User Manual

Multichannel Monitoring Tutorial Booklet (M2TB) rev. 3.5.2

Masataka Nakahara : SONA Corporation

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3-3-1. Direct surround

In the case of direct surround, the placement of the surround speakers involves a trade-off between

“surround panning” and “sense of rear stereo.”

Below, we describe the characteristics of typical direct surround configurations (110˚ ±10˚ (ITU-R), 135˚,

150˚) [Fig. 23].

[Fig. 23] Subtended angle for surround loudspeaker placement (direct surround) ;

110-degree (+/-10deg.), 135-degree, 150-degree

3-3-1-1. ITU-R: 110° ±10°

In the ITU-R placement, which locates the surround speakers at the “side” rather than at the “rear,” there

is good left/right separation for the surround, and it is easy to produce a detailed sound field.

However, surround panning is typically limited to expressions in which the sound image passes rapidly

just behind the listener's head without the localization image having much depth, and it is not easy to

produce surround panning expressions that have a sense of depth. (In other words, sound-source

movement via surround panning does not describe a circle.)

3-3-1-2. 135°

In order for a sound source to be perceived as being “behind” rather than “beside” the listener, it is said

that the surround speakers need to be placed at 135˚ or more toward the rear.

In most households, it is common for the speakers to be placed not at the “side” as in ITU-R, but rather

“behind” at approximately 135˚.

If you want the surround speakers to have a character somewhere between placement at the side

(100˚—120˚) and placement at the rear (150˚), it is good to place the speakers at a position of 135˚.

In such a configuration of LS and RS, the spread between LS and RS will be 90˚, which is the same as the

speaker configuration for the four-channel (2-2) QUAD format that appeared in the 1970's and

subsequently disappeared. However in QUAD, the L and R speakers were also spread at an angle of 90˚,

and it was recommended that all four speakers be placed at equal conditions (in other words, the angle

between L and LS and between R and RS is also 90˚). For this configuration, it was said that its lack of

compatibility with conventional stereo (in which the L and R spread is 60˚) prevented its subsequent

popularization, but recent research has reported that it does have a high degree of sound field

reproducibility, and there are examples in which this configuration is still used today in research systems

for virtual playback. The QUAD placement is often seen with the single-point microphones or IRT-cross

configurations often used to record a surround soundfield, and is a method that allows a surround

soundfield to be efficiently reproduced using a minimum number of channels.

There is also a commonality between the QUAD placement and the ITU-R placement; namely, that the

angle of spread between L and LS and between R and RS is 90˚. Thus, it is thought that a placement of

about 90˚ is favorable for the relationship between L/R and LS/RS. In other words we can conclude that

110

135

150