Hidden Speaker Installation: In-Wall, In-Ceiling, Glass, and Wood Surfaces
Professional techniques for concealed loudspeaker installation — in-wall drywall speakers, in-ceiling co-axial drivers, glass resonance panels, and wooden ceiling acoustic membranes, each connected to KNX amplifier zones with correct impedance matching and cable routing.
Why Hidden Speakers
Visible speaker enclosures are unacceptable in premium residential and hospitality interiors. Hidden speaker technology places the acoustic driver behind a finished surface — the surface itself becomes the radiating membrane, or a standard driver is installed flush in a cutout invisible until pointed out. KNX multi-zone audio (Zennio, Loxone) makes whole-house audio practical only when the speakers match the interior architecture.
In-Wall Drywall Speakers
Standard approach: cut a circular or rectangular aperture in the drywall (plasterboard), insert a backbox (plastic or steel), and mount a frameless in-wall speaker. Recommended products: Sonance SR Series (5.25-inch, 8 ohm, 100W peak), Monitor Audio W180 (8-inch subwoofer), Klipsch CS-18C (in-ceiling).
Cutout process: mark centre point, use a hole saw matching speaker flange diameter (typically 180-230mm). Run 2x2.5mm2 speaker cable through wall cavity before plastering — use 20mm conduit in concrete walls, free-routing in stud partition cavities. Terminate in backbox with push-in spring terminals or screw terminals depending on speaker model. Speaker clips grip drywall from behind — no backbox required for basic frameless models.
Paint the grille cloth in the exact RAL colour of the wall for a truly invisible installation. Most frameless in-wall speakers accept latex paint on the grille — do not use oil-based paint, which blocks the acoustic fabric.
In-Ceiling Co-axial Drivers
For suspended ceilings (aluminium T-grid): use tile-replacement speakers (Biamp Desono, RCF NX 45-A) — 600x600mm format drops into standard tile grid. For solid concrete ceiling with plasterboard soffit: same approach as in-wall, but horizontal cut, and backbox must be rated for ceiling installation (screwed into plasterboard from inside via threaded rod to structure).
Moisture-resistant speakers for bathrooms: Sonance Marine Series or Monitor Audio AW800 (IP55 rated, polypropylene cone). Use vapour-barrier backbox. Never use standard paper-cone drivers in steamy environments.
Fire rating requirement: in commercial buildings (hotels, offices), in-ceiling speakers must have fire-rated backboxes (intumescent sealed lid, e.g. Tenmat FF130E). Required by UK BS 476 and EN 13501-1 in spread-of-flame-controlled zones. Confirm local fire regulations with the main contractor before ordering speakers.
Glass Resonance Panels (SoundTile)
Glass resonance panel technology (SoundTile Pro, Feonic, Invisible Wave): an exciter transducer is bonded to the back of a glass pane. The glass vibrates as a large-area dipole speaker. No visible driver. Applications: glass partition in office, glass splashback in kitchen, glass balustrade.
Installation: bond exciter (typically 40mm diameter, 25mm thick piezoelectric or moving-coil exciter) to glass with epoxy adhesive (Loctite EA 9455). Position at 1/3 of panel width from one vertical edge, and 1/3 of panel height from top. Use two exciters for stereo on left and right panels of a glass double door. Feed from amplifier zone via 2x1mm2 screened cable — exciter impedance typically 4-8 ohm.
Acoustic performance: lower efficiency than conventional drivers (87-90 dB/W/m at 1m), strong in midrange 300Hz-4kHz, weak below 150Hz. Supplement with a hidden subwoofer (under-floor or in-wall) for full-range performance. Best for background music in glass-heavy interiors.
Wooden Ceiling Membrane Speakers
Acoustic membrane panels: a lightweight wooden panel (6-8mm birch plywood or MDF) suspended 30-50mm below the structural ceiling on elastic mounts. An exciter transducer drives the panel from behind. The entire panel surface radiates.
Frame: aluminium angle around perimeter, spring-loaded clips at corners for vibration isolation from structure. Panel surface can be stained, veneered, or fabric-covered. Audibly indistinguishable from the ceiling finish at normal viewing distance.
Performance: better bass extension than glass panels due to larger radiating area and panel compliance. Panel tuning: adjust panel thickness and elastic mount stiffness to set low-frequency resonance (aim for 80-120Hz crossover point with in-ceiling full-range driver for mid-high frequencies).
Impedance and Cable Considerations
Standard in-wall and in-ceiling speakers: 8 ohm nominal. All speakers in one zone must sum to 4 ohm or higher at the amplifier output. Two 8-ohm speakers in parallel = 4 ohm (minimum for ZAS-AUDIO8B). Three 8-ohm speakers in parallel = 2.67 ohm — overload risk. Use impedance-matching volume controls (impedance doubling type) or a 100V line system for more than two speakers per zone.
| Speaker type | Cable | Max run | Notes |
|---|---|---|---|
| In-wall / in-ceiling 8 ohm | 2x1.5mm2 | 12m | Below 0.5 ohm cable resistance per leg |
| In-wall / in-ceiling 8 ohm | 2x2.5mm2 | 20m | Use for longer runs |
| Glass exciter 4-8 ohm | 2x1mm2 screened | 8m | Low power, screening prevents buzz pickup |
| Membrane panel exciter | 2x1mm2 screened | 8m | Same as glass exciter |
Label all speaker cables with zone number and L/R polarity before in-wall installation — correcting polarity errors is impossible after plastering without cutting open the wall. Use permanent marker on the cable sheath at each end, and photograph all cable routes before closing up.
Need a KNX whole-house audio panel with speaker wiring design?
We provide complete KNX audio panel design including speaker zone wiring diagrams, cable gauge calculations, impedance matching recommendations, and amplifier configuration — delivered with full commissioning documentation.
Request a quote →