The “WILLIAMS STAR” Surround Microphone Array
With an ever increasing interest in 5-channel recording for Home Cinema, Television and pure 5-channel Audio, the search for an operationally simple, reliable and high quality surround-sound recording system becomes ever more important. The equal-segment 4-channel and 5-channel arrays described in two AES papers by Michael Williams (see footnote) are attracting more and more interest within the audio industry. However the research for a satisfactory operational microphone configuration cannot be dissociated from the purely mechanical problem of finding a suitable microphone-array support system.
The ‘Williams Star’ Microphone Support System can provide a simple, flexible and reliable microphone-array support system for any equal-segment array design. The visual impact of this system has also been reduced to an absolute minimum. Currently only the 4 and 5 versions seem to meet operational broadcasting requirements, but a 7-channel format is also provided for future developments with respect to the new Blu-ray format.
A central circular hub is used to fix 4, 5 or 7 radial rods of different lengths, according to the directivity of the selected microphones. At the extremities of these radial rods, standard microphone clip mounting for the Schoeps Compact Condenser Microphone range (CCM) is attached, or for the Modular “Colette” microphones (CMC preamplifier + capsule). The development of other microphone-array configurations will of course be a continuous process in order to meet future requirements of the audio industry. For instance the possibility of mounting a microphone on a vertical radial rod for a supplementary microphone is now a standard part of the hub design.
Although the complete Star System developed by Michael Williams can be used independently, it is highly recommended that it should be attached to the anti-vibration mounting developed in collaboration with the company Rycote using their well known ‘Lyre’ suspension from the InVision Broadcast series. This ensures very efficient rejection of handling noise or microphone stand-borne vibration. The fact that it is the entire star microphone system that is attached to the anti-vibration mounting (instead of each individual microphone) means that an even lower fundamental resonant frequency can be obtained, and therefore very efficient vibration filtering can be achieved. A choice between two different Lyre compliances is possible - the INV1 Lyre is suitable for mounting with the Schoeps CCM series, whereas the INV4 Lyre is more suited to mounting the Colette range of microphones.
During on-location recording weight is often an important factor - with five Schoeps CCMs the complete system only weighs about 500gm, whereas with Schoeps Colette Series the total weight does not exceed 950gm. Standard Schoeps or Rycote windshields can of course be mounted on the microphones when required.
Three sets of spokes are provided for the standard 5-channel ‘Williams Star’, each set corresponding to a specific microphone directivity:
Spokes for omnidirectional microphones can be provided but this type of microphone-array system has not produced satisfactory results.
The standard ‘Williams Star’ is made for 5-channel operation, however the central hub already has fixing positions for 4-channel and 7-channel operation. If the 4-channel version or the 7-channel version is used, another set of spokes is required for each configuration and for each of the three standard directivity patterns (Supercardioiod, Cardioid and Hypocardioid/Wide Cardioid). These are available as accessories. The radial-spoke fixing positions are colour-coded: yellow for 4-channel, red for 5-channel and blue for 7-channel.
A series of additional fixings are also provided, colour-coded in white, which in conjunction with the yellow 4-channel configuration allows the MAGIC 7- or an 8-channel configuration to be used.
The standard hub also has a additional fixing to allow a vertical spoke to be mounted as either the low-pass microphone(‘.1’) of the 5.1 system, or simply to create an additional fixing for an omnidirectional microphone which can be added to the 5 channels as required.
Microphone Clip Mounting
It is possible to attach two different microphone-clip mountings to each of the radial spokes, one is the for Schoeps CCM microphone range, whilst the other is for the Colette series of microphones. Both clip mountings have the standard 3/8” Whitworth thread for attaching the microphone clip. The Schoeps CCM mounting however does not allow for adjustment of the radial position of the microphone, the length of the radial spoke is therefore pre-calibrated so that the diaphragm is in the correct position, taking into account the fact that each length of radial spoke corresponds to a specific microphone directivity. It is therefore important to use the miniature Schoeps SGC (SGCM) microphone clip for mounting CCM microphones, whereas the standard CMC clip can be either the Schoeps SG 20 or any proprietary microphone clip – the microphone diaphragm position can then be adjusted to correspond to the exact configuration specification.
The microphone clip mounting cylinder also allows one to rotate the assembly around the radial-spoke axis in order to obtain the correct alignment of the microphone axis with respect to the spoke axis.
Microphone Stand and Rotary Head mounting
The standard 3/8” Whitworth thread is provided for fixing to a microphone stand. If it is necessary to mount a ball-type head, then, by inverting the central hub, a 1/4” thread mounting will permit any ‘photo’ or ‘video’ rotary-ball head to be used.
In general it is advisable to mount the “Williams Star” system onto an anti-vibration subassembly. This was developed in collaboration with the company Rycote and uses their well known ‘Lyre’ system from the InVision 1 or InVision 4 anti-vibration microphone mountings. Depending on the total weight of the ‘Star’, different compliance mountings will be necessary. For CCM microphones the InVision 1 Lyre is recommended, whereas for the Colette series of microphones, with a CMC preamplifier and Capsule, the InVision 4 Lyre mounting will be needed. It is also possible to use a reinforced InVision 4 Lyre.
The anti-vibration subassembly also can be mounted on a standard microphone stand with a 3/8” Whitworth thread, or with a ‘photo’ type rotary head, again simply by inverting the base. The Lyre mountings then have to be rotated through 180° to align with the ‘Star’ radial spokes.
Seven Channel Configuration for Blu-ray
The "Williams Star" system allows a compatible 2-/5-/7-channel MAGIC-Array Configuration to be mounted. An 8-channel MAGIC array is shown below:
The "Wiliams Star" mounting for his 8-channel MAGIC array
Footnote - A series of configurations for simple equal-segment microphone arrays was described by Michael Williams in a paper presented at the 91st Audio Engineering Society Convention in New York, in October 1991 (preprint 3157). These arrays covered designs for 4-channel, 5-channel and 6-channel systems using Supercardioid, Cardioid or Hypocardioid (Wide-Angled Cardioid or Infracardioid) directivities. This publication was made some time before the term ‘multichannel’ was adopted to describe 5-channel systems, and the subsequent normalization of the 5-channel loudspeaker configuration. This paper was updated in 2008 at the 124th AES Convention in Amsterdam (preprint 7480) to include equal-segment array systems using 7- and 8-channels.
These papers and other AES Convention papers by Michael Williams can be downloaded at www.mmad.info.
© 1997 Posthorn Recordings
|Most recent revision November 9, 2011|