v3.1, 20040329, ME
Session M Monday, May 10 12:30 h–15:30 h
LOUDSPEAKERS—PART 2
(focus on systems and applications)
Chair: Ilpo Martikainen, Genelec Oy, Iisalmi, Finland
M-1 Performance Comparison of Graphic Equalization and Active Loudspeaker Room Response Controls—Andrew Goldberg, Aki Mäkivirta, Genelec Oy, Iisalmi, Finland
We compare the room response controls available in active loudspeakers to a third-octave graphical equalizer. The room response controls are set using an automated optimization method presented in earlier AES publications. A third-octave ISO frequency constant-Q graphic equalizer is set to minimize the least squares deviation from linear ? within the passband in a smoothed acoustical response. The resulting equalization performance of the two methods is compared using objective metrics, to show how these standard room response equalizing methods perform. For all loudspeaker models pooled together, the room response controls improve the RMS deviation from a linear response from 6.1 dB to 4.7 dB (improvement 22 percent), whereas graphic equalization improves the RMS deviation to 1.8 dB (improvement 70 percent). Both equalization techniques achieve a similar improvement in the broadband balance, which has been shown to affect a subjective lack of coloration in sound systems. The optimization time for a graphic equalizer is up to 48 times longer compared to that of active loudspeaker room response controls.
M-2 Spatially Consistent Reproduction of the Reverberant Sound Field—Graeme Huon, Zeljko Velican, HuonLabs, Victoria, Australia
A new apparatus for reproducing the reverberant field is described. A model is presented for accurately reproducing direct sound, early reflections, and the reverberant field. The requirements for spatially correct reverberant sound field reproduction are considered and some prior approaches reported on. The authors’ two recently reported studies are reviewed and assessed against the requirements for sound reproduction, namely the Depth Render (DR) human acoustic perception model and its implications for direct sound reproduction and the Wave Focus (WF) model for control of low-frequency room modes. The recent extension of WF for mode-controlled coverage of large audiences is also reviewed. Tests of the new reverberant field apparatus are reported for stand-alone, equidistant surround and DR configurations, both with and without wave focus for low frequencies. Patent applications apply.
M-3 The Beneficial Coupling of Cardioid Low-Frequency Sources to the Acoustics of Small Rooms—Lampos Ferekidis, Uwe Kempe, wvier, Lemgo, Germany
Most low-frequency sources radiate energy in an omnidirectional manner. This often leads to unsatisfying results regarding the reproduction of low frequencies in small listening rooms. The influence of different radiation characteristics is investigated concerning the reproduction of low frequencies in a sparsely modal environment. In this paper the room transfer function characteristic of a monopole, a dipole, and a cardioid are compared. The different room mode excitation mechanisms are explained using comparative measurements taken in a reverberation chamber. Furthermore the effect of a single reflective boundary on the low-frequency response is simulated. The cardioid turns out to be the more preferable low-frequency source for the three types investigated.
M-4 Polar Pattern and Energy Response of Transients in Multiway Loudspeakers—Juha Backman, Nokia, Espoo, Finland
The one-cycle time offset between the high-pass and low-pass sections typical to symmetrical constant-amplitude crossover networks implies that the polar pattern is controlled by a single driver (or driver group) during the onset and end of a sharp transient. This implies that the ratio of overall radiated energy to the input energy near the crossover frequency depends on the duration of the transient, which again affects the sound pressure in a reverberant field.
M-5 Near-Field Beam Forming in Security Relevant Work Spaces Using a Set of Linear Loudspeaker Arrays—Roman Beigelbeck1, Heinrich Pichler2
1 Vienna University of Technology, Vienna, Austria
2 Consultant, Vienna, Austria
In security-relevant work spaces, such as air traffic control rooms, near-field beam forming in small spaces is an important task. In this paper a sound design based on a set of n-linear loudspeaker arrays where each consists of m-elliptic loudspeakers is investigated from a mathematical point of view. Based on these results, optimized array parameters are determined and useful approximations are developed. Three-dimensional near-field directional diagrams of the sound pressure in front of the arrays are shown to visualize the sound field. These diagrams are plotted and evaluated for different frequencies and distances of the field point, in addition to variations in the control signal phases and amplitudes. Finally, these theoretical values are compared with practical results.
M-6 A Multiple Regression Model for Predicting Loudspeaker Preference Using Objective Measurements: Part I—Listening Test Results—Sean Olive, Harman International Industries, Inc., Northridge, CA, USA
Part I of this paper presents the objective measurements and listening test results on 13 loudspeakers rated according to preference, spectral balance, and distortion. In Part II the data provides the framework for the development and verification of a multiple regression model that predicts listeners’ preferences based on objective measurements. We review relevant predictive models and test one model currently used by Consumers Union (CU), a consumer product testing organization in the United States. There is no correlation between listeners’ loudspeaker preference ratings and CU’s predicted accuracy scores (r = 0.05; p = .81). As the CU model is based largely on the loudspeaker’s 1/3-octave sound power response, we conclude that measured sound power, alone, cannot accurately predict its perceived sound quality.
