Report of the meeting of SC-05-05 (Working Group on Grounding and EMC Practices of the SC-05 Subcommittee on Interconnections) held in conjunction with the AES 122nd Convention in Vienna, Austria, 2007-05-05.
The meeting was convened by vice-chair J. Brown.
The report of the previous meeting, held in San Francisco, CA., US., 2006-10-05, and the agenda were approved as written.
Open Projects
AES48-R Review of AES48-2005, AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry
No action was requested or required.
Development Projects
AES-X027 Field Test Methods for Measuring Electromagnetic Interference Susceptibility in Balanced Line-Level Interconnections
It had been proposed in San Francisco to transfer this project to the newly formed TC-EMC, and after some discussion, that decision was affirmed by those present here. It was agreed that content of WG archives relevant to this project should be made available to TC-EMC. We recommend that AES-X027 now be retired.
AES-X125 Input filtering for electromagnetic compatibility
H. Jahne stated that filtering should not be a requirement if a product is designed such that an out of band interfering signal is not detected (for example, by preventing non-linearity). Brown concurred, and suggested that the resulting document simply require conformance with a defined level of performance with respect to immunity and describe filtering techniques as one method of achieving that goal. J. Woodgate voiced a concern that an AES Standard not attempt to cover the same ground as a CISPR or Cenelec document, and should thus not specify performance limits, but should rather be an information document on filtering. Brown countered that a document without such a requirement was of little value and missed the point. After a long discussion, it was agreed that Jahne will write language that spells out the requirements for immunity. R. Caine agreed to contribute language that would include performance requirements and a tutorial on filtering as an informative annex.
AES-X152 Signal levels and impedances of analog audio interfaces
A skeleton draft produced by J Brown was discussed, and will be posted to the SC-05-05 reflector. Woodgate noted that this appeared to be a rewrite of IEC 61938. Comments on the draft: the definition of maximum output level or rated distortion should be clarified, and should match the IEC definition. Definitions should be included for all terms, either in the main document or in and informative annex. Definitions should include a diagram showing two boxes hooked together, with a Thevenin equivalent source and a parallel resistor and capacitor as a load. To avoid confusion, the words "output source impedance" should be used rather than output impedance.
To define output levels for some specialized self-powered and limited power-source products, it will likely be necessary to define a duty cycle and form factor. For example, a small power amplifier integral to a small loudspeaker that is part of a distributed reinforcement system for a legislative body might derive its power via an Ethernet cable that also carries audio. Woodgate advised that defining a duty cycle would likely be a stumbling block. IEC 60268-3 defines the specification of circuit balance, and also measuring output of power amplifiers.
Those present felt that AES-X152 should not address A/D and D/A linearity. Some of those present felt that this matter is adequately addressed by AES17.
AES-X147B Shielding of balanced audio wiring within passive connector panels and passive mic splitters
Some questions were raised about AES-X147B arising from the recent secretariat formatting.
M. Yonge recommended removing the reference to AES-X147A in NOTE 1 of 4.1.4. No objections were raised.
In the note to 4.2.2, Yonge suggested removing the words "which constitutes an equipment grounding conductor." No objections were raised.
At the end of 4.2.2, Yonge recommended removing "and/or." No objectives were raised.
Concern was voiced regarding Note 1 to 4.2.2. Several alternate wordings were suggested, and it was also suggested that Note 1 might be deleted?
Brown's edits of 4.4.3 to remove references to AES-X147A were reviewed. No objections were raised.
AES-X147A Connection of cable shields within connectors attached to balanced audio cables
There was no discussion.
AES-X147C Shields of microphone level outputs of active equipment other than microphones
There was no discussion.
New projects
No new projects were proposed
Old Business:
In San Francisco, S. Macatee had suggested that the AES provide some arrangement for use of logo or bug on data sheets to show AES48 compliance. Yonge replied that AES policy would not allow use of the AES logo in such a manner.
New business
There was no new business
The next meeting will be scheduled to take place in conjunction with the AES 123rd convention in New York, 2007-10.
