How the 5.1 AttackWall Works

Transcript of a seminar presented by Arthur Noxon P.E., President of Acoustic Sciences Corporation, at the Surround 2001 International Conference and Technology Showcase, December 7-8, 2001, Beverly Hills, CA.

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Part 5

A conventional recording studio design is called a LEDE type studio, Live-End Dead-End. Although the original LEDE type studio concept was a study in pure geometry, a room shape that gave no early reflections, one that did not use absorptive or diffusive devices. This oddity quickly gave way to a more conventional way of setting up a studio in a rectangular room. The front half of the room was made acoustically dead and the back end of the studio was made acoustically diffusive or live. As long as the distance to the back wall was about 12 feet, the requirement of a LEDE room was met. However, these rooms had the clear distinction of one end being dead and one end being live, hence the acronym LEDE. But when it comes to surround audio, there is no "End". What is the Dead-End for one speaker becomes the Live-End for another speaker. 5.1 Studio design seems to not be able to meet the LEDE requirement, at least using conventional design practice.

The baffles used in the ATTACK Wall are double sided. The front faces the mix position and is full bandwidth absorptive. The backside faces the bare walls of the room and is very diffusive. Each set of baffles is open at the bottom and top. Sound that hits the ceiling bounces over the baffles and sound that hits the floor bounces under the baffles. These rays hit the wall behind and are reflected onto the diffusive backside of the baffles. At this point the sound has been sufficiently delayed and diffused. It is scattered back again towards the bare wall where it is finally reflected back over and under the baffle wall and into the engineering location.


Vertical Circulation Paths


In addition to the over and under action by the vents above and below the baffles, there are also lateral vents in the overall 5.1 ATTACK Wall setup. By ray tracing sound from each speaker that exits through each vent and on through a sequence of wall reflections, a lateral condition of diffusive backfill is created. The space between the reflective side of the baffle system and the bare walls works well when kept in the 3 to 6 foot range. Larger rooms retain the reflection free condition but the onset of the diffusive backfill becomes more time delayed and weaker in level.


Lateral Circulation Paths


By using properly designed and positioned acoustic baffles, essentially gobos, the three stages of proper recording studio design can be met. The strong and undistorted direct signal is launched from the speaker array. The sequence of early reflections that distort musicality and imaging are eliminated and a backfill of time delayed diffusive energy is returned to the mix environment. The most interesting aspect of this is that not only the speakers are in a surround configuration but the diffusive backfill is also delivered to the engineer in a surround format. The old fashioned Live-End Dead-End style of studio design cannot produce a surround mixing environment. In this new medium the ETC definition for studio design remains the same but its spatial or geometric representation is forever changed. The new design criteria is identified by the acronym LSDS ™, Live-Surround Dead-Surround ™.


Typical "LSDS"™ Type ETC Signature


The original reflection free zone first conceived by Chip Davis was a geometric space that was reflective but sized and shaped to avoid reflections during the first 25 milliseconds following the direct signal. Nobody really built these rooms but the idea spawned two decades of one-dimensional Live-End Dead-End studio designs. Now, studio design has come full circle due to the seemingly insurmountable mutually exclusive requirements of surround studio speaker positions. What started as a geometric surround studio design concept has become an acoustic surround studio design reality. Although it took TubeTraps to pioneer the concept, it will be up to the professional studio designers to adopt this next wave in studio design, the LSDS ™ type studio.


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