Front Height Left and Front Height Right speakers: These are mounted above the front left and right speakers, creating a vertical dimension in the audio. These are speakers nine and ten.

This setup allows you to experience immersive audio as it was meant to be heard, bringing movies, music, and other content to life in a way that traditional stereo setups or binaural rendering does not match.

Atmos objects are audio tracks with metadata linked to them. This metadata includes positional data (X, Y, and Z coordinates) indicating where the sound should be placed. Upon playback, the local Dolby renderer maps that position to the actual room configuration.

Later, I attended an AES conference in the UK focused on immersive audio at the University of Huddersfield, chaired by Professor Hyunkook Lee. This solidified my belief in the necessity of all the speakers for a genuinely immersive experience. It also provided an opportunity to ask questions, absorb knowledge, and learn from some of the world's leading experts on the subject.

I built an 8RU rack case specifically for this project using half a sheet of ¾” Baltic Birch. The dimensions are shown in the diagram. Note that the sides are ⅛” longer than the exact dimensions of 8 Rack Units to ensure the rails fit properly. I finished the case and the subwoofer with Ebony stain and semi-gloss polyurethane. In addition to the audio interface and amplifier, I included an 8-channel mic pre to ADAT interface as I already owned it.

Before we can properly manage the speakers, we need to set up Reaper for 7.1.4. I'll combine the steps since Reaper handles speaker management. Once set up, we'll create a few new templates for various ways of mixing immersive audio. Follow these steps in a new session:

I have a spreadsheet with all of the parts used for the build. There are a few specific things called out in the steps as your system may vary. Specifically how you mount the speakers etc. Here are links to the miscellaneous things:

Other than the Zobel and “R-L” parts, they had everything I was looking for including the ability to connect the supply rails between boards. I ordered 15 of the boards and had them built with 2 Oz copper. Meaning the traces are thicker copper, better for conductivity and power handling on the board. Then I put a BOM together for Mouser and ordered all the parts. I already had two power supplies capable of supplying 36V each so there was my +/-36V supply for all the boards. I built one board and tested it with my bench power supply and one of the Dayton Audio C-Note speakers. Worked great. Then I built the rest of the boards and mounted them to heat sinks and built two “modules” consisting of 3 heatsinks with 2 boards per heat sink. I took all the XLR and Speakon connectors out of the original chassis and mounted them onto single RU Panels with 12 XLR holes (Redco is amazing) and tested them. Not only did they work, they were super quiet, clean and sounded great. They are so quiet that when I turned them on initially, I was afraid they didn't work! If there is enough interest and I have time (so many projects in my head!) I will lay out a 12 channel version that includes everything.

Today, technology has improved and become more affordable, making it easier to record and playback multiple audio channels. The current bottlenecks are: Proprietary standards, user confusion, and the need to maintain backward compatibility with existing systems.

As a microphone builder, I realized I couldn't advance my microphone designs immersively without a proper playback system. Hence, the Sound Sleuth 7.1.4 Mixing Rig was born!

I designed the subwoofer using two Dayton Audio 10” drivers in an isobaric enclosure, a design first proposed by Henry F. Olson in the 1950s. There are several pros and cons to this design, but my primary advantage is that it halves the box volume, making the subwoofer more compact. It is built with ¾” 13-ply Baltic Birch. Using the Thiele and Small parameters for the driver I selected and a system Q of 0.707 for the box volume results in a smooth roll-off below resonance. The subwoofer is powered by a 300W plate amplifier from Dayton Audio. Wiring the two woofers in parallel reduces the impedance by half, allowing more power from the amplifier, which is rated for 300W into 4 ohms while the drivers are 8 ohms each. This setup produces a nice low end that is easy to integrate into the overall system. Construction uses butt joints with wood glue. The bottom panel is not glued and is screwed on during final assembly.

I had a surround sound setup in my media room back in the day and loved it—especially for watching movies. Some audio releases on DVD, including concerts, were mixed this way, but as an audio-only format, it never really took off.

