SC-04-03 meeting, San Francisco, 2008-10

Report of the meeting of the SC-04-03 Working Group on Loudspeaker Modeling and Measurement of the SC-04 Subcommittee on Acoustics, held in San Francisco, California, USA, 2008-10-02

Committee Scope: The scope of the SC-04-03 Working Group on Loudspeaker Modeling and Measurement includes the specification, modeling, and measurement of the electromechanical and free-field radiation characteristics of loudspeakers, individually and in arrays, intended for propagation of audio signals within the scope of SC-04.

The meeting was convened by chair J. Stewart.

The agenda and the report of the previous meeting, 2008-05-17, were accepted as written.

Open Projects

AES-1id-R: Review of AES-1id-1991 (r2003): Plane-Wave Tubes: Design and Practice
Project scope: to establish, expand, and improve the practice for the design and use of plane-wave tube measurement techniques, as recommended in section 2.2.1 of AES2-1984, "Recommended Practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement."

Assigned to: SC-04-03, Initiated: 2003
Intent: Revision, Target: 2008
Current goal: PTD, Goal date: 2007-10

Status: Secretariat-formatted draft submitted. Graph awaited from M. Buck to finalize an update. Finalized draft submission expected in November.

Discussion: Updates to highlighted areas of the draft included deletion of "high frequency", confirmation of speed of sound in meters, replacement of ANSI standard with IEC-61094-[many], and confirmation of one inch tube.

Post-release ideas included the addition of references to G. Behler publications, and the possibility of refining the information document into a standard or a measurement procedure.

Revision must be released by the end of the year or we will have to act to reaffirm the current version.

This group agreed the section-by-section email reflector review is not warranted for this update.

AES-5id-R: Review of AES-5id-1997 (r2003): 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
Project scope: This document provides guidelines for measuring, presenting, and predicting polar data from a single acoustic source or from an array of acoustic sources. It describes and quantifies possible errors, defined as differences in numeric values, associated with measurement resolution, presentation resolution, prediction techniques and measurement environments.

Assigned to: SC-04-03, Initiated: 2003-03
Intent: Review, Target: 2008
Current goal: Status report, Goal date: Continuing

Status: Proposal to be withdrawn upon release of AES56

Discussion: AES56 Call for Comment period ends in mid-December.

AES2-R: Review of AES2-1984 (r2003): AES Recommended Practice - Specification of loudspeaker components used in professional audio and sound reinforcement
Project scope: This Recommended Practice establishes a set of primary specifications to be followed by manufacturers in describing loudspeaker components used in professional audio and sound-reinforcement system design.

Assigned to: SC-04-03-A, Initiated: 2003
Intent: Revision, Target: 2007
Current goal: PTD, Goal date: 2007-07

Status: Part 1 approved for Call-For-Comment with email reflector revisions.

Discussion:

All were congratulated on the completion of part 1.

Part 1 will be used as a format reference for part 2.

A discussion on the scope of Part 2 ensued. The intent is to cover single, high-level input, passive systems, with a defined bandwidth, which may include enclosures or directivity-controlling devices. The scope discussion will continue over the reflector.

The overall plan was reviewed:

  1. Drivers - Direct Radiators, Compression Drivers, and Driver-Waveguide combinations
  2. Systems - Passive
  3. Systems - Active (Passive systems with external, powered, electronic components)
  4. Systems - Powered (Systems with internal, powered, electronic components)
  5. added to cover systems of arrays (arrays of systems?)
  6. added for system evaluation in a room (car, hall)

The meeting agreed that Part 1 would drop Driver-Waveguide combinations. It was suggested that an additional part 2.5 could cover external crossovers.

Project AES-X168 was assigned to the part 2 development project. Marshall Buck volunteered to lead this work. It was also suggested to follow the completion of part 2 with part 4.

The meeting felt that active, digital processing devices are not well enough understood to standardize.

It was proposed that angular measurements should reference AES56. It was suggested that measurements should be taken for at least two distances in order to locate "center".

It was noted that a 50 ms burst amplifier rating might also require speaker testing with a 50 ms burst.

The matter of specifying horns was recognised but not resolved

Clear definitions of system nomenclature will be required.

Development Projects

AES-X129 : Loudspeaker Distortion Perception and Measurement
Project scope: to research the correlation of loudspeaker distortion perception with old and new distortion measures.

Assigned to: SC-04-03-D, Initiated: 2001-05
Intent: Information document, Target: 2008
Current goal: Status report, Goal date: 2007-10

Status: Continuing work in task group

Discussion: This work is required to complete other future projects.

  • What is a useful, consistent, power rating?
  • A 3-dB power compression point can be useful.
  • Warranty claim power?

In specifying compression one can't ignore the difference between low frequency excursion limitations and thermal compression.

Liaisons:

An ANSI mounting hardware standard was discussed. One problem is the specification of thread lock on driver mounting screws to T-Nuts. A liaison with ESTA was suggested.

New Projects:

Launch of AES-X168

New business:

There was no new business.

The next meeting will be scheduled in conjunction with the AES 126th Convention in Munich, Germany, 2009-05.

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