Sonos Beam (Gen 2): Immersive Sound, Simplified Home Theater

In 1931, a brilliant and tragically short-lived British engineer named Alan Blumlein walked out of a cinema frustrated. The new “talkies” had a glaring flaw: the voice of an actor walking across the screen remained locked to a single, static speaker. It was a disconnect, a crack in the illusion. In a stroke of genius, he invented stereophonic sound, a system designed not just to reproduce audio, but to conjure a sense of space and direction. His goal, nearly a century ago, was to create an auditory illusion.

Today, we face a similar, albeit inverted, problem. Our screens are magnificent 8K portals, offering breathtaking visual fidelity. Yet the sound that accompanies this spectacle is often trapped, a thin, lifeless whisper emanating from tiny, downward-facing speakers. The illusion is once again broken. The quest to fix this has led us down a path Blumlein could have only dreamed of—a path where the most powerful tool isn’t a bigger speaker, but a smarter algorithm. This is the world of computational audio, and one of its most compelling ambassadors is a compact soundbar: the Sonos Beam (Gen 2).

To understand the Beam is to understand that it’s less a piece of audio hardware and more of a sonic ventriloquist. It uses a potent cocktail of physics, neuroscience, and sophisticated software to perform a seemingly impossible feat: creating a vast, three-dimensional soundscape that extends far beyond its physical borders.

The Cinema’s Grand Revolution, Distilled

For decades, immersive sound meant more channels. We went from stereo (two channels) to 5.1 surround sound (six channels), a system that painted sound on a flat, horizontal canvas around the listener. The revolution came with Dolby Atmos. It fundamentally changed the game by shifting from a channel-based model to an object-based one.

Think of it this way: in a 5.1 system, a sound designer had to decide, “I will send the sound of this helicopter to the rear-left speaker.” With Atmos, they can simply say, “The helicopter is an audio object. Here is its precise GPS coordinate in the room and its flight path.” The Atmos renderer—in the cinema or in your soundbar—then takes this data and uses whichever speakers are available to recreate that object in its intended position. It’s the difference between coloring by numbers and painting on a three-dimensional canvas.

This is astounding in a cinema with dozens of speakers. But how do you replicate that sense of height and immersion with a single, two-foot-long bar sitting under your TV? The answer isn’t just about bouncing sound off the ceiling. It’s about hacking the most sophisticated audio processor we know: the human brain.

The Ghost in the Auditory Machine

The true magic behind the Beam lies in the science of psychoacoustics. Our ability to locate sound isn’t magic; it’s a biological calculation. Your brain determines a sound’s origin by analyzing microscopic differences in the signal received by your two ears. The two primary cues are:

1. Interaural Time Difference (ITD): A sound coming from your right will reach your right ear a fraction of a millisecond before it reaches your left.
2. Interaural Level Difference (ILD): That same sound will be slightly louder in your right ear than your left, as your head creates an “acoustic shadow.”

The shape of your outer ear (the pinna) adds another layer, subtly coloring sounds with unique frequency shifts depending on whether they come from above, below, in front, or behind. All these cues combine to form your personal Head-Related Transfer Function (HRTF)—a unique neural fingerprint that your brain uses to instantly map sound in 3D space.

The Sonos Beam’s Digital Signal Processor (DSP) is engineered to be an expert forger of these cues. It doesn’t just play a sound; it deconstructs it and then reconstructs it as a series of precisely aimed “sound beams.” For an overhead effect like rainfall, it doesn’t just fire sound upwards. It projects a complex audio signal that, after reflecting off your ceiling, arrives at your ears with the exact timing, volume, and frequency modifications that perfectly mimic the HRTF cues for a sound originating from above.

It’s an act of auditory ventriloquism on a digital level. The soundbar is the puppeteer, but the voice—the rain, the passing starship—appears to come from an entirely different location. This is why it can feel so uncannily real, tricking you into looking over your shoulder for a sound that was, in reality, born from an algorithm just a few feet in front of you.

Taming the Tyranny of the Room

Yet, creating this illusion is only half the battle. The greatest adversary to good sound isn’t the speaker; it’s the room it’s in. Every room is an acoustic entity with its own personality, and often, it’s a problematic one.

The principles of room acoustics are ruthless. Parallel walls can create standing waves, where bass frequencies of a specific wavelength get trapped, causing a boomy, one-note drone in some spots and a complete dead zone in others. Hard surfaces like windows and wooden floors cause sound to reflect uncontrollably, muddying detail and making dialogue hard to understand. This measure of reflection is known as reverberation time.

This is where Sonos’s Trueplay technology comes in. It’s a consumer-grade application of a process that audio professionals have used for decades: digital room correction. By using the microphone in an iOS device to listen to a series of test tones, Trueplay performs an acoustic “CT scan” of your living space. It maps the room’s frequency response, identifying the peaks caused by standing waves and the dips caused by cancellations.

With this map, the Beam’s processor builds a custom filter, a corrective prescription for your room’s specific acoustic ailments. It surgically reduces the booming bass frequency, boosts frequencies that are being absorbed by your thick carpet, and applies subtle delays to tame harsh reflections. It effectively removes the room from the equation, ensuring the psychoacoustic illusions it works so hard to create arrive at your ears with pristine clarity. It’s a crucial step that transforms the Beam from a smart speaker into a truly adaptive audio system.

The Intelligence Tax

This profound intelligence, however, comes with its own set of modern complexities. The Beam, like the entire Sonos ecosystem, eschews Bluetooth in favor of a more robust Wi-Fi connection. This isn’t an oversight; it’s a deliberate engineering choice. Wi-Fi provides the bandwidth necessary for high-resolution audio and the stability required to keep multiple speakers across different rooms in perfect, millisecond-accurate synchronization—a feat impossible with standard Bluetooth.

More contentiously, the setup process has drawn criticism for requiring location access permissions on a mobile device. This understandably raises privacy flags. However, the root of this requirement lies not with Sonos, but with the security architecture of iOS and Android. To prevent malicious apps from tracking users by scanning nearby Wi-Fi network names (SSIDs), these operating systems bundled the permission to scan for Wi-Fi devices with the permission to access location services. To find the Beam on your network for the first time, the app must ask for a permission that feels invasive. It’s a clumsy but well-intentioned security measure, and a perfect example of the design compromises and user-education challenges inherent to the entire smart home industry.

In the end, the Sonos Beam (Gen 2) is a fascinating artifact of our time. Its true innovation isn’t just in its five drivers and three passive radiators, but in the millions of lines of code running every second. It’s a device that weaponizes physics, exploits the elegant quirks of our own biology, and leverages computational power to overcome the limitations of its own small stature. It reminds us that Alan Blumlein’s original quest for an auditory illusion is still alive and well, only now, the magic is woven not just from wires and cones, but from the invisible, powerful ghost in the machine: the algorithm.