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 New York, NY., US., 2015-10-31
The meeting was convened by chair S. Hutt.
The agenda and the report of the previous meeting, held in Warsaw, Poland, 2015-05-09, were approved as written.
Projects assigned to this group but not mentioned here had no action requested or required - see www.aes.org/standards/meetings/project-status.cfm for details.
Development projects
AES-X168 Characterization of loudspeaker systems
Background: It had been expected that SC-04-03 would update AES2 in two parts; part 1 for loudspeaker drive units, part 2 for systems. But, after much consideration it was decided that AES2-2012 should be a loudspeaker drive-unit standard and a new standard should be developed for loudspeaker systems with the project identified as AES-X168.
In the meantime IEC and CEA in particular were developing separate standards for loudspeaker systems and SC-04-03 agreed to pause its own development pending the outcome of these documents and standards.
Status:
IEC is looking at three proposals with relevance to SC-04-03. At this stage, it is not proposed automatically to revise IEC 60268-5. That decision will be made when the three task forces have completed their work. These are:
TF-1 proposal from Germany
TF-2 proposal from China focused on micro speakers
TF-3 proposal from USA, CEA
TF-1: W. Klippel provided a concise overview to the German proposal. This is to produce two new standards, at present called ‘Part A’ and ‘Part B’.
Part A
• black box approach
• only addresses what comes out of the box acoustically
• input may be at low level to an internal amplifier.
• rated maximum input value Umax
• rated maximum output SPL
• use a multitone input signal calibrated to the rms value of the stimulus.
• A multitone signal can measure distortion as well as generate the properties of pink noise, but is completely reproducible.
Klippel says this multitone stimulus has similarities with a pseudorandom noise.
Part B
• a kind of 'grey' box approach
• Transducer & system integrator
• include DSP as necessary
• all parameters are for driver units
TF-2: The draft New Work proposal has been submitted to the Chinese National Committee. (New Work Item proposals normally come from National Committees, although this is not essential. Subsequent work is carried out within IEC, without National Committee involvement until the Committee Draft (CD) and subsequent stages.)
TF-3: Waiting for more information. IEC will ask CEA if it is intended to proceed with this project.
Comments:
IEC is approaching these projects much in line with the SC-04-03 vision, but there is still possible further work to do. For example, Klippel suggested that SC-04-03 might focus on a standard for professional horns. With respect to IEC procedural status, J. Woodgate informed the meeting that the IEC projects are at stage 0, but the German ‘Part A’ has now been approved New Work, so is entering Stage 1 (when a time-scale for progress to CD, CDV and FDIS must be proposed and adhered to). This project is seeking expert participation from three more countries. The UK will appoint at least one expert.
Actions:
• Drafts of the IEC 60268-5 update proposal will be made available to SC-04-03 via the standards secretary.
• Need USA input from CEA.
• W. Klippel suggested that USA should bring on D. Keele's tone-burst test.
AES-X223: Loudspeaker Driver Correlation Chamber
Background: Replicating non-anechoic loudspeaker driver measurements in different locations - such as loudspeaker driver performance confirmation checks during manufacture - is a well-known and challenging endeavor due to numerous influences and degrees of freedom. G. Hill and E. Simon have contributed concepts to this draft Information Document. A generic draft will be presented to this group's email reflector before the meeting in Paris, 2016-05.
Discussions: Hill uploaded a draft to the reflector that most agreed was moving in the right direction but is somewhat biased to a specific proprietary approach. What we need is a somewhat generic description of repeatable measurement results, then some guidance on how to achieve those results. Hill's procedure appears to be useful and robust but there may be alternative methodologies, even if less accurate. It is our intention to provide guidance to the objective and how to achieve that with the user determining which specific procedure and hardware they want to utilize.
AES-X194 Report on loudspeaker terminology
Background: Some on-line resources such as Electropedia cover many definitions relavant to SC-04-03, however not all. The committee is interested to develop a resource of terminology and semantics that help with communication in our field.
Discussion: Simon suggested to scan relative documents and then to search key words.
Chris Struck informed that they do that at ASA. Simon recommended that the reflector could be a useful tool to promote dialog on terminology. Hill will continue to refine the draft and all members are encouraged to review and comment.
Liaisons:
ALMA International: ALMA's standards activity focuses on loudspeaker drivers and sub-components such as spiders, cones, surrounds, voice-coils etc. more so than systems. Hill participated in an ALMA standards meeting in 2015-06, and reported that no topics specifically relevant to SC-04-03 were discussed.
New Projects:
The chair proposed to open a discussion on the definition of “program power”. This is a tricky subject that cannot be defined without discrete knowledge of devices, systems, sources, duration and numerous other factors. Both IEC and ALMA have definitions, however neither provide clear guidance or procedures. Can we provide a definition and guidance that is pertinent and useful without distraction and persuasion from multiple non-scientific stakeholders? Any work SC-04-03 might do in this area should be coordinated with the Maintenance Team for IEC 60268-5.
New Business:
John Woodgate informed us (as he did in Warsaw) that a Japanese group is looking to develop a measurement method for a bone conduction transducer applied to the pinna.
The next meeting will be scheduled in conjunction with the AES 140th Convention in Paris, France, 2016-06.