This journey began when I built an Ambisonic microphone and started experimenting with immersive audio. I discovered various ways to decode it into binaural and other stereo methodologies. I was fascinated by the possibilities, but something always felt not fully immersive. To delve deeper, I reached out, emailed, networked, and chatted with multiple experts in the field. Everyone I met was supportive and encouraging. I also joined the Audio Engineering Society (AES), which I highly recommend.

To turn this all into a functional pro level system we need more than just the amp circuit boards. We need to think about the power supplies, turning it on and off, and electrical safety. Let's start with the power supplies. Back in the day building an amplifier required a huge transformer in the power supply. Big ones, full of copper, that weigh a lot, and cost a lot. A 500W version we would use for this weighs 9 Lbs and costs $128 on Digikey. Conversely a 36V switching supply rated for 340W costs less than $40. Two of those and we are all set. We need a dual supply of +36V and -36V. To make this, we connect the “+” of one to the “-” of the other and that becomes our circuit ground point. I made a decision to have the power supplies on all the time and switch the DC to the amplifiers when they are used. I used an old school toggle switch for the retro vibe, and two 60 Amp relays, one for the +36V and one for -36V. The relays are 12V so I also needed a voltage converter. Those are readily available these days. The one I selected is a buck converter and is adjustable. You have to set it for 12VDC. Connect it to +24VDC or more then adjust to 12VDC.

Industry-standard systems, such as those from Genelec, are used by the world's best studios. These systems can cost between $35K to well over $100K due to their advanced features like Dante and built-in DSP. However, from a DIY perspective, we can create a setup that works well, sounds amazing, and is much more affordable.

When we talk about "Height" in speaker placement, there are a couple of considerations that depend on ceiling height. The goal is to position the main and surround speakers near ear level, with the height speakers positioned at twice that height and facing the mixing "sweet spot." Dolby provides extensive literature and even a design tool to assist with these setups. It's important to note that Dolby specifies different setups for consumer listening versus the mixing environment, which can be a bit confusing.

Confused yet? All of these decisions are made by the Dolby renderer engine during playback. There are settings that determine how this happens. Beds are ideal for static elements that aren’t intended to move or for sounds that you’ve recorded or mixed exactly as you want them. The real magic of Atmos comes with objects. One of my favorite statements from Dolby is, “If you have a concern about a sound, try switching it to an object.” Which is interesting as you won’t know how it will behave until it plays back on a different system with more or fewer speakers.

7.1.4 sound (or higher) is amazing. I am super happy with how this all came together. Having this will totally help me design my next generation of immersive audio microphones. Here are the essential takeaways:

On the back mount the ½” plywood piece that goes below the I/O panels. I clamped the power cord with a cable clamp to the base of the case.

Rear Height Left and Rear Height Right speakers: These are mounted above the rear left and right speakers, completing the height dimension and making them speakers eleven and twelve.

If you haven't experienced immersive audio on a 7.1.4 speaker setup or larger, you're missing out on something amazing. Setting one up can be an expensive endeavor, and many recording studios have yet to invest in it. I set out to find a low-cost, yet high-quality, solution. Here are my findings. If you already have an audio interface that can output 12 or more channels, you can build this setup for about $2,500 USD.

I designed the subwoofer using two Dayton Audio 10” drivers in an isobaric enclosure, a design first proposed by Henry F. Olson in the 1950s. There are several pros and cons to this design, but my primary advantage is that it halves the box volume, making the subwoofer more compact. It is built with ¾” 13-ply Baltic Birch. Using the Thiele and Small parameters for the driver I selected, and a system Q of 0.707 for the box volume, resulted in a smooth roll-off below resonance. The subwoofer is powered by a 300W plate amplifier from Dayton Audio. Wiring the two woofers in parallel reduces the impedance by half, allowing more power from the amplifier, which is rated for 300W into 4 ohms while the drivers are 8 ohms each. This setup produces a nice low end that is easy to integrate into the overall system.

So if you do the bottom method, you won't actually render what you are thinking. You need to have all the tracks use an Atmos Beam plugin and go to the Atmos Composer. Play around with it and you will get used to the workflow pretty quickly. We are barely scratching the surface of this.

