Why Your Brain Hears Depth: The Psychoacoustics Behind Spatial Audio

Turn up the volume. Now turn it up more. Does the sound feel closer? Probably. Does it feel like it is coming from above you? Never.

This is the problem with every speaker you have ever owned. They project sound in a single flat plane, forward into the room. Loudness is a one-dimensional lever. It pushes sound toward you or pulls it away.

But human hearing operates in three dimensions. We locate a bird in a tree, a siren around the corner, rain on a tin roof overhead — not because these sounds are loud, but because our auditory system extracts spatial data from subtle acoustic cues that have nothing to do with volume. Traditional speakers, including most soundbars, ignore almost all of this information. They blast a wall of sound forward and hope your ears figure out the rest.

The disconnect between how we hear and how speakers reproduce sound is the central unsolved problem in consumer audio. Dolby Atmos attempted to address it by treating sound as objects in 3D space rather than signals locked to fixed channels. But rendering those objects overhead traditionally requires ceiling-mounted speakers — a non-starter for most living rooms. The OXS S5 soundbar takes a different approach, using two dedicated up-firing drivers to bounce sound off the ceiling and exploit a specific quirk of human psychoacoustics. To evaluate whether this actually works, we first need to understand what your brain is listening for.

The Pinna: Your Built-In Directional Antenna

Hold your ears. Not physically — just consider their shape. The outer ear, or pinna, is not a passive funnel. It is an acoustic filter. When a sound wave arrives from above, it interacts with the ridges and folds of your pinna differently than a sound arriving from below or from the side. These interactions create tiny delays and frequency notches — spectral cues — that your auditory cortex has learned to decode as directional information.

This was demonstrated conclusively in the 1960s by Batteau's experiments at the Naval Electronics Laboratory. Batteau showed that subjects could identify the elevation of a sound source with surprising accuracy, even with one ear blocked, based solely on pinna-derived spectral filtering. Remove the pinna — or bypass it with headphones that inject sound directly into the ear canal — and elevation perception collapses almost entirely.

The implication is stark: for a speaker system to create the illusion of height, the sound must arrive at your ears from a direction that triggers the correct pinna cues. Forward-facing drivers cannot do this. The sound arrives horizontally, and your brain correctly identifies it as coming from in front of you, regardless of how much digital processing is applied.

Virtual Height: Reflection as Deception

This is where ceiling bounce enters the picture. If a driver aims upward at a specific angle, the sound wave travels to the ceiling, reflects, and arrives at the listener from above. The pinna processes this reflected wave and registers it as coming from an elevated source. Your brain constructs a phantom speaker hanging somewhere near the ceiling.

The physics is straightforward: the angle of incidence equals the angle of reflection. If a driver fires at 20 degrees from vertical, the reflected beam arrives at the listening position from approximately 20 degrees above horizontal. The exact geometry depends on ceiling height and the distance between the bar and the listener. In a typical 8-foot ceiling room with the soundbar placed on a TV stand, the reflection angle produces a perceived source roughly 30 to 45 degrees above the horizon — within the range where the pinna provides strong elevation cues.

But this technique has hard constraints. Vaulted ceilings scatter the beam rather than reflecting it cleanly. Acoustic ceiling tiles absorb high-frequency energy, stripping out the spectral cues the brain needs. And the effect weakens dramatically if the listener moves far from the sweet spot, because the reflected wave arrives at the wrong angle. The system works, but only within a defined geometric window.

The 3.1.2 channel designation refers specifically to this architecture: three front channels (left, center, right), one subwoofer channel, and two height channels rendered via up-firing drivers. It is a compromise between the full overhead experience of in-ceiling speakers and the flat soundstage of a conventional bar.

The Bass Compression Problem: Hoffman's Iron Law

Height is only half the spatial equation. The other axis — depth, particularly in the low frequencies — poses a different challenge rooted not in psychoacoustics but in cabinet physics.

Hoffman's Iron Law states that for any given loudspeaker design, you can optimize for at most two of three variables: bass extension (how low the speaker plays), enclosure size, and efficiency (how loud it gets per watt of input). Want deep bass from a small box? You sacrifice efficiency. Want deep bass and high efficiency? You need a large enclosure.

