After cobbling together a complicated D-I-Y system that uses three A/V receivers to derive six height channels of Dolby Atmos audio, how much further could I expand my surround sound experience? Let’s go to eight!
In previous articles on this subject (start here), I’ve described how I integrated two additional AVRs into my home theater system in order to extract Top Middle speaker channels between my Top Front and Top Rear positions. For the purposes of explaining the theory behind that process, I illustrated where the speakers should be mounted, for best results following Dolby speaker position guidelines.
That’s all well and good, but the real world rarely meets such ideals. These graphics do not represent where speakers are actually located in my own home theater. Unfortunately, I have a very compromised height speaker layout due to the way I’d wired and mounted speakers when I built the theater room, before Atmos was ever a concern. Now I have speakers in less-than-ideal locations for Atmos and can’t move them without remodeling the room, which won’t be a realistic option anytime soon. Rather than tear apart my ceiling, I’ve tried to compensate by being creative.
Essentially, my speaker layout would probably work pretty well for Auro-3D, if I cared about that format. Most of my height speakers are high on the side walls rather than on or in the ceiling. They form a ring around the seating position, and the two that I’m calling “Top Front” are up near the front of the room and should probably more accurately be called Front Height. The distance between the height speakers combined with my low ceiling resulted in sounds not imaging above my head properly, leaving a big hole in the soundstage above me.
I tried to fix this by adding two Voice-of-God (VOG) speakers overhead above my viewing seats.
This gives me eight height speakers. Initially, I got sound to the VOG speakers by wiring them to the Top Middle speakers, forming two arrays (one on the left side of the room, one on the right). The VOG-Right was a clone of TM-Right and played identical sound. Same on the left. Effectively, this spread audio from the Top Middle channels to a wider area that filled the hole above me.
This was fine for ambient effects like wind or rain. However, it negatively impacted sound object directionality for anything that required a specific movement through the height channels. My test for this is the helicopter demo on the Sept. 2015 Dolby Atmos Demo Disc. The sound of the chopper is meant to circle the room in a counter-clockwise movement. In my room, rather than make a straight line from Top Front to Top Rear and back again, the sound made arc movements from the far left front of the room, inward to the middle of the room, then out again to the far left rear – and then did the same on the other side. I found this occasionally distracting.
From Atmos to EightmosTM
At this point, I needed a way to get discrete audio to the VOG speakers that was not simply a clone of the Top Middles – and I needed to do it without adding any more A/V receivers. Three of those is complicated enough already. My idea for this was to rewire the VOG speakers to become the “surround” channels in each secondary AVR’s ProLogic system.
In other words, on the right side of the room:
TF = Left
TM = Center
TR = Right
VOG = Surround
On the left side of the room:
TF = Right
TM = Center
TR = Left
VOG = Surround
My thought was that this would put that helicopter back in a straight line as it pans from TF to TM to TR, while the matrixed VOG “surround” would spread some reverb and ambient noises to the center of the room to fill the hole there.
The theory behind this seemed reasonable enough, but I wasn’t sure how well it would work in execution. I worried that it would continue to mess with object directionality and wondered what would happen in a case where a sound was intended to pan from side to side. (For example, the Atmos soundtrack on ‘John Wick’ has a scene where a helicopter moves from left to right overhead.) What would wind up in the VOG channels then? The only way to find out was to try.
My second and third A/V receivers are identical to one another. I was able to find a pair of Marantz SR4400s for cheap on Craigslist. This is a no-frills receiver from 2003, but it’s adequate for the purpose of using Dolby ProLogic II processing to extract a Top Middle Speaker from between the Top Front and Top Rear.
In the new configuration, I started by wiring out a VOG speaker to one of the receiver’s Surround terminals. The problem with this is that ProLogic II is designed to upmix two-channel audio to 5.1 speakers, which means that a stereo signal is split between two Surround speakers, each in line with the Left and Right (Top Front and Top Rear in this case). By only wiring one Surround speaker in the middle of the room, I have to choose which receiver terminal to use, Surround Left or Surround Right. Consequently, I’d wind up losing a portion of the audio that the receiver thinks it’s sending to the other channel with no speaker attached.
