Silence is bought by the square metre, but lost at the door

Anyone asking for a soundproofing quote soon discovers the bill has three souls. There is the system — decoupled frame, mineral wool, double board — paid per treated square metre. There is the context: sockets to move, ceilings, finishes, inflating the price as a percentage. And there is the item quotes tuck away at the bottom: the acoustic door with its ventilation silencers — a fixed cost that ignores the square metres and, in a small room, weighs as much as half the walls. This calculator reassembles the three souls and judges them with a dimensionless metric: the quote index, the total divided by the bare bill of the panels.

The formula: the bare bill and its two tolls

The model is the structure of every serious quote: C = A·c·(1 + h/100) + F. The bare bill A·c is the treated area times the system cost; the surcharge h scales it by the real laying conditions; the fixed cost F is added at the end, indifferent to the metres. From here the two reading metrics: the index ι = C/(A·c), saying how many times the total exceeds the bare bill, and the share q = 100·F/C, saying how much of the price is door and fixed items. The first compares quotes with each other; the second tells where the money goes.

The area scale: the small room pays for the door

System at 80 per square metre, context at 30 percent, fixed items 1,400; only the treated area grows:

The reading is all in the last column: in the 10-square-metre booth, door and fixed items are 57.4 percent of the price — you pay more for the door than for the walls — and the 3.05 index says the total is three times the bare bill. At 110 square metres the same door slides to 10.9 percent. The per-square-metre cost of soundproofing does not exist: only your room's does.

A complete numerical example

The typical studio: 40 square metres of walls and ceiling, system at 80 per square metre, context at 30 percent, 1,400 fixed for the acoustic door and silencers. The bare bill is 40 × 80 = 3,200; context takes it to 3,200 × 1.30 = 4,160; the door closes at 5,560. That is 139 per effective square metre — against the 80 list price — with index 1.74 and fixed share at 25.2 percent: a quote within physiology, where the surfaces command and door and context follow in proportion.

How to read the quote index

The four bands of the index tell what you are really buying. Below 1.45 the large room dilutes door and context: the total travels close to the bare bill and the comparison is played on the build-up. Between 1.45 and 1.75 is the well-proportioned job: the physiology of ordinary worksites. Between 1.75 and 2.15 the worksite sounds louder than the panels: context and fixed items are worth as much as the system, and the surcharge should be detailed item by item. Above 2.15 you are buying worksite, not silence: the bulk of the price is work on the room — typical of small rooms and difficult contexts — and reviewing the treated perimeter pays more than any discount.

The system cost: the build-up that stops the decibels

The variable c is the technical heart of the quote: the mass-spring-mass system. At the bottom of the range, 40-60 per square metre, live the simple linings: light framing, wool, one board. In the middle, 80-120, the serious system: a frame decoupled from the existing wall, dense mineral wool, staggered double board of different mass. At the top, 150-200, the certified studio systems: anti-vibration hangers, high-mass boards, damping membranes. The golden rule of building physics: doubling the mass gains about 6 decibels, but decoupling the masses gains more — and it is the decoupling, not the thickness, that separates a real system from a glued panel promising miracles.

The fixed items: the acoustic door that commands the bill

The variable F is the item quotes treat as a side dish when it is the keystone: sound passes through the weak point, and the weak point always has hinges. A 60-decibel wall with an ordinary 25-decibel door is, in practice, a 25-decibel wall: the weak link decides the chain. That is why the acoustic door — heavy frame, double gasket, drop seal — costs as much as many metres of wall, and why the ventilation silencers come with it: a sealed room must breathe without letting the street in. When the fixed share exceeds 30 percent the calculator flags it: not a quote error, but the geometry of the small room — and that is where it is decided whether the promised silence will actually arrive.

