SC-04-03 meeting, SFO, 2006-10

Report of the SC-04-03 Working Group on Loudspeaker Measurement and Modelling of the SC-04 Subcommittee on Acoustics held in San Francisco, CA, US., 2006-10-06

The meeting was convened by chair J. Stewart

The agenda for the meeting and the report of the previous meeting held 2006-05-20 in Paris, were accepted without comment.

Current projects

AES-5id-R, Loudspeaker modeling and measurement - Frequency and angular resolution for measuring, presenting and predicting loudspeaker polar data
No action was requested or required. Review due in 2008.

Recommended to monitor progress in AES-X083, "Loudspeaker Polar Radiation Measurements".

AES2-R, Specification of loudspeaker components used in professional audio and sound reinforcement
Status: Secretariat format draft recommended in Paris.

M. Buck fielded questions and comments based on the draft of 2006-05-21.

The baseline requirement is for a loudspeaker drive unit specification sheet.

The off-axis description is seen as a simplified alternative to AES-X083. It was agreed to add that a directivity index (DI) of 4 or more needs a 5-degree set of data. If the DI is less than 4, a 15-degree set is adequate. AES2 is not intended to be a comprehensive specification for electronic data sheets.

An editorial correction was made to clause 5.2.

Section 8 on Power handling prompted an active discussion. This discussion included concerns about powered and actively equalized systems, power compression, aging, damage, test signal, impedance ratings, and voltages. Some agreements were reached. It was agreed to remove all reference to powered and active systems from Table 1, p7; to change the title of Section 6; to add low resonance to Section 6.6; and to add reference to the AES-X083 document.

The group assembled agreed to a secretariat release for passive systems only for Vienna.

The group also agreed that a new project would be needed to address the concerns raised in the AES2 discussion. The process for starting a new AES Standards project to address the difficulties of active and powered systems was presented. The question of distortion was raised and the validity of the IEC distortion spec was raised. Are separate component, driver, system, performance, interface, and end-user specifications required? Stewart will initiate an email discussion of a new project on the reflector.

AES-1id-R: Plane-Wave Tubes: Design and Practice
Buck fielded questions and comments based on the draft of 2006-03-14.

Information on impedance and couplers will be added and typographic errors will be corrected. Buck will send electronic figures in black & white to the secretariat for inclusion in the document. The title and table of section 8 will be updated prior to secretariat format.

There were some discussion of the proposed conical adaptor. For example, alternative shapes were suggested by A. Voishvillo. Buck mentioned a L. Beranek reference describing the transmission losses in conical connectors. The only plane-wave-tube users at the meeting were Buck and Voishvillo. Question about compression driver impedance measurements which will be different on the tube compared with a horn. Buck's AES preprint of 2004-10, "Plane Wave Tubes - Uses and Limitations", reviews practical implementation issues. For example, Penn State university fills the plane-wave tube with Helium at 10 bar to raise the frequency of acoustic modes and remove them from the relavant part of the spectrum.

The meeting had no objections to going ahead with mentioned corrections to Secretariat format.

Development projects

AES-X129: Loudspeaker Distortion Perception and Measurement
Status: This will be an information document on the state of our understanding of the perception of nonlinear distortion. Two papers were presented at the 121st. The history of conventional methods and identification and perceptual methods with some thoughts on future developments and multi-tone test techniques were presented. There are two sections remaining to be completed.

Liaisons

IEC
PAS 62458, large signal loudspeaker parameters, and 62459, component material properties, have been released and are available for review on the SC-04-03 website. They are scheduled for review in 2009. It is possible that the content of IEC 62458 will be absorbed into standard IEC 60268-5 along with portions of JIS and/or Chinese standards. Klippel expressed concern that IEC 60268-5 will become too cumbersome and suggested that components, drivers and systems be separated.

Yonge attended the IEC maintenance committee meeting and provided an update on the proposed polarity amendment to IEC 60268-5. It is available for review on the SC-04-03 website. The pre-release comment period is closed. It is expected to be released for comment in October. This is a time domain measurement technique that is not consistent with the methods currently used in many of the commercially available western automated test equipment suites. The members of SC-04-03 are strongly encouraged to participate in the IEC through their national council representative.

ALMA
A liaison meeting was held during the 121st Convention. Dan Field, ALMA Standards Chairman reported that this introductory meeting went well.

New business

A new project, relating to powered loudspeakers, active loudspeakers and band-limited loudspeakers will be open for discussion through the SC-04-03 email reflector site prior to formal initiation.

Date of next meeting will be scheduled in conjunction with the AES 122nd Convention, Vienna, Austria, 2007-05.

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