A little over a year ago, I began experimenting with ways to expand my Dolby Atmos surround sound system to beyond the 7.1.4 limitation of current consumer hardware. My continued quest to achieve the best Atmos experience at home has recently driven me to make additional upgrades. These days, my home theater is so crazily complicated that I actually need to run three A/V receivers simultaneously to manage all my speakers.
In most home theaters, 7.1.4 channels of sound should be plenty enough. Even though the Atmos format (as well as its competitor, DTS:X) can support additional speakers, there hasn’t been much demand for that from consumers or much push from manufacturers to do it. Currently, only boutique high-end products such as the $37,000 Trinnov Altitude 32 will decode more than 11 channels at once.
Nonetheless, for some of us, a limit of four height channels isn’t enough to fill the top of the room with sound. My own home theater is a long room with a lot of space behind my seats. That, combined with a low ceiling, makes it difficult for just four speakers (two in the front of the room and two in the back) to image a sound above my head convincingly. This issue is compounded by the fact that the locations where I had installed speakers when I built the home theater (before immersive audio was a concern I gave any thought to) were less than ideal for Atmos. Those speakers are now fixed in place with wiring through the walls and ceiling, and I can’t move them without remodeling the room. That simply isn’t an option.
The better solution is to install additional speakers in the center between the other height channels (Top Middle position). Unfortunately, the asking price for that Trinnov processor is absurdly beyond my budget. I needed to find a way to jury-rig a similar effect for a fraction of the cost.
The First Attempt
I wrote an article last year explaining how I had cobbled together a convoluted system (jokingly dubbed “Zatmos”) utilizing a second A/V receiver to derive extra channels on my ceiling. I advise reading that piece to understand the basic concept of how such a thing is possible.
Even at the time, I was not the only person experimenting with this, and I knew that my Zatmos system was not as ideal as I would have liked it. Over at AVSForum, a member named Scott Simonian had gone even further to use a total of three A/V receivers in unison to create a 7.1.6 configuration (affectionately known as “Scatmos”) more accurate to the intentions of the original Dolby Atmos sound mixers.
For a while, I decided not to go that far. The complexity of installing, connecting and configuring three A/V receivers seemed like overkill to me. I felt that the results I had with Zatmos were good enough to get me most of the way there, and I had a certain amount of egotistical pride that I’d figured out a way to do it with just one extra receiver rather than two.
However, in recent months, my attitude changed and I grew less satisfied with the Zatmos configuration. Eventually, I knew that if I was going to do this, I needed to do it right.
Going Full Scatmos
The silly Zatmos and Scatmos nicknames can be more formally grouped under the heading of “Dolby Atmos Extended.” I want to be clear here that I did not develop the Scatmos process. Credit for that goes to Scott Simonian and others at AVSForum who helped him work it out. With his permission, I’m just trying to explain it here.
For as perhaps ridiculously complicated as they may be to install, one of the saving graces of these experiments is that they can be assembled relatively inexpensively. Although your primary A/V receiver must be a Dolby Atmos (or DTS:X) model capable of decoding 7.1.4 channels of sound from a Blu-ray or UHD immersive audio soundtrack, the secondary receivers don’t need to be nearly as fancy. Any receiver that has, at a minimum, Dolby ProLogic II processing will do. (If using multiple secondary receivers, I recommend that they be identical to each other.)
With a little patience while monitoring For Sale ads on my local Craigslist, I managed to pick up a pair of used Marantz SR4400s for well below $100 each. This is a no-frills, entry-level (or close to it) Dolby Digital/DTS model from 2003. It’s so basic that it doesn’t even have an on-screen menu system. I have to set it up using only the front panel display. The receiver doesn’t have HDMI and cannot handle lossless Dolby TrueHD or DTS-HD Master Audio signals, but it doesn’t need to. All it needs is a pair of analog stereo inputs (which any receiver will have) and ProLogic II.
The simple act of finding a place to put another A/V receiver in my system proved to be far more of an ordeal than I wanted. Because I didn’t have enough space for it on my main equipment shelf, I had to remove all my components, take the shelf apart, rearrange the levels, put most of the equipment back, and hook it up again. Then I had to do the same thing with the second shelf in order to add a level. My Blu-ray and HD DVD players, which had previously been on the main shelf, moved over to the second so that I could keep all the audio equipment together where the speaker wire will reach it. This, in itself, was a tremendous pain to do.
With that finished, here’s the basic idea behind Scatmos: You want to mount six ceiling speakers – in the Top Front, Top Middle and Top Rear positions. (The following sketch does not represent my personal speaker layout, but I’ve drawn it this way to show how it should be done.) Your primary A/V receiver will be set to decode its maximum of 7.1.4 channels, configured as Top Front and Top Rear.
All four of the height channels should be routed to the analog pre-out connections on the primary AVR. You should not attach any speaker wire to those channels on the primary AVR. For all of the height channels, speaker wire will be attached only to the secondary AVRs.
The pre-outs for the Top Front Left and Top Rear Left channels will go into the Right and Left stereo inputs on AVR 2.
The pre-outs for the Top Front Right and Top Rear Right channels will go into the Left and Right (reversed from AVR 2) stereo inputs on AVR 3.
If that sounds confusing already, trying to keep it straight while actually connecting the cables and wires can be truly daunting. I strongly recommend drawing a chart that shows what should go where.
When working properly, each of the secondary downstream AVRs should take a stereo signal consisting of part Front and part Rear, and matrix a Middle channel between them using any mono information in common to both (much as ProLogic II would extract a center channel for dialogue in the front of your room between your left and right speakers under normal circumstances). Thus you get six channels of height information from an original four.
That’s the theory, simplified to its most basic elements. Actually getting it to work properly after your connections are made has some added levels of difficulty that I’ll cover soon in Part 2.