I thought I caught a big break when I discovered that, as a very early ProLogic II receiver, the SR4400 also offers a Dolby ProLogic (I) emulation mode that outputs a single mono Surround signal. Although this was intended to be duplicated into two Surround speakers, the content sent to them is identical. I wouldn’t miss any audio even if I only connected one speaker.
Unfortunately, I found that this wasn’t quite so simple in practice. My first tests delivered some pretty erratic results.
After rewiring the speakers, level matching, and changing the settings in my old Marantz receivers to the ProLogic emulation, I ran the 9.1.6 test tones on the 2015 Dolby Atmos Demo Disc and confirmed that my Top Middle extraction was still working between the Top Front and Top Rear. I next ran the helicopter audio demo on that disc. The helicopter seemed to fly in a wide ring around my seats with nothing calling attention to itself through the VOGs. I reasoned that this may be intentional to the way that clip is mixed, but I’m not certain how far away from me the helicopter is supposed to sound. In my previous configuration, where the VOGs were cloned from the Top Middles, the helicopter flew much closer to me (for obvious reasons). On the other hand, the helicopter moves in much straighter lines now without the arc motion I previously experienced. That’s a decided improvement.
I then disconnected all speakers except the two VOGs in order to isolate the sound coming from just those two speakers. Doing so, I was able to confirm that a small amount of audio did trickle to them, and did pan in the correct direction when the chopper circled behind or in front of my seat. However, it was barely audible and the audio cut in and out repeatedly. Worse, each speaker experienced a brief moment of crackling distortion when the sound moved from one to the other. I worried that something was wrong with the speakers, but when I disconnected them from VOG and plugged the same speakers into the TM outputs on the receivers instead, they sounded fine. I put the speakers back to VOG and tried the ProLogic II and DTS Neo:6 decoder modes instead. Unlike the ProLogic I setting, neither of those caused any distortion. The sound still cut in and out, but slightly less so. Neo:6 pulled a little more audio to the VOGs than PLII.
The helicopter demo was the only test I ran that had this distortion problem. The rain shower demo on the same disc sounded much better. That one generated consistent audio through the VOG speakers at a decently audible volume with no crackling. Sound only traveled to the VOGs intermittently in some of the other Atmos demos, but that’s to be expected since they don’t have constant overhead activity through all channels like the rain shower does.
I reconnected all of the other height speakers and played the scene in ‘John Wick’ where the helicopter moves from Top Front Left to Top Rear Left and then over to Top Rear Right. I’ve always felt that the movement from left to right sounded more like a jump than a pan, and I hoped that these new VOGs would stabilize the transition. Unfortunately, they don’t. Although some sound does pass through them, it’s faint and the movement still sounds like a jump. However, this may have more to do with the way the track is mixed than with my system. I recall that the movie was originally mixed in channel-based Auro-3D and was later converted to Atmos for the Blu-ray.
With all speakers working, I felt that the two VOG channels helped to fill the audio hole above my seats without ruining object directionality as they had in my last configuration. They sounded better with ambient noises (rain, wind, etc.) than discrete sounds, but that’s mostly what the surround matrixing would pull to them anyway.
While making all these changes, I also decided to swap out the speakers I’d been using for Voice-Of-God (which were a direct-radiating type that matched my Top Middles) with a couple of old bipole speakers that had been sitting in a box in my closet. This had the benefit of making overhead sounds more diffuse so that I don’t notice hotspotting directly over my head or any additional object directionality issues.
I’m not sure what’s causing the distortion in PLI emulation, but it happens in both SR4400 receivers. That would seem to rule out one unit being defective. However, it could simply be that the emulation mode in this model of receiver was always faulty.