As we are building the amp into the rack case, there is a bit of crossover with the case and the amp build. To allow that we need to add four ¾” birch plywood pieces that are 2” X 7” in the corners. About 2 inches in from the back and right behind the front rack rails. This lets us put a shelf in above the amps and enclose them. There is enough scrap from the build to provide this.

Positional Accuracy – If you move an Atmos object up and to the left behind you, the positional metadata will ensure it’s placed correctly during playback, regardless of the playback system’s configuration.

As part of this whole endeavour, I upgraded my audio interface. I put a lot of thought into this and I bought a Focusrite Red Line 16. This provides balanced line level outputs on DB25 connectors. This lets me use two DB25 to XLR breakout cables. Which all go in the back of the rack. The output for the subwoofer plugs into XLR output #4 and connects with an XLR to RCA cable – See Rane note #110 for how to wire it. Yes, we are actually not using one of the twelve audio channels of the amplifier. The other thing the Focusrite provides is the ability to use one of the front panel knobs as a monitor level adjustment. And, link multiple channels to it. Think of it as a 12 channel volume control. Having this ability is a critical piece of an immersive audio setup. There are other solutions including standalone monitor controllers. These run anywhere from $1000 to over $6K for the Grace Designs one. There is also a just released interface specifically for this type of setup, the Audient ORIA. I have read some mixed reviews of it and it is not drastically cheaper than the Focustrite, which is now the brains of my studio.

There is also one other component value change I made. The LM3886 supports a mute pin and the data sheet shows using a 100uF and 1K resistor (Rm and Cm) This gives a time constant of .1 seconds. The way I am powering the amp up there is a chance that one power supply rail comes up before the other – which could cause an amplifier pop in the speakers. I checked the as-built schematic for the Gainclone boards I had originally built from a company called Chipamp, which no longer is around. They used 10K for Rm which gives 1 second. I upped that to 20K.

First, let's break down the numbers: they represent the number of audio channels and their configuration. Think of Mono as "1" and Stereo as "2". Surround sound, or 5.1, consists of five speakers and one subwoofer. In a 7.1.4 setup, there are seven speakers at ear level, one subwoofer, and four additional speakers for height. This is where the magic happens. The extra height speakers, along with the speakers arranged around you in a circle, create an immersive experience that you have to hear to fully appreciate. It is truly amazing.

There are a couple ways to test these. You can do one or two channels at a time with a pair of the speakers. This can be done with any stereo source you can connect via an XLR and a pair of the speakers. You will need to ensure that the output of your source is adjustable as there is no level adjustment on the amps themselves. As this was my third amplifier design, I already had the speakers setup and placed. I connected my Audio Interface and tested that way

Dolby Atmos takes advantage of this setup by allowing sound to move freely around the listener, creating a three-dimensional audio experience. Sounds can be placed and moved precisely anywhere in the room, including above the listener, making it feel as though you are truly immersed in the audio environment.

Side Left and Side Right speakers: These are positioned to the left and right sides of the listening area, making them speakers five and six. They add depth and a sense of space to the audio experience.

Once you have the mounting holes sorted out we want to add the speaker wires and the input wiring prior to mounting the PCB’s to the heat sinks.

If we just added two rear channels, we would have Surround Sound or 5.1. To move to 7.1.4, we add the remaining speakers as follows:

Once everything is tested, dress in the cables with tie wraps, mount the toggle switch on the front panel and drill holes in the front panel that lets you screw it to the front rack rails

There is a standard called out for this. Interestingly it calls for all the speakers to mounted the same distance from the listener or time aligned to 100uSec. Hmmm that is 3.4cm assuming speed of sound is 340M/sec. I'm not meeting that requirement, and neither are you. Which is totally OK. Ask yourself this: Do you go into the studio and take a tape measure to the stereo monitors and the mixing chair? As we shall hear, it is not as critical as one might think.

Speaker management involves ensuring all speakers are level-matched and potentially applying some EQ if needed. In my case, my two existing stereo mains have different sensitivity levels compared to the Dayton Audio C-Notes, as does the subwoofer. We can use these tools to tune the room as well, but that is beyond the scope of this document. And, as I quickly learned not really necessary. I'm expecting blowback on that statement but I stand by it.

