Audio Engineering Society Standards Committee

May 2001 meeting of SC-04-03

[Last printing 9 August 2001] Report of the SC-04-03 Working Group on Loudspeaker Modeling and Measurement of the SC-04 Subcommittee on Acoustics meeting, held in conjunction with the AES 110th Convention in Amsterdam, The Netherlands, 2001-05-14

Chair D. Prince convened the meeting. The agenda and the report from the previous meeting were approved as written.

Current development projects

AES-1id-R Review of information document AES-1id-1991 Plane-Wave Tubes: Design and Practice

No action was taken. The document was distributed and the chair requested that members review the document for the next meeting. J. Woodgate requested that AES-1id discussions be kept independent from AES2.

AES-5id-R Review of AES-5id-1997 AES information document for Room acoustics and sound-reinforcement systems -- Loudspeaker modeling and measurement -- Frequency and angular resolution for measuring, presenting and predicting loudspeaker polar data

No action was taken.

AES2-R Revision of AES2-1984 (r1996) Specification of loudspeaker components used in professional audio and sound reinforcement

A report of SC-04-03-A meeting on 01-05-12 was given by Woodgate. Considerable discussion ensued the chair feels stemmed from a misunderstanding of a certain terms, these notes intend to summarize the resolved discussions. J. Brown requested clarification on impedance plots. The current intent is that the frequency axis be specified and the vertical axis have several ranges in linear format with a log scale allowed. Difficulty in covering large ranges was acknowledged. Brown desired to see a log axis. S. Temme noted that it is hard to get a number off a log graph and preferred a linear scale.

W. Ahnert questioned the status of polar resolution and phase information. Prince noted that the distributed PTD did not include the latest revisions on polar information. The WG will reference AES-5id and define a minimum number of angles for measurement within the specified coverage angle. AES2 could also reference material developed im project AES-X83 but does not have a proposed document yet.

Prince asked for input from anyone interested in adding to the SC-04-03-A work, particularly on power compression.

A target date for a PWD was set for the 2001-09.

Woodgate encouraged manufacturers to use the PDF format rather than paper for issuing specifications..

B. Webb pointed out that many designers of simpler systems do not need such detailed information as suggested in discussions. Brown argued that he does. Prince suggested that AES2 provide a detailed specification of professional speakers. If a smaller manufacturer targeting less complex systems does not comply with AES2, he felt that is the manufacturers decision and that it is up to consultants and consumers to request compliance with AES2 if they need it. D. Queen and Brown noted that the scope of AES2 was to define a minimum data set for speaker designers to do their job.

At one point after some debate about the scope of AES2 Woodgate expressed concern about members who only offer negative criticism. The AES2 PTD had been on the FTP site for some time and it appeared that some wanted to change the scope late in the process.

Ahnert pointed out that the document has to work for the next twenty years and needs to look forward.

Baird requested that AES-5id be referenced with respect to polar resolution.

Prince reiterated that there are only three or four active members contributing to SC-04-03-A and those with further concern should get involved.

Prince noted also that the current use of small signal parameters and the variations in measurement may warrant an annex or a separate information document exhibiting the errors in method and the limitations of such measures.

J. Stewart volunteered to see if a study of the different measurement techniques was available at Harman.

Woodgate reiterated that the IEC document calls for vented box measurement and that measurement descriptions for the other methods have not been forthcoming for AES2 so he would attempt to describe them himself.

Hutt volunteered to see if D. Small would consider writing a summary on the limitations of small signal measurement.

L. Fincham pointed out that these original authors readily acknowledge that it is a simplified model and only approximate in the linear range which is easily exceeded in regular operation. He noted that the mechanical parameters are to be understood but not the derived.

Woodgate noted that he looks at a V-I figure on a scope in doing impedance sweeps and rarely finds them to be well behaved but points out that it is a qualitative not quantitative measure.

Klippel points out that small-signal parameters have been in good use for some time and just need to be extended. He thinks that large- and small-signal parameters should be examined together and not separately. Accordingly, the examination of small signal parameters could be added to the work in SC-04-03-C.

AES19-R Review of AES19-1992 (r1998) AES-ALMA Standard Test Method for Audio Engineering -- Measurement of the lowest resonance frequency of loudspeaker cones

No action was taken.

AES-X72 Acoustic Center of Loudspeakers

Status report from task group SC-04-03-B was presented. A technical report is planned for 2001-09 in fulfillment of the project.

AES-X103 Large Signal Parameters of Low-Frequency Loudspeaker Drivers

A status report from task group SC-04-03-C was presented. W. Klippel reported that work has been delayed. Prince requested that discussions take place continuously on the e-mail reflector.

Klippel will summarize the current status and put information on the FTP site and reflector. A more complete report will be given in 2001-09.

New projects

Prince introduced the idea of a project to address the perception of distortion as the sound pressure level (SPL) increases, as raised at the 2000-09 meeting and in the work of other task groups within the SC-04-03 group. A. Voishvillo had begun a summary of distortion with respect to multi-tone testing within SC-04-03.

S. Olive noted that he was hoping to pursue research as part of PhD work starting this fall.

Discussion differentiating maximum SPL, frequently used for limits before damage occurs to a speaker, and SPL without distortion ensued. Woodgate pointed out that the maximum SPL measurement methods are defined already within IEC 60268-5 which is referenced by AES2. Webb noted the lack of standards of current measures of maximum SPL.

Woodgate pointed out the difficulty in driver maximum SPL usage since it is dependent on loudspeaker design and construction. But it would be good to define the standard so we at least know what was measured.

Brown pointed out that D. Cabot presented a paper recently on the subject. S. Temme agreed to head up the investigation into this subject. A project will be initiated.

New Business

There was no new business.

The next meeting is scheduled to be held in conjunction with the AES 111th Convention in New York, New York, US.

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