Report of the SC-04-04 Working Group on Microphone Measurement and Characterization of the SC-04 Subcommittee on Acoustics meeting, held in New York, 2009-10-10
The meeting was convened by chair D. Josephson.
The agenda and previous meeting report were approved, with the addition of new project AES-X189.
Open Projects
AES42-R, Review of AES42-2006: AES Standards for Acoustics - Digital
interface for microphones
There was no meeting of task group SC-04-04-D at this convention. The next meeting of this task group, and the next update of the revision process for AES42, will be scheduled for the meeting at the AES 128th Convention in London, 2010-05.
Development projects
AES-X085, Detailed Professional Microphone Specifications
The chair gave a report on the progress of AES-X085. The noise-source round-robin test is progressing, with one participant needing more than a few months to complete the tests for its participation in this work. This has now been completed, and four participants remain in the round-robin sequence.
There was some discussion about ongoing work on the detailed microphone specification format. Josephson reported on his earlier proposal to aim, instead of a graphic format, for a database format instead, with defined fields that could be populated with manufacturer's, or other, test data in accordance with Table 3 of IEC 60268-4. The database standard would include the adoption of recommended procedures within the very wide possibilities of IEC 60268-4, as have been discussed in this project in years past. C. Struck offered to join the effort and he and Josephson will report on their efforts at the next meeting.
Instead of frequency response curves and polar plots, for instance, it was suggested that 1/12 octave (or another suitable value) response curves be tabulated. Display applications could then calculate and show polar plots in any desired format, on-axis and random-incidence curves, frequency response curves normalized to flat or on-axis, etc. E.B. Brixen suggested that response be tabulated in 5-degree increments of azimuth, to be comparable to the data format developed for loudspeaker response. There was agreement that the format should be as universally readable as possible, and Struck reported on success with using Excel or another spreadsheet program and perhaps a comma-delimited ASCII format for the data.
AES-X189, Connector for surround microphones
Following a proposal that Brixen made to the reflector, AES-X189 was assigned as a new project for the definition of a microphone connector interface for surround-sound microphones and arrays. There was some discussion around three major issues: connector choice, number of pairs, and color code. There was general agreement that we wanted primarily to consider only standardized rather than proptietary connectors, that six pairs was probably enough, and that the commonly used professional color code should be adopted. The connector is the 19-pin variant of the M16 screw-lock "DIN-type" connector, as listed in committee draft for vote (CDV) for IEC 61076-2-106. Both Mogami and Belden are working on cables for this standard, the Mogami with copper conductors and individual shields, and the Belden with alloy conductors of bonded pairs and an overall shield.
AES-X093, Recommendations for revisions of IEC 61938 Clause 7, Phantom power
There was a brief discussion of AES-X093. At its 2008-10 meeting, the working group passed comments to IEC TC100 within this project, which comments are on the document site as "x93-josephson-081013a". IEC has now convened a maintenance team (MT) for IEC 61938 and AESSC is moving forward to add a representative to this MT who will advance the concerns discussed in AES-X093.
Liaisons
It was noted that the decisions of the WG in regard to recommendations to IEC TC100 on the revision of IEC 60268-4 had not been included by the IEC in their report on the revision of this standard, although J. Woodgate had informally relayed this message and AESSC Secretary M. Yonge had made a formal submission. The issue is still, as reported in the meeting of 2009-10, that no response from the MT to these comments had been provided, and the leader of the MT (who is also a member of SC-04-04) reported that he was unaware that such response was required.
New Projects
There were no new projects, and no further discussion of the wireless microphone project proposal mentioned at the previous meeting.
New Business
There was no new business.
The date of the next meeting was noted to be in conjunction with the AES 128th Convention in London, UK, 2010-05.
