AES San Francisco 2008
Paper Session P6
Friday, October 3, 9:00 am — 1:00 pm
P6 - Loudspeaker Design
: Alexander Voishvillo
, JBL Professional - Northridge, CA, USAP6-1 Loudspeaker Production Variance
, Equity Sound Investments - Bloomington, IN, USA; Laurie Fincham
, THX Ltd. - San Rafael, CA, USA
Numerous quality assurance philosophies have evolved over the last few decades designed to manage manufacturing quality. Managing quality control of production loudspeakers is particularly challenging. Variation of subcomponents and assembly processes across loudspeaker driver production batches may lead to excessive variation of sensitivity, bandwidth, frequency response, and distortion characteristics, etc. As loudspeaker drivers are integrated into production audio systems these variants result in broad performance permutation from system to system that affects all aspects of acoustic balance and spatial attributes. This paper will discuss traditional electro-dynamic loudspeaker production variation.
Convention Paper 7530 (Purchase now)P6-2 Distributed Mechanical Parameters Describing Vibration and Sound Radiation of Loudspeaker Drive Units
, University of Technology Dresden - Dresden, Germany; Joachim Schlechter
, KLIPPEL GmbH - Dresden, Germany
—Wolfgang Klippel, University of Dresden, Dresden, Germany; Joachim Schlechter, Klippel GmbH, Dresden, Germany
The mechanical vibration of loudspeaker drive units is described by a set of linear transfer functions and geometrical data that are measured at selected points on the surface of the radiator (cone, dome, diaphragm, piston, panel) by using a scanning technique. These distributed parameters supplement the lumped parameters (T/S, nonlinear, thermal), simplify the communication between cone, driver, and loudspeaker system design and open new ways for loudspeaker diagnostics. The distributed vibration can be summarized to a new quantity called accumulated acceleration level
(AAL), which is comparable with the sound pressure level (SPL) if no acoustical cancellation occurs. This and other derived parameters are the basis for modal analysis and novel decomposition techniques that make the relationship between mechanical vibration and sound pressure output more transparent. Practical problems and indications for practical improvements are discussed for various example drivers. Finally, the usage of the distributed parameters within finite and boundary element analyses is addressed and conclusions for the loudspeaker design process are made.
Convention Paper 7531 (Purchase now)P6-3 A New Methodology for the Acoustic Design of Compression Driver Phase-Plugs with Radial Channels
, Celestion International Ltd. - Ipswich, UK,and GP Acousics (UK) Ltd., Maidstone, UK; Jack Oclee-Brown
, GP Acousics (UK) Ltd. - Maidstone, UK, and University of Southampton, Southampton, UK
Recent work by the authors describes an improved methodology for the design of annular-channel, dome compression drivers. Although not so popular, radial channel phase plugs are used in some commercial designs. While there has been some limited investigation into the behavior of this kind of compression driver, the literature is much more extensive for annular types. In particular, the modern approach to compression driver design, based on a modal description of the compression cavity, as first pioneered by Smith, has no equivalent for radial designs. In this paper we first consider if a similar approach is relevant to radial-channel phase plug designs. The acoustical behavior of a radial-channel compression driver is analytically examined in order to derive a geometric condition that ensures minimal excitation of the compression cavity modes.
Convention Paper 7532 (Purchase now)P6-4 Mechanical Properties of Ferrofluids in Loudspeakers
—Guy Lemarquand, Romain Ravaud, Valerie Lemarquand, Claude Depollier
, Laboratoire d’Acoustique de l’Université du Maine - Le Mans, France
This paper describes the properties of ferrofluid seals in ironless electrodynamic loudspeakers. The motor consists of several outer stacked ring permanent magnets. The inner moving part is a piston. In addition, two ferrofluid seals are used that replace the classic suspension. Indeed, these seals fulfill several functions. First, they ensure the airtightness between the loudspeaker faces. Second, they act as bearings and center the moving part. Finally, the ferrofluid seals also exert a pull back force on the moving piston. Both radial and axial forces exerted on the piston are calculated thanks to analytical formulations. Furthermore, the shape of the seal is discussed as well as the optimal quantity of ferrofluid. The seal capacity is also calculated.
Convention Paper 7533 (Purchase now)P6-5 An Ironless Low Frequency Subwoofer Functioning under its Resonance Frequency
, Université du Maine - Le Mans, France, Orkidia Audio, Saint Jean de Luz, France; Guy Lemarquand
, Université du Maine - Le Mans, France; Bernard Nemoff
, Orkidia Audio - Saint Jean de Luz, France
A low frequency loudspeaker (10 Hz to 100 Hz) is described. Its structure is totally ironless in order to avoid nonlinear effects due to the presence of iron. The large diaphragm and the high force factor of the loudspeaker lead to its high efficiency. Efforts have been made for reducing the nonlinearities of the loudspeaker for a more accurate sound reproduction. In particular we have developed a motor totally made of permanent magnets, which create a uniform induction across the entire intended displacement of the coil. The motor linearity and the high force factor of this flat loudspeaker make it possible to function under its resonance frequency with great accuracy.
Convention Paper 7534 (Purchase now)P6-6 Line Arrays with Controllable Directional Characteristics—Theory and Practice
—Laurie Fincham, Peter Brown
, THX Ltd. - San Rafael, CA, USA
A so-called arc line array is capable of providing directivity control. Applying simple amplitude shading can, in theory, provide good off-axis lobe suppression and constant directivity over a frequency range determined at low-frequencies by line length and at high-frequencies by driver spacing. Array transducer design presents additional challenges–the dual requirements of close spacing, for accurate high-frequency control, and a large effective radiating area, for good bass output, are incompatible with the use of multiple full-range drivers. A novel drive unit layout is proposed and theoretical and practical design criteria are presented for a two-way line with controllable directivity and virtual elimination of spatial aliasing. The PC-based array controller permits real-time changes in beam parameters for multiple overlaid beams.
Convention Paper 7535 (Purchase now)P6-7 Loudspeaker Directivity Improvement Using Low Pass and All Pass Filters
, Excelsior Audio Design & Services, LLC - Gastonia, NC, USA
The response of loudspeaker systems employing multiple drivers within the same pass band is often less than ideal. This is due to the physical separation of the drivers and their lack of proper acoustical coupling within the higher frequency region of their use. The resultant comb filtering is sometimes addressed by applying a low pass filter to one or more of the drivers within the pass band. This can cause asymmetries in the directivity response of the loudspeaker system. A method is presented to greatly minimize these asymmetries through the use of low pass and all pass filters. This method is also applicable as a means to extend the directivity control of a loudspeaker system to lower frequencies.
Convention Paper 7536 (Purchase now)P6-8 On the Necessary Delay for the Design of Causal and Stable Recursive Inverse Filters for Loudspeaker Equalization
—Avelino Marques, Diamantino Freitas
, Polytechnic Institute of Porto - Porto, Portugal
The authors have developed and applied a novel approach to the equalization of non-minimum phase loudspeaker systems, based on the design of Infinite Impulse Response (recursive) inverse filters. In this paper the results and improvements attained on this novel IIR filter design method are presented. Special attention has been given to the delay of the equalized system. The boundaries to be posed on the search space of the delay for a causal and stable inverse filter, to be used in the nonlinear least squares minimization routine, are studied, identified, and related with the phase response of a test system and with the order of the inverse filter. Finally, these observations and relations are extended and applied to multi-way loudspeaker systems, demonstrating the connection of the lower and upper bounds of the delay with the loudspeaker’s crossover filters phase response and inverse filter order.
Convention Paper 7537 (Purchase now)