Toronto AES Section Bulletin logo

March 1996: Volume 4, Number 7


Microphone Diaphragm Refurbishing

Presented by Doug Walker, Walker Microphones

What's Inside

This Month's Meeting Preview

The Topic:Microphone Diaphragm Refurbishing

This month, AES Toronto has invited Doug Walker to give a presentation of a precision technique for replacing the old diaphragms on AKG's and NEUMANN's.

In this technique, the old microphone capsule is dismantled and cleaned. A new diaphragm is manufactured by vacuum evaporating a uniform layer of pure gold to a depth of 300 angstroms on a 6 micron thick, heat stabilized, Mylar C polyester foil. The new diaphragms are manually tensioned and cemented to the mounting rings or to the common centre electrode.

Performance tests include measurements of capsule capacity and diaphragm deflection sensitivity. A further test ensures that the diaphragm will not adhere to the capsule centre electrode under maximum polarization conditions. The capsule is next mounted on a microphone for response measurements. Frequency response is measured using anechoic MLS techniques.

What's Inside

February Meeting Reviews:

Sony SDDS Review, 12 February.

The Toronto section of the SMPTE invited the Toronto AES, to a demonstration of the Sony Dynamic Digital Sound system at the York Cinema. The demo movie was Screamers. Tim Archer, who mastered its soundtracks, explained reserving the top 20 dB for only the more spectacular sound effects. Tim enjoyed doing his 5 channel mix, plus a separate subwoofer channel, incorporating lots of foley tricks and some screams from his baby daughter.

Ray Callahan (youll recall him from our November SDDS meeting) then gave us a quick overview of the SDDS technology, mastering, and reported the special problems SDDS faces in China (lots of oil on the film), and in Australia (the worst prints in the world). Ray screened the Sony SDDS demo film, to illustrate the issues of audio sync, channel ID, etc., followed by some demo music tracks.

The first 20 minutes of the movie Screamers followed. It has lots of nasty 3-6 KHz audio content (near clipping) giving us a pain-level appreciation of the SDDS dynamic range and 5 channel sound localization. Ray noticed 5 incidents of switching to a backup channel in the movie, the theater people heard 3, as a soft clicking. I did not note anything amiss, except perhaps some clipping. A question and answer session gave us more system detail: the film digital dots are 22x24 microns, in the cyan dye layer; audio processing is uncompressed until just before printing; the raw digital playback stream is 1.4 Mbit/s. An interesting time was had by us 75 or so.

What's Inside


Digital Versatile Disc [DVD] Meeting Review, February 27

Denis Tremblay (of Sony Music, Canada) gave 45 members and friends an expert and detailed account of the many kinds of Digital Versatile Discs we'll use soon. As an extension of the current Compact Disc, backward compatibility of DVD players is assured. Briefly, by reducing the DVD optical pit and track sizes, using a 680 or 635 nm (visible red) playback laser wavelength, using more compact error reduction codes, and reducing the polycarbonate disk from 1.2 mm to 0.6 mm thick, about 7 x more data can fit on a side: 4.7 Gb versus 680 Kb.

To retain standard 1.2 mm CD compatibility, a single-sided DVD will have a 0.6 mm thick backing layer, made of any compatible material, such as recycled dud DVDs. Using two 0.6 mm disks back-to-back, or stacking two, using a part-reflective middle layer, are two ways to double the data. It will be possible to stack two 0.3 mm disks back to back with two more (four sides), for computer data storage of about 18 Gb.

Audio and simple CD-ROM usage may not employ audio compression, but DVD-Video will employ Dolby AC-3 and MPEG-2. Denis attended demonstrations that confirmed the video quality is better than Laser Disk, and we already know about AC-3.

The important gains over the old CD practice are: compatibility of molds, machines, methods, while gaining new uses. Scrap product can now be recycled in back layers. Raw playback data rate goes from 0.6 Mbit/sec to 10 Mb/s. That opens-up the video, CD-ROM and computer data disk uses.

There is now a very broad spectrum of interested parties, setting standards such as the UDF, universal for the popular PC operating systems. Only one product version needs to be stocked, which will be extended for CD ROM, CD WORM, and write-many applications. There may be an 8 channel, 48 to 96 Kb, 16 to 24 bit PCM, non-lossy compression, audio recording (per side) standard. Denis imagined a 16 track recorder (using both sides of a disk, with two optical mechanisms), in a very small box. Many auxiliary channels will be standardized, such as 3 to 5 languages for the movie dialog track and 4 subtitle channels, to reduce versions of product.

Not everything is rosy with the DVD. The pit size is the same as recent IC features, which ups the standards in clean rooms, to match the current (over 90%) yield of CDs. Also, a given surface scratch quadruples in its effect, because it is impractical to expand error correction to cope: the real problem is now track-skipping, not errors. Mastering will take much longer due to the increased content, and at half-speed. New failure modes are de-lamination of the bonded disks, and bubbles at the bond. The demands on QA and QC will increase dramatically.

These problems can be reduced with surface hard-coating, new QA machines, automation, and new procedures. That all adds up to lower yield and higher costs, and a significant learning curve. The CD and CD-ROM will be with us for a while yet!

Denis's QA / QC slant to the DVD was very enlightening and enjoyable, many audience questions were answered, and we all had a good time.

What's Inside




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