Acoustical Design Discussion 

              For the serious technologically minded.

Edition #1 - L,C,R Placement and Calibration

White Paper - Each month we look at a different acoustical design or calibration element. Taken from the HAA Acoustic Design and Calibration Review checklists, these elements detail the many attributes that define high end home theater sound. An HAA Calibrator can perform an analysis of your system by reviewing each of the over 80 elements. This month we look at ADR Element #10.

Acoustical Design Element 10: Front LCR  are movable within the room length and width wise and there is sufficient available space to allow repositioning including “toe-in” to optimize response and sound stage presentation or positions have been acoustically selected and equalization is planned.
 
   
One of the hardest things a sound room designer must do is decide in advance the exact spot in a room to place a speaker to optimize performance. Expensive computer modeling aside, it is nearly impossible to account for all acoustical possibilities. The best approach is to design an area of adjustment or leeway for minor changes in speaker position. Ideally, an area at least 3 to 4 feet from the front and side walls will leave room for correction of various response problems. Otherwise, one must depend on luck if you're superstitious.
   
    
This element has become one of the more controversial of the ADR and ACR. It’s not that anyone can argue that tweaking the position of the Left, Center and Right (LCR) speakers is not a common approach to getting better performance. It’s because it appears to damn in-wall or built-in speakers to a low grade in terms of the System Report Card. The truth be told, if a manufacturer for high quality in-wall speakers provides detailed direction on the installation of their product, an “A” grade is still possible if the speakers are properly equalized. This means a careful review of the design of the system in advance of cutting in the speakers. Why is the “fine-tuning” of speaker position such an important issue?

The answer lies in the myriad of other elements we review in the ADR. Each element states its case on the need for one speaker location versus another. Placement near a boundary can increase the bass excessively, symmetrical positioning can exacerbate certain interference effects, the wrong height…, wrong angle…; each represents a significant factor in controlling the outcome. The value of element 10 is mostly for the typical system and calibrator where a precise understanding of the influence of each of these other elements may be limited. What situations present a limited understanding of the acoustical effects of placement?

I am fond of pointing out the value in keeping the design of a system (focusing on the room) simple. I stress the value of rectangular shape and the benefits of a simple layout of seating and furnishings. This isn’t because such a design automatically sounds better, rather it’s because the final outcome of acoustical effects can be more readily predicted. One can make accurate predictions using basic software tools. The more accurately one can predict the result the more reliably one can plan the final position of all the components of a system. At issue in the real world is the lack of such simplicity in many systems.

In most rooms the position of couch has more to do with the traffic flow than with acoustical elements. The installation of the speakers is very often more a function of a cabinet or television design. And what acoustical effects will an "ell" or non-doored opening have on your elegant predictions. Short of entering all the data into acoustical analysis software, how can we be sure the final position of the speakers will yield that spine tingling reality we were striving for? Often, it is the final adjustment of toe-in or separation that snaps the soundstage into focus and makes the calibration complete. On other occasions it is the radical movement of a sub along a side wall that brings success.

We build theaters into real rooms and thus live in a world of compromise. The simpler and thus more predictable the acoustical environment is, the less element 10 needs to be heeded. It is possible to get outstanding results with built in and immovable speakers. If you Audio Guru Contractor has full control of the design as well as the calibration of the system; they will likely render element 10 as N/A "not applicable". But the installation needs to be carefully designed and modeled for the best results. For the less savvy acousticians among us, it often makes sense to build in a range of flexibility in placement that allows us to compensate for the real worlds lack of predictability.

I am sometimes confronted, during friendly discussions with clients, about the relative importance of one or another "minor" acoustic or setup flaws in their home theater. Does proper setup and calibration really matter that much balanced against other priorities? In the final analysis, just what is missing due to any of these seemingly innocuous misalignments? I think the answer is best explained from my perspective as a music lover relating how I am occasionally teleported in time and space by the majesty of an amazing recorded performance. If never on a quiet evening in your home, a recording has astonished you with its realism and moved you emotionally, which among these few subtle acoustical flaws has robbed you of the experience? If you have not been surprised recently by your sound system, perhaps Element 10 could be a contributing factor, of course, don't forget about the many other Design and Calibration elements in the mix. Next month another Element.

From "The Home Acoustic Alliance by Gerry Lemay (Gerry is the Director of the HAA, President of Quest Convergence Systems, and writes the Home Theater Rx column for Home Theater Magazine)