Audio Engineering Society Standards Committee

May 2002 meeting of SC-04-03

[Last printing 11 July 2002] Report of the SC-04-03 Working Group on of the SC-04 Subcommittee on Acoustics meeting, held in conjunction with the AES 112th Convention in Munich, Germany 2002-05-12.

S. Temme convened the meeting at the request of SC-04. The agenda and the report from the previous meeting at the AES 111th Convention were approved as written.

Current development projects

AES-1id-R Review of information document, AES-1id-1991 (r1997) Plane-Wave Tubes: Design and Practice

M. Buck submitted a report on new measurements. D. Queen suggested amending the document to incorporate the new measurements and new references. Task group SC-04-03-D was set up under the leadership of Buck to report with a PTD of the amendment 2002-10. J. Woodgate pointed out that the document is referenced in AES2 so there needs to be coordination of the new additions.

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

The meeting attendees recommended that the group be asked if there are any objections to reaffirmation, considering that there is insufficient time for revisions within the review period. Work on revision, if needed, can then take place after reaffirmation.

AES2-R Revision of AES2-1984 (r1997) Specification of loudspeaker components used in professional audio and sound reinforcement

Woodgate posted a revised PWD on the FTP site before the meeting.

A discussion of the power testing signal took place. Buck suggested that the the crest factor of the currently specified signal is too high after the signal is high passed. He proposed creation of sound files on a Compact Disk (CD) containing the standard noise with various high-pass filtering on different tracks thereby controlling the crest factor. D. Keele was recommended to help with the development because of his experience preparing the EIA-426B CD. Buck also recommended altering the clipping method such to reduce its effect on the spectrum.

Queen suggested a task group be formed to develop the test signal. Buck, Klippel, R. Mihelich and Keele volunteered. Woodgate mentioned that the IEC has worked on the problem. He cautioned that completion of the current AES2 revision should not be dependant on the progress of this task group.

The attention of the meeting then turned to the sensitivity specifications. Woodgate questioned continuing the use of a single-frequency measurement. Temme suggested a third-octave-band sensitivity. J. Brown preferred an average of several third-octave bands. Woodgate replied that wording could state that the sensitivity frequency is specified as the geometric mean of the pass-band frequencies or 1kHz. Queen mentioned that the sensitivity specification in AES2 can be used as a reference point for a frequency response. Woodgate countered that sensitivity at one frequency is not good for many types of loudspeakers but that he would use the new points in the discussion in the new PWD.

He then asked if Thiele-Small parameters should be specified for high-frequency drivers. He will make suggests in the new PWD.

The meeting then turned to the specification of maximum diaphragm displacement (Xmax). Woodgate noted that the specification, although in AES2-1982, is not in the current PWD. No report on the specification was submitted by SC-04-03-C, but W. Klippel presented his independent work. Woodgate suggested that the work could be incorporated in AES2, and that the specification should be applicable to all drivers including high-frequency drivers.

Buck added his belief that the symbol, Xmax, should be abandoned because it has so many meanings to different people.

Klippel countered that Xmax should be better specified by adding a threshold, for example, Xmax = 7 mm at 10% D. D would indicate a basis distortion type such as D2 for second Harmonic, D3 for third Harmonic, D for total Harmonic, D2,I for second-order intermodulation distortion (IM), D3,I for third order IM, and so on. The bases would be actual distortion measurements. The highest distortion could be listed on the data sheet for Xmax. T. Welti added that the end user might want more than just the highest distortion number as it may not be applicable to a particular application. Woodgate cautioned that AES2 is for a manufacturer generated data sheet containing ratings the manufacturer wishes to stand behind. He expressed the opinion that the data sheet must be one page but that the manufacturer can always be asked to provide more information.

Queen asked if the data sheet should also show mechanical excursion limits.

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

Queen suggested the AES should withdraw its edition and give full jurisdiction to the Association of Loudspeaker Manufacturing Acoustics International - (ALMA). Temme said that he is on the ALMA standards committee and will ask its consent to the change.

AES-X72 Acoustic Center of Loudspeakers

A summary report from SC-04-03-B was posted on the WG FTP site. J. Woodgate felt that the last paragraph on the first page is most important where it states that there are three definitions of acoustic center in use, adding that the AES should produce a document to explain differences among the definitions. Queen advised that a standards project report would be the best form because it requires only working-group consensus as confirmed by the subcommittee and is available in the same manner as standards in print. He said the summary report should be sent back to the task group for production of a standards project report.

AES-X129 Loudspeaker Distortion Perception and Measurement

Temme reported that several members have independently posted references on the FTP site or described them on the WG reflector. He asked for a clearer guidance on what data to collect before proceeding. Queen asked if a task group was to be set up to help with such guidance. Woodgate mentioned that he may have some work studying the audibility of frequency modulation. Work by Klipsh was mentioned and Temme cited Zwicker as a good reference. Klippel cited an Acustica reference on audibility of distortion in single tones.

Queen asked if the concern is for tones or music. He cited extensive publication of work on tones in acoustical journals, but less on music even though work on perceptual anomalies in music listeners is extensive. Special sessions on the subject have been presented at AES conventions.

Klippel emphasized that the amplitude of the signals matters. He asked also if the project concerns a typical situation, a rare situation, a likely situation, or some combination, noting that some artists may consider two pure tones music, He recommended a framework that guides marketing based on our understanding of types of distortion. Woodgate added that numbers on data sheets mean little to the listener but AES should provide a document to explain them. Queen added that the document could explain which distortion specifications should be of concern in what situations.

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

By error, the project itself was not placed on the agenda. Discussion of one part of the project relating to a specification in AES2 took place under AES2-R, but no report was presented by task group Sc-04-03-C.

New projects

No project requests were received or introduced.

New Business

There was no new business

The next meeting is scheduled to be held in conjunction with the AES 113th Convention in Los Angeles, CA, US.

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