International perspective: the same physics in every currency

The model is deliberately currency-neutral: enter the costs in your own money and read total and per-square-metre cost in the same unit. Europe thinks in square metres and R_w insulation decibels under ISO 717; North America measures in square feet and STC class under ASTM (1 m² ≈ 10.8 sq ft), with the same mass-spring-mass physics behind different labels. Everywhere the door is the weak point and the context inflates the bill. And the quote index is dimensionless: 1.74 in Milan, Austin or Hamburg tells the same proportion between total and bare bill — the metric that travels without exchange rates.

Model limits and correct use

This is the parametric quote for soundproofing a room against the neighbours: it is not an acoustic design. It does not cover interior treatment — sound-absorbing panels, reverberation time — which is the other trade of acoustics and adds separately; nor floors against footfall, which want floating screeds, nor façades against traffic, where the windows do the work. The area should be counted on the walls to treat plus the ceiling — not the footprint — and the airtightness declared in the specification, because one gap gives back in a day what the discount had promised. For the room's full picture, the insulation cost calculator covers the thermal front of the same wall, and the window replacement calculator puts a price on the other weak point of silence — because a quiet room is a chain, and every link is paid for.

The context scale: twenty points, one band

A 40-square-metre studio, system at 80, fixed items 1,400; only the context surcharge grows:

The progression is regular and merciless: every twenty points of context are worth 0.20 of index — from the empty room at 1.54 to the limit case at 2.24, crossing all four bands. And the 70 percent row is a border lesson: index 2.14, a breath under the 2.15 frontier — the difficult worksite that has not yet become "buying worksite, not silence". Note the fixed share falling while everything rises: context inflates the proportional part, and the door — which does not change — weighs ever less in percentage.

The fixed scale: the door that eats the quote

The same 40-square-metre studio, system at 80, context at 30 percent; only the fixed items grow:

The last three rows are flagged territory: from the certified door upward, the share exceeds 30 percent and the door commands the silence — at 4,000 of fixed items, half the quote never touches a wall. It is not waste: it is the small room or the high requirement shifting the bill's centre of gravity onto the door. But it is the moment to ask whether the double-door lobby is really needed, or whether one class below — with the same airtightness — brings the same silence at a more honest index.

The exact borders of the bands

The model's frontiers can be touched by hand. A 50-square-metre room, budget system at 40, minimum context at 10 percent, fixed 700: total 2,900, per square metre 58, index exactly 1.45 — the border belongs to the physiology band, not to dilution. The same room with context at 30 and fixed 900: total 3,500, 70 per metre, index 1.75 exact — the first step into the band where the worksite sounds louder than the panels. With context at 80 and fixed 700: total 4,300 and index 2.15 on the nose — the doorway of the extreme band. And the 20-square-metre bedroom at 50 with context 40 and fixed 600 closes the picture: a round 2,000 total, 100 per square metre, index 2.00 and fixed share at exactly 30.0 percent — the first millimetre of the territory where the door commands.

Three typical worksites: bedroom, studio, home theatre

The bedroom against the neighbours: only the shared wall plus the ceiling is treated, 25-30 square metres, medium system, high context because the room is lived-in and furnished — and the fixed items often stay under 1,000, because the internal door gets improved rather than replaced with a true acoustic one. The home recording studio: all surfaces, 40-50 square metres, serious system, acoustic door and silencers mandatory — the profile of our example, index between 1.7 and 2.0. The dedicated home theatre: the room-within-a-room when the budget allows, certified system, lobby, heavy context for audio systems and ventilation — indexes above 2.2 are physiological, because here you really are buying a small worksite. Three rooms, three different weights of the same four levers: the calculator exists precisely to see them before signing.

How to lower the bill without losing decibels

The good levers sit at the ends of the formula. On the area: treat the right surfaces, not all of them — the wall towards the neighbours and the ceiling often make the bulk of the result, and every avoided square metre saves the full cost with its surcharge. On the context: empty the room before the worksite — the 50 percent context of a furnished room drops towards the 20 of an empty one, and it is the cheapest negotiation of the project. On the fixed items: bundle — if two rooms get soundproofed, one campaign splits the setup across two bills. There is only one bad lever: cutting the quality of the system or the door. The decibel lost there comes back with no discount — and the formula shows it: the system is the only item that buys silence, the others buy conditions.