So, how are these speakers set up? How are they connected, and how can you get started? Let's begin with the classic stereo setup: left and right main speakers. These are actually the foundation and the starting point. Interestingly, there is an expectation that the immersive mix can "collapse" down into stereo, much like how we used to worry about mono compatibility with stereo. These are speakers one and two, left and right. Next, we add a center channel, which is the third speaker. Then we add the LFE (Low Frequency Effects) or subwoofer, making it four speakers.

An Atmos bed track maps out all speaker channels in your DAW setup. For example, a 7.1.4 setup has twelve channels. If played back on a different setup (e.g., 9.1.6), there might be silence on channels that don't exist in the original bed, depending on how the rendering engine is configured. You can specify how to handle these channels, leaving some final decisions to the system. If you have LFE content, it has to come through on a Bed.

Cut two pieces of aluminum angle 12” long. We are going to mount three heats sinks to each. You will need to drill holes on each end to allow them to be screwed down on the bottom of the amp case. On the other side we will need two holes for each of the heat sinks. You want the heat sink to not touch the bottom of the amp case ¼” is a good amount of clearance. I am not giving exact measurements for you as you can use ¾” up to 1-½” angle based on what you can source. Both Lowes and Home Depot carry this. See the photos for how I did it. Note that I already had 6 heat sinks as my parts bin is extensive.

This one I knew I would have to build. I started with a multichannel amp board that has 6 channels and I used two of them for 12 channels total. These boards use the TDA7498 chip set and are Class D amplifiers. I quickly learned that Class D amps are not the option to go with due to self generated EMI. They work great when close to the speaker they are powering as in most powered speakers. One six channel boards by itself worked great. When multiple ones are in a system with long speaker runs I got a very weird hiss and almost a fan noise type of sound. So I started sleuthing and troubleshooting. The data sheet for the TDA mentions that if you use more than one, the clocks need to be syncronized. One master driving the rest. Now I know why. The final nail in the coffin was when I put Ferrite chokes on all the speaker cables leaving the amp case. That lowered the noise but didn't eliminate it. So I went back to an old school solution: The LM3886. I used these before and knew they would work. I wish I had started there as it would have saved me about 6 weeks of time and some coin. I found a pre laid out PCB on PCBWAY and ordered 15. They come in multiples of 5. I needed to add two things for robustness and was good to go.

This is a bit up to you. I settled upon gray “hammered” finish paint. MDF needs to be prepped in order to get the paint to look good. There are many YouTube videos on this. Some of mine came out better than others but all look decent. My takeaways are:

My goal was to create a fully functional 7.1.4 setup for mixing and demoing immersive audio. Let's start with speakers. I chose passive speakers, which require multi-channel amplification and an active subwoofer. I use Reaper as my DAW, which is highly configurable for immersive audio and, in my opinion, the gold standard for this purpose. Although DAWs are primarily designed for stereo, we can adapt them for immersive audio.

There are a couple ways to do this and even a couple “standard” positions. I encourage you to google “7.1.4 speaker placement” You will get multiple results, all with variations of where to place them. Movie theaters vs home listening. Even in the studio. This to me, translates as there is no perfect setup and I look at these as guidelines. In the studio you want a sweet spot to mix to. In the home or theater, you need multiple people to be in the sweet spot. Question of the day: How “exact” is your stereo setup? My thoughts here are to get the speakers placed as best as you can and let's start listening! My room setup evolved from my original mixing desk with Left and Right speakers. My height front speakers are mounted wider than my main speakers while the rear height are symmetrical on the back wall. See the photos. I have seen the heights closer together and directly above the mix location. I have it on high authority that several grammy winning mixer/producers, who shall remain nameless, have ceiling mounted 8 inch coaxial speakers as height speakers. One with an 8 foot ceiling and adding in just a tiny amount of delay to make them further away. Having them is more important than what they are. Just make sure all four are equivalent. After positioning all the speakers and connecting them I did an initial test to ensure they were all working. I am using a Mac. Go to Audio Midi setup and set your speaker setup to 7.1.4. Use the built in test buttons for each speaker to make sure they are where you think they are. Initially I had my rear left/right height speakers crossed. Yet one more example of why Speakon connectors are so worth it!

