March 2003 meeting of SC-05-05

Report of the SC-05-05 Working Group on Grounding and EMC Practices of the SC-05 Subcommittee on Interconnections meeting, held in conjunction with the 114th Convention in Amsterdam, The Netherlands, 2003-03-22

Vice-chair J. Brown convened the meeting.

The agenda for this meeting was amended. Brown proposed that he present relevant details of two papers he authored with B. Whitlock and D. Josephson prior to discussion of active projects. That proposal was accepted without discussion.

The report of the previous meeting was approved as written.

Matters arising

Brown and Whitlock presented their research on Shield Current Induced Noise (SCIN), confirming Muncy's hypotheses that SCIN increases linearly with increasing frequency, is strongly related to shield construction, is much greater in cables having drain wires and is strongly related to the fraction of shield current carried by a drain wire. Measured SCIN data were presented for seventeen different cable types and six different shield constructions over the range of 10 kHz to 4 MHz. It was shown that SCIN increases approximately linearly with frequency over the range of the measurement for most cables tested, and for most cable types showed no sign of deviating from that law above that range. Measured data was also presented for the level of the current induced in a typical cable shield by AM broadcast stations of various power levels, and interpolated to a distance of one mile from transmitting antennas. Manufacturers' data was also presented for HF loss in digital audio cables.

Brown presented his research on EMI to condenser microphones at VHF and UHF, hypothesizing that Pin 1 problems and poor filtering of the signal leads were the primary causes of susceptibility. It was shown how relatively short wires or component leads that have significant reactance at VHF and UHF can be components of significant pin 1 problems at these frequencies while being negligible at lower frequencies. The research showed that a new EMC connector being developed by Neutrik can be quite effective in reducing susceptibility, primarily because it "works around" the Pin 1 problem, but secondarily by making the VHF/UHF shielding more continuous at the connector-to-equipment interface. The connector tested used a 10 nF capacitor of annular construction and a ferrite bead around pin 1.

Brown reported on testing of Neutrik's EMC connector with microphone input equipment that experienced strong susceptibility to both FM and VHF TV signals due to a serious Pin 1 problem. In addition, the female connector integral to the input equipment was of a type that provided intermittent contact between its shell and the shell of the EMC connector. When the shells made good contact, the EMC connector eliminated the susceptibility. When the shells did not make good contact, the EMC connector had no effect.

Development projects

AES-X13 Guidelines for Shielding
A draft document addressing the "Pin 1" problem prepared by the Secretariat was posted on the reflector following the Los Angeles meeting. That document, as well as Brown's comments posted to the reflector in December, were discussed in detail. The comments were generally accepted, with a few exceptions. Specific wording was agreed and detailed notes were made of the discussion. It was agreed that Whitlock's drawings should be added to the document. Whitlock will provide wording regarding the inclusion of the power supply ground with the star connection of the cable shields. The Secretariat will post a revised version of the document.

AES-X27 Test Methods for Measuring Electromagnetic Interference Susceptibility in Balanced Line-Level Interconnections
A paper by Brown and D. Josephson has shown the usefulness of devices like cell phones and VHF/UHF handheld transmitters as signal generators in those countries where regulations permit such use. No progress has been made on development of an inexpensive broadband test generator for direct connection to equipment to assess susceptibility, but Whitlock hopes to have a prototype ready for field testing in advance of the NY meeting.

AES-X35 Installation Wiring Practices
No progress was reported.

AES-X112 Insulating Cable-Mount XL Connectors
It is proposed that this project should be incorporated into AES-X35.

AES-X125 Input Filtering for Electromagnetic Compatibility
R. Chinn agreed to work on a document. Whitlock can help with modeling. It was agreed that the amplitude and phase response of the filter within the audio passband must be an important part of the document. The document must address outputs as well as inputs. Auxiliary outputs and headphone outputs are often problematic because they are often ignored.

New projects

No new projects were requested or proposed.

New business

There was no new business.

The next meeting is scheduled to be held in conjunction with the AES 115th Convention in New York, NY, US, 2003-10.

AES - Audio Engineering Society