Soundproof cabins for a calming environment

The extent to which the sound level is reduced by a closed and sound-absorbing lined soundproof cabin essentially depends on the airborne sound insulation of the cabin wall. However, the theoretically possible value is rarely achieved in practice, as openings and leaks impair the sound insulation. Heavy walls (e.g. metal sheets, wooden panels, etc.) are required to achieve a high level of airborne sound insulation. To further increase the airborne sound insulation, the interior wall of the cabin can also be supplemented with a Teroform plastic heavy foil or a Teroform bitumen heavy foil.

The airborne sound emanating from the sound source hits the surface of the interior wall of the cabin and is reflected there. The reflections can result in a level increase inside the cabin. With hard surfaces such as sheet steel, the level can increase so much that the effectiveness of the cabin is impaired. Effective sound absorption of the interior wall of the cabin is therefore of crucial importance. Absorbent sound insulation mats are porous and relatively light. The lower the frequency to be absorbed, the thicker the material should be. As a rule, it is sufficient to use dimpled foam, flat foam or melamine foam with a thickness of 30 mm.

The theoretically maximum possible level reduction of a soundproof booth is not achieved in most cases, as various unavoidable openings and leaks worsen the result:

• Openings for ventilation and air extraction
• Openings for material feed and removal
• Opening surfaces for pipe or shaft feedthroughs

The maximum level reduction that can be achieved with a soundproofing enclosure depends not only on the structure of the enclosure wall (airborne sound insulation), but in particular on the total free cross-section of the openings. Approximately 1 % openings reduce the possible level reduction by approx. 50 %.

If the airborne sound level of a sound source is mainly determined by the structure-borne sound of the system, this further reduces the achievable effect of the sound insulation enclosure. Possible transmission paths for structure-borne sound are:

• Missing or inadequate structure-borne sound insulation of the bearing
• Rigid connection of the sound source to the capsule wall

The structure-borne sound transmitted in this way is finally emitted as airborne sound outside the enclosure.

Good encapsulation includes appropriate airborne sound insulation, effective sound absorption on the inside, the smallest possible openings and structure-borne sound insulation tailored to the conditions. Vibraplast AG has a wide range of sound insulation materials that can be customised. Vibraplast AG supplies the sound-absorbing materials, but does not build complete soundproof cabins or enclosures. If noise measurements or expertises are required on site, a partner company of Vibraplast AG is available on request. Further information can be found in the SUVA brochure: ‘Noise abatement through enclosures’.