I already had a great pair of main speakers that I built myself. As a DIY enthusiast, I considered designing my own surround speakers. I started by looking at drivers on Parts Express, my usual source. I found the C-Notes kit, which looked great on paper and was reasonably priced. After building and testing a pair, I took them to a friend's studio in the DFW area. I found they sounded really good, holding up well in an A/B comparison and were only “bested” by a pair of Adam A77x speakers. Encouraged, I ordered five more pairs.

At the start of this project I intended on building a 12 channel amplifier in a 2RU case. That didn't work as you will see in the amplifier section. My completed project has the amp modules and power supplies mounted to the bottom of the case. So I added a birch veneered ½” plywood shelf and ¼” front panel to the case to enclose the amps. I also replaced the I/O panel from the 2RU case I originally intended to use with two single RU rack panels that both have 12 Neutrik XLR cutouts. These became the I/O panels, one with female XLR’s for the inputs and one with Speakon connectors for the outputs. The build is straightforward, just a box, and takes less than half a sheet of Baltic Birch. We will use the second half for the subwoofer. See the pictures.

Making all this come together and function as a system requires a bit of planning. Most obvious is physical placement of the speakers. Then we have Speaker Management,  which is the signal processing needed for each channel. Finally, we need to set Reaper up to support multiple channels of audio. This one is interesting as there are both the output channel requirements and track channel requirements. Just what does an immersive audio track look like? We shall see!

If you are unfamiliar with this chip, it is a power operational amplifier specifically designed to be used as an audio amplifier. It originally found its way into an amplifier called a gaincard by 47 laboratories. It used about $100 in parts, sold for $3000, and got rave reviews from the audiophile community. It was also so simple that the audio community started building DIY versions called “Gainclones”. I was one of those people and I can attest to how well they worked and ease of build. Let's look at the schematic and see how it works and then what is critical to making it work successfully. This is your classic Operational Amplifier gain stage. The input resistor and feedback resistor (1KΩ and 20KΩ) set the overall gain of the amp to 20, or about 26dB. This is plenty for what we are doing. Note the two capacitors at the supply rails: CS. These are our first “critical components” for proper operation. They need to be close to the LM3886 and they need to be large. We are using 1000uF caps that are also bypassed with small .1uF caps. Next up are two features that ensure the amp does not oscillate or “ring” at high frequencies. The first is a Zobel network. It is simply a small resistor and capacitor in series across the amplifier output. We are using a 3 Ω resistor and .1uF capacitor. It really helps when there is no load on the amplifier. In my case, I am building 12 channels and will use 11 of them 90% of the time so this is important. Finally, due to potentially long speaker cables, we are also including “L” and “R” from the data sheet. A small inductance in parallel with a resistor to decouple capacitance of longer speaker cable runs. We actually are winding the coil with 10 turns of magnet wire around a 10Ω resistor. Both of these are added off the board due to its design but they ensure the whole build is bullet proof.

Take two of the boards, hold them onto the Heatsink and mark the spots to drill and tap M3 holes. The LM3886 has to be flush with the flat surface of the heat sink for proper heat transfer. WHen you hold the PCB to the heatsink, look at that edge of the PCB, it extends just a bit more than the LM3886 and you need to take that into account when you mark the hole.

The board is 2Oz copper and the ground plane connections will pull away a lot of heat making soldering difficult. You need to raise the soldering iron temperature and be patient.

The metadata is exported as part of an Audio Definition Model (ADM) file. These can be quite large, as they contain all the audio and metadata for each object. An ADM file can handle up to 128 channels of audio. As of summer 2024, the ADM file format and its practical use remain the biggest hurdles. ADM files are what get exported from our DAW via the Dolby Renderer, but they aren’t designed to be portable or directly used by an end user. They can be shared via large file-sharing services or portable drives, but this is not their intended use case.

When all these speakers are combined, you get a 7.1.4 setup: seven speakers at ear level, one subwoofer, and four height speakers. 12 Audio Channels in total.

