Acoustic specification texts for public tenders

1. General requirements for all acoustic elements

1.1 Acoustic result

1. Before execution, the tenderer measures the reverberation time of each room in accordance with NBN EN ISO 3382-2, ‘engineering’ accuracy level (at least 2 source positions, 2 microphone positions and 6 combinations), and submits the measurement results in octave bands from 125 to 4000 Hz.
2. Target values: for schools, NBN S 01-400-2; for offices, hospitality, healthcare and other non-residential buildings, NBN S 01-400-3:2026; additionally, DIN 18041 where no Belgian target value exists.
3. For each room, the tenderer provides a calculation of the reverberation time after installation, based on the measurement and the absorption values of the finished product.
4. After installation, a follow-up measurement with report is carried out, included in the price.
5. Guarantee on the result: if the measured reverberation time (average of 500 and 1000 Hz) exceeds the calculated value by more than 10%, the tenderer installs additional absorption free of charge until the calculated value is achieved.

1.2 Construction and testing

1. Absorbent core of mineral wool (stone wool), at least 50 mm thick.
2. The absorption values are determined on the finished product, not just on the core, in accordance with ISO 354 by an independent accredited or university laboratory. The test report is provided on request.
3. The finished element has no visible profiles: the frame is fully covered.

1.3 Fire safety

1. Core: Euroclass A1 (non-combustible) in accordance with NBN EN 13501-1.
2. Covering: at least B-s1,d0 in accordance with NBN EN 13501-1, in the mounting method as supplied (not bonded).

1.4 Sustainability and circularity

1. The core is fully recyclable. The manufacturer uses up to 50% recycled raw materials for new stone wool and takes back residual material through its own recycling service.
2. A verified Belgian environmental product declaration (B-EPD) is available for the core.
3. The covering carries the EU Ecolabel. A fabric made of 100% recycled polyester is available as an option.
4. Elements can be dismantled without damage to the substrate (magnets or mechanical suspension, no adhesive) and reused in the event of a move or refurbishment.
5. Product documentation (technical data sheets, EPD) is provided on request.

1.5 Aesthetics and integration

1. Choice of at least 30 standard colours in a covering that complies with 1.3.2, with physical colour samples on site.
2. Additional fabrics and colours as an option. Not every optional fabric achieves the fire classification of 1.3.2; where the specification requires that classification, the standard covering is supplied.
3. Option of photo printing and a decorative cord finish.
4. The tenderer prepares a layout proposal with a colour scheme for each room.
5. An on-site demonstration with real elements is possible before the contract is awarded.

1.6 Execution and guarantee

1. Installation by the tenderer's own permanent installation team.
2. 10-year guarantee on products and installation.
3. Delivery period: maximum 8 weeks after order.

2. Wall and ceiling panels

For spaces where acoustics and interior need to work together: classrooms, canteens, meeting rooms, reception areas, halls.

1. Rectangular and round panels in at least four standard sizes, plus custom-made up to 150 × 400 cm.
2. Thickness 50 mm; core in accordance with 1.2 and 1.3.
3. Acoustically transparent covering, tightly stretched over the frame, not bonded to the core; no visible seams or profiles on the exposed face.
4. Ceiling mounting with magnets directly against the ceiling; wall mounting with a mechanical suspension system (French cleat). Each panel can be removed individually.
5. Option of photo printing on the panel at no extra cost compared with a plain colour.

3. Panels for large spaces and baffles

For sports halls, gyms, canteens and multi-purpose halls with high ceilings, where a lot of absorption is needed on a limited budget.

1. Panel 120 × 60 × 5 cm, core in accordance with 1.2 and 1.3.
2. Covering in accordance with 1.3.2.
3. Horizontal or vertical suspension from hangers, individually or in groups, coordinated with lighting and sprinklers.
4. Installation exclusively by the tenderer (no self-assembly), including an aerial work platform where needed.
5. Absorption per object (A_obj) in accordance with ISO 354, freely suspended, measured by the KU Leuven acoustics laboratory:

4. Free-standing absorbers and dividing elements

For spaces where nothing may or can be fixed to walls or ceilings: open-plan offices, libraries, reception areas, listed buildings.

1. Free-standing column absorbing on all sides, total height at least 180 cm, core in accordance with 1.2 and 1.3, absorption per object in accordance with ISO 354 (KU Leuven):

2. Free-standing acoustic dividers in at least two heights (140 and 200 cm), also as a corner arrangement, without fixing to floor or wall.
3. Side and front desk panels, in at least three standard widths per type and custom-made.
4. Same colour range and finish as the wall and ceiling panels, so that all elements form a coherent whole.

5. Stillr technical data

Environmental profile of the core (B-EPD of a stone wool board from the same product line, 60 mm): 2.40 kg CO₂-eq per m² for production (A1–A3).

Guarantee: 10 years on products and installation, plus a satisfaction guarantee: if you are not satisfied within five working days of installation, we will look for a solution together; if that fails, we refund the investment and collect the products.

6. Proposed award criteria

A contract awarded on price alone rewards the cheapest square metre of absorption, not the best result in the room. We propose the following weighting: