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Tradeoff, TANSTAAFL And Triage

The compromises involved in the underlying principles of system design and optimization...

As audio engineers, we’re constantly presented with choices that involve compromise and give and take. Many of these are budgetary and/or based on realities of what’s available or possible for a given application.

Tradeoff, TANSTAAFL and triage are underlying principles to my decision-making process in the design and optimization of sound systems. The concept of the tradeoff is simple: give up something to get something.

TANSTAAFL is an acronym created by sci-fi writer Robert Heinlein: “There ain’t no such thing as a free lunch.” You face TANSTAAFL every time you get that email from “Mr. Smith” who is ready to give you part of his $20,000,000 fortune with your help and access to your bank account.

Triage is a resource prioritization method for situations where there is not an infinite supply to solve all problems. The obvious example is a hospital’s blood bank in a mass casualty emergency. We could drain the entire supply into a single patient that is sure to die anyway, or hold it out to potentially benefit hundreds of others. Sounds harsh but the answer is clear. 

The list of tradeoffs, TANTAAFL and triage for even a single job can be endless, but let’s look at some prime examples in this field. As you’ll see, these three concepts are highly interdependent.

Question 1: Center cluster or left/right? The tradeoffs are potentially large. A center cluster can probably use fewer loudspeakers, so for a given budget we could get better (higher quality/power, etc.) components. Another tradeoff is intelligibility; the center cluster typically wins the day in this category.

But TANSTAAFL says we have to give something up to get that superior intelligibility: image width and spatiality. The center cluster is 100 percent localizable as a singular sound image source.

This is fine for a spoken word performance since it’s totally natural for a person’s voice to come from a single point, but is a serious drawback for a musical performance, especially one with a lot of performers. How many musicians can you pack into a phone booth? That’s the sonic effect of a center cluster on a band or symphony. Spreading the mains to left and right widens the horizontal image for most listeners. 

Figure 1 – Comparison of horizontal sonic image effects between center and left/right mains. Listening perspectives of (A) center, (B) left/center, and (C) left positions are shown in a transverse section view. Panel D shows the listener and speaker locations in plan.

Even if the sound is clearly localizable to one side, the image is stretched with some ambiguity by the arrival from the other side (the very same thing that degrades the intelligibility). This is true of left/right systems even if the mix is 100 percent mono. Two spread sources do not sound like a single concentrated one, even in the exact center of the room.

So now we face triage. Do we allocate all resources to intelligibility and go with a center cluster? Only if we know for certain that the only application for the system is voice. If the hall can be used for other things, then left/right is the way to go.

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Question 2: How about left, center and right? Vocals can go to center and left/right can carry the music. We must re-apply our principles again. We just added the need for more loudspeakers, rigging, wiring, and processing. The triage perspective reveals fixed resources that we must stretch or shrink (for a given budget).

Figure 2 – Comparison of vertical plane effects for center and left/right mains on (A) sonic image, and (B) on range ratio, direct-to-reflected ratio, and required coverage angle.

The operation of an L/C/R system presents a tradeoff between capabilities and ease of operation. The mix happens in the air as much as it does in the console, which means that a lot of time must be spent walking around to figure out how it is coming together. An L/C/R system works well for doing the same show over and over, such as in musical theater.

But the approach is a huge waste for a road house that brings in visiting engineers for a single night, who don’t have time to sort out such uncertainty. They live in a left/right world and will either not use the center (wasted resources) or sum left and right into the center (TANSTAAFL says that the added loudspeakers cost combing and intelligibility).

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