Most soundbars solve this by offloading bass to a separate powered subwoofer — a large box you place on the floor. The S5 integrates the subwoofer into the main bar, a decision that fundamentally constrains bass extension. The specified frequency response extends down to 55Hz, which covers the fundamental frequencies of most voices, guitars, and drums but misses the sub-bass region (20-40Hz) where you feel movie explosions in your chest.

To reach 55Hz from a compact enclosure, the design uses a ported cabinet. The internal port creates a Helmholtz resonance — the same principle that makes a bottle hum when you blow across its opening — tuned to boost output at the lower end of the frequency range. Combined with a high-excursion driver that moves more air per stroke than a conventional driver of the same diameter, the system produces perceivable bass weight without an external box. It is an exercise in living within the boundaries Hoffman's Law draws.

The Data Pipeline: Why Compression Kills Spatial Audio

Psychoacoustic cues — the spectral notches, the interaural time differences, the phase relationships — are fragile. They survive in uncompressed or lightly compressed audio. Aggressively compress the signal, and the fine structure that carries spatial information gets smeared into noise.

This is why HDMI eARC exists. Standard optical (TOSLINK) connections cap out at roughly 1.5 Mbps — enough for stereo PCM or compressed 5.1 Dolby Digital, but insufficient for uncompressed Dolby Atmos object audio with its per-object spatial metadata. The older HDMI ARC protocol shares the same bandwidth ceiling. HDMI eARC increases the pipe to roughly 37 Mbps, carrying the full Atmos bitstream with its positional data intact.

Without eARC, an Atmos-compatible soundbar receives a downmixed, compressed version of the audio. The spatial objects get flattened back into channel-based surround. The up-firing drivers still fire, but the precise instructions telling them where to place each sound object in 3D space are gone. The ceiling reflection still happens, but the psychoacoustic effect is degraded because the timing and frequency data that make the illusion convincing have been discarded by the compression stage.

The practical implication is that the cable connecting your TV to your soundbar is not just a convenience — it is an active participant in whether spatial audio works at all.

Dialog Clarity: The Frequency Masking Problem

There is a reason the most common complaint about modern TV audio is not missing explosions but missing words. Film soundtracks are mixed with enormous range between quietest and loudest sounds — the gap between the quietest whisper and the loudest explosion can exceed 60 dB. On high-end theater systems with dedicated center speakers, this range is manageable. On flat-panel TV speakers, which compress everything into two small downward-firing drivers, the result is chaos.

The physics of frequency masking makes this worse. When a low-frequency sound (explosion, bass note, rumble) plays simultaneously with a mid-frequency sound (human voice), the low-frequency energy overwhelms the cochlear response in the same critical band, effectively making the voice inaudible. This is not a volume problem — turning up the overall level makes the explosion louder too, preserving the masking relationship.

A dedicated center channel addresses this by giving the dialog its own driver and its own amplification path. DSP-based dialog enhancement goes further by applying selective compression to the center channel — raising the level of the vocal frequency range (roughly 300 Hz to 3 kHz) relative to the surrounding frequencies. The trade-off is that aggressive DSP processing can introduce artifacts, making voices sound processed rather than natural. Multiple EQ presets (the S5 offers five: Standard, Movie, Music, Voice, Night) allow different compression profiles for different content, trading spatial fidelity for intelligibility depending on the situation.

The Unresolved Paradox of Compact Audio

The tension at the heart of soundbar design is between size and physics. You cannot cheat Hoffman's Law. You cannot make a speaker that is simultaneously small, loud, and deep. You cannot generate convincing height cues without the geometric cooperation of your room's ceiling. And you cannot transmit uncompressed spatial audio through a bandwidth-limited cable.

What you can do is stack compromises intelligently. Use the ceiling as a reflector to gain a vertical axis without mounting hardware. Accept 55Hz as the bass floor in exchange for eliminating a separate subwoofer box. Require eARC as the entry price for spatial rendering. Apply DSP judiciously to isolate dialog from the frequency chaos of action soundtracks.

The result is not a replication of a theater. It is something different: a system that operates within the physics of a domestic living room, using the room itself as an acoustic component rather than fighting against it. Whether that is enough depends on what you are listening for — and, more fundamentally, on how much of the three-dimensional world your brain is willing to construct from reflected sound.