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Speaker Layouts for DTS:X Immersive Surround Sound

By Tony Verkuijl

Up until the moment of this writing, DTS has not shared speaker layouts for its new DTS:X codec. However, it is object-based codec technology (similar to the description of Dolby Atmos), and we  pointed out in our DTS:X Overview article, the name is incredibly close to “DTS Headphone:X” that is clearly based on a “classic 11.1” setup, as DTS’s own demonstrations have showed. Other projects in which DTS is involved, for example the native 3D Audio recordings with Hans Zimmer, have been done in 11.1 as well.

Speaker layout: “Classic 11.2” used for Atmos

Yamaha’s “Classic 11.2”, expands the basic 7.1 with clockwise (Figure 6):

  1. Presence Left (Dolby and Audyssey call these “Front Height Left”)
  2. Presence Right (“Front Height Right” in Dolby and Audyssey)
  3. Rear Presence Right
  4. Rear Presence Left
  5. Subwoofer (Subwoofer L and Subwoofer R in the image, hence the .2)

 Yamaha 11.2 Speaker Layout

Figure 6: "Classic 11.2". Courtesy of Yamaha.

 

If we want to use the “Classic 11.2” speaker layout for Atmos playback, we should mount the presence speakers at a certain height. The vertical angles Dolby has specified for the in-ceiling speakers are useful for this. Only some basic mathematics is needed: the tangent of the vertical angle (like 30°, 45° or 55°) needs to be multiplied by the distance to the presence speaker on the floor plane (Figure 7): 

 

h = l*tan(θ)
h = height of presence speaker
l = distance to presence speaker on floor plane
θ = (theta) vertical angle
 

Height Channel Angles

Figure 7: Height vs. Distance calculation.

It’s important to select similar sounding speakers for ALL channels to guarantee the homogeneity of the system

Sitting in a typical listening position means the average height of the listener’s ear is 3 feet (≈ 1 meter). At a distance of 9 feet, one can mount a presence speaker at a height of h = 9 * tan (30°) + 3 = 8 feet minimum to meet Dolby’s advice. If we want to calculate the height of the rear presence speakers, the formula is the same, but with a negative distance. Is the back wall at a distance of 9 feet, we calculate h = -9 * tan (150°) + 3 = 8 feet. Graphics 1 and 2 display the height of the presence speaker at any given distance. All this works for smaller rooms only, as for very large rooms the minimum height exceeds the height of the ceiling. For example, an average American ceiling (assuming 8 feet high), at 30° the maximum distance from a presence speaker to the listening position would be d = (8-3) / tan (30°) = 9 feet. In the metric countries assuming a ceiling height of 3 meters d = 3 - 1 / tan (30°) = 3.5 meters. But even in larger rooms, presence speakers mounted at a slightly lower than 30° angle would still do the job, how many Home Cinemas do you know that respect the horizontal angles of 22° - 30° for the Fronts and 90° - 110° for the Surrounds (Figure 2) and still sound great?

The next figures show all presence speaker heights for the minimum, optimum and maximum vertical angles (30°, 45°, 55°), for any distance from the listening position to the presence speaker on the floor plane up to 15 feet (Figure 8), or up to 5 meters (Figure 9).
 

Front Height vs Distance New

Figure 8: Front Height vs. Distance [feet].

 

Front Height vs Distance New (meters)

Figure 9: Front Height vs. Distance [meters].

We see the line of 30° for the front presence speakers (hence 150° for the rear presence speakers) crossing the ceiling height of 8 feet or 3 meters at a wall distance of 9 feet or 3.5 meters. Having front and rear wall at 9 feet or 3.5 meters, the room can be on and about 18 feet or 7 meters long to mount front and rear presence speaker close to the ceiling and still meet Dolby’s vertical angle. For small to medium sized rooms we can use this speaker layout.

Speaker layouts: Yamaha Atmos Enabled AV Receivers

With the latest firmware upgrade that enabled Dolby Atmos in Yamaha’s two top receivers came a document with additional information that proposes three speaker configurations for Dolby Atmos:

  1. “Front Height/Rear Height”: basic 7.2 with two front presence and two rear presence speakers (as introduced on the Z11, “classic 11.2,” upper left)
  2. “Overhead”: basic 7.2 with four in-ceiling speakers (as proposed by Dolby, lower right)
  3.  “Dolby Enabled SP”: basic 7.2 with upward-firing speakers (as proposed by Dolby, lower left)

Yamaha 3Spk Layout

Figure 10: Speaker layouts. Courtesy of Yamaha.

 

Analysis

“Overhead” is arguably the Best Technical Means (BTMs) of speaker layout for Dolby Atmos, with in-ceiling speakers. This is the closest approach of the speaker layout in professional Atmos-certified cinemas. A system of 7+4 speakers of similar performance would do best. It is however hard to build a Home Cinema with in-ceiling speakers that sound tonally-similar to conventional wall-mounted surround speakers of the basic 7.1 layout. For presence speakers I have always advised to buy the smallest speaker of the same model range of the front speakers (IE: if fronts are Klipsch RF-82, for presence buy Klipsch RB-41). In-ceiling speakers however tend to be completely different in design.  They are different not only in the drivers utilized, but think of the volume and the materials of the enclosure (if one is included). As of today it is very hard if to find an in-ceiling speaker that sounds even reasonably similar to a tower or bookshelf speaker of the same brand. In the basic 7.1 layout, it’s important to select similar sounding speakers to guarantee the homogeneity of the system. The same goes for the upper .4 speakers! Another solution could be mounting small matching bookshelf speakers in-ceiling or appending them from the ceiling. However this can compromise the safety of the listeners since consumer bookshelf speakers are not designed for this kind of mounting.

 

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