Saturday, October 5 9:00 am 11:30 am
SESSION A: TRANSDUCERS, PART 1
Chair: Marshall Buck, Gibson Labs, Redondo Beach, CA, USA; Psychotechnology Inc.,
A-1 Which Loudspeaker Parameters Are Important to Create the Illusion of a Live Performance in the Living Room? Siegfried Linkwitz, Linkwitz Lab, Corte Madera, CA, USA
The preference in loudspeaker product design is for a small size, while preserving maximum low-frequency extension and output volume. If the goal is to create a realistic reproduction of a live event, then certain speaker parameters must be adequately controlled, such as volume displacement, intermodulation distortion, stored energy, and off-axis frequency response. Components must be carefully selected for low distortion performance. Parameters like phase linearity and cabinet diffraction are sometimes overrated. Multichannel loudspeaker setups require propagation delay correction and bass management if not all of the loudspeakers cover the full frequency range. These issues are reviewed at the advent of high resolution surround sound. The new technology can only fulfill its promise and expand into more than a niche market if capable loudspeakers are widely available.
Convention Paper 5637
A-2 Characterizing the Amplitude Response of Loudspeaker SystemsAllan Devantier, Harman International Industries, Inc., Northridge, CA, USA
The amplitude response of a loudspeaker system is characterized by a series of spatially averaged measurements. The proposed approach recognizes that the listener hears three acoustical events in a typical domestic environment: the direct sound, the early arrivals, and the reverberant sound field. A survey of fifteen domestic multichannel installations was used to determine the typical angle of the direct sound and the early arrivals. The reflected sound that arrives at the listener after encountering only one room boundary is used to approximate the early arrivals, and the total sound power is used to approximate the reverberant sound field. Two unique directivity indices are also defined, and the in-room response of the loudspeaker is predicted from anechoic data.
Convention Paper 5638
A-3 Graphing, Interpretation, and Comparison of Results of Loudspeaker Nonlinearity MeasurementAlexander Voishvillo, Alex Terekhov, Gene Czerwinski, Sergei Alexandrov, Cerwin-Vega Inc., Simi Valley, CA, USA
Harmonic distortion and THD do not convey sufficient information about nonlinearity in loudspeakers and horn drivers. Multitone stimulus and Gaussian noise produce more informative nonlinear response. Reaction to Gaussian noise can be transformed into a coherence or incoherence function. They provide information about nonlinearity in the form of easy-to-grasp frequency-dependent curves. Alternatively, the results of multitone measurement are difficult to interpret, compare, and overlay. A new method of depicting the results of multitone measurements has been developed. The distortion products are averaged in a moving frequency window. The result of the measurement is a single, continuous, frequency-dependent curve that takes into account the level of distortion products and their density. The curves can be easily overlaid and compared. Future development of a new method may lead to correlation between the level of distortion curves and the audibility of nonlinear distortion.
Convention Paper 5639
A-4 The Effects of Voice-Coil Axial Rest Position on Amplitude Modulation Distortion in Loudspeakers Ryan J. Mihelich, Harman/Becker Automotive Systems, Martinsville, IN, USA
The magnetic field in the air gap of a conventional loudspeaker motor is often an asymmetric nonlinear function of axial position. Placement of the voice-coil into this asymmetrical field yields an asymmetric nonlinear force-factor, Bl, which is a primary cause of amplitude modulation distortion in loudspeakers. Adjustment of the rest position of the voice-coil in this field can alter the nature of this modulation distortion. Common practice is to nominally set the voice-coil at the geometric center of the gap or at the position generating maximum Bl. A time-domain nonlinear simulator has been used to investigate effects of voice-coil placement in an asymmetric flux field on amplitude modulation distortion.
Convention Paper 5640
A-5 Nonlinearity in Horn DriversWhere the Distortion Comes From? Alexander Voishvillo, Cerwin-Vega Inc., Simi Valley, CA, USA
Compared to other components of professional sound systems (omitting free propagation distortion), horn drivers have the worst nonlinear distortion. Some of the drivers distortions can be mitigated by proper mechanical measures. However, distortions caused by nonlinear air compression and propagation are inherent to any horn driver. In this paper the comparison of nonlinear distortions caused by different sources is carried through measurements and modeling. The new dynamic model of the compression driver is based on the system of nonlinear differential and algebraic equations. Complex impedance of an arbitrary horn is considered by turning the impedance into a system of differential equations describing the pressure and velocity at the horns throat. The comparison is carried out using harmonic distortion and the reaction to multitone stimulus.
Convention Paper 5641