Saturday, October 5 2:00 pm 6:00 pm
SESSION C: TRANSDUCERS, PART 2
Chair: Steve Hutt, Harman/Becker Automotive Systems, Martinsville, IN, USA
C-1 The Bidirectional Microphone: A Forgotten PatriarchRon Streicher1, Wes Dooley2 - 1Pacific Audio-Visual Enterprises, Pasadena, CA, USA; 2Audio Engineering Associates, Pasadena, CA, USA
Despite being one of the progenitors of all modern microphones and recording techniques, the bi-directional pattern is still not very well understood. Its proper and effective use remains somewhat of a mystery to many recording and sound reinforcement engineers. In this paper the bi-directional microphone is examined from historical, technical, and operational perspectives. We review how it developed and exists as a fundamental element of almost all other single-order microphone patterns. In the course of describing how this unique pattern responds to sound waves arriving from different angles of incidence, we show that it very often can be successfully employed where other more commonly-used microphones cannot.
Convention Paper 5646
C-2 Gaussian Mixture Model Based Methods for Virtual Microphone Signal SynthesisAthanasios Mouchtaris, Shrikanth S. Narayanan, Chris Kyriakakis, University of Southern California, Los Angeles, CA, USA
Multichannel audio can immerse a group of listeners in a seamless aural environment. However, several issues must be addressed such as the excessive transmission requirements of multichannel audio, as well as the fact that to date only a handful of music recordings have been made with multiple channels. Previously, we proposed a system capable of synthesizing the multiple channels of a virtual multichannel recording from a smaller set of reference recordings. In this paper these methods are extended to provide a more general coverage of the problem. The emphasis here is on time-varying filtering techniques that can be used to enhance particular instruments in the recording, which is desired in order to simulate virtual microphones in several locations close to and around the sound source.
Convention Paper 5647
C-3 Driver Directivity Control by Sound RedistributionJan Abildgaard Pedersen, Gert Munch, Bang & Olufsen a/s, Struer, Denmark
The directivity of a single loudspeaker driver is controlled by adding an acoustic reflector to an ordinary driver. The driver radiates upward and the sound is redistributed by being reflected off the acoustic reflector. The shape of the acoustic reflector is nontrivial and yields an interesting and useful directivity both in the vertical and horizontal plane. Two-dimensional FEM simulations and 3-D BEM simulations are compared to free field measurements performed on a loudspeaker using the acoustic reflector. The resulting directivity is related to results of previously reported psychoacoustic experiments.
Convention Paper 5648
C-4 Pressure Response of Line SourcesMark S. Ureda, JBL Professional, Northridge, CA, USA
The on-axis pressure response of a vertical line source is known to decrease at 3 dB per doubling of distance in the near field and at 6 dB in the far field. This paper shows that the conventional mathematics used to achieve this result understates the distance at which the -3 dB to -6 dB transition occurs. An examination of the pressure field of a line source reveals that the near field extends to a greater distance at positions laterally displaced from the centerline, normal to the source. The paper introduces the endpoint convention for the pressure response and compares the on-axis response of straight and hybrid line sources.
Convention Paper 5649
C-5 High Frequency Components for High Output Articulated Line ArraysDoug Button, JBL Professional, Northridge, CA, USA
The narrow vertical pattern achieved by line arrays has prompted much interest in the method for many forms of sound reinforcement in recent years. The live sound segment of the audio community has used horns and compression drivers for sound reinforcement for several decades. To adopt a line array philosophy to meet the demands of high level sound reinforcement, requires an approach that allows for the creation of a line source from the output of compression drivers. Additionally, it is desired that the line array take on different vertical patterns dependent upon use. This requires the solution to allow for the array to be articulated. Outlined in this paper is a waveguide/compression driver combination that is compact and simple in approach and highly suited for articulated arrays.
Convention Paper 5650
C-6 High-Efficiency Direct-Radiator Loudspeaker SystemsJohn Vanderkooy1, Paul M. Boers2 - 1University of Waterloo, Waterloo, Ontario, Canada; 2Philips Research Labs, Eindhoven, The Netherlands
Direct-radiator loudspeakers become more efficient as the total magnetic flux is increased, but the accompanying equalization and amplifier modify the gains thus made. We study the combination of an efficient high-Bl driver with several amplifier types, including a highly efficient class-D amplifier. Comparison is made of a typical simulated driver, excited with a few different amplifier types, using various audio signals. The comparison is quite striking as the Bl value of the driver increases, significantly favoring the class-D amplifier.
Convention Paper 5651
C-7 Audio Application of the Parametric ArrayImplementation through a Numerical ModelWontak Kim1, Victor W. Sparrow2 - 1Bose Corporation, Framingham, MA, USA; 2Pennsylvania State University, University Park, PA, USA
Implementing the parametric array for audio applications is examined through numerical modeling and analytical approximation. The analytical solution of the nonlinear wave equation is used to provide guidelines on the design parameters of the parametric array. The solution relates the source size, input pressure level, and the carrier frequency to the audible signal response including the output level, beam width, and length of the interaction region. A time domain finite difference code that accurately solves the KZK nonlinear parabolic wave equation is used to predict the response of the parametric array. The accuracy of the numerical model is established by a simple parametric array experiment. In considering the implementation issues for audio applications of the parametric array, the emphasis is given to the poor frequency response and the harmonic distortion. Signal processing techniques to improve the frequency response and the harmonic distortion are suggested and implemented through the numerical simulation.
Convention Paper 5652
C-8 Implementation of Straight-Line and Flat-Panel Constant Beamwidth Transducer (CBT) Loudspeaker Arrays Using Signal DelaysD. B. (Don) Keele, Jr., Harman/Becker Automotive Systems, Martinsville, IN, USA
Conventional CBT arrays require a driver configuration that conforms to either a spherical cap-curved surface or a circular arc. CBT arrays can also be implemented in flat-panel or straight-line array configurations using signal delays and Legendre function shading of the driver amplitudes. Conventional CBT arrays do not require any signal processing except for simple frequency-independent shifts in loudspeaker level. However, the signal processing for the delay-derived CBT configurations, although more complex, is still frequency independent. This is in contrast with conventional constant-beamwidth flat-panel and straight-line designs which require strongly frequency-dependent signal processing. Additionally, the power response roll-off of the delay-derived CBT arrays is one-half the roll-off rate of the conventional designs, i.e., 3- or 6-dB/octave (line or flat) for the CBT array versus 6- or 12-dB/octave for the conventional designs. Delay-derived straight-line CBT arrays also provide superior horizontal off-axis response because they do not exhibit the ±90 degree right-left off-axis sound pressure buildup or bulge as compared to conventional circular-arc CBT arrays. In comparison to conventional CBT arrays, the two main disadvantages of delay-derived straight-line or flat-panel CBT arrays are 1) the more complicated processing required, which includes multiple power amplifiers and delay elements; and 2) the widening of the polar response at extreme off-axis angles particularly for arrays that provide wide coverage with beam widths greater than 60 degrees. This paper illustrates its findings using numerical simulation and modeling.
Convention Paper 5653