A Perspective on the Evolution of Sound-System Equalization and its Possible Impact on New Recommended Practices for B-Chain Calibration

SMPTE is exploring processes and technologies that might be used in calibrating the B-chain in movie theater sound systems to improve the overall sound quality and consistency that will be based only on measurements, reducing the need for the subjective judgment recommended in the appendix of SMPTE ST 202:2010. The Audio Engineering Society and InfoComm are also developing new recommended practices and standards for sound-system equalization as well. Time-windowed, 3-dimensional measurements are being considered by all three groups. — The sound-reinforcement industry has been using time-windowed-measurement systems for over 30 years. During this time, a set of measurement techniques have been developed which are very different from those specified in SMPTE's ST 202:2010. These techniques have been shown to be more efficient and accurate, when applied to time-windowed measurements, than the older techniques commonly used for Real-Time Analysis (RTA). Some techniques that have been correctly and effectively applied to RTA measurements, are still being incorrectly applied to time-windowed analysis in the field in both the cinema-sound and sound-reinforcement industries. — The authors are solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of the Society of Motion Picture and Television Engineers (SMPTE), and its printing and distribution does not constitute an endorsement of views which may be expressed. This technical presentation is subject to a formal peer-review process by the SMPTE Board of Editors, upon completion of the conference. Citation of this work should state that it is a SMPTE meeting paper. EXAMPLE: Author's Last Name, Initials. 2011. Title of Presentation, Meeting name and location.: SMPTE. For information about securing permission to reprint or reproduce a technical presentation, please contact SMPTE at jwelch@smpte.org or 914-761-1100 (3 Barker Ave., White Plains, NY 10601). — A brief history of equalization is discussed from the viewpoint of the sound-reinforcement industry. This covers some aspects of the speaker-room interface that have not been applied in the ST-202:2010 standard. This discussion will also cover the evolution of measurement techniques developed specifically for time-windowed measurement, why different techniques are necessary when considering wavelengths above and below the Schroeder Frequency, and why they are more effective than traditional RTA-based techniques when applied to time-windowed measurement. — Finally, a truncated-line-source- (line array) measurement technique will be discussed, as well as issues unique to cinema-sound systems. Hopefully, this paper's discussed techniques will prove to be useful in the development of the new SMPTE sound-system-equalization standard.

Published

2013-10

Content type

Original Research

Keywords

equalization, room curve, ideal room curve, preferred listening curve, room resonances, neutral transfer function, time-windowed, Fast-Fourier Transform, FFT, spectrum analysis, Real-Time Analysis, RTA, time-windowing, ST 202:2010, regenerative method, room modes, room ring modes, standing waves, flat direct sound response, average response

DOI

10.5594/M001502

ISBN

978-1-61482-953-9