Dolby Enabled Reflection Speakers: A Last Resort for Immersive Surround?
Dolby Enabled Speakers could do the job, since sound (mostly high frequencies) do reflect off normal-height flat ceilings in an average home. In those cases, there no need for mounting of additional speakers in-ceiling or on-wall, which makes speaker mounting easiest with this option. With proper DSP and the use of an auto calibration system and ideal geometrics on paper one could get an adequate result though within a somewhat narrow sweet spot. The problem is, as the frequency goes lower, the sound becomes less directional. I have not seen any polar plots of any Dolby Enabled Speakers, but I’ve seen their designs. Their polar plots should not differ too much from normal bookshelf speakers, with exception of the higher frequencies. As it seems the elevation of the Dolby Enabled Speakers is typically 20°, it would be interesting to study a polar plot of a typical full range speaker. In a polar plot we can see how much acoustical energy the speaker radiates to all sides on the vertical plane. In the next Figure 11, a two-way speaker is seen from the side with the woofer and tweeter pointed upwards. The energy radiating from the front side of the speaker is therefore also pointed upwards, in the “twelve o’clock” position. The backside of the speaker is in the “six o’clock” position, upside is “nine o’clock”, and downside is “three o’clock”. Every smaller circle represents an attenuation of 6 dB, which is half the sound pressure level.
Figure 11: Polar Plot of typical speaker. Courtesy of Sound Reinforcement Handbook.
Now we understand the position of the speaker in Figure 11, we know that a) is on-axis, b) is 15° below-axis, c) is 30° below-axis. The red line is 70° below-axis, equivalent to “20° elevated” as most Dolby Enabled Speakers are designed. If this typical speaker was used as a Dolby Enabled Speaker, the high frequencies (right polar plot) would have been attenuated significantly. Beware that the typical speaker in Figure 11 has a hornloaded tweeter, hence is more intentionally directional in high frequencies than speakers designed with normal dome tweeters. The lower frequencies, especially 500 Hz, 250 Hz and 125 Hz, (left polar plot) show attenuation of only 3-8 dB and that makes this speaker “audible” to “clearly audible” to listeners on the 70° below-axis. And “clearly audible” from 125 Hz and above means the listener is able to locate the sound source, so the acoustical separation between upward-firing speakers and the basic 5.1 or 7.1 seems not be as good as with in-ceiling speakers or presence speakers. Audioholics has reported this very phenomenon in their Atmos listening tests with Dolby Enabled speakers.
Dolby Atmos-Enabled Speaker Solution from Onkyo employs a single 3" paper driver
The same problem as in the “Overhead” layout occurs here: how do the Dolby Enabled Speakers of today match the already present Front and Surround speakers? The designs of today are focused on directivity, with absorption foam and other particular constructions, but few of them tonally match the existing Front or Surround speakers, since they are not made with matching driver elements. KEF is producing matching Dolby Enabled Speakers (model R50), but doesn’t provide any polar plots.
Front Height/Rear Height is a practically Classic 11.2. With this layout it is possible to match or get very close to Dolby’s ideal geometry of the additional loudspeakers that create the 3rd dimension of audio. It is easier to mount additional speakers on-wall especially if the Home Cinema is not build as new. It is possible to find additional speakers that match the already present Front and Surround speakers. It is for now the only solution more or less compatible with Auro-3D 9.1, as Auro Technologies does not propose or support upward-firing speakers. Also DTS:X is suspected to adopt this layout. And, what about all older media? Most Blu-ray’s and all DVD’s, TV-series, games, streams and video files don’t have a native 3D audio soundtrack, and the listener will have to go back to DSP-based upmixing formats, in this case the new Dolby Surround Upmixer (DSU) and/or Yamaha CinemaHD3. In the first case the “Overhead” would be first choice, but Classic 11.2 with right vertical angles would not perform less. In the latter case the Classic 11.2 layout is best backward-compatible. The downside of this layout is that in long rooms with low ceilings, it will be difficult or impossible to reach the requested vertical angles for a convincing 3rd audio dimension when playing Atmos.
What Speaker Layout to Choose?
In the old days choosing a speaker layout wasn’t so much an issue, finding a place for one or two speakers is not so difficult. With the rise of “5.1” in the DVD-era things got slightly more difficult: adding a central speaker under the CRT television was easy, placing the surround speakers a little less. But at least the new 5.1 speaker layout could be used for AC3 and DTS (and MPEG Multichannel in Europe). Also the 5.1 upmixing systems of the time, like Dolby Pro Logic II, Yamaha CinemaDSP and Harman Logic 7, used more or less the same 5.1 speaker layout. In the 2000’s Yamaha started to mount additional speakers high on the front wall, followed by Dolby Pro Logic IIz, DTS Neo:X and Audyssey DSX. Although different systems, they used virtually the same speakers, whether called “presence” or “front height” speakers.
Today we are at the dawn of 3D Immersive Surround formats and Dolby has shaken the world with two speaker layouts not seen before: one has to choose between adding in-ceiling speakers or adding upward-firing speakers. It is understandable why Dolby has chosen the solution with in-ceiling speakers, as physically it may be the closest to the professional cinema layout, and it works for any size of room, for Atmos that is. It would be best to have one basic speaker layout that the consumer can use for all formats the industry has to offer. The other 3D Immersive Surround formats, Auro-3D and probably the coming DTS:X format, have adopted a speaker layout close or identical to Classic 11.2. For small to medium sized rooms Classic 11.2 is a valuable option also for Dolby Atmos. In this article we have shown that Classic 11.2 is well adaptable to the Atmos geometry, the height calculations sustain this. This in combination with better choice of similar additional speakers and easier mounting (that leaves your existing precious front and surround speakers alone or you don’t have to install a false ceiling for your in-ceiling speakers) it is hard not to recommend. Even if in a larger room with low ceilings the presence speakers can’t be mounted high enough to meet Dolby’s requested vertical angles, Classic 11.2 is still the next best speaker layout.
The Last, and probably also least recommended speaker layout for immersive sound would involve the Dolby Enabled Speakers. This speaker layout is recommendable over the other speaker layouts ONLY if wall- and ceiling-mounting height speakers is impossible. However, the question remains if this kind of speakers add more intended effects to the movie you’re listening to than unintended side effects. The first impression may be “Hey, I hear sound from above, gotta have it!” Later on the poor channel separation in the mid and lower frequencies and the not improved aesthetics of the loudspeakers the impression could become mildly interesting and downright annoying overtime.
For Dolby Atmos, the Best Technical Means for speaker layout would be the 7.1.4 layout, with in-ceiling speakers. The other systems, Auro 3D and probably DTS:X, for best technical means would follow the 7.1.4 layout with presence speakers (“Classic 11.1”) as presented in the Yamaha Z11 back in 2007. As a result this layout could be proposed as “best practical means overall” in Home Cinema, being more or less “the most compatible solution” for ALL three 3D Immersive Surround codecs and easier to match and mount height speakers. This would make Dolby Enabled Speakers the least favorable option, even with the easiest mounting advantage. But after all, we are after a truly improved immersive surround experience anyways so why use a compromise when more viable options exist?
Right now Audioholics is testing a Yamaha RX-A2040 with Dolby Atmos using presence speakers in “Classic 11.1” layout. The results of this review are coming soon and could confirm if this speaker layout is a good alternative for in-ceiling speakers, or that Dolby Atmos sounds good only with the newly proposed layouts.
Many thanks to Tony Verkuijl of Yamaha Music Europe GmbH - Branch Italy for contributing this article.
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