Saturday, October 11 2:00 pm 5:00 pm
Session I Loudspeakers: Part 2
I-1 A Virtual Loudspeaker Model to Enable Real-Time Listening Tests in Examining the Audibility of High-Order Crossover NetworksBrandon Cochenour, David Rich, Lafayette College, Easton, PA, USA
Higher-order notched networks more consistently retain a desired all-pass response of loudspeakers. However, their noncoincident drivers cause deep spectral notches to occur intermittently in the crossover region. Large phase shifts are also introduced in the loudspeakers transfer response. To evaluate the sonic impact of the deep spectral nulls and phase shifts to the overall listening experience, we propose a real-time listening test that does not involve the design of real loudspeakers or modification of the loudspeakers sound in a listening environment. A speaker system simulation program has been developed using Matlab to process wave files of music clips using a virtual model of the loudspeaker that covers real crossover networks, offset delays, any compensation networks, and raw driver frequency response characteristics. ABX double-blind testing methodology is applied in the program to determine the audibility of the virtual loudspeaker model under test. This approach can isolate audible effects and make them more readily apparent to the listener since other effects, which might mask the changes brought about by the features under study, are eliminated. We expect that the software can serve as a generalized template to examine other phenomena.
I-2 Tracking Changes In Linear Loudspeaker Parameters with Current FeedbackAndrew Bright, Nokia Corporation, Helsinki, Finland
This paper explains how, that if the total moving mass of a loudspeaker can be known in advance, all of the remaining basic linear loudspeaker parameters can be determined using only current feedback. This is explained at a theoretical and practical level. Frequency- and time-domain algorithms for tracking the parameters are presented. Examples of the tracking performance of an adaptive algorithm operating with a real music signal on an actual loudspeaker are shown.
I-3 Comparative Analysis of Moving-Coil Loudspeakers Driven by Voltage and Current SourcesRosalfonso Bortoni, Sidnei Noceti Filho, Rui Seara, Federal University of Santa Catarina, Florianópolis, Brazil
The Thiele-Small method for speaker design considers the linear loudspeaker model driven by voltage sources and operating in a small signal environment. Subsequent studies have been made to introduce into the model some nonlinear characteristics due to the operation with large signals. This paper presents a comparative analysis of the sound pressure level and cone displacement of loudspeaker systems as an infinite baffle, a closed box, a vented box, and band-pass enclosure driven by voltage and current sources, under small and large signals. The nonlinearities of the voice-coil, force factor, and compliance of the loudspeaker are taken into account.
I-4 Loudspeakers Electric Models for Study of the Efforts in Audio Power AmplifiersRosalfonso Bortoni, Studio R Electronics, São Paulo, Brazil; Homero Sette Silva, Selenium Loudspeakers, Nova Santa Rita, Brazil
This paper presents electric models for loudspeakers installed on baffles and enclosures, as closed box, bass-reflex, fourth- and sixth-order band-pass enclosures, using passive crossovers from two-way to three-way, whose impedance curves were derived from MATLAB® simulations. The impedance curves, its module and phase, are presented for each one of the cited models above. The transfer functions are also presented, in addition to the necessary considerations to get the results from the loudspeakers specifications, dimensions, and box tuning. Examples of the efforts caused in the output stages of audio power amplifiers are presented and commented on.
I-5 Nonlinear Versus Parametric Effects in Compression DriversAlexander Voishvillo, Cerwinski Labs Inc., Simi Valley, CA, USA
The compression driver has always been and remains an essential component of sound reinforcement systems despite its unavoidable nonlinear distortion. This distortion is caused by various effects including adiabatic compression of air in the front chamber, modulation of the chambers air stiffness, and modulation of the chambers viscous losses. Each of these sources of distortion is inherent in the drivers operation; each of them adversely affects compression drivers performance in its own specific way; each one is characterized by a different nonlinear signature. Comparative analysis of these distortion sources is undertaken. Nonlinear and parametric effects are explicitly expressed. The influence of diaphragm displacement, compression ratio, and chamber sound pressure on the generation of intermodulation and harmonic distortion is explored. Some design recommendations are given.
I-6 Measurement of Equivalent Input DistortionWolfgang Klippel, Klippel GmbH, Dresden, Germany
A new technique for measuring nonlinear distortion in transducers is presented which considers a priori information from transducer modeling. Transducers are single input-multiple output systems (SIMO) where the dominant nonlinearities can be concentrated in a single source adding nonlinear distortion to the input signal. The equivalent input distortion at this source can easily be derived from the measured sound pressure signal by performing a filtering with the inverse transfer response prior to the spectral analysis. This technique reduces the influence of the acoustical environment (room), removes redundant information, and simplifies the interpretation. It is also the basis for speeding up distortion measurements for the prediction of distortion in the sound field and for the detection of noise and other disturbances not generated by the transducer.