LCR Placement Fundamentals

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A Back-To-Basics Look At Theater Front Speakers Layout

When it comes to home theater room setup, there is nothing more fundamental than choosing proper front-position loudspeaker locations. Through these left, center, and right speakers (LCRs), home theater audience members get the majority of their audio information. Placing these speakers in the correct spots cannot happen without finding the primary listening position first.

Todd B. Adams (todd@dipartner.com) is the CEO of DIpartner, aninternational firm dedicated to education for residential integrators.

The primary listening position can be thought of as a single chair that is located in the best spot for optimal sound reception. Figure 1 shows speaker placement for a 7.1 channel audio system with a single chair indicating the primary listening position. We define the following distances within the theater for placing the front speakers:

We define the following distances within the theater for placing the front speakers:

Primary Listening Distance. This is the distance from the center of the center-channel speaker to the primary listening position.

LR Distance. This is the distance from the center of the center-channel speaker to the center of the left or right front speaker. This plane is tagential to the plane created by the primary listening distance.

TABLE 1

LISTENING
DISTANCE

MIN

MAX

8.0 (2.4)

6.5 (2.0)

9.2 (2.8)

8.5 (2.6)

6.8 (2.1)

9.8 (3.0)

9.0 (2.7)

7.3 (2.2)

10.3 (3.1)

9.5 (2.9)

7.7 (2.3)

11.0 (3.4)

10.0 (3.0)

8.0 (2.4)

11.5 (3.5)

10.5 (3.2)

8.5 (2.6)

12.2 (3.7)

11.0 (3.4)

8.8 (2.7)

12.7 (3.9)

11.5 (3.5)

9.3 (2.8)

12.7 (3.9)

12.0 (3.7)

9.7 (2.9)

13.8 (4.2)

12.5 (3.8)

10.2 (3.1)

14.5 (4.4)

Distances shown in ft (m)


Using trigonometric functions we can calculate:

Minimum LR distance = Tangent
(22o) X (Primary listening distance)

Maximum LR distance = Tangent
(30o) X (Primary listening distance)

Table 1 shows a number of common primary listening distances and the LR distances for them.

Speaker placement
The left, center, and right speakers located in the front of the room are seated at ear height, or within 15 degrees of the plane cut by the seated ear height. If the speakers cannot be placed within this cone, then they should be angled in a vertical plane to cover the entire listening position.

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It is best to have identical speaker models that are tonally matched so as to reproduce sound as identically as possible. They should be oriented in the same fashion, meaning that if the center channel is positioned horizontally, then the left and right should be horizontal as well. The centerchannel speaker is located centered on the screen and each of the LCR speakers should have a clear line of sight from all listening locations.

The LCR speakers should be placed in positions that provide identical sound path distances to the primary listening position. To accomplish this, the center channel will need to be recessed into the wall slightly farther than the left and right. In cases where this cannot be done, the delay time is adjusted for the center channel to match the leftand right.

The LCR speakers should be placed in similar boundary conditions for best low-frequency match. This is accomplished by placing them at identical distances to walls, ceiling, and floor. Each speaker should be mounted in a similar fashion. Additionally, the speakers should be firmly attached to a stable or mechanically well-dampened structure to minimize any rattles as a result of speaker vibrations.

To minimize unwanted reflections, the sound path of the LCR speakers should be unobstructed and clear of furnishings or other objects within 180 degrees of the speaker face to a distance of four feet from the speaker face. In-wall loudspeakers should be mounted flush in the front wall with minimal obstructions or cavities in their vicinity, and mechanically isolated from the wall.

Ideally, conventional box loudspeakers should be located either in a baffle wall or more than 3.5 feet (1m) in front of the wall to the center-line of the box.

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