Acoustic Ceilings and Panelling in Fibreboard
A perforated panel on its own absorbs almost nothing: what absorbs is the system — holes, air cavity and wool behind. Take the wool away and you are left with a pattern; clog the holes with paint and the pattern is all that is left.
Overview
TAV. 00Fibreboard panelling and suspended ceilings are the commonest way of correcting a room's acoustics without giving up a continuous, refined surface, and they are also the field where a lot is spent to achieve nothing. The reason is that the absorption is not in the panel but in the system: the holes let the sound wave in, the air cavity and the mineral wool dissipate it, and the cavity depth decides which frequencies the system works on. From this come the typical errors, all trivial and all final: wool forgotten because “the panel is perforated anyway”, the cavity reduced to gain head height, roller painting that closes the holes one by one. The second chapter is the material: MDF is a board for dry interiors and its moisture swelling is irreversible — where there is water you move to plywood, you do not hope.
The site score
TAV. HThe detail of the craftthe spacing that shows in raking light
The sub-frame and the hanger spacing
Fitting the galvanised steel profiles on adjustable hangers, checking the spacing and the flatness against a laser line.
A ceiling is judged at five in the afternoon, in raking light. Shorten the hanger spacing now.site notebook — editorial synthesis
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
The system, not the panel
Where the sound absorption really comes from
This is the misunderstanding that costs most in this field, because it produces finished, useless work. The perforated panel does not absorb: it lets the wave in. The sound energy is dissipated by the wool through viscous friction, and the cavity depth decides in which frequency band the system is effective. Three components, three distinct roles: remove one and you do not get reduced performance, you get a decorative panel.
The absorption coefficient must be read from the declaration for the complete system — panel, perforation, cavity, wool — and not for the panel alone: they are different figures and only the first describes what is actually built.
Two boards, two environments
MDF or plywood: humidity decides
These are two wood-based products with opposite behaviour towards water, and the difference is structural. MDF is pressed fibre: when wetted the fibres swell and do not return, so the swelling is permanent and starts at the edges, where cutting exposed them. Plywood is made of cross-laminated veneers bonded with moisture-resistant resins: it absorbs, deforms a little, but comes back. Hence the rule: MDF where the environment is dry and conditioned, plywood where water is present or may arrive.
Moisture-resistant MDF exists, and so does interior plywood unsuited to damp: the class is read from the specific board's marking, not inferred from the product family.
How it ages (and what betrays it)
TAV. PQuestions from the site
TAV. QHow do you tell whether an acoustic ceiling works?
The rigorous way is measuring the reverberation time in the finished, furnished room and comparing it with the design value. But there is an immediate check anyone can make on walking in: speak normally and listen for whether your voice comes back. In a properly treated room the sound tail is short and words stay distinct even a few metres away; in an untreated one the voice overlaps itself and to be understood people raise their tone, which everyone does without noticing. If the room is finished and that is still the sensation, the problem is in the cavity or the wool, not in the panel.
Does the whole ceiling need treating?
Almost never, and treating everything is often a waste. Absorption is needed where sound arrives and leaves again, so the most effective surfaces are the ones facing the sources and the ones that generate close reflections — the ceiling above the tables, walls that face each other. A room in which every surface absorbs, however, becomes dead and tiring: the voice loses its naturalness and whoever is speaking feels isolated. Correct acoustic design alternates absorbing and reflecting zones, and this is exactly the advantage of the fibre panel: the same finish can be perforated where it is needed and left solid where it is not, without the difference being visible.
Is timber in a suspended ceiling a fire problem?
It depends on the room, and it has to be verified before ordering. A wood-based panel has a reaction-to-fire class that in ordinary rooms is often acceptable, but in escape routes, in crowded spaces and in buildings subject to fire assessment the required class is stricter, and it is obtained with treated panels or with specific products. The important point is that the class refers to the panel in its actual finish: a coating different from the one that was tested can invalidate the declaration. It is one of the few cases in which the finish is not an aesthetic matter but a documentary one.
Can a damaged panel be replaced?
Yes, and that is the advantage of concealed clip fixing over bonding: the panel unhooks and goes back without touching its neighbours. The practical problem is a different one, and it concerns colour: a panel coated today does not match one coated three years ago, because the original finish has shifted slightly under the light. This is why on large surfaces it is worth keeping a few spare panels from the same batch, stored in the same room: they age together with the others, and it is the only way to get a replacement nobody notices.