Report on AES San Francisco's November 2004 Meeting

by Thomas Merklein

Anthony Grimani, President and Lead Consultant of Performance Media Industries, Ltd., presented a subset of his 117^th AES convention tutorial, project studio acoustics, at Dolby Laboratories in early November. Thirty people attended.

The requirements of the project studio are similar to those of large facilities. If a project studio is used for sound recording, then acoustics must be considered because it contributes over 50% of the sound quality to the recording. For mixing and monitoring tasks, a neutral room environment is ideal. Often, project studios are used for both. Mr. Grimani provided guidelines for understanding and dealing with room acoustics issues which consist of reflections, room echoes, reverberation, standing waves, rattles, background noise, and sound isolation.

The initial consideration is room dimensions which defines how many people and how much equipment will fit in the space. Rectangular rooms work best; trapezoidal shapes merely shift problems.

One of the most predominant problems involves axial standing waves and their influence on the bass response of a room. The subwoofer of a satellite speaker system can be moved to a location that yields the least null spots. Alternatively, two or four smaller subwoofers positioned in a cross pattern will further reduce low frequency standing waves. Frictional bass absorbers including resilient walls can also be incorporated.

The goal of sound isolation is to reduce noise that may interfere with recording or monitoring. Isolation measures include suspended wall construction with PAC RSIC clamps and sound barrier material such as vesco-elastic polymers. A staggered studded wall can be implemented as a retrofit. A floating floor and ceiling may also be used.

Frequency decay measurements provide insight to how dry or wet a room sounds.

The generally preferred decay time in residential settings is 0.25 to 0.3 seconds. A simplified approach to treating a room is to cover 25% of the walls with absorption panels and to spread them around evenly. These should be interleaved with diffusors to scatter the sound. Since reflections from the ceiling are the most audible, a ceiling absorption panel placed between the front speakers and listeners will reduce this problem.

A copy of Mr. Grimani’s presentation is archived in the "past meetings" section of the San Francisco AES web site (www.aessf.org).