Sound insulation

Sound is vibrations in the air (or other media) that spread as waves. Each sound wave has three important properties: frequency (how fast it oscillates, measured in Hz), amplitude (how powerful it is, measured in dB) and wavelength (the distance between two wave crests). We perceive low-frequency sound (below 250 Hz) as a "hum" or "rumble", while high-frequency sound (above 2000 Hz) is "sharp" and "shrill".

Sound in technical installations can be either airborne (sound that spreads through the air, e.g. pump hum heard through a wall) or structure-borne (sound that travels through the building's load-bearing constructions and can show up far from the source). Structure-borne sound is often the worst — it cannot be stopped by heavy walls alone.

It is important to distinguish between two concepts that are often confused:

• Sound insulation is about preventing sound from spreading from one place to another — e.g. from a plant room to an office floor above. Typically measured as reduction in dB.
• Acoustics is about how sound behaves INSIDE a room — reverberation, frequency response, how "full" the room sounds. Used, for example, in concert halls, classrooms and offices.

Both are used in technical installations, but the goals are different. Always clarify what the client actually wants to achieve — is it fewer complaints from the neighbouring flat (sound insulation) or better speech intelligibility in an open-plan office (acoustics)?

Different installations produce sound at different frequencies. The table shows typical sources:

Low-frequency sound is hardest to damp and requires mass. High-frequency sound is damped more easily with absorbing materials.

All sound insulation builds on one or more of these three principles:

1. Mass — heavy materials block sound

The heavier a material is, the harder it is for a sound wave to set it into vibration. The mass law states: every doubling of the mass per square metre gives +6 dB reduction. This is why lead foil and heavy mineral wool are used on particularly noisy pipes.

2. Damping — energy converted to heat

Viscoelastic materials (rubber, special foams) "brake" the sound wave's oscillation and convert the energy into a small amount of heat. This is the principle behind damping panels on compressor housings and pump connections.

3. Decoupling — vibrations stopped

By inserting a soft layer between two constructions (e.g. between pipe and supports), structure-borne sound is prevented from spreading. A small rubber insert in a pipe clamp can remove 90% of mechanical sound transmission.

Acoustic baffles are vertical mineral wool panels hung from the ceiling in, for example, large kitchens, sports halls or atrium walkways. They increase the absorbing surface and significantly reduce reverberation. Typical dimensions: 1200 × 600 × 50 mm with a covering fabric.

Acoustic panels are mounted directly on walls or ceilings. They come in many appearances — from visible acoustic surfaces to invisible "acoustic paint" (special porous paint that absorbs sound).

Reflection attenuators are an intermediate variant: angled panels that both absorb and scatter sound, so echo is broken without the room becoming "dead".

To reduce sound on a noisy pipe run:

1. Soft clamps with elastomeric foam lining — prevent vibration conduction from pipe to the building's construction. This is the single most important measure.
2. Heavy mineral wool around noisy pipes (soil/drain stacks, pump connections) — increases the mass per m and damps airborne sound. Density 80-120 kg/m³.
3. Lead-foil encapsulation on particularly noisy pipes (rare but effective — used on soil/drain stacks in operating theatres).
4. Free-hanging pipes — avoid fixing directly to lightweight walls that vibrate easily.
5. Sound bridges must be avoided — even a small metal clamp that touches both pipe and wall without elastomeric foam lining can ruin the entire sound insulation.

Ventilation systems have their own sound challenges:

• Internal acoustic lining — the duct is lined internally with sound-absorbing material (typically heavy mineral wool with an open-cell surface). Damps sound that travels THROUGH the duct.
• Sound attenuators (splitter or cell types) — separate units mounted in the duct run. Splitter attenuators have parallel "panels" of sound-absorbing material with air gaps between them. Cell attenuators have cells of absorbing material in a matrix.
• Distance attenuation — the distance itself from the source to the listening point damps the sound. Every doubling of the distance = -6 dB in a free field.
• Sound-damping duct supports — springs or rubber linings at the supports prevent mechanical sound transmission.

Angled panel constructions mounted on walls or in ducts. They work by sound waves reflecting in many different directions (instead of one clear direction). This gives less direct echo and a more "pleasant" acoustic. Used, for example, in auditoriums, churches, canteen rooms.