Instead of sending things left or right, we have 12 possible speakers and locations. Just what does that Pan Pot do now? I mean really....? Reaper comes with a Plugin called ReaSuround Pan that lets us access all 12 speakers. And, has great features for linking and automating parameters. There some great YouTube videos on it

Rear Left and Rear Right speakers: These are positioned behind the listening area and are designated as speakers seven and eight. They help create the surround sound effect, placing sounds behind the listener.

At the tail end of Covid, I attended my first AES meeting in The Hague, Netherlands. There, I finally experienced Dolby Atmos and other immersive audio formats on multiple speaker playback systems. It was amazing. I finally understood the true essence of immersive audio. Until you have heard a 7.1.4 system, or greater, you haven't truly experienced immersive audio. I stand by that statement.

Adaptability – An Atmos system will try to place your sound where you intended based on the object’s metadata. For example, a mix created in a 7.1.4 setup will play back correctly on a system with more or fewer speakers. The final Atmos decoder will place each object where it should go.

Starting with the crossovers. I got an assembly line going and built them in pairs. Check each PCB visually when complete and clean off the flux. You may need a little higher wattage iron then small PCB’s as there are wide traces on the board for the current carrying ability of the crossover. I used the supplied wire for the speaker connections and crimp on connectors (see parts list) to connect to the drivers. Note the Tweeter has two terminals of different sizes but isn’t labeled with a red dot for polarity. The larger terminal is Positive! I used separate red and black wires 16” long for the incoming wires. I did that so I could push them out of the Speakon connector hole to solder on the Speakon connector.

This is technically a DIY solution because it involves assembling multiple parts, either from kits or components I've designed. The results are top-notch and suitable for any recording studio to mix immersive content, such as Dolby Atmos.

I didn't design the board we are using or I would have included the zobel parts and the output RL network. This also means that the 1K resistor I replaced with a 20K is labeled 1K on the board. After my time sunk into the Class D amps, and having everything else ready to go, I was looking for the fastest way to get the entire project up and running. I use PCBWay for my PCB builds and they have a shared project section where I found these:

I wanted the setup to be portable for local demonstrations and tours. My mixing room is shared space, so it is not feasible to have the setup permanently installed. The solution was to make the side and rear surrounds quickly detachable. These are set up on speaker stands and connected with speaker cables using Speakon connectors.

Note: The connectors have a silverish tab to press in to unlock the cable when plugged in. This is the top of the panel ;-)

This could take an entire book! Along with this article, I have created a complementary video. Both serve as entry points and are not comprehensive. Immersive audio has been around for a while, but the ability to listen to and mix it is becoming more accessible. The following outlines what I have learned by talking to some of the best in the world, learning, and actually doing. I encourage you to experiment. I find myself rethinking how I record to utilize this format. Tom Dowd famously said, “Always record in stereo,” which I have always done. Now, I need to think, “Always record for immersive.”

The speakers themselves can be easily taken down for transport when needed. The wire and Speakon connectors cost around $400. It is well worth it for the simplicity of setup and use. There was no way I wanted to futz around with 12 pairs of banana jacks or pushing wire through screw down terminals – Not happening!

I also built an 8RU Rack Case to hold the Audio Interface, the amplifier, power supplies and a few additional items. Details for each of these is in the following steps.

Immersive audio playback systems were first used with the Disney movie *Fantasia* in 1940. This was a three-channel system with "Left," "Center," and "Right" channels, designed to create the effect of sounds moving around the audience. In the 1970s, Quadraphonic audio with four channels emerged, but it flopped commercially. Next came what is commonly called Surround Sound or 5.1, featuring five speakers and one subwoofer for Low Frequency Effects (LFE). Essentially, 5.1 is Quadraphonic with a center channel, driven by the film industry to allow dialogue to come from the center (where the screen is) and other sounds to be placed around the audience.

Mount the two I/O panels to the two plywood side rails on the back of the rack. The XLR’s go on top and the Speakon below.

Drill the hole with a 2.5mm drill then tap with an M3 tap. A drop of cutting oil helps here. Clean the heatsink afterwards to ensure no oil remains.

Prep the box for use with a Speakon connector by drilling a 15/16” hole in the back panel. See the parts list for the drill bit I recommend. I centered the hole on the back panel, allowing for consistency if I mounted the speaker in its side or normally, standing up.