Audio Engineering Society Standards Committee

May 2001 report of SC-04-01

[Last printing 18 September 2001] Report of the SC-04-01 Working Group on Acoustics and Sound Source Modeling of the SC-04 Subcommittee on Acoustics meeting, held in conjunction with the AES 110th Convention in Amsterdam, The Netherlands, 2001-05- 11

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

Current development projects

AES-X05 Room and Source Simulators: Specification and Evaluation of Computer Models for Design and Auralization; Recommendations for Transportable Input and Output Files

W. Ahnert had posted to the WG FTP site the EASE (tm) text file export of a proposed model room containing a stage enclosure, a wall subdivision and a free-hanging banner. Campbell entered the geometry into Computer Aided Theater Technique (tm) (CATT). These documents provided a basis for establishing a useful geometric database that can be used for file exchange.

The group recognized that geometry file interchange will require manual intervention by the recipient in most cases. Some detailed adjustments in the room model to make the recipient program run properly will almost always be required.

Some differences in interpretation became apparent, so the group selected the definitions, tokens, and coding to be used. The provisions decided by the group are on the WG FTP site as X05-wg-PTD-010614.pdf.

The group emphasized the importance of cataloging the maximum capability of each room modeling program so that exported geometries do not exceed agreed limits. Some programs, for example, have surface counts that are limited only by memory, but others have a specific numeric limit. The variables associated with this issue were added to the draft.

The group decided that if a wall is subdivided, then the subdivisions are to be listed immediately following the entry for the wall.

Furthermore, if a program uses mirroring to take advantage of symmetry, the mirrored corners are to be exported as unique corners. All export files are to be assumed to have asymmetric geometry. Surface coefficients are to be expressed as a series of absorption coefficients, followed by an alphameric indicator, followed by diffusion coefficients.

It decided that these coefficients should follow the library label of the surface.

Some members of the group pointed out that some programs use corner definitions, including indices, which are separate from surface definitions. The construction of the surfaces or planes of the model proceeds from referencing corner indices. The group felt that an exported interchange text file should not use corner indices, but list the corners grouped as surfaces or planes.

The group further decided that if the exporting program does not use surface labels, the set of quotes shall still be present in the exported file.

The group left undefined for the moment sources that are represented as a point in three-dimensional space relative to the source geometry. Included, for example, were acoustic center, and line-array detail.

The group proposed that sources may have delay expressed in milliseconds, alignment expressed in microseconds, and phase data associated with them.

The group felt that sources may have directivity; but at this point, the draft only accommodates spherical or omnidirectional radiators.

It further proposed that sources may have frequency response expressed as a sensitivity in sound-pressure level at 1 meter for 1-W input.

AES-X70 Smoothing Digitally-derived Frequency Response Data on A Fractional Octave Basis

No action was taken. A status report shall be prepared by 2001-09.

AES-X83 Loudspeaker Polar Radiation Measurements Suitable for Room Acoustics

The chair presented an illustration that describes one possible classification of loudspeaker radiation data density based upon the intended application of loudspeakers. This was extensively discussed, and it was concluded that the subject deserves a project of its own. All agreed that it would be a useful first step in furthering the AES-X83 effort, but that is important enough to warrant a separate project.

The chair agreed to send his presentation slides to to the vive-chair for further editing, then post them on the WG FTP site by 2001-09.

He proposed that the new project be initiated with the title "Loudspeaker Radiation and Acoustical Surface Data Measurements: How They Apply to Usage Environments."

AES-X108 Measurement of the acoustical and electroacoustic characteristics of personal computers

No action was taken. A status report shall be prepared by 2001-09.

New projects

The chair submitted the project initiation request for "Loudspeaker Radiation and Acoustical Surface Data Measurements: How They Apply to Usage Environments" to the secretariat, pending SC-04 approval.

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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