In addition to that, PLI pulled by far the least amount of audio to its “Surround” channels (the VOG speakers). In comparison, I found that DTS Neo:6 is the most aggressive in extracting surround information, and I preferred it the most.
The problem with this, unfortunately, is that Neo:6 works similarly to ProLogic II in sending a stereo signal to its surround channels, not mono. Since I only had one speaker connected, this meant that I lost some audio that was canceled from one front main channel without going anywhere.
Fixing that proved to be another ordeal.
The dilemma is this: On each side of the room, I have an A/V receiver that’s outputting five channels of sound (Left, Center, Right, Surround Left, Surround Right), but I only have four speakers attached (Left, Center, Right, and one Surround). I need to combine the stereo output for Surround Left and Surround Right into a single speaker. This seems like it should be easy to do, but it’s decidedly not.
Can’t I just connect the speaker wire from both receiver terminals to the same speaker? No, this will cause a short circuit that may damage both the speaker and the receiver. It’s a bad idea; don’t ever try it.
After much research, the solution I found is to connect the RCA pre-outs for the Surround Left and Surround Right channels on each receiver to a little device called the Monacor SMC-1 Stereo-to-Mono Converter. (A simple RCA Y-connector won’t work. That brings the same risk of a short circuit as combining speaker wire would.) Two of these converters are required, one for each receiver. These then each “monoize” two channels into one with no loss of audio. Pretty clever, right?
But wait, the pre-outs from each receiver send an unamplified signal. After monoizing them, they still need to be amplified somewhere, and it’s not possible to feed them back into the receivers they came from. This means, unavoidably, that I had to add another amplifier to my system.
My first thought was to purchase an AudioSource AMP100VS stereo amplifier, which is a very popular product among Atmos users whose receivers require external amplification for some channels. Sadly, not only is its current $130 asking price more than I wanted to spend on this project, I actually don’t have any physical space left on my equipment rack to fit one. I would literally have no place to put an amplifier that size.
Fearing that I was out of options, I then discovered a product category that I’d never been aware of previously: Stereo mini-amps. I had no idea these even existed, but apparently there’s a sizable market for small two-channel amplifiers. Looking into that, I lucked upon a blowout sale at Parts Express for the Lepai LP-2020A+ mini-amp. The device is tiny and easily tucks away behind one of the AVRs on my shelf. Although it only advertises 20W of power (and delivers less than that in actual practice), it’s sufficient enough to drive a couple of small bipole speakers in my system. Most importantly, it was cheap. It only cost me $20. (Note that the LP-2020A+ is now discontinued, but Parts Express still carries the LP-2024A+ model.)
I’m not going to pretend that this Lepai mini-amp is an audiophile product. It’s clearly a very cheaply made device. In fact, the first one I received was DOA and I had to return it for a replacement. Even having gotten a working unit, the 3A power supply that it comes packaged with is insufficient to actually power it. I highly recommend replacing that with a 5A adapter, such as this one. It’s pretty ridiculous that I had to buy that separately. The amp also has a rather high noise floor, which is disappointing. However, when all is said and done, this is an inexpensive solution and it works for my needs – at least for now. If I grow tired of it, I may try replacing it with a more expensive amp such as the SMSL SA50, which is a little more powerful and seems to be well regarded.
All the Pieces in Place
To summarize, I now have three A/V receivers and an extra stereo amplifier driving a total of eight discrete height speakers in my Dolby Atmos system. Admittedly, this is convoluted, and probably could have been avoided if I’d been able to install ceiling speakers in the Dolby-recommended positions to start when I built my home theater room. Unfortunately, that didn’t happen, and I’ve had to improvise increasingly-complex solutions to compensate for the limitations of my room.
Am I happy yet? Mostly, I think. The bubble of sound above my head is fuller now, and aggressive Atmos effects such as the rain storm at the end of ‘John Wick’ are more convincing.
Am I done? I want to say yes, but realistically I’m sure I’ll find something else to tinker with soon enough.