The mistakes of the DIY quote

The first mistake is counting the footprint instead of the surfaces: the room with 12 square metres of floor has 35-40 square metres that sound, and the quote doubles at the first visit. The second is the miracle panel: the thin glued material promising 30 decibels does not exist in physics — mass and decoupling are not sold in a tube. The third is forgetting that a sealed room breathes: without ventilation silencers the silence lasts until air is needed, and the open window zeroes the investment. The fourth is comparing quotes with different perimeters: one treats two walls, the other four plus the ceiling — the quote index exists for this, because it normalises the total on the bare bill and finally makes quotes commensurable.

Frequently asked questions

How much does it cost to soundproof a room?

It hangs on four levers: treated area, system cost, context and fixed items. The typical studio — 40 square metres at 80 with 30 percent context and 1,400 fixed — closes at 5,560, that is 139 effective per square metre. The 10-square-metre booth climbs to 244 per metre: the unit cost depends on the room, not the price list.

What is the quote index?

The total divided by the bare bill A·c of the installed panels alone: a dimensionless metric that compares quotes. Below 1.45 the large room dilutes the fixed items; between 1.45 and 1.75 the physiology; between 1.75 and 2.15 the worksite weighs as much as the system; above 2.15 you are mostly buying worksite.

Why does an acoustic door cost so much?

Because sound passes through the weak point and the weak point always has hinges: heavy frame, double gasket and drop seal must stand comparison with the wall. A 60-decibel wall with a 25-decibel door performs like a 25-decibel wall: the weak link decides the chain.

What area should I enter?

The walls to treat plus the ceiling, not the room footprint: a bedroom with a 12-square-metre floor easily has 35-40 square metres of surfaces that sound. You treat the surfaces facing the neighbours or the source, not necessarily all of them.

What does the context surcharge include?

Everything the installation meets: sockets and light fittings to move, ceilings, junctions with windows and services, finishes and skim coats. In empty rooms it runs 10-20 percent; in lived-in homes and old buildings it climbs to 40-80: it is the item to have detailed line by line.

How many decibels do I gain by soundproofing?

A simple lining brings 5-10 decibels; a serious decoupled system 12-18; certified studio build-ups above 20. The real gain hangs on airtightness and flanking paths: the calculator estimates the cost, the acoustic design guarantees the result.

Why does decoupling matter more than thickness?

Because a rigid wall transmits structure-borne sound: doubling the mass gains about 6 decibels, while separating the masses with an independent frame and an air spring gains more at equal thickness. It is the mass-spring-mass principle: a real system is recognised by its frame, not its panel.

Does soundproofing also remove interior reverberation?

No: they are two trades. Insulation stops the sound crossing the walls; interior treatment — exposed absorbing panels — shortens the reverberation inside the room. A serious studio combines them: first the box is sealed, then its voice is tuned.

Why do I need a ventilation silencer?

Because a sealed room must breathe: an air path without a silencer is an acoustic hole that defeats the wall. Silencers — baffled absorbing ducts — let the air through and hold the sound back, and they sit in the fixed items together with the door.

Does the calculator work outside Europe?

Yes: the model is neutral to currency and jurisdiction. Europe speaks of R_w under ISO 717, North America of STC under ASTM, with the same physics behind. The quote index is dimensionless and compares quotes from different markets on the same scale.

When is the fixed share too high?

Above 30 percent the calculator flags it: typical of small rooms, where the door weighs as much as half the walls. It is not an error — it is geometry — but it is the point where bundling several rooms into one worksite, or choosing a different door class, changes the bill more than any discount on panels.

What does the calculation NOT cover?

The acoustic design with on-site measurements, floors against footfall, façades and windows, reverberation treatment, building permits where required. It is the parametric quote of the room against the neighbours: confirmation belongs to the acoustic engineer on the real site.

Updated July 2026