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.
The traditional recording studio has its acoustic package either built into or mounted directly on the surfaces of the room, the walls, ceiling, floor and corners. Acoustic Sciences is fairly well known for the TubeTrap, those cylindrical bass traps that are found standing is the corners of the room and other half and quarter round traps that are mounted onto the surfaces of the room. In 1986 ASC began experimenting with something entirely different. The results were positive and engaging. The system evolved through the help and interest of many people and it is found alive and well in many recording studios today.
The ATTACK Wall is the opposite of traditional room acoustics. It creates an acoustic space that exists well within the room, away from the surfaces. Instead of built in or surface mounted acoustics, the ATTACK Wall is a free-standing acoustic package that is set up well inside the room, away from the walls and corners. It's name, "ATTACK" is an acronym that actually comes from the concept of an All TubeTrap Acoustic Control Kit, although the more aggressive connotation is not completely by accident.
All studio design follows certain basic acoustic principles and so does the ATTACK Wall. We will look into how it satisfies the requirement for promoting a strong and clean direct signal, how it provides a reflection free zone and how it generates a time delayed diffusive backfill. The ATTACK Wall satisfies the LEDE principle in studio acoustic design for both stereo and surround mixing environments.
Recording studios design is based on the well known "LEDE" type principle. Here we see a sound level in dB vs time in milliseconds sketch of the ETC or Energy Time Curve that defines the LEDE type acoustic signature. It begins with the engineer receiving a strong and clear direct signal. Next is the Reflection Free Period that lasts about 25 milliseconds, during which the engineer should not receive any reflected version of the direct signal. Following this, there is to be a time delayed diffusive backfill flushing back into the engineering position. This back fill keeps the recording space alive and comfortable to work in. Without it, one would be working in an anechoic space and that is very exhausting, especially in those late night hours. All recording studio acoustic packages should meet the LEDE type criteria, whether the acoustics are built into the walls, mounted on the walls or set out well into the room, whether the control room is used for stereo or surround mixing.
The piano keyboard represents the musical frequency range. We have middle "C" which separates the musical bass from treble. Most of the sound in the treble range travels along straight lines and is easily represented by ray tracing. The sound in the bass range however expands in all directions equally. Both types of wave front behavior have to be included in the analysis and development of a recording studio. The TubeTrap is an acoustic device, a cylinder, whose entire surface absorbs bass but whose front half reflects treble, the back half absorbs treble. Because of this unique property, the TubeTrap has become a particularly useful device in shaping acoustics in rooms.