AES San Francisco 2008
Paper Session P10
Nonlinearities in Loudspeakers
Friday, October 3, 2:30 pm — 5:00 pm
: Laurie Fincham
, THX Ltd. - San Rafael, CA, USAP10-1 Audibility of Phase Response Differences in a Stereo Playback System. Part 2: Narrow-Band Stimuli in Headphones and Loudspeakers
—Sylvain Choisel, Geoff Martin
, Bang & Olufsen A/S - Struer, Denmark
An series of experiments were conducted in order to measure the audibility thresholds of phase differences between channels using mismatched cross-over networks. In Part 1 of this study, it was shown that listeners are able to detect very small inter-channel phase differences when presented with wide-band stimuli over headphones, and that the threshold was frequency dependent. This second part of the investigation focuses on listeners’ abilities with narrow-band signals (from 63 to 8000 Hz) in headphones as well as loudspeakers. The results confirm the frequency dependency of the audibility threshold over headphones, whereas for loudspeaker playback the threshold was essentially independent of the frequency.
Convention Paper 7559 (Purchase now)P10-2 Time Variance of the Suspension Nonlinearity
, Technical University of Denmark - Lyngby, Denmark; Bo Rhode Petersen
, Aalborg University - Esbjerg, Denmark
It is well known that the resonance frequency of a loudspeaker depends on how it is driven before and during the measurement. Measurement done right after exposing it to high levels of electrical power and/or excursion giver lower values than what can be measured when the loudspeaker is cold. This paper investigates the changes in compliance the driving signal can cause, this includes low level short duration measurements of the resonance frequency as well as high power long duration measurements of the nonlinearity of the suspension. It is found that at low levels the suspension softens but recovers quickly. The high power and long term measurements affect the nonlinearity of the loudspeaker, by increasing the compliance value for all values of displacement. This level dependency is validated with distortion measurements and it is demonstrated how improved accuracy of the nonlinear model can be obtained by including the level dependency.
Convention Paper 7560 (Purchase now)P10-3 A Study of the Creep Effect in Loudspeakers Suspension
, Technical University of Denmark - Lyngby, Denmark; Knud Thorborg, Carsten Tinggaard
, Tymphany A/S - Taastrup, Denmark
This paper investigates the creep effect, the visco elastic behavior of loudspeaker suspension parts, which can be observed as an increase in displacement far below the resonance frequency. The creep effect means that the suspension cannot be modeled as a simple spring. The need for an accurate creep model is even larger as the validity of loudspeaker models are now sought extended far into the nonlinear domain of the loudspeaker. Different creep models are investigated and implemented both in simple lumped parameter models as well as time domain nonlinear models, the simulation results are compared with a series of measurements on three version of the same loudspeaker with different thickness and rubber type used in the surround.
Convention Paper 7561 (Purchase now)P10-4 The Influence of Acoustic Environment on the Threshold of Audibility of Loudspeaker Resonances
, Bang & Olufsen A/S - Struer, Denmark and University of Surrey, Guildford, Surrey, UK; Sylvain Choisel
, Bang & Olufsen A/S - Struer, Denmark
Resonances in loudspeakers can produce a detrimental effect on sound quality. The reduction or removal of unwanted resonances has therefore become a recognized practice in loudspeaker tuning. This paper presents the results of a listening test that has been used to determine the audibility threshold of a single resonance in different acoustic environments: headphones, loudspeakers in a standard listening room, and loudspeakers in a car. Real loudspeakers were measured and the resonances modeled as IIR filters. Results show that there is a significant interaction between acoustic environment and program material.
Convention Paper 7562 (Purchase now)P10-5 Confirmation of Chaos in a Loudspeaker System Using Time Series Analysis
, Queen Mary, University of London - London, UK; Ivan Djurek, Antonio Petosic
, University of Zagreb - Zagreb, Croatia; Danijel Djurek
, AVAC – Alessandro Volta Applied Ceramics, Laboratory for Nonlinear Dynamics - Zagreb, Croatia
The dynamics of an experimental electrodynamic loudspeaker is studied by using the tools of chaos theory and time series analysis. Delay time, embedding dimension, fractal dimension, and other empirical quantities are determined from experimental data. Particular attention is paid to issues of stationarity in the system in order to identify sources of uncertainty. Lyapunov exponents and fractal dimension are measured using several independent techniques. Results are compared in order to establish independent confirmation of low dimensional dynamics and a positive dominant Lyapunov exponent. We thus show that the loudspeaker may function as a chaotic system suitable for low dimensional modeling and the application of chaos control techniques.
Convention Paper 7563 (Purchase now)