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Sound Advice

5.1 Sound Treatment by Jeff Szymanski

In response to growing questions about the acoustical treatment of 5.1 surround studios, I would like to offer some advice. I have seen quite a few advertisements and press photos showing the mix position of new 5.1 rooms. In many cases, the wall behind the front and centre speakers (the front wall of the studio), and in some cases the walls to the left and right of the mix position, are treated with a generous amount of acoustical diffusion. While I don’t argue that diffusion increases acoustical control without absorbing a lot of sound energy, I question the application in a room where proper imaging is crucial.

The most popular application for diffusion is in a control room built in the Live-End, Dead-End (LEDE) tradition. Here, a significant distance is desired between the listener and the rear wall of the studio significant enough to overcome the “Haas” effect. A stereo studio of this size may warrant diffusion, usually depending on the material being mixed. However, in the case of the 5.1 room, rear ambiance is no longer needed — that is what the rear channel is for!

It is crucial for a mix engineer, producer, client, etc. to be able to discern exactly what the true sound is for each channel. So why are we seeing applications of diffusion in the front of 5.1 rooms? How did we get from LEDE to LELE? Room influences are detrimental and undesirable in 5.1 environments. Ram Hidley, whose articles and wisdom with respect to studio design have been enjoyed by many over the years, has recently written several articles expressing the importance of room symmetry and absorptive treatments in 5.1 environments. Recently, I noticed a room originally designed with diffusion on the front wall, had absorptive panels placed over the diffusers by the mix engineer. The only explanation I can think of is that perhaps the architect, for aesthetic reasons, adds diffusion to the most visible part of the room.

I have no doubt that a 5.1 surround studio treated with acoustical diffusion is better than the same room with no treatment at all. However, it is more appropriate to approach the design of a 5.1 room with absorptive wall and ceiling treatments as well as bass trapping in mind. Early reflections from both the front and rear of the room (the mix position tends to be equidistant from all sound sources and hence all walls) should be heavily absorbed. The resulting high direct-to-reflected sound ratio provides the mix engineer with the precise aural information needed to make accurate artistic and technical decisions.

Jeff Szymanski is the Head Acoustical Engineer and Consultant for Auralex Acoustics, Inc. His design and consulting experience ranges from vocal booths to 4,000 seat auditoriums. Live-End, Dead-End and LEDE are trademarks of Chips Davis and G.E. Meeks.

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