9057 (Purchase now)
P7-6 Mechanical Nonlinearities of Electrodynamic Loudspeakers: An Experimental Study—Balbine Maillou, Université du Maine - LAUM CNRS UMR 6613 - Le Mans, France; Pierrick Lotton, Université du Maine, UMR CNRS 6613 - Le Mans, France; Antonin Novak, Orkidia Audio - Ascain, France; Université du Maine, UMR CNRS 6613 - Les Mans, France; Laurent Simon, Université du Maine, UMR CNRS 6613 - Le Mans, France
Spider and surround suspensions are at the origin of viscoelastic and nonlinear behaviors of loudspeakers because of their assembly geometry and their intrinsic materials. We propose here a new dynamic experimental method to characterize these properties. We drive the loudspeaker moving part with a shaker and measure the driving force, the acceleration, the velocity, and the displacement. Results are presented and discussed for a given loudspeaker, which surround suspensions exhibit viscoelastic behavior.
Convention Paper 9058 (Purchase now)
P7-7 Active Loudspeaker Heat Protection—Stéphan Tassart, STMicroelectronics - Paris, France; Simon Valcin, STMicroelectronics - Grenoble, France; Michel Menu, STMicroelectronics - Grenoble, France
Loudspeakers are devices that accumulate heat during their transduction process. The rise of temperature is potentially harmful for the voice-coil and must be countered by the active heat control (AHC) process when other passive and mechanical dissipation schemes become inefficient. Known AHC aim at limiting the voice-coil temperature through a closed-loop approach and may lead to oscillations and audio artifacts when temperature measurements are available with latency. This paper establishes that an open-loop AHC relying on a dynamic range compressor configured as a brick-wall limiter whose threshold is modulated by the temperature of the magnetic components insures a bounded voice-coil temperature. The temperature of the magnetic assembly and the driving force of the loudspeaker can be both estimated in real-time, respectively by a linear quadratic observer (a Kalman filter) and by an envelope follower. The new AHC scheme is demonstrated and compared to closed-loop AHC on a simulation example.
Convention Paper 9059 (Purchase now)
P7-8 A Novel Moving Magnet Linear Motor—Claudio Lastrucci, Powersoft S.p.a. - Scandicci (FI), Italy
Electrical to acoustic conversion approach has not changed since the beginning of acoustics. New technologies in the electronic amplification domain and latest magnetic materials open a door in the field of alternative methods of acoustic transduction. A new electrodynamic device that considerably improves electrical to acoustical conversion efficiency, sound quality, robustness, and power handling has been developed. A fully balanced and symmetrical moving magnet motor design, along with anysotropic magnetic compound integration, delivers substantial performances in terms of acceleration, linearity, and efficiency providing additional degrees of freedom in high quality professional speaker design.
Convention Paper 9060 (Purchase now)