The technology that turns a plasterboard wall, a door or a mirror into a loudspeaker. What it really sounds like, which surfaces it fits, and what to expect in the bass.

There is a recurring moment when someone hears a sound system without seeing the speakers for the first time: “where is that coming from?”. The answer, in many recent installs, is the wall itself — turned into a loudspeaker by acoustic exciters coupled from behind.

This article explains how the technology works, which surfaces can be converted into a speaker, what real-world performance to expect (especially in the bass — the key question), and where it makes sense, and where it doesn’t.

The principle: making the surface vibrate

A conventional loudspeaker has a diaphragm — the cone — that pushes air to generate sound. In an invisible speaker system based on an exciter, the diaphragm is the architectural surface itself: a plasterboard panel, a rigid furniture board, a door, or a mirror.

The exciter (also called a contact transducer or electro-acoustic actuator) is a small device attached to the back of the surface. Instead of moving air directly, it transmits mechanical vibration to the panel, which then becomes a sound radiator across its whole area.

Result: the wall plays. No grille, no visible cone, no box. The acoustic source is distributed across the entire surface.

Which surfaces work well

Efficiency depends on the mechanical properties of the panel: stiffness, mass, internal damping, and freedom to vibrate.

Surfaces where it performs best, from real projects:

Plasterboard (drywall) panels on standard metal-frame construction. The most common scenario in Spanish housing and offices — very good results with proper mounting.
Rigid furniture boards: plywood or MDF of sufficient thickness, free to vibrate in a well-designed piece.
Interior doors of solid or rigid-core wood.
Mirrors of tempered glass of enough size, mounted with fixings that allow vibration.
Suspended ceilings of acoustic tile or plaster.

What doesn’t work well: solid brick or concrete walls (too stiff, don’t vibrate at audible frequencies), panels that are too small (can’t radiate bass), or mountings without mechanical freedom.

What it sounds like: the realistic range

A well-installed exciter on a suitable surface delivers sound that is:

Spatially broad: the source is the whole surface, not a point. The stereo image is enveloping, with presence across the room.
Clear in voices and mids: vocal range and film dialogue have excellent intelligibility.
Very good in highs: transients transmit well across the rigid surface.
Defined in mid-bass: guitars, pianos, drums have body and resolution.

And the bass

The honest question. An exciter system on plasterboard rolls off usefully down to around 80 Hz. That covers:

All instrumental, vocal, classical, jazz and acoustic music.
Most pop and electronic music without extreme sub-bass demands.
All dialogue and film score content in a domestic context.

What the system on its own does not cover is the deep sub-bass (< 60 Hz) of action cinema or bass-heavy electronic music. For someone who demands that range, a concealed subwoofer can complement the system — but it isn’t a universal requirement, it depends on use.

Our recommendation when in doubt: listen first without a subwoofer. In most residential rooms the surprise is that it isn’t needed.

Installation: what makes the difference

The difference between a “correct” invisible speaker system and an excellent one lies almost entirely in the installation. Quality exciters are commercially available; what isn’t off-the-shelf is how you couple them to the panel.

Factors that matter:

Coupling point: where exactly the exciter attaches to the panel. It changes the modal response of the panel itself and, therefore, its tonal balance.
Added mass and damping: how the wall is built (frame, insulation, board density). It directly affects bass performance.
Spacing between exciters: in stereo installs, distance and layout determine the sound image.
Room acoustic treatment: an invisible speaker sounds only as good as the room around it. Reflections and reverberation are the same problems affecting any system.

Installation process on plasterboard: what has to be right

In the most common install — exciter on plasterboard, finished with a skim plaster coat — three details separate a correct job from a failed one:

Maximum skim thickness: 2 mm over the panel. Above that, the added mass starts to damp the panel’s vibration and high-frequency response degrades. It is not a ballpark figure: it is a technical threshold. An average plasterer handles 2 mm without issue, but you have to specify it explicitly before the work starts.
Audible test before plastering over. Once the board is closed and plastered, reaching the exciter means demolition. The test has to be done with cabling connected, amplifier powered, and real music playing — not just a test tone. If something sounds wrong, you fix it before closing.
Edge finishing. The joint between boards and around the exciter is filled and taped before the final skim, like any quality drywall work. A poorly resolved joint becomes audible over time: parasitic vibration, cracks.

It also works behind wood panelling, with one condition

Besides plasterboard, the system works well behind MDF or plywood panels veneered in real wood, provided the panel is routed from the back in the exciter area down to roughly 2 mm. The exciter bonds to that thinned section; the rest of the panel keeps its original decorative thickness. It is a strong solution for interiors with wood-panelled walls, where neither skimmed plasterboard nor a visible speaker would be acceptable.

Where invisible speakers make sense

Cases where this technology is clearly the best choice:

Housing with high aesthetic demand: living room, bedroom, library where the interior design doesn’t tolerate visible speakers.
Offices and commercial spaces: even sound distribution without taking wall space, no visible acoustic hardware.
Hospitality and retail: sound integrated into the architecture, reduced maintenance, clean aesthetic.
Multi-zone installations: audio across many spaces without repeating the “speaker” component in each.
Heritage rehabilitation: interventions where adding speaker boxes would damage the architectural value.

Where a conventional speaker still wins

For technical honesty: it’s not the answer to everything.

Critical listening for the audiophile: if the goal is maximum tonal precision and dynamics in near-field listening, a well-treated monitor system remains the reference.
High-end home cinema with demanding sub-bass: action cinema at high volume may require dedicated subwoofers that a purely invisible system doesn’t cover.
Very tight budget: invisibility has a cost; if aesthetics aren’t a priority, a traditional system offers more performance per euro.

”Exciter” vs “DML”

The term DML (Distributed Mode Loudspeaker) circulates online as a synonym. Technically DML is one specific implementation of this transducer family that prioritises modal distribution on the panel. In current professional practice, the best invisible speaker systems combine DML principles with optimised coupling designs that don’t 100% fit that label.

At Sonarq we prefer to speak of acoustic exciters and invisible surface loudspeakers — describing what the system is, without tying it to a single technology.

Next step

If the technology interests you for a project, the useful step isn’t picking the exciter from a catalogue — it’s designing the whole system: surface, coupling, room treatment. Get in touch and we’ll assess your space, with an audible demonstration where possible.

Invisible speakers: how surface acoustic exciters actually work